An Overview of Deep-water Turbidite Deposition
Henry W. Posamentier, Venkatarathnam Kolla, LIU HuaQing
Deep-water turbidites commonly are deposited in water depths below storm wave base. These depths range from a few tens of meters to thousands of meters. Turbidite systems tend to be most active when depocenters lie at or near shelf margins,and this proximity of depocenters to shelf margins tends to be associated most commonly with times of relative sea level lowstand. Deep water depositional episodes can be divided into early and late lowstand time. Deposition during early lowstand is characterized by progressively larger and more frequent flow events,whereas deposition during late lowstand is characterized by progressively smaller and less frequent flow events. Consequently,during early lowstand time,erosion of channels tends to dominate such that channels tend to become progressively deeper with minimal preservation of deposits within feeder channels;successive flows are overfit. Subsequently during late lowstand progressively smaller flows tend to be underfit resulting in preservation of channel fill deposits. Turbidite systems tend to be characterized by three discrete regions:Region 1 corresponds to the most proximal reaches of turbidite systems dominated by canyons that commonly are tributive. Region 2 corresponds to that part of the turbidite system characterized by a single feeder channel complex that was characterized by flows with heights greater than confining walls,hence associated with levees. Region 3 corresponds to that part of the system distally, that is characterized by frequent avulsions and sand-prone overbank as well as channel-fill deposits,which can be described geomorphologically as a terminal fan. From a process perspective,Region 3 can be described as a frontal splay. From a sequence stratigraphic perspective,lowstand deposits commonly are bracketed by mud prone distal highstand and transgressive systems tract deposits. The succession of early to late lowstand deposition commonly is characterized by sand-rich Region 3 fan deposits overlain by leveed channel deposits of region 2.
[Review Details]
Advances and Prospects of Terrestrial Thermal Spring Travertine Research
WEN HuaGuo, LUO LianChao, LUO XiaoTong, YOU YaXian, DU Lei
A thermal spring travertine is a form of terrestrial carbonate rock/deposit formed in Ca2+ and HCO3- enriched hot springs(generally T ≥ 30℃). Its unique depositional environment,petrological and mineralogical characteristics, geochemical features,and fluid characteristics are of great significance to studies of paleoenvironment,paleoclimate,origin of early life,neotectonic evolution,terrestrial hydrothermal sedimentology,geothermal resources,etc. Although geologists have carried out many studies related to thermal spring travertines,their spatial and temporal distribution,sedimentary characteristics,mineral composition,geochemical characteristics,microbial processes,fluid origins,diagenesis,and paleoclimate significance are still unclear because of the complex depositional and diagenetic conditions of thermal spring travertines,and further studies are needed. Based on a detailed literature review and our previous studies, this study:1) reviewed the current research progress of thermal spring travertines, 2) summarized the significance of thermal spring travertine research,and 3) proposed the current problems and next directions in thermal spring travertine research. Combining this information,this study can help us better understand the geological features of thermal spring travertines and their significance and provide new insights into further research.
[Review Details]
Microbially Induced Sedimentary Structures (MISS) in Mesoproterozoic Changzhougou Formation Sandstone, Xingcheng Area, Liaoning Province, China
XiaoBo LI, YiNi WANG, Han WANG
Numerous crack structures are found in the intertidal facies sandstone of the Mesoproterozoic Changzhougou Formation in Jiashan, Xingcheng area, Liaoning Province. The structures comprise 0.8-3.0 cm spindle-shaped short cracks, and extended cracks over 7 cm long. They are mainly isolated, some partially connected. By comparing them with other similar surface crack structures and the desiccation cracks developed in modern microbial mats, they are explained as shrinkage cracks in microbial mats ('mat-cracks'). Unconnected spindle-shaped mat-cracks indicate incomplete mat shrinkage; mat-crack polygons form when shrinkage is complete. The presence of MISS indicates that the microbial ecosystem was already affecting the paleocoastal geological processes during the early transgression stage of the North China Craton in the Mesoproterozoic. This information is crucial for reconstructing the biosedimentary mechanisms and paleoenvironment of the aulacogenic Yanshan Basin during its early evolution.
[Review Details]
Unconventional Petroleum Sedimentology: Connotation and prospect
QIU Zhen, ZOU CaiNeng
The theoretical framework of Unconventional Petroleum Geology has been gradually established along with the rapid progresses in exploration and development of unconventional petroleum resources. It is now imperative for innovative new insights into the unconventional petroleum sedimentology. Herein, the concept and scientific connotations of “Unconventional Petroleum Sedimentology” are proposed and briefly introduced. The research progresses are summarized for the sedimentology of typical unconventional petroleum resources in China, such as Wufeng-Longmaxi Shale gas in Sichuan Basin and tight oil and shale oil of Yanchang Formation in Ordos Basin. Further research themes and challenges of Unconventional Petroleum Sedimentology are discussed. Sedimentary enrichment of unconventional petroleum resources can be closely related with some critical environmental changes, which would be the result of coupling sedimentology from several geological events such as global or regional tectonic activities, sea (lake) level changes, volcanic eruptions, climate changes, anoxic bottom water, biotic mass extinctions and radiations, and gravity currents. For better understanding of Unconventional Petroleum Sedimentology in future, the Earth Systems Science view and “unconventional” insights should be applied to its research by analyzing geological events in details, which can play an important role in the discovery of new unconventional petroleum resources.
[Review Details]
Sedimentary Characteristics of Ephemeral and Intermittent Channels: A case study of the Baiyanghe fan, Xinjiang, China
ChangMin ZHANG, XuLong WANG, Zhe CHEN, Tao WU, XiangHui ZHANG, Kang ZHAO, YuanGuang HUANG, Tan ZHANG, WenJie FENG, Rui YUAN
A topographical investigation of modern deposits of the Baiyanghe fan in Xinjiang show that two types of fluvial channels are developed on the surface of the fan:intermittent channels and ephemeral channels. The latter, which have flow occupancy between < 50% and zero, are mainly formed by occasional flooding during summer rains. The occupancy rate of intermittent channel flow is about 50%, and their flow output is between that of ephemeral and perennial channels. The main Baiyanghe channel is intermittent, occupying 2.1% of the fan surface area. Its deposits are mainly coarse-grained gravels, highly rounded, well sorted, and with low mud content and higher imbricated characteristics. The course of the channels change, with sediments fining downstream. Ephemeral channels, which are distributed over about 97.9% of the fan surface area, contain finer sediment with low roundness, poor sorting and higher mud content. The scale of ephemeral channels decreases downstream and bifurcation increases. Intermittent channels are dominated by seasonal runoff, and the source of the sediment load is mainly remote from the fan. The sediment carried by ephemeral channels is dominated by sheet flow and debris flow from colluvium and debris-flow deposits near the apex of the fan, together with some sediment from earlier deposits within the fan itself. The fan lobe are mainly constructed by intermittent channels, whereas ephemeral channels play a role in re-shaping the fan. This study has increased the understanding of the sedimentary process and characteristics of alluvial fans in arid areas and enriched the sedimentary model of fan research.
[Review Details]
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, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.078
Abstract:
[Objective] During the Early Jurassic, multiple significant perturbations of the carbon-cycle occurred that coincided with abrupt and extreme changes in climate and environment. However, existing research has primarily focused on the western Tethys and northern Europe, with limited attention given to carbon cycle disturbances in the eastern Tethys and the quantitative assessment of their impact on biota. [Methods] This study examined the biological (larger benthic foraminifera), sedimentological, and carbon-isotope (δ13C) stratigraphy from the southern Tibetan Kioto Platform formed in the southeastern Tethys during the Late Pliensbachian–Earliest Toarcian interval to investigate the influence of carbon-cycle perturbations and corresponding climatic and environmental variations on the evolution of carbonate-platform biota in the region. In addition, this study quantitatively analyzed the content of carbonate skeletal grains, the number and species changes of lager benthic foraminifera, and the distribution of Lithiotis Fauna to explore the impact of these events on biota. [Results] Three foraminiferal zones were recognized: Pliensbachian Bosniella oenensis–Cyclorbitosella tibetica (?) and Streptocyclammina liasica, as well as the Earliest Toarcian Siphovalvulina sp. A. According to the sedimentary structure and the quantitative analysis of grains composition and content, this study identified nine carbonate microfacies (MF) from the Pupuga Formation in the Dongqiu section. These microfacies included mudstone (MF1), dolomitic peloidal wackestone (MF2), bioclastic peloidal packstone (MF3), bioclastic wackestone/packstone (MF4), intraclastic packstone–grainstone (MF5), lump grainstone (MF6), Lithiotis rudstone (MF7), bioclastic grainstone (MF8), and oolitic grainstone (MF9). The sedimentary microfacies and microfacies assemblages reveal that the Pupuga Formation in the Dongqiu section represented the shallow–water carbonate platform deposit, characterized by minimal influence from terrigenous input. Furthermore, temporal variation in microfacies demonstrated that the Dongqiu section provided a comprehensive record of a sedimentary succession, delineating a gradual transition from the open platform and platform margin to the inner platform, succeeded by a swift reversion towards the open platform and platform margin. Based on biostratigraphy, two carbon isotope excursion events in the Late Pliensbachian were identified: the margaritatus zone event (ME) characterized by positive carbon isotope excursion and the margaritatus–spinatum zone boundary event (MSBE) with negative carbon isotope excursion as a feature. [Conclusions] During the ME period, there was an increase in skeletal grain content, maintenance of high species diversity and abundance of larger benthic foraminifera, and the occurrence and spread of Lithiotis Fauna. This may indicate that the persistent burial of organic matter consumed atmospheric pCO2 generated during the Late Sinemurian to Early Pliensbachian interval, creating more suitable marine environmental conditions for biotic survival. In contrast, during the MSBE period, there was a decrease in the abundance and size of Lithiotis Fauna and skeletal grain content, along with the extinction of several index larger benthic foraminifera. This evidence indicates a possible relationship between biotic crises and sea-level fall. Although there were changes in the size and frequency of occurrence of the Lithiotis Fauna, it is undeniable that they flourished throughout the Tethyan shallow carbonate platform during the Pliensbachian interval, and the conditions for skeletal production of carbonates were not completely destroyed until the Toarcian oceanic anoxic event.
[Objective] During the Early Jurassic, multiple significant perturbations of the carbon-cycle occurred that coincided with abrupt and extreme changes in climate and environment. However, existing research has primarily focused on the western Tethys and northern Europe, with limited attention given to carbon cycle disturbances in the eastern Tethys and the quantitative assessment of their impact on biota. [Methods] This study examined the biological (larger benthic foraminifera), sedimentological, and carbon-isotope (δ13C) stratigraphy from the southern Tibetan Kioto Platform formed in the southeastern Tethys during the Late Pliensbachian–Earliest Toarcian interval to investigate the influence of carbon-cycle perturbations and corresponding climatic and environmental variations on the evolution of carbonate-platform biota in the region. In addition, this study quantitatively analyzed the content of carbonate skeletal grains, the number and species changes of lager benthic foraminifera, and the distribution of Lithiotis Fauna to explore the impact of these events on biota. [Results] Three foraminiferal zones were recognized: Pliensbachian Bosniella oenensis–Cyclorbitosella tibetica (?) and Streptocyclammina liasica, as well as the Earliest Toarcian Siphovalvulina sp. A. According to the sedimentary structure and the quantitative analysis of grains composition and content, this study identified nine carbonate microfacies (MF) from the Pupuga Formation in the Dongqiu section. These microfacies included mudstone (MF1), dolomitic peloidal wackestone (MF2), bioclastic peloidal packstone (MF3), bioclastic wackestone/packstone (MF4), intraclastic packstone–grainstone (MF5), lump grainstone (MF6), Lithiotis rudstone (MF7), bioclastic grainstone (MF8), and oolitic grainstone (MF9). The sedimentary microfacies and microfacies assemblages reveal that the Pupuga Formation in the Dongqiu section represented the shallow–water carbonate platform deposit, characterized by minimal influence from terrigenous input. Furthermore, temporal variation in microfacies demonstrated that the Dongqiu section provided a comprehensive record of a sedimentary succession, delineating a gradual transition from the open platform and platform margin to the inner platform, succeeded by a swift reversion towards the open platform and platform margin. Based on biostratigraphy, two carbon isotope excursion events in the Late Pliensbachian were identified: the margaritatus zone event (ME) characterized by positive carbon isotope excursion and the margaritatus–spinatum zone boundary event (MSBE) with negative carbon isotope excursion as a feature. [Conclusions] During the ME period, there was an increase in skeletal grain content, maintenance of high species diversity and abundance of larger benthic foraminifera, and the occurrence and spread of Lithiotis Fauna. This may indicate that the persistent burial of organic matter consumed atmospheric pCO2 generated during the Late Sinemurian to Early Pliensbachian interval, creating more suitable marine environmental conditions for biotic survival. In contrast, during the MSBE period, there was a decrease in the abundance and size of Lithiotis Fauna and skeletal grain content, along with the extinction of several index larger benthic foraminifera. This evidence indicates a possible relationship between biotic crises and sea-level fall. Although there were changes in the size and frequency of occurrence of the Lithiotis Fauna, it is undeniable that they flourished throughout the Tethyan shallow carbonate platform during the Pliensbachian interval, and the conditions for skeletal production of carbonates were not completely destroyed until the Toarcian oceanic anoxic event.
, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.082
Abstract:
[Objective] Laizhou Bay is located at the southern part of the Bohai Sea, where the Quaternary history of regional environmental changes during the transition from land to sea has been continuously recorded in coastal sediments. Studying these geological records can provide critical insights into geographical and environmental reorganization of the Northeast Asia during the Quaternary. Previous studies have reported that there was a major transition from a lake environment to a shelf environment in the middle Pleistocene, and three transgression events have been dated to marine isotope stage (MIS) 7-6, MIS 5-3, and the Holocene, respectively. However, the evolution of the “Bohai Paleolake” is not clear, since the framework of these lacustrine deposits has not been established yet. [Methods] To reveal the history of how the “Bohai Paleolake/Sea” evolved, 11 drilling cores from the Laizhou Bay were employed to establish a preliminary framework by analyzing the sedimentary strata in the Quaternary. The main analyses include magnetostratigraphy, sediment grain size, and stratigraphic correlation. [Results] The main results are listed as follows: (1) Three new cores were analyzed in terms of magentostratigraphy, and the new obtained magnetozones can be generally correlated to the Brunhes, Matuyama, and Gauss chrons in the geological polarity timescale, which is consistent with previous studies in the Laizhou Bay; (2) Three major types of the sediments in the Quaternary were identified, including fluvial-alluvial, lacustrine, and continental-shelf, and the sedimentary properties and the relationships of sediment grain-size parameters are distinct among them, illustrating the potential of paleoenvironmental inferences; (3) Based on stratigraphic analyses and isochronous strata (Brunhes and Matuyama chrons) correlation, it is found that the Laizhou Bay may have experienced significant subsidence in the early Pleistocene; (4) By establishing a stratigraphic framework of Quaternary sediments in the Laizhou Bay, 17 alternations between sea/lake water extension and shrinking were identified, including 1 in Holocene, 2 in the late Pleistocene and the late part of the middle Pleistocene, 7 in the middle Pleistocene, and 7 in the early Pleistocene; (5) The preliminary framework indicates the predominant periodicities in the upper transgression-related strata and the lower lacustrine-fluvial strata are 100 kyr and 200 kyr, respectively, inferring a dominant role of orbital eccentricity in regional paleoenvironmental processes; (6) Correlating the Quaternary strata around the Bohai basin and correlating isochronous strata based on the Jaramillo subchron, it is found that the eastern and northwestern margins of the basin significantly subsided during the Middle Pleistocene. [Conclusions and Prospects] Based on these results, it is speculated that the land-sea transition of the Bohai basin has gone through the following processes: the alluvial and diluvial system in the early Pliocene or earlier, the lake-group environment prior to the early part of the early Pleistocene, the latest stage of “Bohai Paleolake” in the early Pleistocene, the shrinking lake and weak transgression in the Middle Pleistocene, and the shelf depositional environment since the late Pleistocene. These identified stages of the Bohai basin can be preliminary correlated to the evolution of a series of paleolakes in the middle and upper reaches of the Yellow River, possibly inferring a potential covariation. However, the main findings in the work are lack of fossil evidence, which are worthy of further investigation in future.
[Objective] Laizhou Bay is located at the southern part of the Bohai Sea, where the Quaternary history of regional environmental changes during the transition from land to sea has been continuously recorded in coastal sediments. Studying these geological records can provide critical insights into geographical and environmental reorganization of the Northeast Asia during the Quaternary. Previous studies have reported that there was a major transition from a lake environment to a shelf environment in the middle Pleistocene, and three transgression events have been dated to marine isotope stage (MIS) 7-6, MIS 5-3, and the Holocene, respectively. However, the evolution of the “Bohai Paleolake” is not clear, since the framework of these lacustrine deposits has not been established yet. [Methods] To reveal the history of how the “Bohai Paleolake/Sea” evolved, 11 drilling cores from the Laizhou Bay were employed to establish a preliminary framework by analyzing the sedimentary strata in the Quaternary. The main analyses include magnetostratigraphy, sediment grain size, and stratigraphic correlation. [Results] The main results are listed as follows: (1) Three new cores were analyzed in terms of magentostratigraphy, and the new obtained magnetozones can be generally correlated to the Brunhes, Matuyama, and Gauss chrons in the geological polarity timescale, which is consistent with previous studies in the Laizhou Bay; (2) Three major types of the sediments in the Quaternary were identified, including fluvial-alluvial, lacustrine, and continental-shelf, and the sedimentary properties and the relationships of sediment grain-size parameters are distinct among them, illustrating the potential of paleoenvironmental inferences; (3) Based on stratigraphic analyses and isochronous strata (Brunhes and Matuyama chrons) correlation, it is found that the Laizhou Bay may have experienced significant subsidence in the early Pleistocene; (4) By establishing a stratigraphic framework of Quaternary sediments in the Laizhou Bay, 17 alternations between sea/lake water extension and shrinking were identified, including 1 in Holocene, 2 in the late Pleistocene and the late part of the middle Pleistocene, 7 in the middle Pleistocene, and 7 in the early Pleistocene; (5) The preliminary framework indicates the predominant periodicities in the upper transgression-related strata and the lower lacustrine-fluvial strata are 100 kyr and 200 kyr, respectively, inferring a dominant role of orbital eccentricity in regional paleoenvironmental processes; (6) Correlating the Quaternary strata around the Bohai basin and correlating isochronous strata based on the Jaramillo subchron, it is found that the eastern and northwestern margins of the basin significantly subsided during the Middle Pleistocene. [Conclusions and Prospects] Based on these results, it is speculated that the land-sea transition of the Bohai basin has gone through the following processes: the alluvial and diluvial system in the early Pliocene or earlier, the lake-group environment prior to the early part of the early Pleistocene, the latest stage of “Bohai Paleolake” in the early Pleistocene, the shrinking lake and weak transgression in the Middle Pleistocene, and the shelf depositional environment since the late Pleistocene. These identified stages of the Bohai basin can be preliminary correlated to the evolution of a series of paleolakes in the middle and upper reaches of the Yellow River, possibly inferring a potential covariation. However, the main findings in the work are lack of fossil evidence, which are worthy of further investigation in future.
, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.080
Abstract:
Eolian deposition, as a product of wind erosion, transportation, and accumulation on the Earth's surface, has a wide spatial and temporal distribution in geological history. Its formation and evolution are closely related to arid climatic conditions and relatively continuous subsidence of paleogeographic backgrounds, making it an important carrier and ideal material for regional paleogeography and paleoclimatology research. After nearly a century of research, a relatively complete theoretical system of eolian deposition has been formed internationally, which has effectively promoted the identification and interpretation of ancient eolian deposits. However, there is currently no systematic introduction to the theoretical system of eolian deposition in China. In recent years, with the discovery and reporting of more ancient desert basins in China, research on ancient eolian deposition has gradually attracted widespread attention both domestically and internationally. In order to better promote research on aeolian deposition in China, this article provides a detailed introduction to the theoretical system of eolian deposition based on previous research, including the atmospheric flow characteristics, fluid properties and wind fields, sediment transport, composition and structure of eolian deposits, eolian bedform morphology, eolian stratigraphy, eolian interfaces, eolian depositional systems, formation and preservation of eolian deposits, etc. The current problems in eolian deposition research are discussed, and important future research directions are proposed.
Eolian deposition, as a product of wind erosion, transportation, and accumulation on the Earth's surface, has a wide spatial and temporal distribution in geological history. Its formation and evolution are closely related to arid climatic conditions and relatively continuous subsidence of paleogeographic backgrounds, making it an important carrier and ideal material for regional paleogeography and paleoclimatology research. After nearly a century of research, a relatively complete theoretical system of eolian deposition has been formed internationally, which has effectively promoted the identification and interpretation of ancient eolian deposits. However, there is currently no systematic introduction to the theoretical system of eolian deposition in China. In recent years, with the discovery and reporting of more ancient desert basins in China, research on ancient eolian deposition has gradually attracted widespread attention both domestically and internationally. In order to better promote research on aeolian deposition in China, this article provides a detailed introduction to the theoretical system of eolian deposition based on previous research, including the atmospheric flow characteristics, fluid properties and wind fields, sediment transport, composition and structure of eolian deposits, eolian bedform morphology, eolian stratigraphy, eolian interfaces, eolian depositional systems, formation and preservation of eolian deposits, etc. The current problems in eolian deposition research are discussed, and important future research directions are proposed.
, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.063
Abstract:
[Objective] To understand the sedimentary characteristics of shell limestone-shale mixed strata in the Da’anzhai Member of Sichuan Basin and its influence on favorable shale oil horizon, field profiles in Dazhou Tieshan Jinwo and Liangping Fuluzhen of the northeast Sichuan Basin were studied. [Methods] The lithology and sequence, source and reservoir quality, and favorable strata of the Da’anzhai Member were evaluated in detail by using rock thin sections, X-ray diffraction (XRD) whole rock and organic geochemical analyses. [Results] The results show that: 1) The Da’anzhai Member is a set of limestone-shale mixed strata, and different lithologies are superimposed in an orderly way to form a variety of upward shallower sequences. From shallow lake to semi-deep lake-deep lake, six kinds of upward shallower decimeter to meter lithofacies sequences are identified: ①shale-shell shale, ②shale-thin shell limestone, ③shale-medium shell limestone, ④shale-nodular micrite, ⑤thin shale-shell limestone-crystalline limestone, and ⑥shell limestone-siltstone/fine sandstone. 2) The quality of source and reservoir varies greatly among different lithologic sequences. Black shales in sequence 1–3 are developed with the best source quality. The organic carbon content of black shales in a single sequence shows a trend of higher and lower organic carbon content, and total organic carbon (TOC) gradually decreases with the increase of shell limestone. Different lithologic properties vary greatly. The porosity of shale is higher than that of limestone and siltstone, but the clay content is high, the pore size is small, and the seepage capacity is poor. Limestone easily develops joint fractures, and the density of joints decreases exponentially with the increase of limestone thickness. Therefore, Sequence 2–4 developed middle and thin layer limestone has better reservoir performance. 3) The field oil seedling shows that the shale oil reservoir of the Da’anzhai Member is characterized by the separation of source and reservoir and thin high-quality reservoir. The shale oil seepages in the field are mainly distributed near the joints of the medium–thin layer shell limestone. The favorable reservoir is primarily controlled by the sedimentary conditions, micro-fractures, and configuration of source and reservoir. [Conclusions] Sequences 2 and 3 have the best source and reservoir configuration conditions, which are favorable intervals for shale oil.
[Objective] To understand the sedimentary characteristics of shell limestone-shale mixed strata in the Da’anzhai Member of Sichuan Basin and its influence on favorable shale oil horizon, field profiles in Dazhou Tieshan Jinwo and Liangping Fuluzhen of the northeast Sichuan Basin were studied. [Methods] The lithology and sequence, source and reservoir quality, and favorable strata of the Da’anzhai Member were evaluated in detail by using rock thin sections, X-ray diffraction (XRD) whole rock and organic geochemical analyses. [Results] The results show that: 1) The Da’anzhai Member is a set of limestone-shale mixed strata, and different lithologies are superimposed in an orderly way to form a variety of upward shallower sequences. From shallow lake to semi-deep lake-deep lake, six kinds of upward shallower decimeter to meter lithofacies sequences are identified: ①shale-shell shale, ②shale-thin shell limestone, ③shale-medium shell limestone, ④shale-nodular micrite, ⑤thin shale-shell limestone-crystalline limestone, and ⑥shell limestone-siltstone/fine sandstone. 2) The quality of source and reservoir varies greatly among different lithologic sequences. Black shales in sequence 1–3 are developed with the best source quality. The organic carbon content of black shales in a single sequence shows a trend of higher and lower organic carbon content, and total organic carbon (TOC) gradually decreases with the increase of shell limestone. Different lithologic properties vary greatly. The porosity of shale is higher than that of limestone and siltstone, but the clay content is high, the pore size is small, and the seepage capacity is poor. Limestone easily develops joint fractures, and the density of joints decreases exponentially with the increase of limestone thickness. Therefore, Sequence 2–4 developed middle and thin layer limestone has better reservoir performance. 3) The field oil seedling shows that the shale oil reservoir of the Da’anzhai Member is characterized by the separation of source and reservoir and thin high-quality reservoir. The shale oil seepages in the field are mainly distributed near the joints of the medium–thin layer shell limestone. The favorable reservoir is primarily controlled by the sedimentary conditions, micro-fractures, and configuration of source and reservoir. [Conclusions] Sequences 2 and 3 have the best source and reservoir configuration conditions, which are favorable intervals for shale oil.
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Abstract:
In situ U-Pb and trace element analysis were carried out by using LA-ICP-MS technique on detrital zircons of sheeted meta-quartzite from the Taiyangsi Formation in the Tianshui area of West Qinling. Four main age populations were obtained from 39 analyses, with clusters at 429~530Ma，757~1902Ma，2119~2280Ma，2518~2544Ma, respectively. The 429~530Ma zircons is about 31% and the 757~1902 Ma zircons is about 56% of this dataset. The youngest discrete population of four grains yielded a weighted-mean age of 430.6±3.4Ma, which can be considered the maximum depositional age of the Taiyangsi Formation as Early Silurian. The detrital zircon geochronological results confirm that the Proterozoic basement of North Qinling microcontinent was the predominant source area for the sediments, the Early Paleozoic magmatic arc should be another important source area. The trace element compositions of these zircons suggest that they were mainly derived from felsic igneous rocks on continental crust. In Early Silurian, an magmatic arc was superimposed on the basement of North Qinling microcontinent. The sediments have been shed into platform of the wide arc-trench gap at this time, which derived from the recycled detritus of the basement of North Qinling microcontinent and the magmatic arc. Siliciclastic rocks of the Taiyangsi Formation record the sedimentary response of tectonism during the incipient volcanic-arc stage.
In situ U-Pb and trace element analysis were carried out by using LA-ICP-MS technique on detrital zircons of sheeted meta-quartzite from the Taiyangsi Formation in the Tianshui area of West Qinling. Four main age populations were obtained from 39 analyses, with clusters at 429~530Ma，757~1902Ma，2119~2280Ma，2518~2544Ma, respectively. The 429~530Ma zircons is about 31% and the 757~1902 Ma zircons is about 56% of this dataset. The youngest discrete population of four grains yielded a weighted-mean age of 430.6±3.4Ma, which can be considered the maximum depositional age of the Taiyangsi Formation as Early Silurian. The detrital zircon geochronological results confirm that the Proterozoic basement of North Qinling microcontinent was the predominant source area for the sediments, the Early Paleozoic magmatic arc should be another important source area. The trace element compositions of these zircons suggest that they were mainly derived from felsic igneous rocks on continental crust. In Early Silurian, an magmatic arc was superimposed on the basement of North Qinling microcontinent. The sediments have been shed into platform of the wide arc-trench gap at this time, which derived from the recycled detritus of the basement of North Qinling microcontinent and the magmatic arc. Siliciclastic rocks of the Taiyangsi Formation record the sedimentary response of tectonism during the incipient volcanic-arc stage.
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Abstract:
Abstract Making use of indoor qualitative data, the author has summed up the tectonic environment evolution of Jinhua-Quzhou basin, having given an integrated analysis. And it is also quantitative and qualitative distinguished based on geochemistry, including facts of outside field surveying. The description of Jinhua-Quzhou basin’s tectonic environment evolution involes such aspects as the basin’s basement, lanthanon, microelements, isotopes and so on, with a view to their characteristics. The paper lets us know that the basin’s tectonic environment evolution has speciality of multi-phase.
Abstract Making use of indoor qualitative data, the author has summed up the tectonic environment evolution of Jinhua-Quzhou basin, having given an integrated analysis. And it is also quantitative and qualitative distinguished based on geochemistry, including facts of outside field surveying. The description of Jinhua-Quzhou basin’s tectonic environment evolution involes such aspects as the basin’s basement, lanthanon, microelements, isotopes and so on, with a view to their characteristics. The paper lets us know that the basin’s tectonic environment evolution has speciality of multi-phase.
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Multiple lithologic reservoirs exist on Yanchang formation in Jiyuan area of Ordos basin, and the problem of oil-source becomes main difficulty and hotspot for accumulation mechanism domain. Based on the physicochemical properties analysis of crude oil, oilfield water and source-rock, such as group compositions and gas chromatograms of saturated hydrocarbon, as well as characteristics of terpane, sterane and other biomarkers, the results show that the crude oil properties are especially complex in member 8, member 6 and member 4+5 of Yanchang formation. The crude oil characteristics take on obvious difference in thermal maturity, source rock depositional environment and type and so on. The qualities of organic matter differ in member 9, member 8, member 7, member 6 and member 4+5 according to the potential source-rock appraisement, but they all were provided with the ability of hydrocarbon generation and expulsion. The crude oil of member 8, member 6 and member 4+5 respectively comes from organic matter of member 7 and member 8, member 7 and member 6, member 6 based on oil-source correlation. Otherwise, the possible instances of mixed oils and member 9 oil-source are speculated in local plays.
Multiple lithologic reservoirs exist on Yanchang formation in Jiyuan area of Ordos basin, and the problem of oil-source becomes main difficulty and hotspot for accumulation mechanism domain. Based on the physicochemical properties analysis of crude oil, oilfield water and source-rock, such as group compositions and gas chromatograms of saturated hydrocarbon, as well as characteristics of terpane, sterane and other biomarkers, the results show that the crude oil properties are especially complex in member 8, member 6 and member 4+5 of Yanchang formation. The crude oil characteristics take on obvious difference in thermal maturity, source rock depositional environment and type and so on. The qualities of organic matter differ in member 9, member 8, member 7, member 6 and member 4+5 according to the potential source-rock appraisement, but they all were provided with the ability of hydrocarbon generation and expulsion. The crude oil of member 8, member 6 and member 4+5 respectively comes from organic matter of member 7 and member 8, member 7 and member 6, member 6 based on oil-source correlation. Otherwise, the possible instances of mixed oils and member 9 oil-source are speculated in local plays.
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Gravity flow channel developed in Dainan Formation, Paleogene in Gaoyou Sag, Subei Basin. Based on the integrated analysis on the data of seismic, logging, core and laboratory rock tests, the sedimentary characteristics and distribution rules of gravity flow channel were discussed. The formation of gravity flow channel is due to the intermittent floodwater and its scouring, re-transportation, and re-deposition of sediments of delta. The gravity flow channel is developed along the fault-trough formed by syn-depositional fault in the sag, and can be divided into two subfacies: channel and lateral margin. The lateral margin can be subdivided into two microfacies of levee and overflows. Vertical sedimentary sequence model is established based on integrated studies. The gravity flow channel is an favorable oil & gas bearing facies. This study provides a new oil & Gas exploring realm in Subei Basin.
Gravity flow channel developed in Dainan Formation, Paleogene in Gaoyou Sag, Subei Basin. Based on the integrated analysis on the data of seismic, logging, core and laboratory rock tests, the sedimentary characteristics and distribution rules of gravity flow channel were discussed. The formation of gravity flow channel is due to the intermittent floodwater and its scouring, re-transportation, and re-deposition of sediments of delta. The gravity flow channel is developed along the fault-trough formed by syn-depositional fault in the sag, and can be divided into two subfacies: channel and lateral margin. The lateral margin can be subdivided into two microfacies of levee and overflows. Vertical sedimentary sequence model is established based on integrated studies. The gravity flow channel is an favorable oil & gas bearing facies. This study provides a new oil & Gas exploring realm in Subei Basin.
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Abstract : During the Depositional period of Tabyin and Pondaung formation, due to the complexity of the basin tectonic and changes of provenance-the depositional disperse system formed the complex basin depositional system. The main development of depositional systems are: rivers, deltas, debris coast, shallow marine deposition, it is a depositional group of the river prograding to the ocean basin to form a set of clastic deposition. More favorable reservoir are mainly distributed in the proximal bar of delta front and underwater distributary channel of the lower part of Tabyin formation, longshore bar of shallow marine deposition of the upper part of Tabyin formation, distributary channel of delta plain of the lower part of Pondaung formation, sand flat of eulittoral zone of middle part of Pondaung formation. During the depositonal period of Tabyin formation, The basin formed the paleogeographic framework of marginal sea under the low compression, the provenance mainly from the east and northeast. During the depositonal period of Pondaung formation, palaeogeographic change for the Gulf opening from north to south under the high compression, and receiving the Western and eastern provenance, and the river , delta depositional system is continuously prograding to the basin. The distribution of sedimentary facies has the characteristics of from west to east, from south to north.
Abstract : During the Depositional period of Tabyin and Pondaung formation, due to the complexity of the basin tectonic and changes of provenance-the depositional disperse system formed the complex basin depositional system. The main development of depositional systems are: rivers, deltas, debris coast, shallow marine deposition, it is a depositional group of the river prograding to the ocean basin to form a set of clastic deposition. More favorable reservoir are mainly distributed in the proximal bar of delta front and underwater distributary channel of the lower part of Tabyin formation, longshore bar of shallow marine deposition of the upper part of Tabyin formation, distributary channel of delta plain of the lower part of Pondaung formation, sand flat of eulittoral zone of middle part of Pondaung formation. During the depositonal period of Tabyin formation, The basin formed the paleogeographic framework of marginal sea under the low compression, the provenance mainly from the east and northeast. During the depositonal period of Pondaung formation, palaeogeographic change for the Gulf opening from north to south under the high compression, and receiving the Western and eastern provenance, and the river , delta depositional system is continuously prograding to the basin. The distribution of sedimentary facies has the characteristics of from west to east, from south to north.
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Datong volcanic activity left many records in regional lacustrine sediments and loess ones, and some of them have not been recognized. In this research, the authors got some findings through field investigation, analysis on the magnetic susceptibility, chemical component and grain size of the sediment samples in the laboratories. 1) Volcanic clastic layers deposited in different stages near former lakeside display incline with different dip angles, respectively. 2) There are four fine volcanic clastic layers in the grayish-green lacustrine sediment in the former inshore. 3) There exist four sediment layers in the center of former lake which display high magnetic susceptibility value, implying some volcanic ash may deposited in them. 4) There exist three sediment layers in the loess section in the land away from the former lake, which display high magnetic susceptibility value and low Rb/Sr one, implying some volcanic ash may deposit in them. Besides, the grain size of the four lacustrine layers with high magnetic susceptibility in the center of the former lake is much coarser than that of others. Based on these facts, the authors deduced that 1) Datong volcanoes experienced four active stages in the past and there took place many volcanic eruptions during each stage; 2) each of the active stages is synchronous with that of the lake regressions in the basin, respectively. These research results will provide more clues to investigate the ages of each volcanic active stage.
Datong volcanic activity left many records in regional lacustrine sediments and loess ones, and some of them have not been recognized. In this research, the authors got some findings through field investigation, analysis on the magnetic susceptibility, chemical component and grain size of the sediment samples in the laboratories. 1) Volcanic clastic layers deposited in different stages near former lakeside display incline with different dip angles, respectively. 2) There are four fine volcanic clastic layers in the grayish-green lacustrine sediment in the former inshore. 3) There exist four sediment layers in the center of former lake which display high magnetic susceptibility value, implying some volcanic ash may deposited in them. 4) There exist three sediment layers in the loess section in the land away from the former lake, which display high magnetic susceptibility value and low Rb/Sr one, implying some volcanic ash may deposit in them. Besides, the grain size of the four lacustrine layers with high magnetic susceptibility in the center of the former lake is much coarser than that of others. Based on these facts, the authors deduced that 1) Datong volcanoes experienced four active stages in the past and there took place many volcanic eruptions during each stage; 2) each of the active stages is synchronous with that of the lake regressions in the basin, respectively. These research results will provide more clues to investigate the ages of each volcanic active stage.
The Discovery of the CORBs and Upper Cretaceous Foraminiferal Biostraigraphy in Duina, Yadong, Tibet
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The shallow strata of the Mahu slope area in Junggar Basin have been considered to be shallow buried and high profit, but it has poor results through many rounds of exploration. Based on a large number of logging, three-dimensional seismic, analytical and laboratory data, the overall study to the shallow strata in slope area is carried out. The study of basic petroleum geological conditions shows that the shallow strata in the slope area of Mahu Sag have good reservoir-seal assemblages, large reservoir scale, shallow burial depth, good physical properties, and superior migration conditions, easy to form fault-lithologic trap groups for matching with faults, and have the geological conditions of forming clustered fault-lithologic accumulations. The shallow and deep strata in the slope area of Mahu Sag are characterized by relay accumulating, the oil and gas enriched areas of which have certain inheritance. Therefore, the shallow strata have broad resource prospect and great exploration potential, and is a favorable area for further exploration of high-efficiency reserves.
The shallow strata of the Mahu slope area in Junggar Basin have been considered to be shallow buried and high profit, but it has poor results through many rounds of exploration. Based on a large number of logging, three-dimensional seismic, analytical and laboratory data, the overall study to the shallow strata in slope area is carried out. The study of basic petroleum geological conditions shows that the shallow strata in the slope area of Mahu Sag have good reservoir-seal assemblages, large reservoir scale, shallow burial depth, good physical properties, and superior migration conditions, easy to form fault-lithologic trap groups for matching with faults, and have the geological conditions of forming clustered fault-lithologic accumulations. The shallow and deep strata in the slope area of Mahu Sag are characterized by relay accumulating, the oil and gas enriched areas of which have certain inheritance. Therefore, the shallow strata have broad resource prospect and great exploration potential, and is a favorable area for further exploration of high-efficiency reserves.
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The restricted environment reservoirs in the Middle East are thick and rich in oil and gas, but it is difficult to develop effectively. To deep the understanding of reservoir heterogeneity, the reservoirs types, characteristics and genesis in restricted environment in the Mishrif Formation, M oilfield, in the Middle East was examined comprehensively based on the core observation and description, casting thin sections, the physical property analysis and the mercury intrusion experiments. The result showed that there were three types of reservoir which were the Reservoir Type 1, Reservoir Type 2 and Reservoir Type 3 in the restricted environment. The Reservoir Type 1 are developed in high-energy depositional environments such as tidal channels and intra-platform shoals and experienced dissolution in the quasi-contemporaneous period. The reservoirs are mainly grainstone with medium-high porosity and medium-high permeability. The reserve space is mainly composed of intergranular pores and dissolved pores. It is the preferred target reservoir type for reservoir development as it has huge scale and stable distribution. The Reservoir Type 2 are mainly developed in high-energy depositional environments such as lagoon and experienced dissolution in the quasi-contemporaneous period. The reservoirs include grain-bearing limestone, wackstone and packstone. The physical properties are mainly medium-high porosity and medium-low permeability. The primary intergranular pores are not developed, and the reserve space is matrix-host micropores, mold pores and intercrystalline pores. The diagenetic reservoir has the largest development scale, but the thickness of the single layer is thin, the frequency of development of interlayers is high, and the development is difficult. The Reservoir Type 3 is formed in the intra-platform shoals and experienced Quasi-contemporaneous dolomitization. The reservoirs are mostly dolomite with medium-high porosity and medium-low permeability. The Reservoir Type 3 are small in scale and are only locally developed in the upper part of the Mishrif Formation. The study concluded that the genesis of Reservoir Type 1 is mainly controlled by sedimentation, which controls the original structural components of the rock, which in turn controls the type and intensity of diagenesis in the quasi-contemporaneous period. The Reservoir Type 2 have weak sedimentary hydrodynamic conditions and the primary intergranular pores are not developed. Reservoir spaces are mainly formed by constructive diagenesis such as selective dissolution. The Reservoir Type 3 has undergone greater diagenetic reformation, severe damage to the original structural components, local residual biological debris indicating that it was formed in a medium-high energy sedimentary environment, and the reservoir was formed by mixed dolomitization.
The restricted environment reservoirs in the Middle East are thick and rich in oil and gas, but it is difficult to develop effectively. To deep the understanding of reservoir heterogeneity, the reservoirs types, characteristics and genesis in restricted environment in the Mishrif Formation, M oilfield, in the Middle East was examined comprehensively based on the core observation and description, casting thin sections, the physical property analysis and the mercury intrusion experiments. The result showed that there were three types of reservoir which were the Reservoir Type 1, Reservoir Type 2 and Reservoir Type 3 in the restricted environment. The Reservoir Type 1 are developed in high-energy depositional environments such as tidal channels and intra-platform shoals and experienced dissolution in the quasi-contemporaneous period. The reservoirs are mainly grainstone with medium-high porosity and medium-high permeability. The reserve space is mainly composed of intergranular pores and dissolved pores. It is the preferred target reservoir type for reservoir development as it has huge scale and stable distribution. The Reservoir Type 2 are mainly developed in high-energy depositional environments such as lagoon and experienced dissolution in the quasi-contemporaneous period. The reservoirs include grain-bearing limestone, wackstone and packstone. The physical properties are mainly medium-high porosity and medium-low permeability. The primary intergranular pores are not developed, and the reserve space is matrix-host micropores, mold pores and intercrystalline pores. The diagenetic reservoir has the largest development scale, but the thickness of the single layer is thin, the frequency of development of interlayers is high, and the development is difficult. The Reservoir Type 3 is formed in the intra-platform shoals and experienced Quasi-contemporaneous dolomitization. The reservoirs are mostly dolomite with medium-high porosity and medium-low permeability. The Reservoir Type 3 are small in scale and are only locally developed in the upper part of the Mishrif Formation. The study concluded that the genesis of Reservoir Type 1 is mainly controlled by sedimentation, which controls the original structural components of the rock, which in turn controls the type and intensity of diagenesis in the quasi-contemporaneous period. The Reservoir Type 2 have weak sedimentary hydrodynamic conditions and the primary intergranular pores are not developed. Reservoir spaces are mainly formed by constructive diagenesis such as selective dissolution. The Reservoir Type 3 has undergone greater diagenetic reformation, severe damage to the original structural components, local residual biological debris indicating that it was formed in a medium-high energy sedimentary environment, and the reservoir was formed by mixed dolomitization.
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Guizhou Province is an important production base of aluminum with a recoverable reserve of bauxite of 1.289 billion ton, accounting for 17% of the national total and ranking 2nd in China. The bauxite deposits are characterized by enrichments in critical metals, such as Li, Ga, Sc and REE. By studying geological characteristics of the aluminiferous rock series of Guizhou bauxite deposits and critical metal distributions, we summarized the characteristics of the critical metal enrichments and evaluated their resource potentials.The results show that Li, Ga, Sc and REE are, to varying degrees, enriched in aluminiferous rock series. Li contents are higher in the Wu-Zheng-Dao bauxite ore-concentrated area, northern Guizhou Province, compared with other areas of study, and the element mainly occurs in the dense bauxite in the middle-upper section of the aluminiferous rock series. Ga is higher in the Wu-Zheng-Dao and Zunyi-Weng′an (central Guizhou) bauxite ore-concentrated areas and mainly present in the claylike and clastic bauxite in the middle section of the aluminiferous rock series. REE are relatively higher in the Wu-Zheng-Dao and Xiuwen-Qingzhen (southwest Guizhou) bauxite ore-concentrated areas and mainly hosted in the chlorite mudstone and ferruginous claystone in the lower section of the aluminiferous rock series. Sc has a relatively homogeneous distribution in both horizontal and vertical directions. Among the various rocks (ores) of the aluminous rock series, Li, Ga, Sc, and REE mainly occur as sorption onto mineral surface and fractures and as isomorphic substitution into the structures of clay minerals, Al-minerals and accessory minerals. A small amount of REE is present as independent minerals. Comprehensively, resource potentials of Li, Ga, Sc, and REE in the aluminous rock series in Guizhou Province and their potential economic values are huge. Further work is needed to strengthen systematic study and comprehensive utilization, which helps to achieve maximum economic and environmental benefits.
Guizhou Province is an important production base of aluminum with a recoverable reserve of bauxite of 1.289 billion ton, accounting for 17% of the national total and ranking 2nd in China. The bauxite deposits are characterized by enrichments in critical metals, such as Li, Ga, Sc and REE. By studying geological characteristics of the aluminiferous rock series of Guizhou bauxite deposits and critical metal distributions, we summarized the characteristics of the critical metal enrichments and evaluated their resource potentials.The results show that Li, Ga, Sc and REE are, to varying degrees, enriched in aluminiferous rock series. Li contents are higher in the Wu-Zheng-Dao bauxite ore-concentrated area, northern Guizhou Province, compared with other areas of study, and the element mainly occurs in the dense bauxite in the middle-upper section of the aluminiferous rock series. Ga is higher in the Wu-Zheng-Dao and Zunyi-Weng′an (central Guizhou) bauxite ore-concentrated areas and mainly present in the claylike and clastic bauxite in the middle section of the aluminiferous rock series. REE are relatively higher in the Wu-Zheng-Dao and Xiuwen-Qingzhen (southwest Guizhou) bauxite ore-concentrated areas and mainly hosted in the chlorite mudstone and ferruginous claystone in the lower section of the aluminiferous rock series. Sc has a relatively homogeneous distribution in both horizontal and vertical directions. Among the various rocks (ores) of the aluminous rock series, Li, Ga, Sc, and REE mainly occur as sorption onto mineral surface and fractures and as isomorphic substitution into the structures of clay minerals, Al-minerals and accessory minerals. A small amount of REE is present as independent minerals. Comprehensively, resource potentials of Li, Ga, Sc, and REE in the aluminous rock series in Guizhou Province and their potential economic values are huge. Further work is needed to strengthen systematic study and comprehensive utilization, which helps to achieve maximum economic and environmental benefits.
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The geological history of water activity on the surface of Mars has always been the focus of scientific research, which directly affects the research direction of Mars exploration. According to the comparability between Mars and Earth, this paper establishes a data set which fused 345 modern fluvial fan deposits of Earth and forms a high-precision fan area prediction model. Combined with the fan characteristics of the data set, a typical fluvial fan deposit with an area of about 84.35 km2 is identified near Holden Crater in the southern highland of Mars. Based on the neural network model, the annual average surface water runoff required for the formation of the fan is predicted to be 1,882,800 m3. According to the comparative analysis with the runoff of fluvial fans in the Earth, it is found that the runoff in this area of Mars is not composed of single precipitation, but is presumed to be a variety of sources of precipitation and melting water of snow-capped mountains (glaciers). This achievement is the application of fluvial fan research in planetary sedimentology, and provides a new method for further studying the surface water activities of Mars and other celestial bodies.
The geological history of water activity on the surface of Mars has always been the focus of scientific research, which directly affects the research direction of Mars exploration. According to the comparability between Mars and Earth, this paper establishes a data set which fused 345 modern fluvial fan deposits of Earth and forms a high-precision fan area prediction model. Combined with the fan characteristics of the data set, a typical fluvial fan deposit with an area of about 84.35 km2 is identified near Holden Crater in the southern highland of Mars. Based on the neural network model, the annual average surface water runoff required for the formation of the fan is predicted to be 1,882,800 m3. According to the comparative analysis with the runoff of fluvial fans in the Earth, it is found that the runoff in this area of Mars is not composed of single precipitation, but is presumed to be a variety of sources of precipitation and melting water of snow-capped mountains (glaciers). This achievement is the application of fluvial fan research in planetary sedimentology, and provides a new method for further studying the surface water activities of Mars and other celestial bodies.
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dolomitic rocks in the second and third members of Permian Fengcheng Formation in Wuerhe area, northwest margin of Junggar basin are very developed. They are mainly concentrated in deep lake-semi deep lake area on the plane and slightly thinner towards shore shallow lake. They are important reservoir rocks in this area. Through core observation of several wells in this area, combined with rock and mineral analysis such as rock thin section, X-ray diffraction, electron microprobe and scanning electron microscope, as well as test and analysis of trace elements, rare earth elements, stable isotopes, fluid inclusions and laser Raman, the rock and mineral characteristics, geochemical characteristics and genetic mechanism of cloud rocks of Fengcheng Formation are systematically clarified and revealed. The results of carbon and oxygen isotope test show that in dolomite δ The variation range of 13cdol is 1.0 ~ 7.1 ‰ (average 4.33 ‰), oxygen isotope δ The variation range of 18odol is - 15.1 ~ 4.4 ‰ (average - 2.94 ‰), indicating hydrothermal activity; The REE chondrite distribution pattern shows that hydrothermal fluid activity exists in different periods; The homogenization temperature of fluid inclusions in dolomite cement varies from 51.7 to 123.8 ℃, and the salinity is 15.2 wt% ~ 22.7wt% NaCl. Combined with the inclusion composition test results, it shows that the hydrothermal fluid belongs to the hydrothermal fluid of medium low temperature, medium high salinity, rich in CH4 gas and H2O NaCl system. The trace element test results are y / Ho > 28, europium positive anomaly (EU / EU * > 1), cerium positive anomaly (CE / CE * > 1), U / th > 1.25, V / (V + Ni) > 0.54 and V / Cr > 2. Combined with the right inclination of rare earth element distribution mode, they all indicate the typical alkali lake environment affected by high salinity, strong reduction and heating solution. This paper comprehensively analyzes and establishes the genetic model of dolomite in the study area. It is considered that there are two causes: one is evaporation, which mainly forms irregular laminar dolomite, and the other is hydrothermal metasomatism, which mainly forms massive, evenly distributed and fracture filled dolomite.
dolomitic rocks in the second and third members of Permian Fengcheng Formation in Wuerhe area, northwest margin of Junggar basin are very developed. They are mainly concentrated in deep lake-semi deep lake area on the plane and slightly thinner towards shore shallow lake. They are important reservoir rocks in this area. Through core observation of several wells in this area, combined with rock and mineral analysis such as rock thin section, X-ray diffraction, electron microprobe and scanning electron microscope, as well as test and analysis of trace elements, rare earth elements, stable isotopes, fluid inclusions and laser Raman, the rock and mineral characteristics, geochemical characteristics and genetic mechanism of cloud rocks of Fengcheng Formation are systematically clarified and revealed. The results of carbon and oxygen isotope test show that in dolomite δ The variation range of 13cdol is 1.0 ~ 7.1 ‰ (average 4.33 ‰), oxygen isotope δ The variation range of 18odol is - 15.1 ~ 4.4 ‰ (average - 2.94 ‰), indicating hydrothermal activity; The REE chondrite distribution pattern shows that hydrothermal fluid activity exists in different periods; The homogenization temperature of fluid inclusions in dolomite cement varies from 51.7 to 123.8 ℃, and the salinity is 15.2 wt% ~ 22.7wt% NaCl. Combined with the inclusion composition test results, it shows that the hydrothermal fluid belongs to the hydrothermal fluid of medium low temperature, medium high salinity, rich in CH4 gas and H2O NaCl system. The trace element test results are y / Ho > 28, europium positive anomaly (EU / EU * > 1), cerium positive anomaly (CE / CE * > 1), U / th > 1.25, V / (V + Ni) > 0.54 and V / Cr > 2. Combined with the right inclination of rare earth element distribution mode, they all indicate the typical alkali lake environment affected by high salinity, strong reduction and heating solution. This paper comprehensively analyzes and establishes the genetic model of dolomite in the study area. It is considered that there are two causes: one is evaporation, which mainly forms irregular laminar dolomite, and the other is hydrothermal metasomatism, which mainly forms massive, evenly distributed and fracture filled dolomite.
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Since the Paleogene, with the uplift of the Qinghai-Tibet Plateau and the large-scale thrust and strike-slip of the strata, many inland basins have been formed in the northern part of the Qinghai-Tibet Plateau. Because of the particularity of the location of these basins, the evolution of paleoclimate and paleo-vegetation in the basin is of great significance to clarify the climatic evolution characteristics of the Paleogene in Eurasia. In this study, the evolution history of paleoclimate and paleo-vegetation in Nangqian basin of 51.8~37.5Ma was reconstructed by using biomarkers and total organic carbon (TOC) in Paleogene sedimentary stratigraphic profile of Nangqian basin in central and eastern Qinghai- Tibet Plateau. The evolution history of Paleogene climate index in Nangqian basin can be divided into three stages, and the changes of sedimentary facies in each stage are also different. Stage I: 51.8~46.4Ma, the sedimentary facies in this stage are mainly fluvial facies and short-term lacustrine facies, the values of CPI and total organic carbon (TOC) are lower, and the values of Paq are higher. ACL and nC27/nC31 show an obvious change trend in this period, which may be affected by the mixing of terrestrial sediments brought by rivers, most of the main peak carbon is nC22 and nC23, the vegetation type is dominated by woody plants, and the climate conditions are relatively humid. Stage Ⅱ: 46.4~42.7Ma, in which Paq value and nC27/ nC31 value gradually decreased, ACL value gradually increased, the carbon number of the main peak gradually changed from low carbon number to medium or high carbon number, the vegetation type gradually changed from woody to herbaceous plants, and the climate conditions gradually became drought, accompanied by alternating drought and wet climatic characteristics. Stage III: 42.7 to 37.5 Ma ,Paq, nC27/nC31 and ACL values changed little, the carbon number of the main peak increased significantly, the n-alkanes with high carbon number increased significantly, and the degree of drought further increased, while the organic carbon content (TOC) significantly increased, indicating the increasing of total vegetation productivity, which may be a response to the warm and the Middle Eocene Climatic Optimum (MECO). In addition, by comparing with the research results of climate change in the study area and adjacent basins, it is considered that the climate change during 51.8~37.5Ma in Nangqian basin is mainly affected by global climate change and the retreat of the Tethys Sea. The uplift of Qinghai-Tibet Plateau and the increase of altitude have great influence on water vapor in Nangqian basin, while monsoon has little influence on water vapor.
Since the Paleogene, with the uplift of the Qinghai-Tibet Plateau and the large-scale thrust and strike-slip of the strata, many inland basins have been formed in the northern part of the Qinghai-Tibet Plateau. Because of the particularity of the location of these basins, the evolution of paleoclimate and paleo-vegetation in the basin is of great significance to clarify the climatic evolution characteristics of the Paleogene in Eurasia. In this study, the evolution history of paleoclimate and paleo-vegetation in Nangqian basin of 51.8~37.5Ma was reconstructed by using biomarkers and total organic carbon (TOC) in Paleogene sedimentary stratigraphic profile of Nangqian basin in central and eastern Qinghai- Tibet Plateau. The evolution history of Paleogene climate index in Nangqian basin can be divided into three stages, and the changes of sedimentary facies in each stage are also different. Stage I: 51.8~46.4Ma, the sedimentary facies in this stage are mainly fluvial facies and short-term lacustrine facies, the values of CPI and total organic carbon (TOC) are lower, and the values of Paq are higher. ACL and nC27/nC31 show an obvious change trend in this period, which may be affected by the mixing of terrestrial sediments brought by rivers, most of the main peak carbon is nC22 and nC23, the vegetation type is dominated by woody plants, and the climate conditions are relatively humid. Stage Ⅱ: 46.4~42.7Ma, in which Paq value and nC27/ nC31 value gradually decreased, ACL value gradually increased, the carbon number of the main peak gradually changed from low carbon number to medium or high carbon number, the vegetation type gradually changed from woody to herbaceous plants, and the climate conditions gradually became drought, accompanied by alternating drought and wet climatic characteristics. Stage III: 42.7 to 37.5 Ma ,Paq, nC27/nC31 and ACL values changed little, the carbon number of the main peak increased significantly, the n-alkanes with high carbon number increased significantly, and the degree of drought further increased, while the organic carbon content (TOC) significantly increased, indicating the increasing of total vegetation productivity, which may be a response to the warm and the Middle Eocene Climatic Optimum (MECO). In addition, by comparing with the research results of climate change in the study area and adjacent basins, it is considered that the climate change during 51.8~37.5Ma in Nangqian basin is mainly affected by global climate change and the retreat of the Tethys Sea. The uplift of Qinghai-Tibet Plateau and the increase of altitude have great influence on water vapor in Nangqian basin, while monsoon has little influence on water vapor.
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Abstract：Recently, a breakthrough has been made in the gas exploration of the bauxite rock series of the Permian Taiyuan formation in the Longdong area of the southwestern margin of the Ordos Basin, opening up a new field of gas reservoir exploration. As a new type of reservoir, the research of bauxite rock series reservoir have important research value. In this paper, based on the experimental methods of core observation, rock slice analysis, Whole rock analysis by X-ray diffraction and scanning electron microscope energy spectrum and other experimental methods, For the first time, the petrological characteristics and pore structure characteristics of bauxite reservoirs were systematically studied. Furthermore, the exploration significance of bauxite reservoirs in the basin is expounded.The results show that: 1)The main mineral composition of the bauxite rock series of Taiyuan formation is aluminiferous mineral and clay mineral, the main minerals are diaspore, kaolinite, illite and chlorite,and the crystals of the minerals are small, mainly cryptocrystalline, microcrystalline and cryptocrystalline masses; 2)the lithologic sequence is characterized by three segments in vertical direction. The upper and lower parts are composed of aluminiferous mudstone, the middle part is composed of bauxite, and the solution pores are developed, which is the main reservoir development section of bauxite rock series;3)The reservoir spaces of bauxite are mainly composed of intragranular solution pores, matrix solution pores, intergranular dissolution pores, intercrystalline pores and micro-fractures. The pore size is mainly in the range of 20μm～200μm.The average porosity and permeability of the reservoir are 10.6% and 4.04 mD, 36% of which are larger than 0.3 mD, and the reservoir performance is good. 4) The pore size of the mainstream throat of the reservoir is in the range of 150 nm～4μm, and nanoscale pores are less developed, better pore structure, high mercury removal efficiency.On the whole, the pores are mainly sub-micron pores and micron pores;5)According to preliminary assessment, the favorable area of bauxite gas reservoir exploration is about 7000 km2, and the natural gas resource exceeds 5000×108m3, which has achieved a major breakthrough in the new type of bauxite gas reservoir in Paleozoic of the Ordos Basin.
Abstract：Recently, a breakthrough has been made in the gas exploration of the bauxite rock series of the Permian Taiyuan formation in the Longdong area of the southwestern margin of the Ordos Basin, opening up a new field of gas reservoir exploration. As a new type of reservoir, the research of bauxite rock series reservoir have important research value. In this paper, based on the experimental methods of core observation, rock slice analysis, Whole rock analysis by X-ray diffraction and scanning electron microscope energy spectrum and other experimental methods, For the first time, the petrological characteristics and pore structure characteristics of bauxite reservoirs were systematically studied. Furthermore, the exploration significance of bauxite reservoirs in the basin is expounded.The results show that: 1)The main mineral composition of the bauxite rock series of Taiyuan formation is aluminiferous mineral and clay mineral, the main minerals are diaspore, kaolinite, illite and chlorite,and the crystals of the minerals are small, mainly cryptocrystalline, microcrystalline and cryptocrystalline masses; 2)the lithologic sequence is characterized by three segments in vertical direction. The upper and lower parts are composed of aluminiferous mudstone, the middle part is composed of bauxite, and the solution pores are developed, which is the main reservoir development section of bauxite rock series;3)The reservoir spaces of bauxite are mainly composed of intragranular solution pores, matrix solution pores, intergranular dissolution pores, intercrystalline pores and micro-fractures. The pore size is mainly in the range of 20μm～200μm.The average porosity and permeability of the reservoir are 10.6% and 4.04 mD, 36% of which are larger than 0.3 mD, and the reservoir performance is good. 4) The pore size of the mainstream throat of the reservoir is in the range of 150 nm～4μm, and nanoscale pores are less developed, better pore structure, high mercury removal efficiency.On the whole, the pores are mainly sub-micron pores and micron pores;5)According to preliminary assessment, the favorable area of bauxite gas reservoir exploration is about 7000 km2, and the natural gas resource exceeds 5000×108m3, which has achieved a major breakthrough in the new type of bauxite gas reservoir in Paleozoic of the Ordos Basin.
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The South Kunsong Sag is located in the western part of the Wan'an Basin. Since the Cenozoic, the Wan'an Fault has been accompanied by multiple periods of left- and right-handed movement. On the basis of the sequence stratigraphic division of the study area, the interpretation of two-dimensional seismic data and the analysis of logging data are carried out in the study area. Through the fine description of seismic facies, the seismic reflection characteristics of the three subfacies at the shelf edge delta are based on , Focusing on the analysis of the three subfacies on the plane of the shelf margin delta since the Late Miocene in the South Kunsong Sag. Combining the relationship between several important tectonic events in the study area, comprehensively discuss the sedimentary filling evolution model since Miocene in the South Kunsong Depression. The results of the study showed that the South Kunsong Sag mainly deposited the strata since the Oligocene; during the Early Miocene, the South Kunsong Sag was mainly characterized by rapid deposition, with near-source deltas, small deltas in the north, and deltas in the southern slope. The sedimentary source is mainly from the Natuna Uplift. During the Miocene, the South Kunsong Sag entered a period of strike-slip transformation. After the Miocene, the Kunsong Uplift gradually submerged under the water, and the Mekong River system crossed the Mekong. The basin gradually affected the sedimentation of the South Kunsong Sag, and shelf margin deltas began to develop in the study area. During the Late Miocene, the South Kunsong Sag entered a stage of thermal subsidence, and the Kunsong Uplift produced rifts and valleys, forming a large number of intermountain water systems. The Kunsong sag has become the main sedimentary area of the Mekong source; during the Pliocene-Pleistocene, the Mekong delta developed on a large scale, accumulating from west to east, and the delta front entered the central area of the Wan'an Basin.
The South Kunsong Sag is located in the western part of the Wan'an Basin. Since the Cenozoic, the Wan'an Fault has been accompanied by multiple periods of left- and right-handed movement. On the basis of the sequence stratigraphic division of the study area, the interpretation of two-dimensional seismic data and the analysis of logging data are carried out in the study area. Through the fine description of seismic facies, the seismic reflection characteristics of the three subfacies at the shelf edge delta are based on , Focusing on the analysis of the three subfacies on the plane of the shelf margin delta since the Late Miocene in the South Kunsong Sag. Combining the relationship between several important tectonic events in the study area, comprehensively discuss the sedimentary filling evolution model since Miocene in the South Kunsong Depression. The results of the study showed that the South Kunsong Sag mainly deposited the strata since the Oligocene; during the Early Miocene, the South Kunsong Sag was mainly characterized by rapid deposition, with near-source deltas, small deltas in the north, and deltas in the southern slope. The sedimentary source is mainly from the Natuna Uplift. During the Miocene, the South Kunsong Sag entered a period of strike-slip transformation. After the Miocene, the Kunsong Uplift gradually submerged under the water, and the Mekong River system crossed the Mekong. The basin gradually affected the sedimentation of the South Kunsong Sag, and shelf margin deltas began to develop in the study area. During the Late Miocene, the South Kunsong Sag entered a stage of thermal subsidence, and the Kunsong Uplift produced rifts and valleys, forming a large number of intermountain water systems. The Kunsong sag has become the main sedimentary area of the Mekong source; during the Pliocene-Pleistocene, the Mekong delta developed on a large scale, accumulating from west to east, and the delta front entered the central area of the Wan'an Basin.
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The seabed pockmark is not only activity records and instructions of the seabed fluid, but also the key factors affecting oilfield and offshore platform,so it is very important to study the seabed pockmark. According to the high resolution 3D seismic data and so on, carried out on Sedimentary characteristics and genetic mechanism and research significance of seabed pockmarks of West Africa, seabed pockmark have been identified at West Africa,five Sedimentary characteristics seabed pockmark have illustrated, and explore the significance of the research of seabed pockmarks of West Africa.
The seabed pockmark is not only activity records and instructions of the seabed fluid, but also the key factors affecting oilfield and offshore platform,so it is very important to study the seabed pockmark. According to the high resolution 3D seismic data and so on, carried out on Sedimentary characteristics and genetic mechanism and research significance of seabed pockmarks of West Africa, seabed pockmark have been identified at West Africa,five Sedimentary characteristics seabed pockmark have illustrated, and explore the significance of the research of seabed pockmarks of West Africa.
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Tight sandstone reservoir has the characteristics of small pore throat, various pore throat types and strong heterogeneity. Clarifying the micro morphology of pore throat, dividing the level of reservoir pore structure, and multi angle semi quantitative evaluation of reservoir reservoir characteristics and seepage capacity are helpful to clarify the reservoir types with high productivity potential. In this paper, the effects of reservoir microstructure parameters on macro physical properties are quantitatively analyzed by means of cast thin section, scanning electron microscope and high-pressure mercury injection, and the fractal dimension calculation and hierarchical evaluation of reservoir pore structure are carried out of Ledong area in Yinggehai Basin. The results show that the pore structure of large pore throat is one of the important factors affecting the reservoir capacity and seepage capacity of tight sandstone reservoir; The closer the fractal dimension is to 3, the more complex the pore structure is and the less connected large pore throats are. According to the classification characteristics of pore throat, diagenetic facies and the complexity of pore structure, four types of models for classification evaluation of pore structure are established: ① it is a small pore throat dominant reservoir with strong cemented lithofacies, the porosity of large pore throat is less than 45%, and Dmax is 2.75 ~ 2.9, which is a tight reservoir; Type ② is a large pore throat continuous reservoir with weak cementation weak dissolution diagenetic facies. The porosity of large pore throat accounts for 45% ~ 70% and Dmax is 2.7 ~ 2.85. It is a low-permeability reservoir; Type ③ is a dominant reservoir with large pore throat, strong dissolution diagenetic facies, large pore throat porosity accounts for more than 70%, Dmax is 2.55 ~ 2.65, and it is a high-quality reservoir; Type ④ is a single peak reservoir with large pore throat, strongly compacted diagenetic facies, large pore throat porosity accounts for 50% ~ 60%, Dmax is 2.65 ~ 2.75, and it is a low-permeability reservoir. Through the Fisher discrimination method, logging prediction models of four reservoir types are established. It is found that class ③ reservoir has high gas production efficiency and good exploration value. The research results provide a new idea for the evaluation and classification of tight sandstone reservoirs in Huangliu formation, and make it clear that the characteristics of reservoir pore structure control the distribution of gas and water.
Tight sandstone reservoir has the characteristics of small pore throat, various pore throat types and strong heterogeneity. Clarifying the micro morphology of pore throat, dividing the level of reservoir pore structure, and multi angle semi quantitative evaluation of reservoir reservoir characteristics and seepage capacity are helpful to clarify the reservoir types with high productivity potential. In this paper, the effects of reservoir microstructure parameters on macro physical properties are quantitatively analyzed by means of cast thin section, scanning electron microscope and high-pressure mercury injection, and the fractal dimension calculation and hierarchical evaluation of reservoir pore structure are carried out of Ledong area in Yinggehai Basin. The results show that the pore structure of large pore throat is one of the important factors affecting the reservoir capacity and seepage capacity of tight sandstone reservoir; The closer the fractal dimension is to 3, the more complex the pore structure is and the less connected large pore throats are. According to the classification characteristics of pore throat, diagenetic facies and the complexity of pore structure, four types of models for classification evaluation of pore structure are established: ① it is a small pore throat dominant reservoir with strong cemented lithofacies, the porosity of large pore throat is less than 45%, and Dmax is 2.75 ~ 2.9, which is a tight reservoir; Type ② is a large pore throat continuous reservoir with weak cementation weak dissolution diagenetic facies. The porosity of large pore throat accounts for 45% ~ 70% and Dmax is 2.7 ~ 2.85. It is a low-permeability reservoir; Type ③ is a dominant reservoir with large pore throat, strong dissolution diagenetic facies, large pore throat porosity accounts for more than 70%, Dmax is 2.55 ~ 2.65, and it is a high-quality reservoir; Type ④ is a single peak reservoir with large pore throat, strongly compacted diagenetic facies, large pore throat porosity accounts for 50% ~ 60%, Dmax is 2.65 ~ 2.75, and it is a low-permeability reservoir. Through the Fisher discrimination method, logging prediction models of four reservoir types are established. It is found that class ③ reservoir has high gas production efficiency and good exploration value. The research results provide a new idea for the evaluation and classification of tight sandstone reservoirs in Huangliu formation, and make it clear that the characteristics of reservoir pore structure control the distribution of gas and water.
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The different well-logging records were taken to investigate the effects of strata component content variation and the K logging series were chosen to be the best proxy in Lower Cambrian Qiongzhusi Formtion in the southwest Sichuan Basin. The K logging series has been divided into four segments, the detailed spectra analyze were conducted in each segment and evolutional spectra analysis were conducted in the whole Qiongzhusi Formation. Orbital cycles of 405-kyr, 131-kyr, 95-kyr, 6-kyr and 28-kyr have been identified in the sedimentary records. Based on the Gaussian filtering on 405-kyr cycle, and the control ages of 526.86 ± 0.16 Ma from relational region, we constructed a floating astronomical time scale which contained 29 long eccentricity cycles, and the optimal sedimentation rate of each segment are 2.5, 2.9, 3.4 and 4.8cm/kyr. The sedimentary noise model of DYNOT and ρ1 were built on the 405-kyr tuning time series, and then get the relative sea-level change curves in time domain. Through the analysis of relative sea-level change, four third ordered sequences have been recognized, as well as four maximum flooding surface and the T-R cycles. The depositional times of each sequence from early to late are 3.18, 2.03, 2.97 and 3.63 Ma respectively, and each sequence are contained 8, 5, 7 and 9 long eccentricity cycles. The relative sea-level decreased is corresponded to the global carbon isotope negative excursion, it is presumably to be the decreasing sea-level lead to the oxidation of the organic, and the lighter carbon isotopes were released, and then the negative excursion of carbon isotope were formed.
The different well-logging records were taken to investigate the effects of strata component content variation and the K logging series were chosen to be the best proxy in Lower Cambrian Qiongzhusi Formtion in the southwest Sichuan Basin. The K logging series has been divided into four segments, the detailed spectra analyze were conducted in each segment and evolutional spectra analysis were conducted in the whole Qiongzhusi Formation. Orbital cycles of 405-kyr, 131-kyr, 95-kyr, 6-kyr and 28-kyr have been identified in the sedimentary records. Based on the Gaussian filtering on 405-kyr cycle, and the control ages of 526.86 ± 0.16 Ma from relational region, we constructed a floating astronomical time scale which contained 29 long eccentricity cycles, and the optimal sedimentation rate of each segment are 2.5, 2.9, 3.4 and 4.8cm/kyr. The sedimentary noise model of DYNOT and ρ1 were built on the 405-kyr tuning time series, and then get the relative sea-level change curves in time domain. Through the analysis of relative sea-level change, four third ordered sequences have been recognized, as well as four maximum flooding surface and the T-R cycles. The depositional times of each sequence from early to late are 3.18, 2.03, 2.97 and 3.63 Ma respectively, and each sequence are contained 8, 5, 7 and 9 long eccentricity cycles. The relative sea-level decreased is corresponded to the global carbon isotope negative excursion, it is presumably to be the decreasing sea-level lead to the oxidation of the organic, and the lighter carbon isotopes were released, and then the negative excursion of carbon isotope were formed.
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The establishment of sedimentary pattern of ancient salt lake basins is often based on the investigation of modern salt lake deposits. Under natural conditions, salt lake water evaporates slowly and is generally in a specific stage of relative static state. Indoor evaporation experiment can provide dynamic and continuous deposition evolution process, observe the crystallization characteristics of sodium chloride and analyze the relationship between halite crystallization and sedimentary environment, which can provide beneficial supplement for the sedimentary research of salt lake basin. The results show that the location of halite deposition is affected by the crystallization habit, and the crystals can be deposited above the brine interface. Besides the action of evaporation pump, its formation dynamics are also controlled by air humidity and halite deliquensce. Herringbone crystals are generally formed on the base of funnel crystals, when its growth space is limited, the lamina grown around different funnel nuclei are obliquely crossed to form herringbone crystals. The two crystalline forms can be deposited on water surface at the same time. Before the salt lake dries up, it may experience the phenomenon of the salt layer blocking the water surface, and may affect the clastic sediment in the adjacent layer.
The establishment of sedimentary pattern of ancient salt lake basins is often based on the investigation of modern salt lake deposits. Under natural conditions, salt lake water evaporates slowly and is generally in a specific stage of relative static state. Indoor evaporation experiment can provide dynamic and continuous deposition evolution process, observe the crystallization characteristics of sodium chloride and analyze the relationship between halite crystallization and sedimentary environment, which can provide beneficial supplement for the sedimentary research of salt lake basin. The results show that the location of halite deposition is affected by the crystallization habit, and the crystals can be deposited above the brine interface. Besides the action of evaporation pump, its formation dynamics are also controlled by air humidity and halite deliquensce. Herringbone crystals are generally formed on the base of funnel crystals, when its growth space is limited, the lamina grown around different funnel nuclei are obliquely crossed to form herringbone crystals. The two crystalline forms can be deposited on water surface at the same time. Before the salt lake dries up, it may experience the phenomenon of the salt layer blocking the water surface, and may affect the clastic sediment in the adjacent layer.
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The Argillaceous Banded Limestone Member of the Upper Ordovician Lianglitage Formation in Well Zhong-15, Tazhong area, Tarim Basin represents open-platform deposition in an intra-platform depression. A set of dark gray argillaceous banded oncolitic limestone and bioclastic argillaceous oncolitic limestone with a thickness of about 12.3 m are developed in the middle and upper parts of this member, with large particle size and high abundance of oncoids. The core is made up of the early platform-margin bioclasts and intraclasts. The cortex of oncoids is thick and rich in bacterial lamina. The matrix is mostly filled with plaster and fine biological fossil fragments, with commonly seen argillaceous bands. It represents a sedimentary origin of in-situ or little transportation with weak water agitation and transportation. The oncoids can be divided into four types in terms of shapes, namely spherical, dome-like, strip-shaped and ellipsoidal oncoids, in which dome-like and spherical ones are dominant. Vertically, there are three sequences of oncolitic development, within each of which the content and particle size of oncoids tend to increase from the bottom to the top. Spherical and dome-like oncoids are formed in the environment where the water body is in the alternating state of agitation and stasis and the sedimentary conditions are relatively stable, while strip-shaped oncoids are formed in the low-energy environment of weak agitation. The oncoids of Well Zhong-15 result from various factors such as global sea level rise in Ordovician, biological radiation attributed to organic coupling of rich core material sources (bioclasts and intraclasts in the platform-margin), highly developed bacterial adhesion and growth, and stable or weakly fluctuating sedimentary environment.
The Argillaceous Banded Limestone Member of the Upper Ordovician Lianglitage Formation in Well Zhong-15, Tazhong area, Tarim Basin represents open-platform deposition in an intra-platform depression. A set of dark gray argillaceous banded oncolitic limestone and bioclastic argillaceous oncolitic limestone with a thickness of about 12.3 m are developed in the middle and upper parts of this member, with large particle size and high abundance of oncoids. The core is made up of the early platform-margin bioclasts and intraclasts. The cortex of oncoids is thick and rich in bacterial lamina. The matrix is mostly filled with plaster and fine biological fossil fragments, with commonly seen argillaceous bands. It represents a sedimentary origin of in-situ or little transportation with weak water agitation and transportation. The oncoids can be divided into four types in terms of shapes, namely spherical, dome-like, strip-shaped and ellipsoidal oncoids, in which dome-like and spherical ones are dominant. Vertically, there are three sequences of oncolitic development, within each of which the content and particle size of oncoids tend to increase from the bottom to the top. Spherical and dome-like oncoids are formed in the environment where the water body is in the alternating state of agitation and stasis and the sedimentary conditions are relatively stable, while strip-shaped oncoids are formed in the low-energy environment of weak agitation. The oncoids of Well Zhong-15 result from various factors such as global sea level rise in Ordovician, biological radiation attributed to organic coupling of rich core material sources (bioclasts and intraclasts in the platform-margin), highly developed bacterial adhesion and growth, and stable or weakly fluctuating sedimentary environment.
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The sand body structure of braided river reservoir and the spatial distribution of its seepage barrier are the key geological factors affecting the water injection development effect of Nanpu2-1 area. This paper comprehensively applies core, logging, three-dimensional seismic and production performance data to carry out fine reservoir characterization based on the spatial distribution of level 4 architecture units of braided river reservoir. According to the dense well pattern anatomy, the level 4 architecture units of three genetic types of braided bar, braided channel and overflow in NgⅡ-6 ( Neogene Guantao Formation Ⅱ oil group 6th sublayer) of Nanpu2-1 area are identified, and three vertical superposition types (braided bar-braided bar superposition, braided channel- braided bar superposition and overflow-braided bar superposition) and three lateral splicing types (braided bar downstream progradation overlapping splicing type, braided channel separated braided bar type and braided bar distributing braided channel type) are established. Using the root mean square amplitude and frequency division RGB fusion stratigraphic slicing technology, the plane distribution of level 4 architecture units of NgⅡ-6 in Nanpu2-1 area is predicted, and the geometric shape, scale and contact relationship between braided bar reservoir unit and braided channel as seepage barrier are revealed, which provides a direct geological basis for the optimization and adjustment of oilfield water injection development scheme and improving oilfield development effect.
The sand body structure of braided river reservoir and the spatial distribution of its seepage barrier are the key geological factors affecting the water injection development effect of Nanpu2-1 area. This paper comprehensively applies core, logging, three-dimensional seismic and production performance data to carry out fine reservoir characterization based on the spatial distribution of level 4 architecture units of braided river reservoir. According to the dense well pattern anatomy, the level 4 architecture units of three genetic types of braided bar, braided channel and overflow in NgⅡ-6 ( Neogene Guantao Formation Ⅱ oil group 6th sublayer) of Nanpu2-1 area are identified, and three vertical superposition types (braided bar-braided bar superposition, braided channel- braided bar superposition and overflow-braided bar superposition) and three lateral splicing types (braided bar downstream progradation overlapping splicing type, braided channel separated braided bar type and braided bar distributing braided channel type) are established. Using the root mean square amplitude and frequency division RGB fusion stratigraphic slicing technology, the plane distribution of level 4 architecture units of NgⅡ-6 in Nanpu2-1 area is predicted, and the geometric shape, scale and contact relationship between braided bar reservoir unit and braided channel as seepage barrier are revealed, which provides a direct geological basis for the optimization and adjustment of oilfield water injection development scheme and improving oilfield development effect.
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In order to determine the origin and enrichment of crude oils, the aromatics geochemical characteristics of crude oils from the lower member of Paleogene Xinguozui Formation in Jiangling Depression were analyzed by GC-MS.Studies showed that crude oil could be divided into two main types:Type Ⅰ located in wancheng fault structural belt and Gongan monocline belt,it was formed in a semi-deep lacustrine sedimentary environment with a certain salinity in general reducing environment.Naphthalene series compound and the ratio of the high molecular weight isomers of the triaromatic sterane series reflected the characteristics of better parent material types and less input from terrigenous higher plants.It was in mature-high maturity stage,moreover Wan13 and Wan12 in wancheng fault belt and Yao5 in Gongan monocline belt belonged to highly mature crude oil, which were presumed to be in the position closest to the reservoir charging point in their respective tectonic units.Type Ⅱ located in Jingzhou anticline belt and its maturity was lower than Type Ⅰ,its parent materials were mainly imported from lower aquatic organisms but received more input from higher terrestrial plants than type Ⅰ,it was formed in a deep lacustrine sedimentary environment with high salinity and strong reduction.Compared with type Ⅱ1, type Ⅱ2 had lower maturity and more terrestrial higher plant inputs.Oil-source correlation showed that:Type Ⅰ was mainly from the X-Ⅱ and X-Ⅲ of Wancheng area,and the source rocks which were from the X-Ⅰ of Jingzhou anticline belt also had certain contribution to it,the high maturity characteristics might indicate the contribution of other regions or formations.Type Ⅱ was mainly from the X-Ⅱ of Wancheng area and Jingzhou anticline belt,and it also had some contribution from the X-Ⅲ of northern Jingzhou anticline belt.
In order to determine the origin and enrichment of crude oils, the aromatics geochemical characteristics of crude oils from the lower member of Paleogene Xinguozui Formation in Jiangling Depression were analyzed by GC-MS.Studies showed that crude oil could be divided into two main types:Type Ⅰ located in wancheng fault structural belt and Gongan monocline belt,it was formed in a semi-deep lacustrine sedimentary environment with a certain salinity in general reducing environment.Naphthalene series compound and the ratio of the high molecular weight isomers of the triaromatic sterane series reflected the characteristics of better parent material types and less input from terrigenous higher plants.It was in mature-high maturity stage,moreover Wan13 and Wan12 in wancheng fault belt and Yao5 in Gongan monocline belt belonged to highly mature crude oil, which were presumed to be in the position closest to the reservoir charging point in their respective tectonic units.Type Ⅱ located in Jingzhou anticline belt and its maturity was lower than Type Ⅰ,its parent materials were mainly imported from lower aquatic organisms but received more input from higher terrestrial plants than type Ⅰ,it was formed in a deep lacustrine sedimentary environment with high salinity and strong reduction.Compared with type Ⅱ1, type Ⅱ2 had lower maturity and more terrestrial higher plant inputs.Oil-source correlation showed that:Type Ⅰ was mainly from the X-Ⅱ and X-Ⅲ of Wancheng area,and the source rocks which were from the X-Ⅰ of Jingzhou anticline belt also had certain contribution to it,the high maturity characteristics might indicate the contribution of other regions or formations.Type Ⅱ was mainly from the X-Ⅱ of Wancheng area and Jingzhou anticline belt,and it also had some contribution from the X-Ⅲ of northern Jingzhou anticline belt.
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Deep water turbidite sand bodies in passive continental margin basins have become a new field of oil and gas exploration. Based on high-resolution 3D seismic data on the typical passive margin deepwater Namibe basin, the seismic response of the limited channel sedimentary characteristics on submarine quaternary sedimentary strata are finely depicted and analyzed, which were less affected by the tectonic activities and sedimentary compaction and keep the inherent channel sedimentary configuration. The research shows, that the erosion of confined turbidity channels is generally greater than the sedimentation. The sedimentary mode of single channel is mainly concave bank erosion and convex bank "S" type accretion, which leads to "V" type valley broadening into wide "U" type channel deposition. The sedimentary system of multiple channels can be divided into two modes of lateral and vertical Erosive superposition. The submarine topography of narrow continental shelf and wide gentle continental slope controls the extension direction and length of the limited channel. The frequency of paleoclimate events controlled the developing times of turbidite sand bodies in channel system. The research results can provide inspiration for reservoir prediction and sedimentary architecture analysis of channel turbidite sand body for oil and gas exploration of deep formation.
Deep water turbidite sand bodies in passive continental margin basins have become a new field of oil and gas exploration. Based on high-resolution 3D seismic data on the typical passive margin deepwater Namibe basin, the seismic response of the limited channel sedimentary characteristics on submarine quaternary sedimentary strata are finely depicted and analyzed, which were less affected by the tectonic activities and sedimentary compaction and keep the inherent channel sedimentary configuration. The research shows, that the erosion of confined turbidity channels is generally greater than the sedimentation. The sedimentary mode of single channel is mainly concave bank erosion and convex bank "S" type accretion, which leads to "V" type valley broadening into wide "U" type channel deposition. The sedimentary system of multiple channels can be divided into two modes of lateral and vertical Erosive superposition. The submarine topography of narrow continental shelf and wide gentle continental slope controls the extension direction and length of the limited channel. The frequency of paleoclimate events controlled the developing times of turbidite sand bodies in channel system. The research results can provide inspiration for reservoir prediction and sedimentary architecture analysis of channel turbidite sand body for oil and gas exploration of deep formation.
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In order to further clarify the tertiary oil recovery development layer series combination and development sequence of Gaotaizi Reservoir, and guide the overall planning and deployment of tertiary oil recovery of Gaotaizi Reservoir, the sedimentary evolution and reservoir heterogeneity characteristics of Gaotaizi Reservoir are systematically studied within the Daqing Placanticline.Using the multi-dimensional and three-dimensional research idea of point line plane, first start with the core description of 11 coring wells in Placanticline, the sedimentary environment types of different horizons and locations are determined through system description; Then study the evolution law of sedimentary sequence through the north-south and east-west sections; Finally, the sedimentary model and heterogeneous characteristics of sand body are determined by describing the microfacies of sand body in different units. Based on the research results, it is clear that Gaotaizi Reservoir is a set of lacustrine regression lacustrine accumulation lacustrine regression sedimentary evolution sequence developed on the overall lacustrine regression background, the boundary positions of lake shoreline, inner and outer front boundary and outer front pinch out line of each unit are determined, Three types and six subtypes of delta sedimentary models of river controlled branch, wave controlled sheet and flow controlled lumpy are established. It is clear that the second and third types of Gaotaizi Reservoir are developed, and the third type of Reservoir is subdivided into IIIA, IIIB and IIIc. According to the distribution characteristics of different types of sand bodies, the layer series combination optimization design is carried out. Lamadian and Sazhong Oilfields can be combined into 3-4 sets of layer series, and Sabei and Sanan Oilfields can be combined into 1-3 sets of layer series. According to the combination results, the field test of polymer injection in Lamadian 182 block was carried out, realize uniform production of oil reservoir, the stage enhanced oil recovery was 10.4%, and good development results were obtained.
In order to further clarify the tertiary oil recovery development layer series combination and development sequence of Gaotaizi Reservoir, and guide the overall planning and deployment of tertiary oil recovery of Gaotaizi Reservoir, the sedimentary evolution and reservoir heterogeneity characteristics of Gaotaizi Reservoir are systematically studied within the Daqing Placanticline.Using the multi-dimensional and three-dimensional research idea of point line plane, first start with the core description of 11 coring wells in Placanticline, the sedimentary environment types of different horizons and locations are determined through system description; Then study the evolution law of sedimentary sequence through the north-south and east-west sections; Finally, the sedimentary model and heterogeneous characteristics of sand body are determined by describing the microfacies of sand body in different units. Based on the research results, it is clear that Gaotaizi Reservoir is a set of lacustrine regression lacustrine accumulation lacustrine regression sedimentary evolution sequence developed on the overall lacustrine regression background, the boundary positions of lake shoreline, inner and outer front boundary and outer front pinch out line of each unit are determined, Three types and six subtypes of delta sedimentary models of river controlled branch, wave controlled sheet and flow controlled lumpy are established. It is clear that the second and third types of Gaotaizi Reservoir are developed, and the third type of Reservoir is subdivided into IIIA, IIIB and IIIc. According to the distribution characteristics of different types of sand bodies, the layer series combination optimization design is carried out. Lamadian and Sazhong Oilfields can be combined into 3-4 sets of layer series, and Sabei and Sanan Oilfields can be combined into 1-3 sets of layer series. According to the combination results, the field test of polymer injection in Lamadian 182 block was carried out, realize uniform production of oil reservoir, the stage enhanced oil recovery was 10.4%, and good development results were obtained.
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Dolostones are widely developed in the Middle Permian rocks of East Yunnan and West Guizhou (China). A series of studies were conducted on the genesis of these dolostones, and various dolostone formation mechanisms have been proposed. However, it remains controversial about the source of magnesium ion and the main controlling factor of dolomitization. These problems severely hinder the oil-gas extended exploration of East Yunnan and West Guizhou. This study analyses the regularities of distribution of dolostone, the petrographic characteristics of dolostone, and the geochemical characteristics of dolostone in detail by the comprehensive use of outcrops, cores and drilling data and proposes a new model of dolomitization: open thermal convection dolomitization. In this new dolomitization model, dolostones can be divided into two types based on their occurrence in single beds: massive dolostones and patchy dolostones. The massive dolostones and patchy dolostones are of the same origin, with the only difference being the degree of dolomitization. Mg2+ in dolomitizing fluids originates mostly from seawater, with a minor component coming from deep hydrothermal fluids. The dolomitizing fluid mainly migrates through pores in bioclastic grainstone and faults and fracture systems. Driven by spatial variations in temperature, the fluid migrates along the circulation flow pathways, resulting in fast and pervasive dolomitization of Middle Permian limestone. The main controlling factors of dolostone development are shoal facies and Emei mantle plume (active area).
Dolostones are widely developed in the Middle Permian rocks of East Yunnan and West Guizhou (China). A series of studies were conducted on the genesis of these dolostones, and various dolostone formation mechanisms have been proposed. However, it remains controversial about the source of magnesium ion and the main controlling factor of dolomitization. These problems severely hinder the oil-gas extended exploration of East Yunnan and West Guizhou. This study analyses the regularities of distribution of dolostone, the petrographic characteristics of dolostone, and the geochemical characteristics of dolostone in detail by the comprehensive use of outcrops, cores and drilling data and proposes a new model of dolomitization: open thermal convection dolomitization. In this new dolomitization model, dolostones can be divided into two types based on their occurrence in single beds: massive dolostones and patchy dolostones. The massive dolostones and patchy dolostones are of the same origin, with the only difference being the degree of dolomitization. Mg2+ in dolomitizing fluids originates mostly from seawater, with a minor component coming from deep hydrothermal fluids. The dolomitizing fluid mainly migrates through pores in bioclastic grainstone and faults and fracture systems. Driven by spatial variations in temperature, the fluid migrates along the circulation flow pathways, resulting in fast and pervasive dolomitization of Middle Permian limestone. The main controlling factors of dolostone development are shoal facies and Emei mantle plume (active area).
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Lacustrine dolomites is a special oil and gas reservoir found in Qingshankou Formation of Songliao Basin. In order to explore its sedimentary environment and genetic mechanism, a comprehensively study with multiple sedimentary and geochemical proxies is presented here. The sedimentary environment and genetic mechanism of dolomites in lacustrine area of Qingshankou Formation are analyzed. The results shows that dolomites in lacustrine area of Qingshankou Formation in Songliao basin is mainly argillaceous dolomites, and the mineral components are mainly iron dolomite, clay and calcite, with a thickness of 1-25cm. It is distributed in thick lacustrine mudstones and shales in a layered or lenticular shape. The δ 13C value is positive, the oxygen isotope δ 18O value is negative, rare earth element of δEu is obvious negative anomaly, and rich hydrothermal nutrients such as Ca, Si, Fe, Mg, Al and Na are rich. It is speculated that it was a primary dolomite caused by methanogenic bacteria in the early stage and was transformed by hydrothermal action in the later stage, forming in a saline lake environment under relatively dry climate conditions. The analysis of sedimentary environment and genetic mechanism of dolomite in lacustrine area is of great significance for the study of sedimentary evolution and reservoir evaluation in Songliao basin.
Lacustrine dolomites is a special oil and gas reservoir found in Qingshankou Formation of Songliao Basin. In order to explore its sedimentary environment and genetic mechanism, a comprehensively study with multiple sedimentary and geochemical proxies is presented here. The sedimentary environment and genetic mechanism of dolomites in lacustrine area of Qingshankou Formation are analyzed. The results shows that dolomites in lacustrine area of Qingshankou Formation in Songliao basin is mainly argillaceous dolomites, and the mineral components are mainly iron dolomite, clay and calcite, with a thickness of 1-25cm. It is distributed in thick lacustrine mudstones and shales in a layered or lenticular shape. The δ 13C value is positive, the oxygen isotope δ 18O value is negative, rare earth element of δEu is obvious negative anomaly, and rich hydrothermal nutrients such as Ca, Si, Fe, Mg, Al and Na are rich. It is speculated that it was a primary dolomite caused by methanogenic bacteria in the early stage and was transformed by hydrothermal action in the later stage, forming in a saline lake environment under relatively dry climate conditions. The analysis of sedimentary environment and genetic mechanism of dolomite in lacustrine area is of great significance for the study of sedimentary evolution and reservoir evaluation in Songliao basin.
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The Early Cretaceous is the latest period of the Ordos Basin evolution in the Mesozoic. The tectonic environment and sedimentary provenance system have undergone significant changes, which are of great significance to the evolution of the basin and the exploration of multi-energy mineral deposits (products). This paper takes the Lower Cretaceous Yijun Formation in the Southern Ordos Basin as the main research object, uses the detrital zircon LA-ICP-MS U-Pb dating method, and combines the characteristics of zircon U-Pb age spectrum peaks and structural evolution characteristics of neighboring geological bodies , to trace the source of sedimentary material of Yijun Formation and discuss its geological significance. The results show that the U-Pb ages of detrital zircons from the Yijun Formation are mainly distributed in the Early Mesozoic (195-250 Ma±) and Early Paleozoic (400-500 Ma±) periods, with peak ages of 218 Ma±and 450 Ma±respectively. which are obviously consistent with the age of the widely exposed rock masses in the North Qinling area today, while the Proterozoic-Archaean zircon ages are not only small in number, but have no obvious peaks. Based on regional comparison, it is believed that the sediments of the Yijun Formation are the response to the Late Jurassic tectonic events in the Qinling Orogenic Belt, and the provenance mainly comes from the North Qinling Orogenic Belt. It has been uplifted and exposed to the surface at the beginning of the Cretaceous and began to provide a large amount of provenance to the southern part of the basin. This restrained the Qinling uplift and exhumation in the Late Mesozoic to a certain extent, it also restricts the time limit for the development of the Weibei Uplift. The research has a certain guiding role in determining the uranium ore sources and ore-forming distribution of Mesozoic sandstone-type uranium deposits in the southern part of the basin.
The Early Cretaceous is the latest period of the Ordos Basin evolution in the Mesozoic. The tectonic environment and sedimentary provenance system have undergone significant changes, which are of great significance to the evolution of the basin and the exploration of multi-energy mineral deposits (products). This paper takes the Lower Cretaceous Yijun Formation in the Southern Ordos Basin as the main research object, uses the detrital zircon LA-ICP-MS U-Pb dating method, and combines the characteristics of zircon U-Pb age spectrum peaks and structural evolution characteristics of neighboring geological bodies , to trace the source of sedimentary material of Yijun Formation and discuss its geological significance. The results show that the U-Pb ages of detrital zircons from the Yijun Formation are mainly distributed in the Early Mesozoic (195-250 Ma±) and Early Paleozoic (400-500 Ma±) periods, with peak ages of 218 Ma±and 450 Ma±respectively. which are obviously consistent with the age of the widely exposed rock masses in the North Qinling area today, while the Proterozoic-Archaean zircon ages are not only small in number, but have no obvious peaks. Based on regional comparison, it is believed that the sediments of the Yijun Formation are the response to the Late Jurassic tectonic events in the Qinling Orogenic Belt, and the provenance mainly comes from the North Qinling Orogenic Belt. It has been uplifted and exposed to the surface at the beginning of the Cretaceous and began to provide a large amount of provenance to the southern part of the basin. This restrained the Qinling uplift and exhumation in the Late Mesozoic to a certain extent, it also restricts the time limit for the development of the Weibei Uplift. The research has a certain guiding role in determining the uranium ore sources and ore-forming distribution of Mesozoic sandstone-type uranium deposits in the southern part of the basin.
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Through 2D seismic profiles, recognized a canyon groups system makeup by 19 canyon in the Mergui slope, eastern Andaman Sea, single canyon in seismic profile show 3 types in shape: W, U, V; from upper segments to lower segments, the number of the canyon increasing obviously, incised deeper, and the width narrows, Canyon group system show form in a southward migrating stacking pattern. The evolution of the canyon groups system can be divided into three stages, the initial development stage from Late Miocene-Pliocene, the expansion development stage from Pliocene-Quaternary, and the modern development stage from Quaternary-present, The canyon groups in the Mergui slope was controlled by submarine topographical slope, sedimentary supplying, sea level changes and. This result has a considerable values in revealing development and evolution of the canyon as well as the prediction of excellent reservoirs.
Through 2D seismic profiles, recognized a canyon groups system makeup by 19 canyon in the Mergui slope, eastern Andaman Sea, single canyon in seismic profile show 3 types in shape: W, U, V; from upper segments to lower segments, the number of the canyon increasing obviously, incised deeper, and the width narrows, Canyon group system show form in a southward migrating stacking pattern. The evolution of the canyon groups system can be divided into three stages, the initial development stage from Late Miocene-Pliocene, the expansion development stage from Pliocene-Quaternary, and the modern development stage from Quaternary-present, The canyon groups in the Mergui slope was controlled by submarine topographical slope, sedimentary supplying, sea level changes and. This result has a considerable values in revealing development and evolution of the canyon as well as the prediction of excellent reservoirs.
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Uncertainty for the provenance systems of the upper part of the fourth member to third member of the Paleogene Shahejie Formation (i. e. E2s4s and E2s3, respectively) in the Jiangjiadian area occurs, increasing difficulties of prediction of sand bodies and high-quality reservoirs. Characteristic elements analysis, Q-type cluster analysis to lithological components and percentage statistics of sand-conglomerates are performed to identify provenance system and transporting routes of clastic matters, subsequently build evolutionary model of provenance and discuss its significance to petroleum exploration. Distributional patterns of the characteristic elements of Sequence Ⅰ to Ⅴ in i. e. E2s4s and E2s3 are in overall accordance with those of Mesozoic formations, displaying obviously high Mg/Mn and Al/Mg ratios along with relatively high Al/Na and Ba/Mn ratio. 5 QFR assemblages, extracted from Q-type cluster analysis results of all lithological components reveal that 3 main provenance regions exist. During development Sequence Ⅰ and Ⅱ, the provenance systems supply abundant clastic matters to the sedimentary region, forming a large scale of sandstones. The provenance systems recede during Sequence Ⅲ, causing the scale of sand-bodies getting smaller. Subsequently, the provenance systems move forwards during Sequence Ⅳ and Ⅴ, making the sand-bodies to extensively develop.
Uncertainty for the provenance systems of the upper part of the fourth member to third member of the Paleogene Shahejie Formation (i. e. E2s4s and E2s3, respectively) in the Jiangjiadian area occurs, increasing difficulties of prediction of sand bodies and high-quality reservoirs. Characteristic elements analysis, Q-type cluster analysis to lithological components and percentage statistics of sand-conglomerates are performed to identify provenance system and transporting routes of clastic matters, subsequently build evolutionary model of provenance and discuss its significance to petroleum exploration. Distributional patterns of the characteristic elements of Sequence Ⅰ to Ⅴ in i. e. E2s4s and E2s3 are in overall accordance with those of Mesozoic formations, displaying obviously high Mg/Mn and Al/Mg ratios along with relatively high Al/Na and Ba/Mn ratio. 5 QFR assemblages, extracted from Q-type cluster analysis results of all lithological components reveal that 3 main provenance regions exist. During development Sequence Ⅰ and Ⅱ, the provenance systems supply abundant clastic matters to the sedimentary region, forming a large scale of sandstones. The provenance systems recede during Sequence Ⅲ, causing the scale of sand-bodies getting smaller. Subsequently, the provenance systems move forwards during Sequence Ⅳ and Ⅴ, making the sand-bodies to extensively develop.
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The Lower Jurassic lacustrine and delta deposits in eastern Sichuan basin have great hydrocarbon exploration potential, but the lag of basic geological research restricts the exploration process. Paleo-water-depth reconstruction of Lower Jurassic has great guiding significance to lithofacies paleogeography and shale oil -gas exploration in eastern Sichuan basin. According to the rock types, sedimentary structures and the distribution characteristics of paleontological fossils, combined with Fe/Mn ratio, (Al+Fe) / (Ca+Mg) ratio and kerogen type, the paleo-water-depth variation trend of Ziliujing Formation and Liangshan Formation in eastern Sichuan basin is studied. The early Jurassic paleo-water-depth was reconstructed quantitatively via La-Co method, TOC method and Th/U ratio method. The characteristics of sedimentary structure and paleontological distribution indicate that the central part of eastern Sichuan basin was in a low-lying position of lake basin for a long time in early Jurassic, and the variation trend of Fe/Mn ratio and (Al+Fe) / (Ca+Mg) ratio show that the northeast and south of the study area are nearshore shallow water. The results of paleo-water-depth reconstruction via LA-Co method, TOC method and Th/U ratio method are quite different. The paleo-water-depth reconstructed based on La-Co method is in great contradiction with sedimentary facies. Th/U ratio method is more reliable for paleo-water-depth reconstruction in shallow lake sedimentary area, but less reliable in lakeside and semi-deep lake sedimentary areas. The paleo-water-depth reconstruction result based on TOC method is the most reliable and has the highest coincidence with sediments. The base surface of lake-wave in eastern Sichuan is about 15m in early Jurassic. Paleo-water-depth reconstruction results based on TOC method indicates that the Lower Jurassic semi-deep lakes were widely developed in the eastern Sichuan basin, and the maximum water depth of the early Jurassic lakes was about 60m. Semi-deep lake deep lake deposits are widely developed in Guang'an-Wanzhou area, which is beneficial to the enrichment and preservation of organic matter and is a favorable position for shale oil and gas exploration.
The Lower Jurassic lacustrine and delta deposits in eastern Sichuan basin have great hydrocarbon exploration potential, but the lag of basic geological research restricts the exploration process. Paleo-water-depth reconstruction of Lower Jurassic has great guiding significance to lithofacies paleogeography and shale oil -gas exploration in eastern Sichuan basin. According to the rock types, sedimentary structures and the distribution characteristics of paleontological fossils, combined with Fe/Mn ratio, (Al+Fe) / (Ca+Mg) ratio and kerogen type, the paleo-water-depth variation trend of Ziliujing Formation and Liangshan Formation in eastern Sichuan basin is studied. The early Jurassic paleo-water-depth was reconstructed quantitatively via La-Co method, TOC method and Th/U ratio method. The characteristics of sedimentary structure and paleontological distribution indicate that the central part of eastern Sichuan basin was in a low-lying position of lake basin for a long time in early Jurassic, and the variation trend of Fe/Mn ratio and (Al+Fe) / (Ca+Mg) ratio show that the northeast and south of the study area are nearshore shallow water. The results of paleo-water-depth reconstruction via LA-Co method, TOC method and Th/U ratio method are quite different. The paleo-water-depth reconstructed based on La-Co method is in great contradiction with sedimentary facies. Th/U ratio method is more reliable for paleo-water-depth reconstruction in shallow lake sedimentary area, but less reliable in lakeside and semi-deep lake sedimentary areas. The paleo-water-depth reconstruction result based on TOC method is the most reliable and has the highest coincidence with sediments. The base surface of lake-wave in eastern Sichuan is about 15m in early Jurassic. Paleo-water-depth reconstruction results based on TOC method indicates that the Lower Jurassic semi-deep lakes were widely developed in the eastern Sichuan basin, and the maximum water depth of the early Jurassic lakes was about 60m. Semi-deep lake deep lake deposits are widely developed in Guang'an-Wanzhou area, which is beneficial to the enrichment and preservation of organic matter and is a favorable position for shale oil and gas exploration.
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The Cryogenian snowball Earth glaciation represents the most extreme icehouse climate in Earth’s history. During the snowball Earth, icesheets may have extended to the low latitudes or even the paleo-equator area, leading to a globally frozen earth and inspiring a snowball Earth. However, marine chemistry and biogeochemical cycles during the Snowball Earth remains unconstrained. In order to address this issue, he we carried out detailed geochemical analysis of two section of Fulu Formation (the Yazhai and Fengmu section) at the northern Guangxi province, Yangtze Block. The Fulu Formation at northern Guangxi area mainly consists of sandstones with rare occurrences of carbonate interbeds within it. Stratigraphic correlations suggest these carbonate may deposit during the Sturtian glaciation. Geochemical analysis shows nearly uniform carbonate carbon isotope values:?13Ccarb from the Yazhai section ranging from -5.0‰ to -3.0‰ with the mean value of -3.9‰, ?13Ccarb from the Fengmu section ranging from -3.45‰ to -3.04‰ with the mean value of -3.19‰. The carbonate carbon isotopes are decoupled with the organic carbon isotope variation. The carbon isotopic compositons of the Fulu carbonate indicate active marine primary productivity during the Sturtian glaciation. Massive P released from marine hydrothermal activities may provide nutrients for sustaining synglacial organic matter production.
The Cryogenian snowball Earth glaciation represents the most extreme icehouse climate in Earth’s history. During the snowball Earth, icesheets may have extended to the low latitudes or even the paleo-equator area, leading to a globally frozen earth and inspiring a snowball Earth. However, marine chemistry and biogeochemical cycles during the Snowball Earth remains unconstrained. In order to address this issue, he we carried out detailed geochemical analysis of two section of Fulu Formation (the Yazhai and Fengmu section) at the northern Guangxi province, Yangtze Block. The Fulu Formation at northern Guangxi area mainly consists of sandstones with rare occurrences of carbonate interbeds within it. Stratigraphic correlations suggest these carbonate may deposit during the Sturtian glaciation. Geochemical analysis shows nearly uniform carbonate carbon isotope values:?13Ccarb from the Yazhai section ranging from -5.0‰ to -3.0‰ with the mean value of -3.9‰, ?13Ccarb from the Fengmu section ranging from -3.45‰ to -3.04‰ with the mean value of -3.19‰. The carbonate carbon isotopes are decoupled with the organic carbon isotope variation. The carbon isotopic compositons of the Fulu carbonate indicate active marine primary productivity during the Sturtian glaciation. Massive P released from marine hydrothermal activities may provide nutrients for sustaining synglacial organic matter production.
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The Liangshan Formation and Qixia Formation of the Lower Permian in the southwest of Sichuan Basin are studied, comprehensive use of field profiles, drilling cores and logging data, based on the analysis of rock types and sedimentary facies, the principles and methods of Marine carbonate sequence stratigraphy are applied, four third-order sequence interfaces were identified in qixia Stage, from bottom to top, there are the bottom interface of Liangshan Formation (SB I), the inner interface of Qixia Formation group 1 section(SB II), the interface of Qixia Formation Group 1 section \ Qixia Formation Group 2 section(SB II) and the interface of Qixia Group/Maokou Group (SB I). It can be divided into three tertiary sequences, each sequence consists of transgressive domain and high-order domain. Through the comparative analysis of sequence stratigraphic framework, we believe that SQ0 sequence of the lower Part of the Qixia Stage corresponds roughly to the Liangshan Formation and the lower part of Qixia Formation Group 1 section, SQ0 is only developed in the paleogeomorphic lowland in the study area, and it has the sequence filling characteristic of overlapping to the palaeogeomorphic highland. SQ1 sequence in the middle and SQ2 sequence in the upper are distributed throughout the whole area. The single-factor analysis and multi-factor comprehensive mapping method is adopted, taking the three-level sequence as the mapping unit and combining with the principle of dominant phase, SQ0+SQ1 and SQ2 sequence lithofacies paleogeography maps of Qixia Stage in the study area were drawn respectively. it is found that the sequence lithofacies palaeogeographic pattern of Qixia Stage in the southwest of Sichuan basin is a Marine carbonate platform bordering the Kang-Dian ancient land in the west, with obvious differentiation of palaeogeomorphology and sedimentary facies. From west to east : the kang-Dian land and its eastern margin are tidal flat, intraplatform depression, intraplatform mound-shoal, and open semi-confined platform, in addition, the intra - platform mound-shoal beach developed along the intra - platform slope break zone tends to surround the intra - platform depression. By analyzing the influence of slope break zone in platform on carbonate reservoir formation, it is pointed out that SQ2 sequence is the most favorable reservoir facies belt of Qixia Stage in the study area. There are favorable exploration areas in the area around the intraplatform mound-shoal facies belt developed around the depression and slope break zone in the platform. A new understanding of the filling law and lithofacies paleogeographic characteristics of Qixia Stage from the perspective of sequence stratigraphy can provide a new framework for the subsequent reservoir research and the prediction of favorable exploration areas of Qixia Formation.
The Liangshan Formation and Qixia Formation of the Lower Permian in the southwest of Sichuan Basin are studied, comprehensive use of field profiles, drilling cores and logging data, based on the analysis of rock types and sedimentary facies, the principles and methods of Marine carbonate sequence stratigraphy are applied, four third-order sequence interfaces were identified in qixia Stage, from bottom to top, there are the bottom interface of Liangshan Formation (SB I), the inner interface of Qixia Formation group 1 section(SB II), the interface of Qixia Formation Group 1 section \ Qixia Formation Group 2 section(SB II) and the interface of Qixia Group/Maokou Group (SB I). It can be divided into three tertiary sequences, each sequence consists of transgressive domain and high-order domain. Through the comparative analysis of sequence stratigraphic framework, we believe that SQ0 sequence of the lower Part of the Qixia Stage corresponds roughly to the Liangshan Formation and the lower part of Qixia Formation Group 1 section, SQ0 is only developed in the paleogeomorphic lowland in the study area, and it has the sequence filling characteristic of overlapping to the palaeogeomorphic highland. SQ1 sequence in the middle and SQ2 sequence in the upper are distributed throughout the whole area. The single-factor analysis and multi-factor comprehensive mapping method is adopted, taking the three-level sequence as the mapping unit and combining with the principle of dominant phase, SQ0+SQ1 and SQ2 sequence lithofacies paleogeography maps of Qixia Stage in the study area were drawn respectively. it is found that the sequence lithofacies palaeogeographic pattern of Qixia Stage in the southwest of Sichuan basin is a Marine carbonate platform bordering the Kang-Dian ancient land in the west, with obvious differentiation of palaeogeomorphology and sedimentary facies. From west to east : the kang-Dian land and its eastern margin are tidal flat, intraplatform depression, intraplatform mound-shoal, and open semi-confined platform, in addition, the intra - platform mound-shoal beach developed along the intra - platform slope break zone tends to surround the intra - platform depression. By analyzing the influence of slope break zone in platform on carbonate reservoir formation, it is pointed out that SQ2 sequence is the most favorable reservoir facies belt of Qixia Stage in the study area. There are favorable exploration areas in the area around the intraplatform mound-shoal facies belt developed around the depression and slope break zone in the platform. A new understanding of the filling law and lithofacies paleogeographic characteristics of Qixia Stage from the perspective of sequence stratigraphy can provide a new framework for the subsequent reservoir research and the prediction of favorable exploration areas of Qixia Formation.
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There are many meandering river depositional models in the lower Minghuazhen formation in Penglai oilfield group. In order to reveal their sedimentary models and the evolution law, the meandering rivers’ characteristics and their paleogeological background in different periods are systematically analyzed by using paleontological data, core, wall core, well logging and seismic data, and furtherly the evolution law is summarized. The study shows that during the sedimentary period of the lower Minghuazhen formation, there are 5 kinds of meandering rivers developing successively in the study area. The river type of L44 sublayer is braided-meandering symbiotic model. The river type of the L42-L40 sublayer is a high-curvature meandering river. The river type of the L32 sublayer is restricted high-curvature meandering river. The river type of the L30 sublayer is string-beads meandering river. The river type of the L2 oil group is low-curvature meandering river under lake-level. During the sedimentary period of the lower Minghuazhen formation, the paleogeological background of the studied area also evolved continuously. Because of the coupling effect of different paleogeological factors, such as sedimentary base level cycles, paleoclimate, paleogeomorphology and the water environment in sedimentary area, various types of meandering river formed in different period.
There are many meandering river depositional models in the lower Minghuazhen formation in Penglai oilfield group. In order to reveal their sedimentary models and the evolution law, the meandering rivers’ characteristics and their paleogeological background in different periods are systematically analyzed by using paleontological data, core, wall core, well logging and seismic data, and furtherly the evolution law is summarized. The study shows that during the sedimentary period of the lower Minghuazhen formation, there are 5 kinds of meandering rivers developing successively in the study area. The river type of L44 sublayer is braided-meandering symbiotic model. The river type of the L42-L40 sublayer is a high-curvature meandering river. The river type of the L32 sublayer is restricted high-curvature meandering river. The river type of the L30 sublayer is string-beads meandering river. The river type of the L2 oil group is low-curvature meandering river under lake-level. During the sedimentary period of the lower Minghuazhen formation, the paleogeological background of the studied area also evolved continuously. Because of the coupling effect of different paleogeological factors, such as sedimentary base level cycles, paleoclimate, paleogeomorphology and the water environment in sedimentary area, various types of meandering river formed in different period.
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The organic carbon (TOC), major elements, trace elements and rare earth elements of Maidiping and Qiongzhusi formation samples from well JS1 were analyzed in order to reveal the intrinsic relationship between the early Cambrian geochemical characteristics and paleoenvironmental evolution in the southwestern margin of Sichuan Basin. The results show that the material source of Maidiping and Qiongzhusi formation is relatively consistent, the parent rock is mainly sedimentary rock and granite, and the material source area is formed in the continental margin environment. The Maidiping formation is enriched in light rare earth elements (LREE) relative to heavy rare earth elements (HREE) ((La/Yb)N=6.05), slightly to the right, and the average δEu is slightly less than 1, indicating normal seawater deposition, shallow water body, and not significantly affected by hydrothermal action. The Qiongzhusi formation has obvious LREE differentiation ((La/Yb)N=7.69), LREE enrichment, HREE depletion, and obvious right dip, with weak negative δCe and δEu anomalies, which may be related to transient or intermittent hydrothermal activity. In addition, the comparative analysis of different wells shows that the water body in the sedimentary period of the Maidiping formation is mainly dominated by the oxidation environment, and the sedimentary system in the region is tidal flat facies - shallow shelf facies. the Qiongzhusi formation as a whole belongs to an anaerobic environment, and its bottom is a reducing environment, the degree of anoxia decreases upwards, and the regional performance is shallow - deep water shelf sedimentary system.
The organic carbon (TOC), major elements, trace elements and rare earth elements of Maidiping and Qiongzhusi formation samples from well JS1 were analyzed in order to reveal the intrinsic relationship between the early Cambrian geochemical characteristics and paleoenvironmental evolution in the southwestern margin of Sichuan Basin. The results show that the material source of Maidiping and Qiongzhusi formation is relatively consistent, the parent rock is mainly sedimentary rock and granite, and the material source area is formed in the continental margin environment. The Maidiping formation is enriched in light rare earth elements (LREE) relative to heavy rare earth elements (HREE) ((La/Yb)N=6.05), slightly to the right, and the average δEu is slightly less than 1, indicating normal seawater deposition, shallow water body, and not significantly affected by hydrothermal action. The Qiongzhusi formation has obvious LREE differentiation ((La/Yb)N=7.69), LREE enrichment, HREE depletion, and obvious right dip, with weak negative δCe and δEu anomalies, which may be related to transient or intermittent hydrothermal activity. In addition, the comparative analysis of different wells shows that the water body in the sedimentary period of the Maidiping formation is mainly dominated by the oxidation environment, and the sedimentary system in the region is tidal flat facies - shallow shelf facies. the Qiongzhusi formation as a whole belongs to an anaerobic environment, and its bottom is a reducing environment, the degree of anoxia decreases upwards, and the regional performance is shallow - deep water shelf sedimentary system.
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In the Dagouli section located in Qingchuan Country，Sichuan Province and geologically in the northwestern Upper Yangtze Region, brown-purple mudstones are outcropped in the second member of the Lower Triassic Feixianguan Formation, interlayering with thin bedded limestones. The sedimentary structure of desiccation crack-like developed in these limestones is named as pseudodesiccation crack in this study. Few studies have focused on this special network structure, resulting in the misunderstanding of formation cause and sedimentary environment. With field investigation and thin section observation, it is revealed that the laminate and tough (or groove)-shaped limestones commonly show single layer of 2-10 cm in thickness. They are grainstones with abundant gastropod, ostracod and bivalve fossils, and faecal pellets as well. The structures of flute and gutter casts indicate that the limestone was formed under frequent storms. The desiccation crack-like structures developed in the thin-bedded limestones show irregular quadrangle or pentagon in the top and bottom interfaces, which actually was cut by calcite veins forming under pressure solution. Compaction and tectonism in the diagenetic stage could be the dynamics inducement for the formation of pseudo-desiccation cracks. The network structures found from the thin-bedded limestones imply the relatively deep-water environment (i.g., shelf) of the Lower Triassic Feixianguan Formation. The identification of Triassic pseudo-desiccation crack might be beneficial to explain the formation of Middle Ordovician cracked limestones in the Baota Formation.
In the Dagouli section located in Qingchuan Country，Sichuan Province and geologically in the northwestern Upper Yangtze Region, brown-purple mudstones are outcropped in the second member of the Lower Triassic Feixianguan Formation, interlayering with thin bedded limestones. The sedimentary structure of desiccation crack-like developed in these limestones is named as pseudodesiccation crack in this study. Few studies have focused on this special network structure, resulting in the misunderstanding of formation cause and sedimentary environment. With field investigation and thin section observation, it is revealed that the laminate and tough (or groove)-shaped limestones commonly show single layer of 2-10 cm in thickness. They are grainstones with abundant gastropod, ostracod and bivalve fossils, and faecal pellets as well. The structures of flute and gutter casts indicate that the limestone was formed under frequent storms. The desiccation crack-like structures developed in the thin-bedded limestones show irregular quadrangle or pentagon in the top and bottom interfaces, which actually was cut by calcite veins forming under pressure solution. Compaction and tectonism in the diagenetic stage could be the dynamics inducement for the formation of pseudo-desiccation cracks. The network structures found from the thin-bedded limestones imply the relatively deep-water environment (i.g., shelf) of the Lower Triassic Feixianguan Formation. The identification of Triassic pseudo-desiccation crack might be beneficial to explain the formation of Middle Ordovician cracked limestones in the Baota Formation.
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Abstract:
Jurassic strata are well exposed in the northeastern Qaidam Basin. However, the formation and scale of the Jurassic prototype-basin in this area has been obscured by intense tectonism, and currently remains unclear. Different views have been expressed regarding the original sedimentary relationships of the residual Jurassic depression. An integrated analysis of the heavy-mineral assemblages comprising whole-rock geochemistry and U-Pb chronology of detrital zircon was conducted to determine the provenance of the Middle Jurassic in this area. Further, the evolution of Jurassic prototype basin in the study area combined with its paleo-tectonic setting and stratigraphic and sedimentary facies research were discussed. The study showed the following. (1) During the Middle Jurassic, five distinct depositional areas existed in the study area, here designated as Areas A, B, C, D and E. (2) The primary source of sediments in the study area was intermediate-to-acidic igneous rock, partially mixed with sedimentary rock. (3) The tectonic setting of the provenance area is dominated by continental island arcs and active continental margin. It is considered that the provenance area was affected by two periods of magmatic events (200–300 and 400–500 Ma). (4) A comparison of the potential source areas and the depositional areas led to the following conclusions: Area A was mainly sourced from the North Qaidam UHP belt near the Xitie Mountain, with minor supplementary material from the Oulongbuluke Block. Area B was derived from the South Qilian Mountain in the northeast of the study area. Areas C and D, which have relatively low ZTR, are believed to be mainly sourced from near-source paleo-uplift. Area E was mainly sourced from the Ela Mountain in the east of the study area. (5) During the Middle Jurassic, the study area developed as a series of small-scale, isolated depressions until J2d7, then evolved into a larger, partially unified depression. These findings are highly significant for gaining an understanding of the evolution of the Qaidam Basin and the temporal-spatial changes of the basin–mountain system at the northern margin of the Tibetan Plateau. It is also important for guiding oil and gas exploration in the Qaidam Basin.
Jurassic strata are well exposed in the northeastern Qaidam Basin. However, the formation and scale of the Jurassic prototype-basin in this area has been obscured by intense tectonism, and currently remains unclear. Different views have been expressed regarding the original sedimentary relationships of the residual Jurassic depression. An integrated analysis of the heavy-mineral assemblages comprising whole-rock geochemistry and U-Pb chronology of detrital zircon was conducted to determine the provenance of the Middle Jurassic in this area. Further, the evolution of Jurassic prototype basin in the study area combined with its paleo-tectonic setting and stratigraphic and sedimentary facies research were discussed. The study showed the following. (1) During the Middle Jurassic, five distinct depositional areas existed in the study area, here designated as Areas A, B, C, D and E. (2) The primary source of sediments in the study area was intermediate-to-acidic igneous rock, partially mixed with sedimentary rock. (3) The tectonic setting of the provenance area is dominated by continental island arcs and active continental margin. It is considered that the provenance area was affected by two periods of magmatic events (200–300 and 400–500 Ma). (4) A comparison of the potential source areas and the depositional areas led to the following conclusions: Area A was mainly sourced from the North Qaidam UHP belt near the Xitie Mountain, with minor supplementary material from the Oulongbuluke Block. Area B was derived from the South Qilian Mountain in the northeast of the study area. Areas C and D, which have relatively low ZTR, are believed to be mainly sourced from near-source paleo-uplift. Area E was mainly sourced from the Ela Mountain in the east of the study area. (5) During the Middle Jurassic, the study area developed as a series of small-scale, isolated depressions until J2d7, then evolved into a larger, partially unified depression. These findings are highly significant for gaining an understanding of the evolution of the Qaidam Basin and the temporal-spatial changes of the basin–mountain system at the northern margin of the Tibetan Plateau. It is also important for guiding oil and gas exploration in the Qaidam Basin.
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Abstract:
Calcium (Ca) is a major rock-forming and biological nutrient element, which actively participates in geochemical cycling processes of the Earth’s surface, recording the marine environment and its evolution. With the development of analysis techniques, calcium isotopes have become an important research method in the field of geochemistry. Owing to various degrees of fractionation by inorganic and organic processes in Earth's surface environment, calcium isotopes are a powerful tool for tracing calcium cycle and are important for understanding the evolution of marine environments. In this study, we first introduced the fundamental principles and fractionation mechanisms of calcium isotopes, the features of the marine calcium cycle, and its isotopes. Based on the current research progress and trend, we further summarized the main application of calcium isotopes for paleoceanography, including the evaluation of carbonate diagenesis, the determination of seawater calcium isotope values, and the reconstruction of marine calcium cycle in deep time. Finally, we proposed suggestions for the future development of calcium isotopes in the field of paleoceanography, which may be helpful for promoting studies on the deep-time calcium cycle.
Calcium (Ca) is a major rock-forming and biological nutrient element, which actively participates in geochemical cycling processes of the Earth’s surface, recording the marine environment and its evolution. With the development of analysis techniques, calcium isotopes have become an important research method in the field of geochemistry. Owing to various degrees of fractionation by inorganic and organic processes in Earth's surface environment, calcium isotopes are a powerful tool for tracing calcium cycle and are important for understanding the evolution of marine environments. In this study, we first introduced the fundamental principles and fractionation mechanisms of calcium isotopes, the features of the marine calcium cycle, and its isotopes. Based on the current research progress and trend, we further summarized the main application of calcium isotopes for paleoceanography, including the evaluation of carbonate diagenesis, the determination of seawater calcium isotope values, and the reconstruction of marine calcium cycle in deep time. Finally, we proposed suggestions for the future development of calcium isotopes in the field of paleoceanography, which may be helpful for promoting studies on the deep-time calcium cycle.
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The Qiongzhusi Formation in the Yangtze region is an essential horizon for shale gas exploration.In order to reveal the weathering degree, paleoclimate, tectonic background and provenance of the sedimentary rock of Qiongzhusi Formation on the eastern margin of the ancient Kangding-Yunnan Land. Based on the profile measurement，sample collection，and analysis of major elements and trace elements of the sedimentary rock of Qiongzhusi Formation in Wulongcun profile on the eastern margin of the ancient Kangding-Yunnan Land, which provides quantitative geochemical data for the weathering degree, paleoclimate, tectonic background and provenance analyses of the Qiongzhusi Formation.The research conclusions are as follows：(1)The sedimentary rock of Qiongzhusi Formation are mainly strongly weathered, and the climate of provenance area is warm and humid during the deposition of Qiongzhusi Formation;(2)The sedimentary rock of the Qiongzhusi Formation were mainly formed in the passive continental margin environment, and the source rocks of sedimentary rock were formed in the continental island arc environment;(3)The sedimentary rock of Qiongzhusi Formation mainly came from tuffaceous sandstone, slate, granite and some basic rocks of the Mesoproterozoic Dongchuan group, Huili Group and Tangdan group in the ancient Kangding-Yunnan Land.
The Qiongzhusi Formation in the Yangtze region is an essential horizon for shale gas exploration.In order to reveal the weathering degree, paleoclimate, tectonic background and provenance of the sedimentary rock of Qiongzhusi Formation on the eastern margin of the ancient Kangding-Yunnan Land. Based on the profile measurement，sample collection，and analysis of major elements and trace elements of the sedimentary rock of Qiongzhusi Formation in Wulongcun profile on the eastern margin of the ancient Kangding-Yunnan Land, which provides quantitative geochemical data for the weathering degree, paleoclimate, tectonic background and provenance analyses of the Qiongzhusi Formation.The research conclusions are as follows：(1)The sedimentary rock of Qiongzhusi Formation are mainly strongly weathered, and the climate of provenance area is warm and humid during the deposition of Qiongzhusi Formation;(2)The sedimentary rock of the Qiongzhusi Formation were mainly formed in the passive continental margin environment, and the source rocks of sedimentary rock were formed in the continental island arc environment;(3)The sedimentary rock of Qiongzhusi Formation mainly came from tuffaceous sandstone, slate, granite and some basic rocks of the Mesoproterozoic Dongchuan group, Huili Group and Tangdan group in the ancient Kangding-Yunnan Land.
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River delta is the sensitive area of land-sea interaction with the intense human activities. It has always been the focus and hot spot of international research. Based on the grain size analysis results
River delta is the sensitive area of land-sea interaction with the intense human activities. It has always been the focus and hot spot of international research. Based on the grain size analysis results
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Abstract:
In order to analyze the pore fractal characteristics and interfering factors of coal measure shale of Taiyuan Formation in the northern Qinshui Basin, the total organic carbon (TOC) content, maturity , X-ray diffraction and low-temperature nitrogen adsorption experiments were carried out on samples of Taiyuan Formation in Yangquan Block. The fractal dimension of sample pore was calculated based on FHH theoretical model, and analyzes the influence of mineral content, organic geochemical characteristics, and pore structure parameters on the pore fractal dimension. The results show that the TOC content of coal measure shale in Taiyuan Formation is between 0.57% and 6.40%, the average is 3.18%, the vitrinite reflectance of organic matter (Ro) is between 1.96% and 3.24%, and the average is 2.49%. The coal-measure shale micro pores have double fractal characteristics, of which D1 is between 2.5079 and 2.6639. D2 is between 2.5271 and 2.80936, and the organic matter content and maturity are positively correlated with D1 and D2. The pore structure parameters have a good positive correlation with D1 and D2, but the correlation coefficient with D2 is higher than that of D1, indicating that micropores have stronger influence on pore structure parameters. The input of terrigenous clastic quartz with high sorting and roundness leads to regular pore morphology, resulting in negative correlation between quartz content and D1 and D2. Carbonate minerals and feldspar mainly provide macropores, Its content are related to shale. Both D1 and D2 are negatively correlated, and the pore size of clay minerals decreases under long-term compaction, the number of micropores increases, and the pore shape is complex, which is positively correlated with fractal dimensions D1 and D2. To sum up, the micro pores of coal measure shale of marine continental transitional facies have dual fractal characteristics. The increase of organic matter content, maturity, pore structure parameters and clay mineral content can lead to the increase of micro pore fractal dimension, and the increase of terrigenous clastic quartz, feldspar and carbonate mineral content can lead to the decrease of micro pore fractal dimension.
In order to analyze the pore fractal characteristics and interfering factors of coal measure shale of Taiyuan Formation in the northern Qinshui Basin, the total organic carbon (TOC) content, maturity , X-ray diffraction and low-temperature nitrogen adsorption experiments were carried out on samples of Taiyuan Formation in Yangquan Block. The fractal dimension of sample pore was calculated based on FHH theoretical model, and analyzes the influence of mineral content, organic geochemical characteristics, and pore structure parameters on the pore fractal dimension. The results show that the TOC content of coal measure shale in Taiyuan Formation is between 0.57% and 6.40%, the average is 3.18%, the vitrinite reflectance of organic matter (Ro) is between 1.96% and 3.24%, and the average is 2.49%. The coal-measure shale micro pores have double fractal characteristics, of which D1 is between 2.5079 and 2.6639. D2 is between 2.5271 and 2.80936, and the organic matter content and maturity are positively correlated with D1 and D2. The pore structure parameters have a good positive correlation with D1 and D2, but the correlation coefficient with D2 is higher than that of D1, indicating that micropores have stronger influence on pore structure parameters. The input of terrigenous clastic quartz with high sorting and roundness leads to regular pore morphology, resulting in negative correlation between quartz content and D1 and D2. Carbonate minerals and feldspar mainly provide macropores, Its content are related to shale. Both D1 and D2 are negatively correlated, and the pore size of clay minerals decreases under long-term compaction, the number of micropores increases, and the pore shape is complex, which is positively correlated with fractal dimensions D1 and D2. To sum up, the micro pores of coal measure shale of marine continental transitional facies have dual fractal characteristics. The increase of organic matter content, maturity, pore structure parameters and clay mineral content can lead to the increase of micro pore fractal dimension, and the increase of terrigenous clastic quartz, feldspar and carbonate mineral content can lead to the decrease of micro pore fractal dimension.
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Abstract:
Triassic strata are absent in the Yungang basin in the northcentral North China, while the Shihezi formation at the top of the Yangquantou section within the Yungang basin is assigned to the lower Triassic Liujiagou Formation according to regional geological survey results of 1:50000 Shijiatun map. In order to settle the dispute and determine the reliability of this new understanding, this paper conducted lithostratigraphic correlation and detrital zircon dating of the Shihezi Formation of Madaotou and Yangquantou sections within the Yungang basin. Results show that the so-called Liujiagou Formation identified in the upper part of Yangquantou section has similar lithofacies associations and gravel compositions with the Shihezi Formation in Madaotou section, and they are all characterized by grey-green or yellow-green medium- to thick-bedded medium- to coarse-grained sandstone interbedded with thin-bedded purple-red siltstone and sandy mudstone, as well as several layers of thick conglomerates, rather than the diagnostic characteristics of the Liujiagou Formation in Fugu, Ningwu, Taiyuan Xishan and Qinshui basins in the North China, which are characterized by abundant light red to fresh red thick-bedded medium- to fine-grained arkose. Moreover, the youngest detrital zircons ages (288.0±4.7 Ma) constrained its maximum depositional age to Middle Permian. Therefore, the strata at the top of the Yangquantou section is assigned to Middle Permian Shihezi formation, not the Liujiagou Formation. It is infered that the orogenic belts in the north and northern margin of North China probably experienced intense compression and uplift during the Late Triassic, resulting in the denudation of the Triassic strata within the Yungang basin, which was then unconformable covered by the Lower Jurassic strata.
Triassic strata are absent in the Yungang basin in the northcentral North China, while the Shihezi formation at the top of the Yangquantou section within the Yungang basin is assigned to the lower Triassic Liujiagou Formation according to regional geological survey results of 1:50000 Shijiatun map. In order to settle the dispute and determine the reliability of this new understanding, this paper conducted lithostratigraphic correlation and detrital zircon dating of the Shihezi Formation of Madaotou and Yangquantou sections within the Yungang basin. Results show that the so-called Liujiagou Formation identified in the upper part of Yangquantou section has similar lithofacies associations and gravel compositions with the Shihezi Formation in Madaotou section, and they are all characterized by grey-green or yellow-green medium- to thick-bedded medium- to coarse-grained sandstone interbedded with thin-bedded purple-red siltstone and sandy mudstone, as well as several layers of thick conglomerates, rather than the diagnostic characteristics of the Liujiagou Formation in Fugu, Ningwu, Taiyuan Xishan and Qinshui basins in the North China, which are characterized by abundant light red to fresh red thick-bedded medium- to fine-grained arkose. Moreover, the youngest detrital zircons ages (288.0±4.7 Ma) constrained its maximum depositional age to Middle Permian. Therefore, the strata at the top of the Yangquantou section is assigned to Middle Permian Shihezi formation, not the Liujiagou Formation. It is infered that the orogenic belts in the north and northern margin of North China probably experienced intense compression and uplift during the Late Triassic, resulting in the denudation of the Triassic strata within the Yungang basin, which was then unconformable covered by the Lower Jurassic strata.
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The exploration practice and the 4th oil and gas resource evaluation of Qaidam Basin show that the remaining petroleum in Qaidam Basin is mainly concentrated in the western area, which exploration level is relatively low due to the complex landform and typical unconventional low permeability reservoirs. In order to further increase the petroleum exploration in the western Qaidam Basin, based on the data of core sedimentary structure, combined with rock slices, X-ray diffraction whole rock analyses and seismic data et al, the sedimentary characteristics of the Pliocene Xiayoushashan Formation in well Xiandong 1 cored interval are comprehensively studied. Research has shown that the gray-black mudstone and shale interbedded with thin-medium massive fine-grained greywacke in the Pliocene Xiayoushashan Formation in Well Xiandong 1. The top and bottom of sand bodies are in abrupt contact with mudstone. The bottom boundary of the sand bodies are obviously uneven erosion surface, and the mudstone and shale beneath the erosion surface developed deformation bedding. The sand bodies are sandy debris flow deposits by re-transport. In the Pliocene Xiayoushashan Formation in well Xiandong 1, the dark gray-gray black calcareous mudstone and shale interbedded calcirudite bearing shell-terrigenous debris and siltstone and silty mass developing obvious deformation bedding which laminae are clear and have obvious deformation direction, which are sprung by clastic slump. The Pliocene Xiayoushashan Formation in well Xiandong 1 is mainly the dark gray-gray black mudstone and shale interbedded with siltstone bearing dolomite, calcite and clay. The mudstone and shale developed horizontal bedding and rhythmic bedding, and the siltstone developed small single inclined cross-bedding with more clay laminae, climbing-ripple lamination and coarsely interlayered bedding, which are mainly semi-deep lake deposits interbedded with weaker bottom flow deposits which are derived from sediment gravity flows. In addition, the deeper water areas of Altun Mountain front should have conditions of developing slump-sediment gravity flow sedimentary reservoirs similar to well Xiandong 1 in different basin development period, but further research is needed.
The exploration practice and the 4th oil and gas resource evaluation of Qaidam Basin show that the remaining petroleum in Qaidam Basin is mainly concentrated in the western area, which exploration level is relatively low due to the complex landform and typical unconventional low permeability reservoirs. In order to further increase the petroleum exploration in the western Qaidam Basin, based on the data of core sedimentary structure, combined with rock slices, X-ray diffraction whole rock analyses and seismic data et al, the sedimentary characteristics of the Pliocene Xiayoushashan Formation in well Xiandong 1 cored interval are comprehensively studied. Research has shown that the gray-black mudstone and shale interbedded with thin-medium massive fine-grained greywacke in the Pliocene Xiayoushashan Formation in Well Xiandong 1. The top and bottom of sand bodies are in abrupt contact with mudstone. The bottom boundary of the sand bodies are obviously uneven erosion surface, and the mudstone and shale beneath the erosion surface developed deformation bedding. The sand bodies are sandy debris flow deposits by re-transport. In the Pliocene Xiayoushashan Formation in well Xiandong 1, the dark gray-gray black calcareous mudstone and shale interbedded calcirudite bearing shell-terrigenous debris and siltstone and silty mass developing obvious deformation bedding which laminae are clear and have obvious deformation direction, which are sprung by clastic slump. The Pliocene Xiayoushashan Formation in well Xiandong 1 is mainly the dark gray-gray black mudstone and shale interbedded with siltstone bearing dolomite, calcite and clay. The mudstone and shale developed horizontal bedding and rhythmic bedding, and the siltstone developed small single inclined cross-bedding with more clay laminae, climbing-ripple lamination and coarsely interlayered bedding, which are mainly semi-deep lake deposits interbedded with weaker bottom flow deposits which are derived from sediment gravity flows. In addition, the deeper water areas of Altun Mountain front should have conditions of developing slump-sediment gravity flow sedimentary reservoirs similar to well Xiandong 1 in different basin development period, but further research is needed.
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Abstract:
The physical properties and geochemical characteristics of oil found in the Northern Slope, Bongor Basin, Chad, are clearly different. Forty-one samples of crude oil were analyzed to determine their differences and the influences on their properties aims to provide practical guidance for the assessment and prediction of oil quality in future oil exploration in this region. It was found that the degree of biodegradation is responsible for the differences. Non-, slightly- or heavily degraded oils were classified according to the relative content and distribution pattern of normal alkanes and acyclic isoprenoids, as well as the baseline characteristics of gas chromatograms. Burial depth is evidently the most important factor constraining the degree of biodegradation. No biodegraded oil was found deeper than 1300 m; the most heavily biodegraded oil occurs shallower than 800 m. In reservoirs between these depths, the degree of biodegradation is associated with distance from main faults, thickness of local caprock and type of trap.
The physical properties and geochemical characteristics of oil found in the Northern Slope, Bongor Basin, Chad, are clearly different. Forty-one samples of crude oil were analyzed to determine their differences and the influences on their properties aims to provide practical guidance for the assessment and prediction of oil quality in future oil exploration in this region. It was found that the degree of biodegradation is responsible for the differences. Non-, slightly- or heavily degraded oils were classified according to the relative content and distribution pattern of normal alkanes and acyclic isoprenoids, as well as the baseline characteristics of gas chromatograms. Burial depth is evidently the most important factor constraining the degree of biodegradation. No biodegraded oil was found deeper than 1300 m; the most heavily biodegraded oil occurs shallower than 800 m. In reservoirs between these depths, the degree of biodegradation is associated with distance from main faults, thickness of local caprock and type of trap.
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Abstract:
As an important type of coarse-grained sedimentary system and oil and gas reservoir in faulted basins, fan deposition has been the hot topic of research on lacustrine sedimentary and reservoir formation, such as distribution area, evolution period and accumulation model. Based on high resolution 3D seismic and drilling and logging data in the A sag of Melut basin in central Africa, with fan sedimentary characteristics analysis as the breakthrough point, the results showed that the types of sedimentary facies of fan in the study area included fan delta and slump fan caused by gravity flow, slump fan had two types of morphology characteristic, the first one was line source slump fan controlled by slope break, the second one was multistage slump fan with single point source controlled by steep topographic slope. Combined with seismic profiles and well logging features, five periods of fans were recognized in the Cretaceous study section. The vertical evolution of multiple periods of fans was characterized by “fisrt progradation and later retrogradation”. The fan distribution was the largest at the end of Renk Formation deposition in the Lower Cretaceous, reaching 148 km2. However, the single-stage fan all had the characteristics of retrogradation, belong to transgressive fan. The fan evolution was mainly influenced by tectonic activity, palaeogeomorphology, provenance supply, and base-level cycle. The fan distribution was larger in the period of strong tectonic activity, abundant provenance supply and large short-axis tectonic uplift, and the slump fan was most developed in the transition period of long-term base-level cycle. A new understanding of the sedimentary pattern transformation occurred in the Early Cretaceous and Late Cretaceous in the A sag was put forward, and A fan reservoir forming model of “direct charging of hydrocarbon generation kitchen, migration and accumulation direction controlled by unconformity and structural ridge, and accumulation influenced by braided channels within the fan” was established. The exploration potential of the fan deposition in the faulted depression is clarified, which guided the exploration deployment.
As an important type of coarse-grained sedimentary system and oil and gas reservoir in faulted basins, fan deposition has been the hot topic of research on lacustrine sedimentary and reservoir formation, such as distribution area, evolution period and accumulation model. Based on high resolution 3D seismic and drilling and logging data in the A sag of Melut basin in central Africa, with fan sedimentary characteristics analysis as the breakthrough point, the results showed that the types of sedimentary facies of fan in the study area included fan delta and slump fan caused by gravity flow, slump fan had two types of morphology characteristic, the first one was line source slump fan controlled by slope break, the second one was multistage slump fan with single point source controlled by steep topographic slope. Combined with seismic profiles and well logging features, five periods of fans were recognized in the Cretaceous study section. The vertical evolution of multiple periods of fans was characterized by “fisrt progradation and later retrogradation”. The fan distribution was the largest at the end of Renk Formation deposition in the Lower Cretaceous, reaching 148 km2. However, the single-stage fan all had the characteristics of retrogradation, belong to transgressive fan. The fan evolution was mainly influenced by tectonic activity, palaeogeomorphology, provenance supply, and base-level cycle. The fan distribution was larger in the period of strong tectonic activity, abundant provenance supply and large short-axis tectonic uplift, and the slump fan was most developed in the transition period of long-term base-level cycle. A new understanding of the sedimentary pattern transformation occurred in the Early Cretaceous and Late Cretaceous in the A sag was put forward, and A fan reservoir forming model of “direct charging of hydrocarbon generation kitchen, migration and accumulation direction controlled by unconformity and structural ridge, and accumulation influenced by braided channels within the fan” was established. The exploration potential of the fan deposition in the faulted depression is clarified, which guided the exploration deployment.
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Abstract:
Carbonate rock represents strong heterogeneity as a source rock and reservoir, in which the formation of stylolite plays a pivotal role in the enrichment of organic matter and geofluid migration within the carbonate rock itself. In order to study the enrichment mechanism of organic matter and geofluid migration mode in the stylolites developed in carbonate rocks, the stylolite-bearing core samples in the Dachigan structural belt in the eastern Sichuan Basin were collected. The stylolite and matrix were respectively subjected to organic carbon and pyrolysis （Rock-Eval）, common thin section observation, thin section observation under fluorescent light, whole rock X-ray diffraction, carbon and oxygen isotope and scanning electron microscopy and other testing items. The organic matter occurred in the stylolite is mainly in the form of three types including soluble organic matter, pyrobitumen, and bitumen, indicating that the organic matter in the stylolite is mainly the secondary migrated organic matter. Secondary dolomite and pyrite are well developed in the stylolite that the intercrystalline pore spaces and fractures are retained, thereby to provide good conditions for the accumulation and migration of oil and gas. The strong cementation on the contact between the stylolite and matrix and the formation of secondary minerals nearby may be the results of fractionation when the hydrocarbon fluid migrates from the matrix to stylolite. The thickness is not uniform in the bulk stylolite and the strong diagenesis is indicated in the location, of which the stylolite is thinner, thereby causing severe fractionation in turn. When the stylolite is developed, the organic matter trapped will be thermally decomposed to generate natural gas at high maturity. It will bias the results of gas source identification when mixed with other types of natural gases. The fractionation on crude oil as a result of acting as the migration channel of geofluid will also cause some interferences to the research on sources of crude oil. Appropriate parameters of biomarker compounds are necessarily selected to analyze the correlation between oil sources, coupled with the consideration of spatial variation law of crude oil properties.
Carbonate rock represents strong heterogeneity as a source rock and reservoir, in which the formation of stylolite plays a pivotal role in the enrichment of organic matter and geofluid migration within the carbonate rock itself. In order to study the enrichment mechanism of organic matter and geofluid migration mode in the stylolites developed in carbonate rocks, the stylolite-bearing core samples in the Dachigan structural belt in the eastern Sichuan Basin were collected. The stylolite and matrix were respectively subjected to organic carbon and pyrolysis （Rock-Eval）, common thin section observation, thin section observation under fluorescent light, whole rock X-ray diffraction, carbon and oxygen isotope and scanning electron microscopy and other testing items. The organic matter occurred in the stylolite is mainly in the form of three types including soluble organic matter, pyrobitumen, and bitumen, indicating that the organic matter in the stylolite is mainly the secondary migrated organic matter. Secondary dolomite and pyrite are well developed in the stylolite that the intercrystalline pore spaces and fractures are retained, thereby to provide good conditions for the accumulation and migration of oil and gas. The strong cementation on the contact between the stylolite and matrix and the formation of secondary minerals nearby may be the results of fractionation when the hydrocarbon fluid migrates from the matrix to stylolite. The thickness is not uniform in the bulk stylolite and the strong diagenesis is indicated in the location, of which the stylolite is thinner, thereby causing severe fractionation in turn. When the stylolite is developed, the organic matter trapped will be thermally decomposed to generate natural gas at high maturity. It will bias the results of gas source identification when mixed with other types of natural gases. The fractionation on crude oil as a result of acting as the migration channel of geofluid will also cause some interferences to the research on sources of crude oil. Appropriate parameters of biomarker compounds are necessarily selected to analyze the correlation between oil sources, coupled with the consideration of spatial variation law of crude oil properties.
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Abstract:
The Lower Jurassic Badaowan and Sangonghe formations in the middle and eastern parts of the Fukang depression are the key intervals for oil and gas exploration, but it is restricted due to the unclear provenance system. The Lower Jurassic provenance system in the middle and eastern part of Fukang depression was analyzed based on rock clastic composition, paleocurrent analysis, heavy mineral composition, cathodoluminescence characteristics and the ratio of sandstone to strata. The results show that the study area was dominated by the provenance of Karameri Mountain during the Early Jurassic, while the influence of the provenances of the Northern Tianshan and Bogda Mountains were limited. However, the Sangonghe Formation was not only influenced by the inherited Kalameri Mountain and the North Tianshan provenance, but also superimposed the enhancing branch provenance from the Bogda Mountain. The change of the Lower Jurassic provenance in the study area clearly responded to the increasing uplift of the Bogda Mountains from east to west. Since the study area is characterized by a south-dipping structural background, the existence of southeast provenance of the Lower Jurassic laid a material foundation for the development of stratigraphic-lithologic traps in the southern slope belt of the Fukang depression, which is of great significance for oil and gas exploration in the future.
The Lower Jurassic Badaowan and Sangonghe formations in the middle and eastern parts of the Fukang depression are the key intervals for oil and gas exploration, but it is restricted due to the unclear provenance system. The Lower Jurassic provenance system in the middle and eastern part of Fukang depression was analyzed based on rock clastic composition, paleocurrent analysis, heavy mineral composition, cathodoluminescence characteristics and the ratio of sandstone to strata. The results show that the study area was dominated by the provenance of Karameri Mountain during the Early Jurassic, while the influence of the provenances of the Northern Tianshan and Bogda Mountains were limited. However, the Sangonghe Formation was not only influenced by the inherited Kalameri Mountain and the North Tianshan provenance, but also superimposed the enhancing branch provenance from the Bogda Mountain. The change of the Lower Jurassic provenance in the study area clearly responded to the increasing uplift of the Bogda Mountains from east to west. Since the study area is characterized by a south-dipping structural background, the existence of southeast provenance of the Lower Jurassic laid a material foundation for the development of stratigraphic-lithologic traps in the southern slope belt of the Fukang depression, which is of great significance for oil and gas exploration in the future.
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Abstract:
Dolomite commonly has higher porosity than surrounding limestones, becoming the preferred targets of petroleum exploration. In marine carbonate successions in the Sichuan Basin, approximately 96.2% of the proved gas reserves comes from dolomite reservoirs. Thus, the dolomitization and the origin of pores in dolomites have attracted great attentions of petroleum geologists, and the significant progress has been made. However, there is still a dispute about how dolomitization affects the development of porosity. By summarizing the main theoretical viewpoints of pore origin, combined with results of various replacement experimental simulations, this paper expounds the formation and evolution of pores during the process of dolomitization, and puts forward the prospect of the research on pore origin. The pores in dolomites may be inherited from the precursor limestones, or resulted from the dissolution of calcite during or after dolomitization; dolomitization might increase, maintain or reduce reservoir porosity, depending on the environment, time and natures of dolomitizing fluids. The common characteristics of replacement from experimental simulations imply that replacement is a micro process of dissolution, migration and precipitation, accompanied by the formation of new pores, which acts as a channel for fluid and ions exchange to maintain the reaction. The formation of pores is not controlled by the molar volume of minerals, but by the relative solubility, that is, the dissolution of reactants is greater than the precipitation of products, resulting in the increase of pore volume. The formation of new pores is accompanied by the whole replacement process, but they are mainly micropores, and their contribution to the effective porosity of the reservoir remains to be further evaluated.
Dolomite commonly has higher porosity than surrounding limestones, becoming the preferred targets of petroleum exploration. In marine carbonate successions in the Sichuan Basin, approximately 96.2% of the proved gas reserves comes from dolomite reservoirs. Thus, the dolomitization and the origin of pores in dolomites have attracted great attentions of petroleum geologists, and the significant progress has been made. However, there is still a dispute about how dolomitization affects the development of porosity. By summarizing the main theoretical viewpoints of pore origin, combined with results of various replacement experimental simulations, this paper expounds the formation and evolution of pores during the process of dolomitization, and puts forward the prospect of the research on pore origin. The pores in dolomites may be inherited from the precursor limestones, or resulted from the dissolution of calcite during or after dolomitization; dolomitization might increase, maintain or reduce reservoir porosity, depending on the environment, time and natures of dolomitizing fluids. The common characteristics of replacement from experimental simulations imply that replacement is a micro process of dissolution, migration and precipitation, accompanied by the formation of new pores, which acts as a channel for fluid and ions exchange to maintain the reaction. The formation of pores is not controlled by the molar volume of minerals, but by the relative solubility, that is, the dissolution of reactants is greater than the precipitation of products, resulting in the increase of pore volume. The formation of new pores is accompanied by the whole replacement process, but they are mainly micropores, and their contribution to the effective porosity of the reservoir remains to be further evaluated.
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Abstract:
The Shanxi Graben System has become an important area of late Cenozoic deformation research in eastern China for its unique tectonic location. However, due to the limitations of the outcrop profile, the complete sedimentary environment evolution of the basins in the graben system is rarely reported, which hinders our understanding of its evolution process. The depositional environments and provenance were analyzed using the detailed sedimentary record from the ZK01 borehole in the Taiyuan Basin. The analysis of the sedimentary environment shows that the Taiyuan Basin underwent a fluvial–delta/lake–river sedimentary environment evolution process. Two mega transgressions generated basin-wide lakes, one at ca. 5.8–4.4 and the other at ca. 2.2–1.6 Ma. Provenance analysis shows that the initial provenance was mainly the Mesozoic sandstones of the Taihang Mountain in the east of the basin, and reveals the erosion and denudation processes of Taihang Mountain. Then the debris of metamorphic and volcanic rocks from the northern part of the Lvliang Mountain began to enter the basin, accompanied by the first development of the lake. Asynchronous processes between paleoclimatic variations and transgressions illustrate the lakes’ spreading processes as mainly influenced by tectonic subsidence, being a structural-geomorphic response to the eastward spreading of the Qinghai-Tibetan Plateau.
The Shanxi Graben System has become an important area of late Cenozoic deformation research in eastern China for its unique tectonic location. However, due to the limitations of the outcrop profile, the complete sedimentary environment evolution of the basins in the graben system is rarely reported, which hinders our understanding of its evolution process. The depositional environments and provenance were analyzed using the detailed sedimentary record from the ZK01 borehole in the Taiyuan Basin. The analysis of the sedimentary environment shows that the Taiyuan Basin underwent a fluvial–delta/lake–river sedimentary environment evolution process. Two mega transgressions generated basin-wide lakes, one at ca. 5.8–4.4 and the other at ca. 2.2–1.6 Ma. Provenance analysis shows that the initial provenance was mainly the Mesozoic sandstones of the Taihang Mountain in the east of the basin, and reveals the erosion and denudation processes of Taihang Mountain. Then the debris of metamorphic and volcanic rocks from the northern part of the Lvliang Mountain began to enter the basin, accompanied by the first development of the lake. Asynchronous processes between paleoclimatic variations and transgressions illustrate the lakes’ spreading processes as mainly influenced by tectonic subsidence, being a structural-geomorphic response to the eastward spreading of the Qinghai-Tibetan Plateau.
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Abstract:
Global warming may increase the risk of expansion of karst rock desertification (KRD) in SW China, where karst landscapes are widespread, so it is important to reconstruct the evolution of KRD in this region. In this study, the regional eco-evolution of the past 4750 years was reconstructed based on 29 230Th ages and 954 δ13C records collected from stalagmite HD12 in Dark Cave, Qianxi County, Guizhou Province. Two significant positive δ13C offsets were found at 4322~3526 and 803~82 a B.P., indicating deterioration of the ecological environment at those times. A significant positive δ13C record of the HD12 stalagmite at about 803 a B.P. persisted for about 290 years with an amplitude of 4.2‰, indicating expansion of KRD in the area. The consistent positive δ13C in stalagmites from several caves in SW China during this period suggests that the large-scale population migration and climatic drought after the Jing-kang event (823 a B.P.) promoted the expansion of KRD in this region. During 4322~3526 a B.P., the positive shift of HD12 stalagmite δ13C values had an amplitude of 4.9‰. The positive shift at 4322~3977 a B.P. corresponds to the 4.2 ka event, and for 3777~3526 a B.P. it corresponds to the 3.7 ka event. These two periods of drought are also reflected in several stalagmite and lake records in SW China, suggesting that the weakened Asian summer monsoon and reduced precipitation at those times may have caused a large reduction in vegetation cover and severe soil degradation in the region.
Global warming may increase the risk of expansion of karst rock desertification (KRD) in SW China, where karst landscapes are widespread, so it is important to reconstruct the evolution of KRD in this region. In this study, the regional eco-evolution of the past 4750 years was reconstructed based on 29 230Th ages and 954 δ13C records collected from stalagmite HD12 in Dark Cave, Qianxi County, Guizhou Province. Two significant positive δ13C offsets were found at 4322~3526 and 803~82 a B.P., indicating deterioration of the ecological environment at those times. A significant positive δ13C record of the HD12 stalagmite at about 803 a B.P. persisted for about 290 years with an amplitude of 4.2‰, indicating expansion of KRD in the area. The consistent positive δ13C in stalagmites from several caves in SW China during this period suggests that the large-scale population migration and climatic drought after the Jing-kang event (823 a B.P.) promoted the expansion of KRD in this region. During 4322~3526 a B.P., the positive shift of HD12 stalagmite δ13C values had an amplitude of 4.9‰. The positive shift at 4322~3977 a B.P. corresponds to the 4.2 ka event, and for 3777~3526 a B.P. it corresponds to the 3.7 ka event. These two periods of drought are also reflected in several stalagmite and lake records in SW China, suggesting that the weakened Asian summer monsoon and reduced precipitation at those times may have caused a large reduction in vegetation cover and severe soil degradation in the region.
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Abstract:
The Jurassic is a period of typical greenhouse climate, during which the climate had been fluctuated and resulted in sedimentary responses in terrestrial basins. There are lots of different large terrestrial basins in China at the time, where discrepancies in records of response could be preserved in variety of sedimentary basins. In this paper, we focused on the study of the Middle-Upper Jurassic terrestrial redbeds in the northeastern Sichuan Basin to delineate the changes of sedimentary environments and paleoclimate, based on the observation of outcrops, analyses of microscopic clastic composition and carbon-oxygen isotopes, and estimate of atmospheric carbon dioxide concentration. Results show that Lithologies are dominated by medium-fine clastic rocks, in which five sandstones are further classified in composition and characterized by the lithic; three sedimentary environmental units are recognized as meandering, lake, and paleosol, simpler than those in western Sichuan Basin; the facies sequence changes upward, pedogenic and low sand/mud ratio meandering mudrocks in the Shaximiao Formation of the Middle Jurassic, lacustrine mudrocks with siltstones in the lower Suining Formation of the lower Upper Jurassic, and upward-coarsing and thickening and high sand/mud ratio meandering sandstones in the upper Suining and Penglaizhen formations of the middle-upper Upper Jurassic. Two and half cycles of semi-arid and arid climate can be differentiated in the Middle-Upper Jurassic sequence by indices of F/Q and F/L, corresponding to the Lower Shaximiao Formation, the Upper Shaximiao Formation + lower Suining Formation, and the upper Suining Formation + Penglaizhen Formation, respectively. According to pCO2, it is postulated that the Middle Jurassic was in relatively cool, the early Late Jurassic was warming, and the middle-late Late Jurassic became hot, roughly consistent with the framework of global marine climate. The climate was overall (semi-) arid in northeastern Sichuan, similar with that in other regions of the Sichuan Basin. It needs to further verify that an intermittence of semi-wet climate occurred in western Sichuan and hot climate was in northeastern Sichuan.
The Jurassic is a period of typical greenhouse climate, during which the climate had been fluctuated and resulted in sedimentary responses in terrestrial basins. There are lots of different large terrestrial basins in China at the time, where discrepancies in records of response could be preserved in variety of sedimentary basins. In this paper, we focused on the study of the Middle-Upper Jurassic terrestrial redbeds in the northeastern Sichuan Basin to delineate the changes of sedimentary environments and paleoclimate, based on the observation of outcrops, analyses of microscopic clastic composition and carbon-oxygen isotopes, and estimate of atmospheric carbon dioxide concentration. Results show that Lithologies are dominated by medium-fine clastic rocks, in which five sandstones are further classified in composition and characterized by the lithic; three sedimentary environmental units are recognized as meandering, lake, and paleosol, simpler than those in western Sichuan Basin; the facies sequence changes upward, pedogenic and low sand/mud ratio meandering mudrocks in the Shaximiao Formation of the Middle Jurassic, lacustrine mudrocks with siltstones in the lower Suining Formation of the lower Upper Jurassic, and upward-coarsing and thickening and high sand/mud ratio meandering sandstones in the upper Suining and Penglaizhen formations of the middle-upper Upper Jurassic. Two and half cycles of semi-arid and arid climate can be differentiated in the Middle-Upper Jurassic sequence by indices of F/Q and F/L, corresponding to the Lower Shaximiao Formation, the Upper Shaximiao Formation + lower Suining Formation, and the upper Suining Formation + Penglaizhen Formation, respectively. According to pCO2, it is postulated that the Middle Jurassic was in relatively cool, the early Late Jurassic was warming, and the middle-late Late Jurassic became hot, roughly consistent with the framework of global marine climate. The climate was overall (semi-) arid in northeastern Sichuan, similar with that in other regions of the Sichuan Basin. It needs to further verify that an intermittence of semi-wet climate occurred in western Sichuan and hot climate was in northeastern Sichuan.
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Abstract:
In order to solve the problems of uncertain reservoir lithology variation and distribution law in the west and Tainei areas of the south section of Feixianguan Trough in East Sichuan, a new method of using machine learning to identify lithology based on logging response characteristics is proposed, the experimental verification and the application effect are analyzed. Considering the low computing speed and large resource consumption of gradient-enhanced decision tree (GBDT) , a lithology identification model is constructed with a stochastic factor, namely, stochastic gradient-enhanced decision tree (SGBDT) . Based on geological data such as CORE, thin section and logging data in Mud logging, 5 logging parameters, namely GR, AC, RT, CNL and Den, were selected to identify the lithology in the area, and a lithology identification model was established and applied to the whole area. Compared with the artificial neural network (Ann) and gradient elevation decision tree (GBDT) algorithm, the improved SGBDT algorithm achieves the Gabriel Cramer coefficient and intersection graph coefficient of 0.945 and 0.920 respectively, and has good generalization ability, it is suitable for complex lithology evaluation of carbonate rocks. Applied to the whole area, the results show that the distribution of oolitic shoal reservoir in the area is obviously different, and the platform edge oolitic shoal is more developed, and the platform palaeogeomorphology high-point oolitic shoal and point shoal are less developed.
In order to solve the problems of uncertain reservoir lithology variation and distribution law in the west and Tainei areas of the south section of Feixianguan Trough in East Sichuan, a new method of using machine learning to identify lithology based on logging response characteristics is proposed, the experimental verification and the application effect are analyzed. Considering the low computing speed and large resource consumption of gradient-enhanced decision tree (GBDT) , a lithology identification model is constructed with a stochastic factor, namely, stochastic gradient-enhanced decision tree (SGBDT) . Based on geological data such as CORE, thin section and logging data in Mud logging, 5 logging parameters, namely GR, AC, RT, CNL and Den, were selected to identify the lithology in the area, and a lithology identification model was established and applied to the whole area. Compared with the artificial neural network (Ann) and gradient elevation decision tree (GBDT) algorithm, the improved SGBDT algorithm achieves the Gabriel Cramer coefficient and intersection graph coefficient of 0.945 and 0.920 respectively, and has good generalization ability, it is suitable for complex lithology evaluation of carbonate rocks. Applied to the whole area, the results show that the distribution of oolitic shoal reservoir in the area is obviously different, and the platform edge oolitic shoal is more developed, and the platform palaeogeomorphology high-point oolitic shoal and point shoal are less developed.
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Abstract:
The exploration practice shows that the sand body of Shanxi formation, the main gas producing layer in Yan 'an gas field in the southeast of Ordos Basin, is distributed in long and narrow strip, which is significantly different from the sand body of Shanxi Formation in the north. Taking the 2nd member of Shanxi Formation in the southeast of the basin as the geological prototype, the flume sedimentation simulation experiment was used to investigate the sand formation and evolution process and control factors. Results show that the gentle slope and low flow intensity is the 2nd member of Shanxi Formation of distributary channel is the important factor of low sinuosity of meander state, the horizontal amplitude rate is the 2nd member of Shanxi Formation of sand control the longitudinal extension of the key factors, sand size and aspect ratio of the coast and the change of flow control, the extension of sand whole distance and length-width ratio were proportional to the scale and rate of water withdrawal. During the sedimentary period of Shanxi formation, under the background that the water level dropped significantly and the shoreline migrated to the lake area for a long distance, the water inlet retreated frequently and the sand in the front of the meander river delta extended for a long distance. The sand superposition style has the characteristics of "vertical superposition", "vertical cutting" and "lateral migration". The results are of great significance to the prediction of sand bodies in Shanxi Formation and the search for high-quality reservoirs.
The exploration practice shows that the sand body of Shanxi formation, the main gas producing layer in Yan 'an gas field in the southeast of Ordos Basin, is distributed in long and narrow strip, which is significantly different from the sand body of Shanxi Formation in the north. Taking the 2nd member of Shanxi Formation in the southeast of the basin as the geological prototype, the flume sedimentation simulation experiment was used to investigate the sand formation and evolution process and control factors. Results show that the gentle slope and low flow intensity is the 2nd member of Shanxi Formation of distributary channel is the important factor of low sinuosity of meander state, the horizontal amplitude rate is the 2nd member of Shanxi Formation of sand control the longitudinal extension of the key factors, sand size and aspect ratio of the coast and the change of flow control, the extension of sand whole distance and length-width ratio were proportional to the scale and rate of water withdrawal. During the sedimentary period of Shanxi formation, under the background that the water level dropped significantly and the shoreline migrated to the lake area for a long distance, the water inlet retreated frequently and the sand in the front of the meander river delta extended for a long distance. The sand superposition style has the characteristics of "vertical superposition", "vertical cutting" and "lateral migration". The results are of great significance to the prediction of sand bodies in Shanxi Formation and the search for high-quality reservoirs.
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Abstract:
A large set of lacustrine carbonate bearing fine-grained sedimentary rocks are developed in Dongying sag, Bohai Bay Basin, Eastern China. Through core and thin section observation, according to sedimentary structural characteristics and mineral composition content, the fine-grained rocks developed in this area are divided into five lithofacies: laminar argillaceous limestone, laminar calcareous mudstone, weakly laminar calcareous mudstone, lenticular argillaceous limestone and massive mudstone. The time series analysis of natural gamma ray (GR) logging curves of 545m thick from the upper submember of the Member 4(Es4u) to the lower submember of the Member 3(Es3l) of the Paleogene Shahejie Formation of Fanye 1 well (F1) in this area is carried out. Considering the differences of sedimentary environment and sedimentary rate, the target interval is divided into four units. The multi taper method (MTM) power spectrum analysis of untuned GR sequence. The results show that the four units record 125kyr, 38.7kyr and 18.7kyr Milankovitch cycle signals. Taking the volcanic ash dating 42.4Ma in the Es4u and Es3l as the "anchor point", a "floating" astronomical chronometer with an accuracy of 38.7kyr is established after calibration by 405kyr long eccentricity cycle. The total duration of fine-grained rocks from the Es4u to the Es3l in Dongying sag is 5.3Myr. By analyzing the 18.7kyr precession cycle and the change of carbonate content, there is a good corresponding relationship between them. It is speculated that the earth orbit parameters 18.7kyr precession cycle and 125kyr eccentricity cycle jointly drive the change of climate and control the sedimentation of carbonate fine-grained sedimentary rocks. Finally, we propose a sedimentary model to explain the relationship between orbital circulation and the genesis of carbonate bearing fine-grained sedimentary rocks. 18.7kyr precession controls the change of insolation, and is also regulated by 125kyr eccentricity. At the maximum value of precession or the minimum value of eccentricity, the insolation increases, the water temperature in the lake basin increases, planktonic algae and bacteria proliferate, and the biochemical action increases, forming a microenvironment conducive to calcite crystallization, mainly limestone deposits. At the minimum value of precession or the maximum value of eccentricity, the insolation decreases, the water temperature in the lake basin decreases, the life activities of planktonic algae and bacteria are inhibited, and the biochemical effect is weakened. The fine-grained materials are mainly imported from land, mainly from mudstone deposition. Based on the theory of cycle stratigraphy, from the perspective of astronomical cycle controlling sedimentation, it has important scientific and guiding significance for unconventional oil and gas exploration and development to restore the characteristics of paleoclimate and paleoenvironment changes of lake sediments and explore the genetic mechanism of lacustrine fine-grained sedimentary rocks.
A large set of lacustrine carbonate bearing fine-grained sedimentary rocks are developed in Dongying sag, Bohai Bay Basin, Eastern China. Through core and thin section observation, according to sedimentary structural characteristics and mineral composition content, the fine-grained rocks developed in this area are divided into five lithofacies: laminar argillaceous limestone, laminar calcareous mudstone, weakly laminar calcareous mudstone, lenticular argillaceous limestone and massive mudstone. The time series analysis of natural gamma ray (GR) logging curves of 545m thick from the upper submember of the Member 4(Es4u) to the lower submember of the Member 3(Es3l) of the Paleogene Shahejie Formation of Fanye 1 well (F1) in this area is carried out. Considering the differences of sedimentary environment and sedimentary rate, the target interval is divided into four units. The multi taper method (MTM) power spectrum analysis of untuned GR sequence. The results show that the four units record 125kyr, 38.7kyr and 18.7kyr Milankovitch cycle signals. Taking the volcanic ash dating 42.4Ma in the Es4u and Es3l as the "anchor point", a "floating" astronomical chronometer with an accuracy of 38.7kyr is established after calibration by 405kyr long eccentricity cycle. The total duration of fine-grained rocks from the Es4u to the Es3l in Dongying sag is 5.3Myr. By analyzing the 18.7kyr precession cycle and the change of carbonate content, there is a good corresponding relationship between them. It is speculated that the earth orbit parameters 18.7kyr precession cycle and 125kyr eccentricity cycle jointly drive the change of climate and control the sedimentation of carbonate fine-grained sedimentary rocks. Finally, we propose a sedimentary model to explain the relationship between orbital circulation and the genesis of carbonate bearing fine-grained sedimentary rocks. 18.7kyr precession controls the change of insolation, and is also regulated by 125kyr eccentricity. At the maximum value of precession or the minimum value of eccentricity, the insolation increases, the water temperature in the lake basin increases, planktonic algae and bacteria proliferate, and the biochemical action increases, forming a microenvironment conducive to calcite crystallization, mainly limestone deposits. At the minimum value of precession or the maximum value of eccentricity, the insolation decreases, the water temperature in the lake basin decreases, the life activities of planktonic algae and bacteria are inhibited, and the biochemical effect is weakened. The fine-grained materials are mainly imported from land, mainly from mudstone deposition. Based on the theory of cycle stratigraphy, from the perspective of astronomical cycle controlling sedimentation, it has important scientific and guiding significance for unconventional oil and gas exploration and development to restore the characteristics of paleoclimate and paleoenvironment changes of lake sediments and explore the genetic mechanism of lacustrine fine-grained sedimentary rocks.
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Abstract:
The development of the "sweet spot" of lacustrine fine-grained sedimentary shale reservoirs is closely related to the enrichment of organic matter. However, there are few related studies on the control factors of organic matter enrichment and the establishment of enrichment models of shale in faulted saline lacustrine basins. The pure upper sub-segment of the upper 4th member of Shahejie Formation （Es4scs） in the Dongying Sag developed a typical continental rifted saline lake basin. In order to deepen the understanding of the enrichment law of organic matter in fine-grained sedimentary shale during this period, this article starts with sedimentology, geochemistry, paleontology and molecular stratigraphy, using thin slice identification, scanning electron microscopy, X-ray diffraction, sporopollen identification, biomarker chromatography-mass spectrometry and other technical means to discuss the control of organic matter enrichment factors. Eventually, organic matter enrichment models at different depositional environment stages will be established. The result shows: ① Organic matter has microscopic occurrence state such as strips, fillings, and dispersions. The source of parent material is mainly lower aquatic organisms such as algae, and a small amount of terrestrial higher plant sources appear in the middle and upper strata. ②The sedimentary environment has experienced three evolutionary stages: shallow water semi-arid low oxygen environment—deep water semi-humid reducing environment—sub-deep water semi-arid oxygen low environment. ③The enrichment of organic matter is mainly controlled by paleoclimate, paleosalinity, paleoredox, paleoproductivity and deposition rate, while paleowater depth, terrestrial input, volcanism and hydrothermal activity are secondary controlling factors. This researchs comprehensively and systematically explores the main controlling factors of organic matter enrichment. And an organic matter enrichment model suitable for the fine-grained sedimentary strata of the continental rifted saline lake basin was established. The research results will be of great significance to the exploration and development of continental shale oil and gas in my country. That is, high productivity, reduction environment and preservation conditions, suitable salinity and deposition rate dominate the high organic matter enrichment of the studied interval. The sedimentary products of this environment are favorable intervals for shale oil and gas exploration.
The development of the "sweet spot" of lacustrine fine-grained sedimentary shale reservoirs is closely related to the enrichment of organic matter. However, there are few related studies on the control factors of organic matter enrichment and the establishment of enrichment models of shale in faulted saline lacustrine basins. The pure upper sub-segment of the upper 4th member of Shahejie Formation （Es4scs） in the Dongying Sag developed a typical continental rifted saline lake basin. In order to deepen the understanding of the enrichment law of organic matter in fine-grained sedimentary shale during this period, this article starts with sedimentology, geochemistry, paleontology and molecular stratigraphy, using thin slice identification, scanning electron microscopy, X-ray diffraction, sporopollen identification, biomarker chromatography-mass spectrometry and other technical means to discuss the control of organic matter enrichment factors. Eventually, organic matter enrichment models at different depositional environment stages will be established. The result shows: ① Organic matter has microscopic occurrence state such as strips, fillings, and dispersions. The source of parent material is mainly lower aquatic organisms such as algae, and a small amount of terrestrial higher plant sources appear in the middle and upper strata. ②The sedimentary environment has experienced three evolutionary stages: shallow water semi-arid low oxygen environment—deep water semi-humid reducing environment—sub-deep water semi-arid oxygen low environment. ③The enrichment of organic matter is mainly controlled by paleoclimate, paleosalinity, paleoredox, paleoproductivity and deposition rate, while paleowater depth, terrestrial input, volcanism and hydrothermal activity are secondary controlling factors. This researchs comprehensively and systematically explores the main controlling factors of organic matter enrichment. And an organic matter enrichment model suitable for the fine-grained sedimentary strata of the continental rifted saline lake basin was established. The research results will be of great significance to the exploration and development of continental shale oil and gas in my country. That is, high productivity, reduction environment and preservation conditions, suitable salinity and deposition rate dominate the high organic matter enrichment of the studied interval. The sedimentary products of this environment are favorable intervals for shale oil and gas exploration.
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Abstract:
Through geochemical methods, 16 sand and mudstone samples from different sections of the Late Triassic Yanchang Formation in the central part of the western margin of Ordos Basin were tested and analyzed, and the sedimentary environment, source rock types and tectonic background of the Yanchang Formation clastic rocks were discussed. The results showed that the sandstone types were mainly lithic sandstone and feldspathic sandstone, and the source areas experienced weak-moderate weathering, and the samples were little affected by the re-cycling. The source is related to the upper crust material; Yanchang Formation as a whole is in an oxidation-weak reduction freshwater sedimentary environment, with an arid-semi-arid paleoclimate, and the third member is in a weak oxidation brackish water environment and a warm and humid paleoclimate. The source rocks are mainly felsic rocks, and the provenance of the third member of Yanchang Formation is complex, with some intermediate rock. The source area of Yanchang Formation is generally in the tectonic background of active continental margin, while the tectonic background of the third member source area is complex, which is related to both the continental island arc and the tectonic background of active continental margin. The provenance and sedimentary environment characteristics traced by elemental geochemical characteristics are in good agreement with the lake basin evolution and regional tectonic environment of Triassic Yanchang Formation.
Through geochemical methods, 16 sand and mudstone samples from different sections of the Late Triassic Yanchang Formation in the central part of the western margin of Ordos Basin were tested and analyzed, and the sedimentary environment, source rock types and tectonic background of the Yanchang Formation clastic rocks were discussed. The results showed that the sandstone types were mainly lithic sandstone and feldspathic sandstone, and the source areas experienced weak-moderate weathering, and the samples were little affected by the re-cycling. The source is related to the upper crust material; Yanchang Formation as a whole is in an oxidation-weak reduction freshwater sedimentary environment, with an arid-semi-arid paleoclimate, and the third member is in a weak oxidation brackish water environment and a warm and humid paleoclimate. The source rocks are mainly felsic rocks, and the provenance of the third member of Yanchang Formation is complex, with some intermediate rock. The source area of Yanchang Formation is generally in the tectonic background of active continental margin, while the tectonic background of the third member source area is complex, which is related to both the continental island arc and the tectonic background of active continental margin. The provenance and sedimentary environment characteristics traced by elemental geochemical characteristics are in good agreement with the lake basin evolution and regional tectonic environment of Triassic Yanchang Formation.
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Abstract:
As the basic properties of sediments, grain size and shape provide information about their transport history, mode, and sedimentary environment. We analyzed the grain size and shape of 252 sediments from 52 beach profiles in Bao’ding Bay using dynamic image analysis. This paper analyzed and discussed the cross-shore and longshore distribution characteristics of the grain size and grain shape. We analyzed the result of the grain size trend analysis and established a grain shape trend analysis model. This study has shown that the grain shape in the same part of the Bao’ding Bay beach (exposed, intermediate and sheltered) has little difference on longshore, and there is a trend of gradual decrease from land to sea cross-shore. When the grain size between different parts of the beach is less than 2.5 Φ, the grain shape gradually shows a downward trend longshore from the exposed section to the sheltered section. The grain shape increase direction can indicate the sediment transport trend. The grain shape trend analysis model has high accuracy and advantages, which can calculate the transport trend of any grain size range and be well combined with other grain size analysis methods to achieve different research purposes. The research results can provide theoretical support for beach evolution mechanism analysis and beach stability research.
As the basic properties of sediments, grain size and shape provide information about their transport history, mode, and sedimentary environment. We analyzed the grain size and shape of 252 sediments from 52 beach profiles in Bao’ding Bay using dynamic image analysis. This paper analyzed and discussed the cross-shore and longshore distribution characteristics of the grain size and grain shape. We analyzed the result of the grain size trend analysis and established a grain shape trend analysis model. This study has shown that the grain shape in the same part of the Bao’ding Bay beach (exposed, intermediate and sheltered) has little difference on longshore, and there is a trend of gradual decrease from land to sea cross-shore. When the grain size between different parts of the beach is less than 2.5 Φ, the grain shape gradually shows a downward trend longshore from the exposed section to the sheltered section. The grain shape increase direction can indicate the sediment transport trend. The grain shape trend analysis model has high accuracy and advantages, which can calculate the transport trend of any grain size range and be well combined with other grain size analysis methods to achieve different research purposes. The research results can provide theoretical support for beach evolution mechanism analysis and beach stability research.
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Abstract:
The paleosedimentary environment of Gulong shale is the basis for the prediction of shale oil desserts. Based on the salinity of modern lakes of Songliao Basin, the common and trace elements, rare earth elements and biomarkers of Gulong shale, the geochemical characteristics of sedimentary environment and the enrichment mechanism of organic matter in Gulong shale were studied. The results show that during the formation of Gulong shale, the climate was warm and humid as a whole, the freshwater brackish water reduction environment was developed, the paleoproductivity was high, the sedimentation rate was low, and the water body was deep, which provided a geological basis for the formation, preservation and enrichment of organic matter. The paleoclimate index CIA during the shale deposition period is between 63-74, which is dominated by warm and humid climate. During the shale deposition period, the paleosalinity Sr/Ba is between 0.23-1.0, which is a fresh - brackish water environment, V/ (V+Ni) is between 0.6-0.9, which is mainly a dysoxic-anoxic environment. The paleowater depth is 25-117m, which belongs to semi deep lake deep lake deposition. The (la/yb) n value fluctuates between 0.9-1.41, representing a low deposition rate. The enrichment of organic matter in Gulong shale is mainly due to the favorable coupling of paleoclimate, paleosalinity, paleowater depth, sedimentation rate and paleoproductivity. The research results can effectively guide the prediction, exploration and development of Gulong shale oil desserts in Songliao basin.
The paleosedimentary environment of Gulong shale is the basis for the prediction of shale oil desserts. Based on the salinity of modern lakes of Songliao Basin, the common and trace elements, rare earth elements and biomarkers of Gulong shale, the geochemical characteristics of sedimentary environment and the enrichment mechanism of organic matter in Gulong shale were studied. The results show that during the formation of Gulong shale, the climate was warm and humid as a whole, the freshwater brackish water reduction environment was developed, the paleoproductivity was high, the sedimentation rate was low, and the water body was deep, which provided a geological basis for the formation, preservation and enrichment of organic matter. The paleoclimate index CIA during the shale deposition period is between 63-74, which is dominated by warm and humid climate. During the shale deposition period, the paleosalinity Sr/Ba is between 0.23-1.0, which is a fresh - brackish water environment, V/ (V+Ni) is between 0.6-0.9, which is mainly a dysoxic-anoxic environment. The paleowater depth is 25-117m, which belongs to semi deep lake deep lake deposition. The (la/yb) n value fluctuates between 0.9-1.41, representing a low deposition rate. The enrichment of organic matter in Gulong shale is mainly due to the favorable coupling of paleoclimate, paleosalinity, paleowater depth, sedimentation rate and paleoproductivity. The research results can effectively guide the prediction, exploration and development of Gulong shale oil desserts in Songliao basin.
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The quartz sandstone of the Changlongshan Formation, Qingbaikou system, Neoproterozoic was encountered during drilling in the southwestern of Liaodong Bay, Bohai Sea. The in-depth study of its provenance characteristics is of great significance to the anatomy of major geological events from Archean to Proterozoic in the North China Craton. Here, the whole rock geochemistry and detrital zircon U-Pb geochronology of five quartz sandstone samples collected near 2482m from well BD4-1a are analyzed. The quartz sandstones have high SiO2 content (88.53%~93.06%), CIA value is 69.5~71.6, ICV value is 0.69~3.99, and the samples show high compositional maturity, structural maturity and moderate weathering. The Th/U ratio range from 3.46 to 4.92, the Cr/Zr ratio of 0.17 ~ 0.35. And the ΣREE is (8.26 ~ 24.12) × 10-6, the LREE/HREE is 6.28 ~ 10.21, the δEu is 0.77 ~ 1.04, which shows a weak negative anomaly. These whole rock geochemistry characteristics suggesting that the material source is mainly from the upper crust felsic rocks. The U-Pb ages of detrital zircons range from 2744 to 1581 Ma; the main age peak is ~1855 Ma, and the subordinate age peaks are ~2725 Ma, ~2585 Ma, ~2335 Ma and ~2225 Ma, respectively. The ~2.7-2.5 Ga detrital zircons are the records of continental crust growth events and tectonic thermal events in the North China Craton. The ~2.2-1.8 Ga detrital zircons coincide with the times of the same crystalline basement event formed by the combination of the eastern and Western blocks of the North China Craton, which is a geological record of the convergence event of the Columbia supercontinent; the ~1.7-1.6Ga detrital zircon ages should record the breakup of the Columbia supercontinent.
The quartz sandstone of the Changlongshan Formation, Qingbaikou system, Neoproterozoic was encountered during drilling in the southwestern of Liaodong Bay, Bohai Sea. The in-depth study of its provenance characteristics is of great significance to the anatomy of major geological events from Archean to Proterozoic in the North China Craton. Here, the whole rock geochemistry and detrital zircon U-Pb geochronology of five quartz sandstone samples collected near 2482m from well BD4-1a are analyzed. The quartz sandstones have high SiO2 content (88.53%~93.06%), CIA value is 69.5~71.6, ICV value is 0.69~3.99, and the samples show high compositional maturity, structural maturity and moderate weathering. The Th/U ratio range from 3.46 to 4.92, the Cr/Zr ratio of 0.17 ~ 0.35. And the ΣREE is (8.26 ~ 24.12) × 10-6, the LREE/HREE is 6.28 ~ 10.21, the δEu is 0.77 ~ 1.04, which shows a weak negative anomaly. These whole rock geochemistry characteristics suggesting that the material source is mainly from the upper crust felsic rocks. The U-Pb ages of detrital zircons range from 2744 to 1581 Ma; the main age peak is ~1855 Ma, and the subordinate age peaks are ~2725 Ma, ~2585 Ma, ~2335 Ma and ~2225 Ma, respectively. The ~2.7-2.5 Ga detrital zircons are the records of continental crust growth events and tectonic thermal events in the North China Craton. The ~2.2-1.8 Ga detrital zircons coincide with the times of the same crystalline basement event formed by the combination of the eastern and Western blocks of the North China Craton, which is a geological record of the convergence event of the Columbia supercontinent; the ~1.7-1.6Ga detrital zircon ages should record the breakup of the Columbia supercontinent.
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Abstract: The lower Cambrian black shale is an important source rock and shale gas exploration target in the Sichuan Basin. But there is still a lack of full understanding on the enrichment mechanism of organic matter in this series of black shale. Here we reported total organic carbon (TOC) contents, sedimentary microfacies, major and trace elements and pyritic framboids size distribution in the lower Shuijingtuo Formation in Chengkou area, Northeast Sichuan Basin in the upper Yangtze platform, providing new evidences to reconstruct the paleogeography and paleoenvironment and main controlling factors of organic matter enrichment. The results show that 1) the black shale succession in the Shuijingtuo Formation developed five sedimentary microfacies related to deep-water shelf slope environment; 2) The changes of Al and Ti concentrations indicate that the continental input is relatively stable. Mo/TOC ratios and cross plot of UEF-MoEF reflect that the sedimentary water of Shuijingtuo Formation was moderately to weakly restricted circulation conditions; 3) redox sensitive elements (Mo and U) and pyrite framboids size distributions points to a anoxic-euxinic environment; 4）the low Baxs and P/Ti ratio values reflect a low level of paleo-productivity during depositional period of the Shuijingtuo Formation; and that 5）the correlation relationship among organic matter and sediment flux, primary productivity, and redox condition parameters show that the organic matter enrichments were mainly controlled by redox conditions during the Early Cambrian in the Northeast Sichuan Basin.
Abstract: The lower Cambrian black shale is an important source rock and shale gas exploration target in the Sichuan Basin. But there is still a lack of full understanding on the enrichment mechanism of organic matter in this series of black shale. Here we reported total organic carbon (TOC) contents, sedimentary microfacies, major and trace elements and pyritic framboids size distribution in the lower Shuijingtuo Formation in Chengkou area, Northeast Sichuan Basin in the upper Yangtze platform, providing new evidences to reconstruct the paleogeography and paleoenvironment and main controlling factors of organic matter enrichment. The results show that 1) the black shale succession in the Shuijingtuo Formation developed five sedimentary microfacies related to deep-water shelf slope environment; 2) The changes of Al and Ti concentrations indicate that the continental input is relatively stable. Mo/TOC ratios and cross plot of UEF-MoEF reflect that the sedimentary water of Shuijingtuo Formation was moderately to weakly restricted circulation conditions; 3) redox sensitive elements (Mo and U) and pyrite framboids size distributions points to a anoxic-euxinic environment; 4）the low Baxs and P/Ti ratio values reflect a low level of paleo-productivity during depositional period of the Shuijingtuo Formation; and that 5）the correlation relationship among organic matter and sediment flux, primary productivity, and redox condition parameters show that the organic matter enrichments were mainly controlled by redox conditions during the Early Cambrian in the Northeast Sichuan Basin.
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Continental slopes have become a major focus in petroleum exploration because of their enormous sediment and hydrocarbon potential. Research on the geomorphic evolution of continental slopes contributes to deep-water sedimentology and petroleum exploration. The morphology and location of an ancient continental slope in different periods vary continuously, and structural activities further complicate the geomorphic evolution. Research on depositional architecture has been conducted on a continental slope of a delta reformed passive continental margin basin, which has an abundant terrigenous supply and is commonly reformed by gravity gliding. The methodology for the restoration of ancient slope geomorphic evolution based on the principle of depositional architecture was discussed. Spatiotemporal evolution of deep-water depositional architecture reveals that the geomorphic evolution of the study area (Miocene~) can be divided into 2 stages. In stage 1, study area transformed from an abyssal plain to continental slope, and the landform was unrestricted. The geomorphic evolution in this stage was driven by the progradation of large deltas. The geomorphic evolution in stage 2 included 3 periods dominated by thrust faults, mud-diapirs, and sedimentation. The landform evolved gradually from restricted to semi-restricted and then to the present non-restricted type. The geomorphic evolution in stage 2 was controlled by gravity sliding. During the thrust faulting, the activity intensity of the underlying flowing mudstone was limited, and the landform was controlled by thrust faults. The study area was located in the remote thrust province of a gravity sliding system. During the mud-diapir period, the intensity of diapir activity increased significantly and was able to change the geomorphic characteristics independently. As a result, the topography of study area began to transform from a thrust to mud-diapir province. The gravity sliding structural system was driven by sedimentary processes, and its spatial combination and evolution characteristics were similar to sedimentary facies. The adjacent extensional, mud-diapir and thrust province were closely related in genesis, which was similar to a sequential sedimentary facies. Therefore, the vertical superposition relationship of different structural activities indicated the macro trend of the continental slope advancing seaward contemporaneously and the increase of topographic gradient in study area. In conclusion, the spatiotemporal evolution characteristics of the gravity flow depositional architecture in the typical deep-water study area can provide important evidence for the restoration of paleogeomorphic evolution of a deep-water continental slope.
Continental slopes have become a major focus in petroleum exploration because of their enormous sediment and hydrocarbon potential. Research on the geomorphic evolution of continental slopes contributes to deep-water sedimentology and petroleum exploration. The morphology and location of an ancient continental slope in different periods vary continuously, and structural activities further complicate the geomorphic evolution. Research on depositional architecture has been conducted on a continental slope of a delta reformed passive continental margin basin, which has an abundant terrigenous supply and is commonly reformed by gravity gliding. The methodology for the restoration of ancient slope geomorphic evolution based on the principle of depositional architecture was discussed. Spatiotemporal evolution of deep-water depositional architecture reveals that the geomorphic evolution of the study area (Miocene~) can be divided into 2 stages. In stage 1, study area transformed from an abyssal plain to continental slope, and the landform was unrestricted. The geomorphic evolution in this stage was driven by the progradation of large deltas. The geomorphic evolution in stage 2 included 3 periods dominated by thrust faults, mud-diapirs, and sedimentation. The landform evolved gradually from restricted to semi-restricted and then to the present non-restricted type. The geomorphic evolution in stage 2 was controlled by gravity sliding. During the thrust faulting, the activity intensity of the underlying flowing mudstone was limited, and the landform was controlled by thrust faults. The study area was located in the remote thrust province of a gravity sliding system. During the mud-diapir period, the intensity of diapir activity increased significantly and was able to change the geomorphic characteristics independently. As a result, the topography of study area began to transform from a thrust to mud-diapir province. The gravity sliding structural system was driven by sedimentary processes, and its spatial combination and evolution characteristics were similar to sedimentary facies. The adjacent extensional, mud-diapir and thrust province were closely related in genesis, which was similar to a sequential sedimentary facies. Therefore, the vertical superposition relationship of different structural activities indicated the macro trend of the continental slope advancing seaward contemporaneously and the increase of topographic gradient in study area. In conclusion, the spatiotemporal evolution characteristics of the gravity flow depositional architecture in the typical deep-water study area can provide important evidence for the restoration of paleogeomorphic evolution of a deep-water continental slope.
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Bedding-parallel fractures (BPFs) are commonly developed in sedimentary reservoirs, and their significance for hydrocarbon exploration and development is increasingly prominent. Scholars at home and abroad have made extensive discussions on the characteristics of BPFs and their relationship with hydrocarbon migration and accumulation, identification and prediction, formation mechanism and major controlling factors. It is concluded that: (1) BPFs are characterized by high linear density and high horizontal permeability. The existence of BPFs is one of the basic conditions affecting the large-scale accumulation of hydrocarbon in unconventional sedimentary reservoirs. (2) Seismic inversion, image logging and conventional logging identification, fracture related major controlling factors prediction, geological parameter modeling and numerical simulation prediction are commonly used to identify and predict fractures; however, there are still limitations of low accuracy, high cost and immature methods. With the application of scanning electron microscopy, automatic mineral quantitative analysis, nanometer and micron CT scanning, and digital core technology, the study of BPFs has gradually entered the level of microscopization, visualization and quantification. (3) The formation of BPFs is the result of complex factors such as sedimentary diagenesis, structure, overpressure and crystallization stress. (4) Sedimentary rock type, bedding type, mineral composition and TOC content are the main internal factors affecting the development of BPFs. The development degree of fault and fold, the distance from fault core and fold axis, the depth of stratum burial and the intensity of uplift and denudation are the main external factors affecting the development of BPFs. However, there is still a lack of comprehensive, systematic and quantitative research on the comprehensive mechanism of BPFs formed by different types of sedimentary rocks and bedding, the establishment of fine identification and quantitative prediction models for different types of BPFs, and the determination of the specific relationship between BPFs and hydrocarbon migration or accumulation. These problems limit the exploration and development of fractured reservoirs to a certain extent, and are also an important direction for future research on BPFs.
Bedding-parallel fractures (BPFs) are commonly developed in sedimentary reservoirs, and their significance for hydrocarbon exploration and development is increasingly prominent. Scholars at home and abroad have made extensive discussions on the characteristics of BPFs and their relationship with hydrocarbon migration and accumulation, identification and prediction, formation mechanism and major controlling factors. It is concluded that: (1) BPFs are characterized by high linear density and high horizontal permeability. The existence of BPFs is one of the basic conditions affecting the large-scale accumulation of hydrocarbon in unconventional sedimentary reservoirs. (2) Seismic inversion, image logging and conventional logging identification, fracture related major controlling factors prediction, geological parameter modeling and numerical simulation prediction are commonly used to identify and predict fractures; however, there are still limitations of low accuracy, high cost and immature methods. With the application of scanning electron microscopy, automatic mineral quantitative analysis, nanometer and micron CT scanning, and digital core technology, the study of BPFs has gradually entered the level of microscopization, visualization and quantification. (3) The formation of BPFs is the result of complex factors such as sedimentary diagenesis, structure, overpressure and crystallization stress. (4) Sedimentary rock type, bedding type, mineral composition and TOC content are the main internal factors affecting the development of BPFs. The development degree of fault and fold, the distance from fault core and fold axis, the depth of stratum burial and the intensity of uplift and denudation are the main external factors affecting the development of BPFs. However, there is still a lack of comprehensive, systematic and quantitative research on the comprehensive mechanism of BPFs formed by different types of sedimentary rocks and bedding, the establishment of fine identification and quantitative prediction models for different types of BPFs, and the determination of the specific relationship between BPFs and hydrocarbon migration or accumulation. These problems limit the exploration and development of fractured reservoirs to a certain extent, and are also an important direction for future research on BPFs.
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Tahe Oilfield is the largest Paleozoic marine oilfield in China, which is rich in oil and gas resources. According to the difference of physical properties, the crude oil in Tabei area can be divided into three categories: heavy, medium and light. In order to clarify the cause of the difference in the composition of crude n-alkane individual carbon isotope (δ13Calkane), this study analyzed the compositional characteristics of δ13Calkane in the total of 17 Ordovician crude oil samples in the northern Tabei area, combined with relevant organic geochemical parameters, from the depositional environment, maturity and biodegradation explain the variation trend of the δ13Calkane value of the three types of crude oil, and the main conclusions are as follows: the δ13Calkane value of the Ordovician crude oil in the northern Tabei area is between -37‰~-31‰. It shows the characteristics of marine crude oil, indicating that the composition and distribution of δ13Calkane of crude oil are controlled by the depositional environment and the type of parent material. From heavy crude oil to medium crude oil and then to light crude oil, the maturity gradually increases, which in turn leads to a heavier δ13Calkane value of crude oil; The δ13Calkane of the low-carbon number part of the heavy crude oil is obviously negative. Compared with the medium crude oil and the light crude oil, the heavy crude oil has the strongest biodegradation effect, indicating that the degree of biodegradation is the main factor affecting the lightening of δ13C14~δ19 values of medium and low molecular weight n-alkanes in heavy crude oil.
Tahe Oilfield is the largest Paleozoic marine oilfield in China, which is rich in oil and gas resources. According to the difference of physical properties, the crude oil in Tabei area can be divided into three categories: heavy, medium and light. In order to clarify the cause of the difference in the composition of crude n-alkane individual carbon isotope (δ13Calkane), this study analyzed the compositional characteristics of δ13Calkane in the total of 17 Ordovician crude oil samples in the northern Tabei area, combined with relevant organic geochemical parameters, from the depositional environment, maturity and biodegradation explain the variation trend of the δ13Calkane value of the three types of crude oil, and the main conclusions are as follows: the δ13Calkane value of the Ordovician crude oil in the northern Tabei area is between -37‰~-31‰. It shows the characteristics of marine crude oil, indicating that the composition and distribution of δ13Calkane of crude oil are controlled by the depositional environment and the type of parent material. From heavy crude oil to medium crude oil and then to light crude oil, the maturity gradually increases, which in turn leads to a heavier δ13Calkane value of crude oil; The δ13Calkane of the low-carbon number part of the heavy crude oil is obviously negative. Compared with the medium crude oil and the light crude oil, the heavy crude oil has the strongest biodegradation effect, indicating that the degree of biodegradation is the main factor affecting the lightening of δ13C14~δ19 values of medium and low molecular weight n-alkanes in heavy crude oil.
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Obstacled deposition is a common sedimentary phenomenon, widely developed in rivers, seashores, beaches, aeolian dunes and other sedimentary environments. The presence of barrier deposits indicates the presence of long-term and stable water flow in the area. The characteristics and scale of barrier deposits in sands formed in different environments have been described in detail but barrier deposits developed on conglomerates have been less well reported and there is a lack of classification studies of barrier deposits. Through a modern sedimentary investigation of the gravelly rivers of the Anjihai and Toutunhe at the southern edge of the Junggar Basin, the barrier deposits developed in the gravelly riverbeds were described and measured in detail, and the depositional patterns and formation mechanisms of the barrier deposits were analysed. The study shows that the morphology of gravelly barrier deposition can be classified into four patterns: cone deposition, pike deposition, rock assemblage and lateral ridge deposition .Cone deposition is a single large gravel as an obstacle, with a fine-grained sediment ridge after the gravel, and the ratio of the length of the sediment ridge to the scour extent in front of the gravel should be 2:1, with the long axis of the sediment ridge indicating the flow direction. Pike deposition is a single large gravel as an obstacle, with small gravels stacking in front of the obstacle gravels and forming sediment ridges after the obstacle gravels. Rock assemblages are multiple gravels of similar size as the main body of the barrier, with a "U" shaped granularly supported fine gravel in the center of the unit. Lateral ridge deposition is the accumulation of large gravels in the side or center of the channel to form a beach dam that acts as a barrier and controls the river boundary. According to the modern sedimentary barrier deposition model, we can finely delineate the barrier deposition phenomenon in the conglomerate layer of the Karaza Formation in the Junggar Basin, and study the genesis type of the barrier deposition and its depositional characteristics, which can shed new light on the determination of the paleocurrent direction.
Obstacled deposition is a common sedimentary phenomenon, widely developed in rivers, seashores, beaches, aeolian dunes and other sedimentary environments. The presence of barrier deposits indicates the presence of long-term and stable water flow in the area. The characteristics and scale of barrier deposits in sands formed in different environments have been described in detail but barrier deposits developed on conglomerates have been less well reported and there is a lack of classification studies of barrier deposits. Through a modern sedimentary investigation of the gravelly rivers of the Anjihai and Toutunhe at the southern edge of the Junggar Basin, the barrier deposits developed in the gravelly riverbeds were described and measured in detail, and the depositional patterns and formation mechanisms of the barrier deposits were analysed. The study shows that the morphology of gravelly barrier deposition can be classified into four patterns: cone deposition, pike deposition, rock assemblage and lateral ridge deposition .Cone deposition is a single large gravel as an obstacle, with a fine-grained sediment ridge after the gravel, and the ratio of the length of the sediment ridge to the scour extent in front of the gravel should be 2:1, with the long axis of the sediment ridge indicating the flow direction. Pike deposition is a single large gravel as an obstacle, with small gravels stacking in front of the obstacle gravels and forming sediment ridges after the obstacle gravels. Rock assemblages are multiple gravels of similar size as the main body of the barrier, with a "U" shaped granularly supported fine gravel in the center of the unit. Lateral ridge deposition is the accumulation of large gravels in the side or center of the channel to form a beach dam that acts as a barrier and controls the river boundary. According to the modern sedimentary barrier deposition model, we can finely delineate the barrier deposition phenomenon in the conglomerate layer of the Karaza Formation in the Junggar Basin, and study the genesis type of the barrier deposition and its depositional characteristics, which can shed new light on the determination of the paleocurrent direction.
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The Quaternary aggradation reticulate red earth has a unique reticulate structure and is widely distributed in the middle and lower reaches of the Yangtze River, which is a record and response to Quaternary environmental changes. Previously, more attention has been paid to the physico-chemical properties of the reticulate red earth, but less research has been done on the morphological characteristics of the white veins. A comprehensive analysis of the characteristics of the white veins in combination with physico-chemical properties is conducive to a more profound understanding of its environmental significance. Therefore, according to the analysis of the reticulate shape and physico-chemical properties of the reticulate red earth section in Jiujiang, Jiangxi, and on the basis of understanding the possible effects of physico-chemical properties on morphology and the mechanism of reticulation, the environmental significance of the morphological characteristics of the white veins is emphatically discussed. Preliminary conclusions are as follows: (i) the white veins shape of the section varies systematically, with the white veins in the upper part of the section being relatively fine, while the lower white veins shape is relatively coarse; (ii) the degree of correspondence between the weathering index ba and the white veins morphological index shows that the white veins shape corresponds to the trend of climate change from warm and humid to cold and dry on the whole, but the morphological characteristics has certain limitations on the climate indication.
The Quaternary aggradation reticulate red earth has a unique reticulate structure and is widely distributed in the middle and lower reaches of the Yangtze River, which is a record and response to Quaternary environmental changes. Previously, more attention has been paid to the physico-chemical properties of the reticulate red earth, but less research has been done on the morphological characteristics of the white veins. A comprehensive analysis of the characteristics of the white veins in combination with physico-chemical properties is conducive to a more profound understanding of its environmental significance. Therefore, according to the analysis of the reticulate shape and physico-chemical properties of the reticulate red earth section in Jiujiang, Jiangxi, and on the basis of understanding the possible effects of physico-chemical properties on morphology and the mechanism of reticulation, the environmental significance of the morphological characteristics of the white veins is emphatically discussed. Preliminary conclusions are as follows: (i) the white veins shape of the section varies systematically, with the white veins in the upper part of the section being relatively fine, while the lower white veins shape is relatively coarse; (ii) the degree of correspondence between the weathering index ba and the white veins morphological index shows that the white veins shape corresponds to the trend of climate change from warm and humid to cold and dry on the whole, but the morphological characteristics has certain limitations on the climate indication.
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Quartz is one of the most important minerals in marine shale and can be found in several forms with multiple origins. In addition, different types of quartz may contribute differently to the geomechanical properties and pore evolution of marine shale, and related research is lacking. This study briefly reviews recent progress in the classification of quartz in typical marine shales. In order to better understand quartz types, silica sources, and the influence of biogenic microcrystalline quartz on geomechanical properties and pore evolution, marine shale samples were collected from the Upper Ordovician Wufeng Formation and the Lower Silurian Gaojiabian Formation, specifically Well Gudi-1 of the Lower Yangtze Platform. These samples were analyzed using thin section-, X-ray diffraction-, and geochemical analysis, optical microscopy, nuclear magnetic resonance, and field-emission scanning electron microscopy combined with cathodoluminescence. The aim was to further reveal the pore evolution pattern in the lower Paleozoic marine shales of the Lower Yangtze Platform from a new perspective and to provide a more reliable geological basis for the storage capacity of shale gas reservoirs. The results show that the quartz in Well Gudi-1 is mainly detrital, microcrystalline, and organism skeletal quartz. Detrital quartz is of terrigenous origin and is characterized by bright luminescence. Most detrital quartz particles are silt-sized and range from 10–30 μm. Microcrystalline quartz is one of the most common authigenic quartz types and can be found in several marine shale formations. Microcrystalline quartz has no or low luminescence, indicative of authigenic origin. Furthermore, microcrystalline quartz can be divided into three categories: clay matrix-dispersed microcrystalline quartz, euhedral microcrystalline quartz, and amorphous microcrystalline quartz cements. Organism skeletal quartz is widely distributed in the studied shale samples and was mostly found in fragments of siliceous organisms, such as radiolarians and sponge spicules. Most radiolarians are oval and round with diameters of approximately 100 μm. Optical microscope evidence was found of siliceous organism fragments, including biogenic silica accounting for approximately 45.17% of the total silica content, as well as characteristics of major and trace elements, such as a non-hydrothermal area located in the Al-Fe-Mn ternary diagram, negative correlations of Zr and SiO2, an Al/(Al+Fe+Mn) ratio of 0.65 to 0.76, and a cross-plot of Si versus Al. Overall, these indicate that siliceous organisms provided an important silica source for microcrystalline quartz. These siliceous organisms provide a relatively rich silica source for the precipitation of authigenic quartz during early diagenesis. This study indicates that biogenic microcrystalline quartz may have implications for rock mechanics and the evolution of porosity. The positive correlation between the silica content and brittleness index of the studied shale reveals that the development of biogenic microcrystalline quartz enhances the brittleness of the shale to a certain extent. Biogenic microcrystalline quartz can be interconnected to form a rigid siliceous matrix framework, which largely promotes the geomechanical properties of the studied shale. Moreover, the positive correlation between the silica content and porosity indicates that the enrichment of biogenic silica is conducive to pore evolution and preservation. Organic matter and clay minerals in shale are susceptible to ductile deformation by compaction, while biogenic microcrystalline quartz can form a rigid framework to enhance its resistance to compaction, which is conducive to the preservation of the internal pore space within shale, especially intergranular- and organic matter pores.
Quartz is one of the most important minerals in marine shale and can be found in several forms with multiple origins. In addition, different types of quartz may contribute differently to the geomechanical properties and pore evolution of marine shale, and related research is lacking. This study briefly reviews recent progress in the classification of quartz in typical marine shales. In order to better understand quartz types, silica sources, and the influence of biogenic microcrystalline quartz on geomechanical properties and pore evolution, marine shale samples were collected from the Upper Ordovician Wufeng Formation and the Lower Silurian Gaojiabian Formation, specifically Well Gudi-1 of the Lower Yangtze Platform. These samples were analyzed using thin section-, X-ray diffraction-, and geochemical analysis, optical microscopy, nuclear magnetic resonance, and field-emission scanning electron microscopy combined with cathodoluminescence. The aim was to further reveal the pore evolution pattern in the lower Paleozoic marine shales of the Lower Yangtze Platform from a new perspective and to provide a more reliable geological basis for the storage capacity of shale gas reservoirs. The results show that the quartz in Well Gudi-1 is mainly detrital, microcrystalline, and organism skeletal quartz. Detrital quartz is of terrigenous origin and is characterized by bright luminescence. Most detrital quartz particles are silt-sized and range from 10–30 μm. Microcrystalline quartz is one of the most common authigenic quartz types and can be found in several marine shale formations. Microcrystalline quartz has no or low luminescence, indicative of authigenic origin. Furthermore, microcrystalline quartz can be divided into three categories: clay matrix-dispersed microcrystalline quartz, euhedral microcrystalline quartz, and amorphous microcrystalline quartz cements. Organism skeletal quartz is widely distributed in the studied shale samples and was mostly found in fragments of siliceous organisms, such as radiolarians and sponge spicules. Most radiolarians are oval and round with diameters of approximately 100 μm. Optical microscope evidence was found of siliceous organism fragments, including biogenic silica accounting for approximately 45.17% of the total silica content, as well as characteristics of major and trace elements, such as a non-hydrothermal area located in the Al-Fe-Mn ternary diagram, negative correlations of Zr and SiO2, an Al/(Al+Fe+Mn) ratio of 0.65 to 0.76, and a cross-plot of Si versus Al. Overall, these indicate that siliceous organisms provided an important silica source for microcrystalline quartz. These siliceous organisms provide a relatively rich silica source for the precipitation of authigenic quartz during early diagenesis. This study indicates that biogenic microcrystalline quartz may have implications for rock mechanics and the evolution of porosity. The positive correlation between the silica content and brittleness index of the studied shale reveals that the development of biogenic microcrystalline quartz enhances the brittleness of the shale to a certain extent. Biogenic microcrystalline quartz can be interconnected to form a rigid siliceous matrix framework, which largely promotes the geomechanical properties of the studied shale. Moreover, the positive correlation between the silica content and porosity indicates that the enrichment of biogenic silica is conducive to pore evolution and preservation. Organic matter and clay minerals in shale are susceptible to ductile deformation by compaction, while biogenic microcrystalline quartz can form a rigid framework to enhance its resistance to compaction, which is conducive to the preservation of the internal pore space within shale, especially intergranular- and organic matter pores.
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Taking the deep-water gravity flow sedimentation of the Chang 7 oil layer group of Triassic Yanchang Formation in the southwestern Ordos Basin as the research object, and based on a large number of cores, well logging, thin section identification, electron microscope scanning , particle size date analysis, X-ray diffraction whole rock analysis and mineral identification analysis and other data. The deep-water gravity flow sedimentation rock types, lithofacies characteristics, lithofacies assemblages, distribution characteristics and sedimentary facies division in the study area were analyzed, and the gravity flow deposition model was established on this basis. The results show that :(1) The deep-water gravity flow sedimentation lithology of the Chang 7 oil layer group is mainly composed of gray and brown-gray fine-grained sandstone, gray and dark gray ultrafine-powder sandstone, dark and black mud shale, with a small amount of tuff; the mineral components are mainly composed of quartz, feldspar and clay minerals; (2) Combined with the lithology characteristics, macroscopic and microscopic sedimentary structure characteristics, it is divided into six lithofacies types : massive bedding fine sandstone facies (Sm), Bouma Sequence siltstone facies (Sb), banded mudstone facies (Mh), Level of laminated shale facies (Sh), Block like shale facies (Mm), tuff facies (T). According to the development of different sedimentary environments, four lithofacies assemblages are summarized :Sm-Mh(Sh),Sm-Sb-Mh(Sh),Sb-Mh(Sh),T-Sh(Mm). It reflects deep-water gravity flow deposition and lacustrine facies sandy debris flows -deep water in situ deposition, sandy debris flows -turbidity current-deep water in situ deposition, turbidity current -deep water in situ deposition, volcaniclastic deposits-deep water in situ deposition; (3) According to the lithofacies assemblages and plane distribution characteristics developed by different types of gravity flow, it is considered that from below the slope break zone to the center of the lake basin, the gravity flow presents the evolution characteristics of sandy debris flows, sandy debris flows- turbidity current, and turbidity current . (4) According to the proportion of sandy debris flows sandstone in gravity flow sandstone, lithofacies types, lithofacies assemblages, GR form and channel scale, the gravity flow deposition is divided into three subfacies : restricted channel, non-restricted channel and Front end lobes.
Taking the deep-water gravity flow sedimentation of the Chang 7 oil layer group of Triassic Yanchang Formation in the southwestern Ordos Basin as the research object, and based on a large number of cores, well logging, thin section identification, electron microscope scanning , particle size date analysis, X-ray diffraction whole rock analysis and mineral identification analysis and other data. The deep-water gravity flow sedimentation rock types, lithofacies characteristics, lithofacies assemblages, distribution characteristics and sedimentary facies division in the study area were analyzed, and the gravity flow deposition model was established on this basis. The results show that :(1) The deep-water gravity flow sedimentation lithology of the Chang 7 oil layer group is mainly composed of gray and brown-gray fine-grained sandstone, gray and dark gray ultrafine-powder sandstone, dark and black mud shale, with a small amount of tuff; the mineral components are mainly composed of quartz, feldspar and clay minerals; (2) Combined with the lithology characteristics, macroscopic and microscopic sedimentary structure characteristics, it is divided into six lithofacies types : massive bedding fine sandstone facies (Sm), Bouma Sequence siltstone facies (Sb), banded mudstone facies (Mh), Level of laminated shale facies (Sh), Block like shale facies (Mm), tuff facies (T). According to the development of different sedimentary environments, four lithofacies assemblages are summarized :Sm-Mh(Sh),Sm-Sb-Mh(Sh),Sb-Mh(Sh),T-Sh(Mm). It reflects deep-water gravity flow deposition and lacustrine facies sandy debris flows -deep water in situ deposition, sandy debris flows -turbidity current-deep water in situ deposition, turbidity current -deep water in situ deposition, volcaniclastic deposits-deep water in situ deposition; (3) According to the lithofacies assemblages and plane distribution characteristics developed by different types of gravity flow, it is considered that from below the slope break zone to the center of the lake basin, the gravity flow presents the evolution characteristics of sandy debris flows, sandy debris flows- turbidity current, and turbidity current . (4) According to the proportion of sandy debris flows sandstone in gravity flow sandstone, lithofacies types, lithofacies assemblages, GR form and channel scale, the gravity flow deposition is divided into three subfacies : restricted channel, non-restricted channel and Front end lobes.
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The tight glutenite reservoir of Shahezi Formation in Xujiazi Fault Depression has great potential for natural gas exploration, and it is expected to become the key replacement field of deep volcanic gas reservoir exploration in Daqing Oilfield. The distribution of sedimentary facies and sedimentary evolution model of Shahezi Formation in Xujiaweizi Fault Depression are studied by comprehensive core, logging, logging and seismic data. The results show that there are braided river delta, fan delta, far shore turbidite fan with supply channel, near shore subaqueous fan, slump turbidite fan in front of fan delta and Shallow lake-semi-deep lake, deep lake in Shahezi Formation of Xujiaweizi Fault Depression. The gentle slope belt on the east side of Anda Depression, Xudong Depression and Zhaozhou Depression received the detritus from Zhaodong-Chaoyanggou basement paleo-uplift, and developed braided river delta deposits, and locally developed lacustrine turbidite fan deposits formed by distant source supply channels; The western steep slope belts such as Anda-Xudong Depression, Xuxi Depression and Zhaozhou Depression received coarse debris from the Central Fault Uplift area and developed fan delta depositional system, which was characterized by near source and short flow. Nearshore subaqueous fan depositions were locally developed, and due to the instability of fan delta depositional bodies developed on the edge of lake basin, slump turbidite fan depositions were formed in front of fan delta depositional bodies.
The tight glutenite reservoir of Shahezi Formation in Xujiazi Fault Depression has great potential for natural gas exploration, and it is expected to become the key replacement field of deep volcanic gas reservoir exploration in Daqing Oilfield. The distribution of sedimentary facies and sedimentary evolution model of Shahezi Formation in Xujiaweizi Fault Depression are studied by comprehensive core, logging, logging and seismic data. The results show that there are braided river delta, fan delta, far shore turbidite fan with supply channel, near shore subaqueous fan, slump turbidite fan in front of fan delta and Shallow lake-semi-deep lake, deep lake in Shahezi Formation of Xujiaweizi Fault Depression. The gentle slope belt on the east side of Anda Depression, Xudong Depression and Zhaozhou Depression received the detritus from Zhaodong-Chaoyanggou basement paleo-uplift, and developed braided river delta deposits, and locally developed lacustrine turbidite fan deposits formed by distant source supply channels; The western steep slope belts such as Anda-Xudong Depression, Xuxi Depression and Zhaozhou Depression received coarse debris from the Central Fault Uplift area and developed fan delta depositional system, which was characterized by near source and short flow. Nearshore subaqueous fan depositions were locally developed, and due to the instability of fan delta depositional bodies developed on the edge of lake basin, slump turbidite fan depositions were formed in front of fan delta depositional bodies.
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A large number of carbonate sediments in Phanerozoic recorded the paleoenvironment and its evolution information, and it was also an important carbon sink of the earth. Under the background of " carbon neutral" in today's society, carbonate factory has become one of the hot spots in carbonate research, and it is indispensable to strengthen the research on the development characteristics and evolution of carbonate factory. Compared with foreign countries, the research on carbonate factory in China started late, mostly focusing on the deposition and evolution of carbonate rocks. The research on the classification and research methods of carbonate factory is still weak, and the understanding of the main control factors of their extinction is also limited. Therefore, based on the research of many scholars, this paper summarizes the research progress in the classification scheme, research methods and main control factors of carbonate factory, and provides some reference for geologists to further develop the operation mechanism of carbonate factory.
A large number of carbonate sediments in Phanerozoic recorded the paleoenvironment and its evolution information, and it was also an important carbon sink of the earth. Under the background of " carbon neutral" in today's society, carbonate factory has become one of the hot spots in carbonate research, and it is indispensable to strengthen the research on the development characteristics and evolution of carbonate factory. Compared with foreign countries, the research on carbonate factory in China started late, mostly focusing on the deposition and evolution of carbonate rocks. The research on the classification and research methods of carbonate factory is still weak, and the understanding of the main control factors of their extinction is also limited. Therefore, based on the research of many scholars, this paper summarizes the research progress in the classification scheme, research methods and main control factors of carbonate factory, and provides some reference for geologists to further develop the operation mechanism of carbonate factory.
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[Objective] The black shale of Upper Ordovician and Lower Silurian in southern Sichuan is the main target of shale gas exploration, which has attracted extensive attention of domestic and foreign scholars. In order to provide theoretical basis for shale exploration and development in the next step, the lithofacies division, sedimentary environment and depositional processes of shale are explored. [Methods] Through observation and analysis of the core with optical microscope and scanning electron microscope, the lithofacies are divided according to the mineral composition and content, sedimentary structural characteristics, and comprehensive consideration of biological process and diagenesis. The Paleo-environment is analyzed by oxidation-reduction indexes (U/Th,V/Cr,V/(V+Ni),Ni/Co), sea level change index (Ce*), hydrographic restriction index (Mo/TOC), paleo-climate index (Sr/Cu), paleo-salinity index (Sr/Ba) and paleo-productivity indexes (Cu, biogenic Ba). Depositional processes is identified by core and thin section observation, X-ray fluorescence scanning and mineral X-ray diffraction whole rock analysis.[Results] Six lithofacies are identified from the shale of Wufeng-Longmaxi Formation: biological siliceous shale, clayey shale, (felsic-calcareous) silty shale, calcareous silty shale, calcareous shale and felsic silty shale. The shale sedimentary environment of Wufeng-Longmaxi Formation underwent five stages of bottom-up changes. The paleo-climate experienced the evolution from warm and humid at the bottom of the Wufeng Formation to dry and hot at the middle and then to dry and cold at the top, and then from dry and hot at the lower part of the Longmaxi Formation to warm and humid at the middle and upper part. In the lower part of Wufeng Formation and the lower part of Longmaxi Formation, the sea level has risen due to two large-scale transgressions. When the sea level is high, the water column is weak in restricted, strong in reduction, low in salinity and high in paleo-productivity. The glacier event at the top of Wufeng Formation caused the sea level to drop. When the sea level is low, the water column is strong in restricted, weak in reduction, high in salinity and low in paleo-productivity. The shale of Wufeng-Longmaxi Formation is mainly formed by suspended sedimentation under low energy conditions. Upwelling sedimentation is developed in the middle of Wufeng Formation and the lower part of Longmaxi Formation. A small amount of storm surge sedimentation is developed at the top of Wufeng Formation. In the upper part of Longmaxi Formation, gravity slumping, debris flow and turbidity current are developed due to the shallowing of water and the increase of terrigenous input. In the end, the sedimentary model of Wufeng-Longmaxi Formation shale is established by integrating the lithofacies, depositional processes type, tectonic evolution and sedimentary environment evolution. [Conclusion] The frequent changes of sedimentary environment and the diversity of depositional processes both control the types and characteristics of lithofacies, further leading to significant differences in organic matter content, porosity, gas content and other reservoir quality factors of different lithofacies. Further research on shale lithofacies and reservoir quality is still needed to provide theoretical basis for shale gas exploration and development.
[Objective] The black shale of Upper Ordovician and Lower Silurian in southern Sichuan is the main target of shale gas exploration, which has attracted extensive attention of domestic and foreign scholars. In order to provide theoretical basis for shale exploration and development in the next step, the lithofacies division, sedimentary environment and depositional processes of shale are explored. [Methods] Through observation and analysis of the core with optical microscope and scanning electron microscope, the lithofacies are divided according to the mineral composition and content, sedimentary structural characteristics, and comprehensive consideration of biological process and diagenesis. The Paleo-environment is analyzed by oxidation-reduction indexes (U/Th,V/Cr,V/(V+Ni),Ni/Co), sea level change index (Ce*), hydrographic restriction index (Mo/TOC), paleo-climate index (Sr/Cu), paleo-salinity index (Sr/Ba) and paleo-productivity indexes (Cu, biogenic Ba). Depositional processes is identified by core and thin section observation, X-ray fluorescence scanning and mineral X-ray diffraction whole rock analysis.[Results] Six lithofacies are identified from the shale of Wufeng-Longmaxi Formation: biological siliceous shale, clayey shale, (felsic-calcareous) silty shale, calcareous silty shale, calcareous shale and felsic silty shale. The shale sedimentary environment of Wufeng-Longmaxi Formation underwent five stages of bottom-up changes. The paleo-climate experienced the evolution from warm and humid at the bottom of the Wufeng Formation to dry and hot at the middle and then to dry and cold at the top, and then from dry and hot at the lower part of the Longmaxi Formation to warm and humid at the middle and upper part. In the lower part of Wufeng Formation and the lower part of Longmaxi Formation, the sea level has risen due to two large-scale transgressions. When the sea level is high, the water column is weak in restricted, strong in reduction, low in salinity and high in paleo-productivity. The glacier event at the top of Wufeng Formation caused the sea level to drop. When the sea level is low, the water column is strong in restricted, weak in reduction, high in salinity and low in paleo-productivity. The shale of Wufeng-Longmaxi Formation is mainly formed by suspended sedimentation under low energy conditions. Upwelling sedimentation is developed in the middle of Wufeng Formation and the lower part of Longmaxi Formation. A small amount of storm surge sedimentation is developed at the top of Wufeng Formation. In the upper part of Longmaxi Formation, gravity slumping, debris flow and turbidity current are developed due to the shallowing of water and the increase of terrigenous input. In the end, the sedimentary model of Wufeng-Longmaxi Formation shale is established by integrating the lithofacies, depositional processes type, tectonic evolution and sedimentary environment evolution. [Conclusion] The frequent changes of sedimentary environment and the diversity of depositional processes both control the types and characteristics of lithofacies, further leading to significant differences in organic matter content, porosity, gas content and other reservoir quality factors of different lithofacies. Further research on shale lithofacies and reservoir quality is still needed to provide theoretical basis for shale gas exploration and development.
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Sand injectites have received more and more attention in recent years and have become one of the hotspots in international sedimentology research. The triggering mechanisms include differential compaction, earthquake, fluid injection, wave, gravity slide, etc. But it is generally believed that earthquake is the most important and common one. At present, the deformation mechanism of the earthquake-triggered sand injectites is still unclear. In order to further study its deformation mechanism, a set of test equipment for simulating the earthquake-triggered sand injectites is established, and the sand injectites triggerd by earthquakes from strong to weak, aftershocks and complete end process are simulated successfully. Through the observation and analysis of the experiment results, the formation process of the earthquake-triggered sand injectites is divided into three stages, namely: (1) In the pre-earthquake stage, some abnormal pressures are produced in local strata under the influence of differential compaction or fluids saturated, resulting in weak fluctuation or no deformation of sandy strata; (2) In the epicenter stage, due to the fast energy transfer of seismic cyclic shear waves, the abnormal pressure of the stratum increases rapidly, once the stratum pressure exceeds the rupture strength of the upper overburden and the overlying formation is broken, and the sandy grains suffer liquefaction and fluidization, inject along the cracks, resulting in a series of deformation structures; (3) In the post-earthquake stage, along with the generation of aftershocks, there is still abnormal formation pressure in the formation, and the liquefied sand will continue to deform and migrate until the earthquake is completely ended, and the overall end shape of the sand injectites is formed. Earthquake can trigger sandstone intrusion independently, and also induce other geological processes to control the formation of sand injectites jointly.
Sand injectites have received more and more attention in recent years and have become one of the hotspots in international sedimentology research. The triggering mechanisms include differential compaction, earthquake, fluid injection, wave, gravity slide, etc. But it is generally believed that earthquake is the most important and common one. At present, the deformation mechanism of the earthquake-triggered sand injectites is still unclear. In order to further study its deformation mechanism, a set of test equipment for simulating the earthquake-triggered sand injectites is established, and the sand injectites triggerd by earthquakes from strong to weak, aftershocks and complete end process are simulated successfully. Through the observation and analysis of the experiment results, the formation process of the earthquake-triggered sand injectites is divided into three stages, namely: (1) In the pre-earthquake stage, some abnormal pressures are produced in local strata under the influence of differential compaction or fluids saturated, resulting in weak fluctuation or no deformation of sandy strata; (2) In the epicenter stage, due to the fast energy transfer of seismic cyclic shear waves, the abnormal pressure of the stratum increases rapidly, once the stratum pressure exceeds the rupture strength of the upper overburden and the overlying formation is broken, and the sandy grains suffer liquefaction and fluidization, inject along the cracks, resulting in a series of deformation structures; (3) In the post-earthquake stage, along with the generation of aftershocks, there is still abnormal formation pressure in the formation, and the liquefied sand will continue to deform and migrate until the earthquake is completely ended, and the overall end shape of the sand injectites is formed. Earthquake can trigger sandstone intrusion independently, and also induce other geological processes to control the formation of sand injectites jointly.
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Surface sediment proxies can indicate modern environmental elements and thus infer palaeoenvironmental evolution, but there is little assessment of when and how humans act on sediments in areas of high human activity, and whether this affects the inversion of surface sediment proxies on the climate of the area. In this study, we collected 456 surface sediments from the Qilian Mountains and surrounding areas and analysed the proxies such as total organic nitrogen (TN), total organic carbon (TOC), carbon to nitrogen ratio (C/N), organic carbon isotope (δ13Corg), carbonate carbon isotope (δ13Ccarb) and oxygen isotope (δ18O). We established relationships between proxies and elevation, latitude and longitude, temperature and precipitation, and explored the influence of modern human activity on the palaeoenvironmental proxies of surface sediments. The research found that the palaeoenvironmental proxies of surface sediments in the anthropogenic zone fluctuate significantly in this region, and the correlation is significantly reduced compared to the other areas, suggesting that the influence of human activities can change the indicative meaning of palaeoenvironmental proxies. This paper systematically analyses and calculates the relationship between surface sediments and environmental elements, explores the influence of human activities on surface sediments, and further clarifies the modern environmental indicators of proxies, thus providing a theoretical basis for the subsequent use of palaeoenvironmental proxies in sedimentary strata to infer past climate change and analyse human activities.
Surface sediment proxies can indicate modern environmental elements and thus infer palaeoenvironmental evolution, but there is little assessment of when and how humans act on sediments in areas of high human activity, and whether this affects the inversion of surface sediment proxies on the climate of the area. In this study, we collected 456 surface sediments from the Qilian Mountains and surrounding areas and analysed the proxies such as total organic nitrogen (TN), total organic carbon (TOC), carbon to nitrogen ratio (C/N), organic carbon isotope (δ13Corg), carbonate carbon isotope (δ13Ccarb) and oxygen isotope (δ18O). We established relationships between proxies and elevation, latitude and longitude, temperature and precipitation, and explored the influence of modern human activity on the palaeoenvironmental proxies of surface sediments. The research found that the palaeoenvironmental proxies of surface sediments in the anthropogenic zone fluctuate significantly in this region, and the correlation is significantly reduced compared to the other areas, suggesting that the influence of human activities can change the indicative meaning of palaeoenvironmental proxies. This paper systematically analyses and calculates the relationship between surface sediments and environmental elements, explores the influence of human activities on surface sediments, and further clarifies the modern environmental indicators of proxies, thus providing a theoretical basis for the subsequent use of palaeoenvironmental proxies in sedimentary strata to infer past climate change and analyse human activities.
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[Objective] To study particle size characteristics of the burst flood sediment in barrier. [Methods]composition of flood sediment particle samples from the "11· 03" Baige dammed lake outburst flood on the Jinsha River were analyzed, and size parameters of sediment were calculated. Changes in sediment characteristics from upstream to downstream and its causes were analyzed. Then, the granularity characteristics of this flood sediment were compared with those of other primary river basins in China, while sand particle size characteristics of ancient flood sediment were discussed. [Results and Discussions] The sediment types of the Baige barrier lake outburst flood were silt, sandy silt, and silty sand, with 23.65%, 64.19% and 12.16%, respectively. All particle sizes of sediment in barrier lake were less than 2.0 mm. The proportion of silt was 55.18%, sand of 32.86%, and clay of 11.97%. The silt content gradually increased, while the sand content gradually decreased from the upstream Maoding village to the downstream Shigu town. Moreover, the clay content always fluctuated around 12%. As the flow rate of the flood was reduced gradually, the ability of hydrodynamic to carry particulate matter was weakened by degrees. The clay was less affected by the hydrodynamic conditions as a result of the small particles and the electric charge, that’s why the clay had a relatively stable proportion during the flood peak process. The median particle size was 41.34 μm, and the average particle size was 31.73 μm. Both of the value decreased gradually in pace with the increasing distance from the White River barrier lake. The skewness value was 0.27, which is a positive deviation. The peak value was 0.94 and was moderately sharp. The sorting coefficient was 0.57, indicating good sorting performance. Bimodal distribution accounted for 52% of the grain size distribution curve of sediment. The main peak was high and narrow, located at 100 μm. And the secondary peak is low and wide, the peak value located at 10 μm. The single peak accounted for 48%, with a narrow peak at 50 μm. All sediment sizes in the profile were less than 2.0 mm. There were very small differences in composition. The predominant component was the sand. The silty content was slightly less than the fine sand, and the proportion of clay content was approximately 11.0%. The median value of particle size was larger than the average, both have a tendency to increase from the surface layer to the bottom. The sorting coefficient was less than 0.6, with the extremely positive deviation and the moderate peak state. Compared with other floods, the "11·03" outburst flood had a finer sediment particle size of mainly silt, followed by a smaller median and average value of particle size, with wider peak state and positive skewness, indicating better sorting performance by this flood. [Conclusions] The research results have important reference value for understanding the sediment characteristics in barrier lake outburst floods, burst flood hydrodynamic transport process and mechanism in the future. It will promote the development of water conservancy and hydropower projects and ecological civilization construction in river basins.
[Objective] To study particle size characteristics of the burst flood sediment in barrier. [Methods]composition of flood sediment particle samples from the "11· 03" Baige dammed lake outburst flood on the Jinsha River were analyzed, and size parameters of sediment were calculated. Changes in sediment characteristics from upstream to downstream and its causes were analyzed. Then, the granularity characteristics of this flood sediment were compared with those of other primary river basins in China, while sand particle size characteristics of ancient flood sediment were discussed. [Results and Discussions] The sediment types of the Baige barrier lake outburst flood were silt, sandy silt, and silty sand, with 23.65%, 64.19% and 12.16%, respectively. All particle sizes of sediment in barrier lake were less than 2.0 mm. The proportion of silt was 55.18%, sand of 32.86%, and clay of 11.97%. The silt content gradually increased, while the sand content gradually decreased from the upstream Maoding village to the downstream Shigu town. Moreover, the clay content always fluctuated around 12%. As the flow rate of the flood was reduced gradually, the ability of hydrodynamic to carry particulate matter was weakened by degrees. The clay was less affected by the hydrodynamic conditions as a result of the small particles and the electric charge, that’s why the clay had a relatively stable proportion during the flood peak process. The median particle size was 41.34 μm, and the average particle size was 31.73 μm. Both of the value decreased gradually in pace with the increasing distance from the White River barrier lake. The skewness value was 0.27, which is a positive deviation. The peak value was 0.94 and was moderately sharp. The sorting coefficient was 0.57, indicating good sorting performance. Bimodal distribution accounted for 52% of the grain size distribution curve of sediment. The main peak was high and narrow, located at 100 μm. And the secondary peak is low and wide, the peak value located at 10 μm. The single peak accounted for 48%, with a narrow peak at 50 μm. All sediment sizes in the profile were less than 2.0 mm. There were very small differences in composition. The predominant component was the sand. The silty content was slightly less than the fine sand, and the proportion of clay content was approximately 11.0%. The median value of particle size was larger than the average, both have a tendency to increase from the surface layer to the bottom. The sorting coefficient was less than 0.6, with the extremely positive deviation and the moderate peak state. Compared with other floods, the "11·03" outburst flood had a finer sediment particle size of mainly silt, followed by a smaller median and average value of particle size, with wider peak state and positive skewness, indicating better sorting performance by this flood. [Conclusions] The research results have important reference value for understanding the sediment characteristics in barrier lake outburst floods, burst flood hydrodynamic transport process and mechanism in the future. It will promote the development of water conservancy and hydropower projects and ecological civilization construction in river basins.
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The quality of different kinds of source rock in Shehezi formation is the key factor for gas exploration in deep layer of Songliao Basin. In order to make clear the difference and its genesis between different kinds of source, we recover the sedimentary facies and water property, on the basis of core observation, organic geochemical analysis, major and trace elements testing, make sure the fault active, sedimentary facies and water property in Shahezi formation, and their controlling on source rock quality. The result is that there are two kinds of source rock such as mudstone and coal in Shahezi formation. The mudstone which focus on 1st Shahezi formation have a high abundance of organic matter, the organic matter type is based on II type and there are little III type at the same time, while coal are chiefly distributed in 2nd Shahezi formation, the organic matter type are all III type. The fault during 1st Shahezi formation is characterized by strong activity, generate a small lake with a great water depth, high salinity and strong reducing property. The fault activity in 2nd Shahezi formation is gradually becoming weak, lake size become greater while water depth become shallow, salinity and reducibility become weakened at the same time. The source rock is mainly controlled by fault activity, sedimentary facies and water property. Downthrown side become an important storage for mudstone because of the fault activity, which determine the thickness of mudstone. The Sedimentary facies take control of the types of source rock by impact on organic matter import. The different between Paleoenvironment which is make up of Paleosalin, Paleowater depth and redox is the key factor for the enrichment and preservation of organic matter, is the main controlling factor for source rock quality distribution diffference.
The quality of different kinds of source rock in Shehezi formation is the key factor for gas exploration in deep layer of Songliao Basin. In order to make clear the difference and its genesis between different kinds of source, we recover the sedimentary facies and water property, on the basis of core observation, organic geochemical analysis, major and trace elements testing, make sure the fault active, sedimentary facies and water property in Shahezi formation, and their controlling on source rock quality. The result is that there are two kinds of source rock such as mudstone and coal in Shahezi formation. The mudstone which focus on 1st Shahezi formation have a high abundance of organic matter, the organic matter type is based on II type and there are little III type at the same time, while coal are chiefly distributed in 2nd Shahezi formation, the organic matter type are all III type. The fault during 1st Shahezi formation is characterized by strong activity, generate a small lake with a great water depth, high salinity and strong reducing property. The fault activity in 2nd Shahezi formation is gradually becoming weak, lake size become greater while water depth become shallow, salinity and reducibility become weakened at the same time. The source rock is mainly controlled by fault activity, sedimentary facies and water property. Downthrown side become an important storage for mudstone because of the fault activity, which determine the thickness of mudstone. The Sedimentary facies take control of the types of source rock by impact on organic matter import. The different between Paleoenvironment which is make up of Paleosalin, Paleowater depth and redox is the key factor for the enrichment and preservation of organic matter, is the main controlling factor for source rock quality distribution diffference.
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The gravelly limestone of Cambrian strata in the western edge of Ordos Basin is developed. This study has conducted a detailed study on the development characteristics of gravelly limestone and typical storm deposition characteristics of Xuzhuang formation in the western edge of Ordos basin through field observation and thin section observation of four sections of Wuhai mohogou, Wuhai Laoshidan, Huanxian yinshixia and Tongxin Qinglongshan. Storm sedimentary structures such as channel mold, bottom scouring surface, mound cross bedding and parallel bedding are developed in Xuzhuang formation in the study area. For the gravelly limestone developed on a large scale in the study area, five gravelly limestone facies are divided according to the shape, arrangement and filling characteristics of gravels: (1) particle supported gravelly limestone facies, (2) imbricate gravelly limestone facies, (3) argillaceous filled gravelly limestone facies, (4) "Chrysanthemum" gravelly limestone facies, and (5) matrix supported gravelly limestone facies. In addition, five typical storm sedimentary sequences of the Xuzhuang formation of the Middle Cambrian in the western margin of Ordos are identified through field measured data, and the storm sedimentary model of the study area is established. The study area is located near the Helan Mountain earthquake zone, which is the reason for the frequent occurrence of storms. The development of storm deposits in the study area reveals that the Ordos Basin was located in the low latitude area near the equator during the Cambrian Xuzhuang formation, which is mutually confirmed by the location of the North China plate restored by paleomagnetism at the same time.
The gravelly limestone of Cambrian strata in the western edge of Ordos Basin is developed. This study has conducted a detailed study on the development characteristics of gravelly limestone and typical storm deposition characteristics of Xuzhuang formation in the western edge of Ordos basin through field observation and thin section observation of four sections of Wuhai mohogou, Wuhai Laoshidan, Huanxian yinshixia and Tongxin Qinglongshan. Storm sedimentary structures such as channel mold, bottom scouring surface, mound cross bedding and parallel bedding are developed in Xuzhuang formation in the study area. For the gravelly limestone developed on a large scale in the study area, five gravelly limestone facies are divided according to the shape, arrangement and filling characteristics of gravels: (1) particle supported gravelly limestone facies, (2) imbricate gravelly limestone facies, (3) argillaceous filled gravelly limestone facies, (4) "Chrysanthemum" gravelly limestone facies, and (5) matrix supported gravelly limestone facies. In addition, five typical storm sedimentary sequences of the Xuzhuang formation of the Middle Cambrian in the western margin of Ordos are identified through field measured data, and the storm sedimentary model of the study area is established. The study area is located near the Helan Mountain earthquake zone, which is the reason for the frequent occurrence of storms. The development of storm deposits in the study area reveals that the Ordos Basin was located in the low latitude area near the equator during the Cambrian Xuzhuang formation, which is mutually confirmed by the location of the North China plate restored by paleomagnetism at the same time.
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The reactions between sulfates and sedimentary organic matter are typical organic?inorganic interactions in sedimentary basins. Investigations of the thermochemical sulfate reduction reaction (TSR) are normally limited in reservoirs, treating S-bearing products as research targets. However, this interaction also exists in the early stage of catagenesis, where the chemical components were influenced by the presence of sulfate. In this study, the effect of gypsum on the thermal evolution of kerogen was investigated by hydrous pyrolysis. The source rock and the corresponding sulfur-bearing kerogen were sampled from the Pingliang Formation on the southwestern margin of the Ordos Basin. Based on the yields and distribution characteristics of dibenzothiophene (DBT), phenanthrene and fluorene after the experiments, it is revealed that the organosulfur compounds (OSC), the precursors of DBT, might be oxidized by sulfate during the early stage of catagenesis. This result verified the reactivity between sulfate and sedimentary organic matter during this process. Therefore, before H2S was generated during the process of TSR, there was a stage of oxidative degradation between sulfate and sedimentary organic matter. In this stage, the majority of production is polar organic compounds, such as oxygen-bearing compounds. The sulfur in DBT was derived from OSC. These understandings enlarged the interaction between sulfate and sedimentary organic matter from high-temperature reservoirs to the gypsum-bearing source rock during catagenesis with lower thermal stress.
The reactions between sulfates and sedimentary organic matter are typical organic?inorganic interactions in sedimentary basins. Investigations of the thermochemical sulfate reduction reaction (TSR) are normally limited in reservoirs, treating S-bearing products as research targets. However, this interaction also exists in the early stage of catagenesis, where the chemical components were influenced by the presence of sulfate. In this study, the effect of gypsum on the thermal evolution of kerogen was investigated by hydrous pyrolysis. The source rock and the corresponding sulfur-bearing kerogen were sampled from the Pingliang Formation on the southwestern margin of the Ordos Basin. Based on the yields and distribution characteristics of dibenzothiophene (DBT), phenanthrene and fluorene after the experiments, it is revealed that the organosulfur compounds (OSC), the precursors of DBT, might be oxidized by sulfate during the early stage of catagenesis. This result verified the reactivity between sulfate and sedimentary organic matter during this process. Therefore, before H2S was generated during the process of TSR, there was a stage of oxidative degradation between sulfate and sedimentary organic matter. In this stage, the majority of production is polar organic compounds, such as oxygen-bearing compounds. The sulfur in DBT was derived from OSC. These understandings enlarged the interaction between sulfate and sedimentary organic matter from high-temperature reservoirs to the gypsum-bearing source rock during catagenesis with lower thermal stress.
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In view of the division and system attribution of different sedimentary bodies such as alluvial fan, ephemeral stream, distributary fluvial system and fluvial fan, which have been the research hotspots in sedimentology in recent years, the analysis of the sedimentary evolution process of Kuqa River Modern alluvial fan and alluvial plain meandering river is carried out, focusing on the boundary changes and control factors of different sedimentary bodies. It is considered that the sedimentary bodies controlled by the same river (Kuqa River) under arid climate develop many types of sedimentary bodies, such as Intermountain braided river, alluvial fan and meandering stream. From the mountain pass to the downstream alluvial plain, the river water is lost, and the Kuqa River extends for more than 100km. The braided channels, debris flows and other deposits of alluvial fan proximal are developed one by one. A large area of braided distributary channel deposits in the alluvial fan middle, and a single runoff channel (low sinuosity meandering river) deposits, and gradually evolved into high sinuosity meandering river deposits on the alluvial plain to the downstream. The mountain braided river and alluvial fan and Meandering river are continuously distributed on the plane. The changes of river morphology and channel width are closely related to the deposition slope. The changes of gravel diameter of gravelly sediments are negatively related to the deposition transportation distance, and the distribution range of sandy sediments increases significantly from proximal source to distal. The distribution range of each sedimentary body is controlled and closely related by the distribution of different types of river channels of Kuqa River, and the changes of river channel types are mainly controlled by the changes of sedimentary slope, sediment characteristics, water flow, etc. It shows that further enlarging the research scale of sedimentary bodies, focusing on the close relationship between different sedimentary bodies in space and revealing their main controlling factors are of great significance to clarify the essential laws and evolution of various types of sedimentary bodies, and to reduce the division of sedimentary bodies attribution and other issues.
In view of the division and system attribution of different sedimentary bodies such as alluvial fan, ephemeral stream, distributary fluvial system and fluvial fan, which have been the research hotspots in sedimentology in recent years, the analysis of the sedimentary evolution process of Kuqa River Modern alluvial fan and alluvial plain meandering river is carried out, focusing on the boundary changes and control factors of different sedimentary bodies. It is considered that the sedimentary bodies controlled by the same river (Kuqa River) under arid climate develop many types of sedimentary bodies, such as Intermountain braided river, alluvial fan and meandering stream. From the mountain pass to the downstream alluvial plain, the river water is lost, and the Kuqa River extends for more than 100km. The braided channels, debris flows and other deposits of alluvial fan proximal are developed one by one. A large area of braided distributary channel deposits in the alluvial fan middle, and a single runoff channel (low sinuosity meandering river) deposits, and gradually evolved into high sinuosity meandering river deposits on the alluvial plain to the downstream. The mountain braided river and alluvial fan and Meandering river are continuously distributed on the plane. The changes of river morphology and channel width are closely related to the deposition slope. The changes of gravel diameter of gravelly sediments are negatively related to the deposition transportation distance, and the distribution range of sandy sediments increases significantly from proximal source to distal. The distribution range of each sedimentary body is controlled and closely related by the distribution of different types of river channels of Kuqa River, and the changes of river channel types are mainly controlled by the changes of sedimentary slope, sediment characteristics, water flow, etc. It shows that further enlarging the research scale of sedimentary bodies, focusing on the close relationship between different sedimentary bodies in space and revealing their main controlling factors are of great significance to clarify the essential laws and evolution of various types of sedimentary bodies, and to reduce the division of sedimentary bodies attribution and other issues.
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There are abundant geothermal resources in Tibet, and most hot springs or sinters are rarely enriched with elements such as B, Li, Rb, Cs. Besides their potential economic value, they are considered as important mineral sources of salt lake resources in Tibet. It is not only of basic theoretical significance, but also of guiding significance to correctly evaluate the potential value of mineral resources to study the provenance, evolution and enrichment law of B, Li, Rb and Cs in geothermal water. Based on the chemical composition and B and Li isotope system analysis of hot springs, rivers and springs in the most typical Yangbajing-Dangxiong rift, it can be seen that boiling springs are mostly Na-Cl type and moderately alkaline, belonging to continental non-volcanic geothermal. The most obvious geochemical characteristic of hot springs is that δ11B value is generally negative, and the higher the concentration of B and Li, the more negative the B and Li isotopes are. Earth's crust remelting residual magma fluid upwelling can reasonably explain the unique element enrichment and combination characteristics, isotope distribution law and extremely high heat storage temperature of geothermal system. The geothermal system like Yangbajing-Dangxiong rift not only has a good prospect of geothermal energy development, but also all kinds of abnormally or supernormally enriched elements such as B, Li, Rb, Cs can be used as mineral resources, based on the coupling relationship between magmatic activity and enrichment laws of various elements.
There are abundant geothermal resources in Tibet, and most hot springs or sinters are rarely enriched with elements such as B, Li, Rb, Cs. Besides their potential economic value, they are considered as important mineral sources of salt lake resources in Tibet. It is not only of basic theoretical significance, but also of guiding significance to correctly evaluate the potential value of mineral resources to study the provenance, evolution and enrichment law of B, Li, Rb and Cs in geothermal water. Based on the chemical composition and B and Li isotope system analysis of hot springs, rivers and springs in the most typical Yangbajing-Dangxiong rift, it can be seen that boiling springs are mostly Na-Cl type and moderately alkaline, belonging to continental non-volcanic geothermal. The most obvious geochemical characteristic of hot springs is that δ11B value is generally negative, and the higher the concentration of B and Li, the more negative the B and Li isotopes are. Earth's crust remelting residual magma fluid upwelling can reasonably explain the unique element enrichment and combination characteristics, isotope distribution law and extremely high heat storage temperature of geothermal system. The geothermal system like Yangbajing-Dangxiong rift not only has a good prospect of geothermal energy development, but also all kinds of abnormally or supernormally enriched elements such as B, Li, Rb, Cs can be used as mineral resources, based on the coupling relationship between magmatic activity and enrichment laws of various elements.
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After the exploration of deep oil and gas in the Fukang Sag, eastern Junggar Basin, the thick-bed conglomerate was drilled for the first time in Lucaogou Formation in Fukang Sag, which broke the understanding that the Lucaogou Formation reservoir was not developed and the whole deposit was fine grained. At present, it is urgent to systematically study the lithofacies types, assemblage characteristics and distribution rules of Lucaogou Formation in oil and gas exploration. Based on core, thin section and logging data, the petrological characteristics and lithofacies types of the conglomerate reservoir in Lucaogou Formation in Fukang Sag are identified and distinguished, and the distribution law of lithofacies is predicted. Results showed that the Lucaougou Formation of longitudinal development under the background of a lake invasion retrogradation sequences, some main development coarse clastic rocks, the upper Lucaogou Formation mainly argillaceous siltstone and mudstone, The thickness is relatively large, and the late mudstone cap overlies the early low region conglomerate reservoir, which has the condition of forming lithologic reservoir. The north and south of Xiquan uplift develop the braided river delta sedimentary system of steep near-shore subaqueous fan and gentle slope respectively. The north wing has poor conglomerate sorting, angular gravel particles with poor orientation, and heterobasic particle support, showing the characteristics of short transport distance, strong hydrodynamic force and gravity flow deposition. The south wing has good sorting, particle support with certain orientation, and obvious traction flow characteristics.According to the comprehensive analysis, the lithofacies characteristics and distribution were controlled by the late Carboniferous and Early Permian volcanism, the paleogeomorphic slope of the Carboniferous top boundary in the North and south Xiquanbi Uplift, and the fluctuation of lake plane.
After the exploration of deep oil and gas in the Fukang Sag, eastern Junggar Basin, the thick-bed conglomerate was drilled for the first time in Lucaogou Formation in Fukang Sag, which broke the understanding that the Lucaogou Formation reservoir was not developed and the whole deposit was fine grained. At present, it is urgent to systematically study the lithofacies types, assemblage characteristics and distribution rules of Lucaogou Formation in oil and gas exploration. Based on core, thin section and logging data, the petrological characteristics and lithofacies types of the conglomerate reservoir in Lucaogou Formation in Fukang Sag are identified and distinguished, and the distribution law of lithofacies is predicted. Results showed that the Lucaougou Formation of longitudinal development under the background of a lake invasion retrogradation sequences, some main development coarse clastic rocks, the upper Lucaogou Formation mainly argillaceous siltstone and mudstone, The thickness is relatively large, and the late mudstone cap overlies the early low region conglomerate reservoir, which has the condition of forming lithologic reservoir. The north and south of Xiquan uplift develop the braided river delta sedimentary system of steep near-shore subaqueous fan and gentle slope respectively. The north wing has poor conglomerate sorting, angular gravel particles with poor orientation, and heterobasic particle support, showing the characteristics of short transport distance, strong hydrodynamic force and gravity flow deposition. The south wing has good sorting, particle support with certain orientation, and obvious traction flow characteristics.According to the comprehensive analysis, the lithofacies characteristics and distribution were controlled by the late Carboniferous and Early Permian volcanism, the paleogeomorphic slope of the Carboniferous top boundary in the North and south Xiquanbi Uplift, and the fluctuation of lake plane.
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Based on the mineralogical and geochemical analysis of the sediments and altered basalt from the north slope (overlying plate) and axis to the south slope (subduction plate) at the Challenger Deep of the Mariana Trench, we studied the main types, geochemical characteristics, and origin of the hadal sediments. The results show that the hadal sediments can be divided into four types: red deep-sea clay, siliceous sediments, micromanganese-rich sediments, and calcareous sediments. The red deep-sea clay is the most common type of hadal sediment, which contribute the most to subducted sediments. Major and trace element geochemical characteristics are similar to those of altered basalt of the oceanic crust, which imply that red clay is mainly derived from the basalt alteration of the subducted and overlying plates, rather than the volcanic and terrestrial inputs. Moreover, intensified organic matter diagenesis has an important influence on the geochemical properties of the hadal sediments, which is the main reason the Challenger Deep sediments have lower rare earth elements and enrich more micromanganese nodules than the adjacent deep-sea sediments.
Based on the mineralogical and geochemical analysis of the sediments and altered basalt from the north slope (overlying plate) and axis to the south slope (subduction plate) at the Challenger Deep of the Mariana Trench, we studied the main types, geochemical characteristics, and origin of the hadal sediments. The results show that the hadal sediments can be divided into four types: red deep-sea clay, siliceous sediments, micromanganese-rich sediments, and calcareous sediments. The red deep-sea clay is the most common type of hadal sediment, which contribute the most to subducted sediments. Major and trace element geochemical characteristics are similar to those of altered basalt of the oceanic crust, which imply that red clay is mainly derived from the basalt alteration of the subducted and overlying plates, rather than the volcanic and terrestrial inputs. Moreover, intensified organic matter diagenesis has an important influence on the geochemical properties of the hadal sediments, which is the main reason the Challenger Deep sediments have lower rare earth elements and enrich more micromanganese nodules than the adjacent deep-sea sediments.
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[Objective] In order to clarify the characteristics of organic shale distribution and shale gas reservoir in different tectonic-depositional differentiation patterns under the sequence framework. [Methods] Based on the T-R sequence model, the sequence of the Qiongzhusi Formation was divided and the sequence stratigraphic framework was established. Under the constraints of the sequence framework, core, logging, geochemical and pore structure data of the Qiongzhusi Formation were analyzed. The characteristics and influencing factors of Qiongzhusi Formation shale gas reservoirs under different structural-sedimentary differentiation patterns were studied. [Results and Discussions] The study shows that four sequence boundaries and three third-order sequences can be identified and classified in the Qiongzhusi Formation. The thickness of each sequence is gradually reduced from the center to the outer edge of the Mianyang-Changning intracratonic rift due to tectonic-deposition differentiation. The thickness of SQ2-RST is significantly thinned in the JS1-JY2 area, and the thickness thinning of SQ3 extends to the Z4-JS1 area. The shale gas reservoir characteristics of the Qiongzhusi Formation under different tectonic-deposition differentiation patterns and the sequence framework are clarified: the TOC content shows that TST is larger than RST, and the center of the rift is larger than the transition zone than the outer edge of rift; the mineral content shows that SQ1 and SQ2 are dominated by feldspar and quartz, but SQ3 changes to be dominated by clay and quartz, and the quartz and pyrite content in the transition zone is higher than the outer edge of the rift; the porosity shows that the transition zone is larger than the outer edge of the rift, SQ1 is lower than SQ3 and SQ2, and the organic matter pore of SQ1 is poorly developed. [Conclusions] It is suggested that the tectonic-deposition differentiation of the Mianyang-Changning intracratonic rift controlled the topography and water depth during the deposition of the Qiongzhusi Formation, resulting in differences in the redox conditions, paleoproductivity level, authigenic mineral formation environment and floor sealing ability in different sequences and tectonic-deposition differentiation patterns, and further influenced the organic matter enrichment, mineral content and pore development characteristics.
[Objective] In order to clarify the characteristics of organic shale distribution and shale gas reservoir in different tectonic-depositional differentiation patterns under the sequence framework. [Methods] Based on the T-R sequence model, the sequence of the Qiongzhusi Formation was divided and the sequence stratigraphic framework was established. Under the constraints of the sequence framework, core, logging, geochemical and pore structure data of the Qiongzhusi Formation were analyzed. The characteristics and influencing factors of Qiongzhusi Formation shale gas reservoirs under different structural-sedimentary differentiation patterns were studied. [Results and Discussions] The study shows that four sequence boundaries and three third-order sequences can be identified and classified in the Qiongzhusi Formation. The thickness of each sequence is gradually reduced from the center to the outer edge of the Mianyang-Changning intracratonic rift due to tectonic-deposition differentiation. The thickness of SQ2-RST is significantly thinned in the JS1-JY2 area, and the thickness thinning of SQ3 extends to the Z4-JS1 area. The shale gas reservoir characteristics of the Qiongzhusi Formation under different tectonic-deposition differentiation patterns and the sequence framework are clarified: the TOC content shows that TST is larger than RST, and the center of the rift is larger than the transition zone than the outer edge of rift; the mineral content shows that SQ1 and SQ2 are dominated by feldspar and quartz, but SQ3 changes to be dominated by clay and quartz, and the quartz and pyrite content in the transition zone is higher than the outer edge of the rift; the porosity shows that the transition zone is larger than the outer edge of the rift, SQ1 is lower than SQ3 and SQ2, and the organic matter pore of SQ1 is poorly developed. [Conclusions] It is suggested that the tectonic-deposition differentiation of the Mianyang-Changning intracratonic rift controlled the topography and water depth during the deposition of the Qiongzhusi Formation, resulting in differences in the redox conditions, paleoproductivity level, authigenic mineral formation environment and floor sealing ability in different sequences and tectonic-deposition differentiation patterns, and further influenced the organic matter enrichment, mineral content and pore development characteristics.
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The material sources and changes of terrigenous clastic rocks are closely related to sedimentary basins and tectonic evolution. Based on the identification of rock thin sections identification, quantitative mineralogical analysis and detrital zircon U-Pb chronology of sandstone samples from Shanxi Formation, Shihezi Formation and Shiqianfeng Formation of Late Paleozoic in Tongchuan area, southern Ordos Basin, the provenance is traced, and the tectonic-sedimentary process of Permian in southern Ordos Basin is discussed. The results show that the detrital zircon from Shanxi group of early Permian has four major age group peaks at 364Ma, 450Ma, 946Ma and 2446Ma. The detrital zircon from Lower Shihezi Formation in the Middle Permian has three major age group peaks at 294Ma, 1963.4Ma and 2499Ma. The main peak value of detrital zircon of the late Permian Shiqianfeng Formation is 1876.5Ma, and the weak peak values are 310.5Ma and 2523Ma, and there is a lack of Neoproterozoic and early Paleozoic detrital zircon records representing the northern Qinling orogenic belt. It is considered that the main provenance of Shanxi Formation is the North Qinling orogenic belt, and the secondary provenance is the structural belt of the southern margin of North China. The provenance of Shihezi Formation is provided by the North Qinling orogenic belt, the structural belt of the southern margin of North China plate and the western segment of Inner Mongolia uplift. The provenance of the Shiqianfeng Formation is the structural belt in the southern margin of North China. During the Shanxi period of the early Permian, the uplift of the southern margin of North China was low, which did not affect the source of the North Qinling orogenic belt. During the Shihezi period, the Mianlue Ocean changed from passive tension to active compression, and the Qinling orogenic belt was in a state of continuous uplift, resulting in the continuous uplift of the southern margin of the North China plate. During the Shiqianfeng period, the southern margin of North China was strongly uplifted, which not only provided material sources for Tongchuan area, but also prevented the materials from the northern Qinling orogenic belt from entering the study area. According to the comparison between the Permian provenance analysis results in Tongchuan area and the zircon data around it, it is found that the south of Ordos Basin uplifted from east to west. This difference in time can reflect the start-up process of scissors-type closed collision between North China plate and South China plate from east to west in Permian, and the evolution of paleotopography and provenance system caused by this.
The material sources and changes of terrigenous clastic rocks are closely related to sedimentary basins and tectonic evolution. Based on the identification of rock thin sections identification, quantitative mineralogical analysis and detrital zircon U-Pb chronology of sandstone samples from Shanxi Formation, Shihezi Formation and Shiqianfeng Formation of Late Paleozoic in Tongchuan area, southern Ordos Basin, the provenance is traced, and the tectonic-sedimentary process of Permian in southern Ordos Basin is discussed. The results show that the detrital zircon from Shanxi group of early Permian has four major age group peaks at 364Ma, 450Ma, 946Ma and 2446Ma. The detrital zircon from Lower Shihezi Formation in the Middle Permian has three major age group peaks at 294Ma, 1963.4Ma and 2499Ma. The main peak value of detrital zircon of the late Permian Shiqianfeng Formation is 1876.5Ma, and the weak peak values are 310.5Ma and 2523Ma, and there is a lack of Neoproterozoic and early Paleozoic detrital zircon records representing the northern Qinling orogenic belt. It is considered that the main provenance of Shanxi Formation is the North Qinling orogenic belt, and the secondary provenance is the structural belt of the southern margin of North China. The provenance of Shihezi Formation is provided by the North Qinling orogenic belt, the structural belt of the southern margin of North China plate and the western segment of Inner Mongolia uplift. The provenance of the Shiqianfeng Formation is the structural belt in the southern margin of North China. During the Shanxi period of the early Permian, the uplift of the southern margin of North China was low, which did not affect the source of the North Qinling orogenic belt. During the Shihezi period, the Mianlue Ocean changed from passive tension to active compression, and the Qinling orogenic belt was in a state of continuous uplift, resulting in the continuous uplift of the southern margin of the North China plate. During the Shiqianfeng period, the southern margin of North China was strongly uplifted, which not only provided material sources for Tongchuan area, but also prevented the materials from the northern Qinling orogenic belt from entering the study area. According to the comparison between the Permian provenance analysis results in Tongchuan area and the zircon data around it, it is found that the south of Ordos Basin uplifted from east to west. This difference in time can reflect the start-up process of scissors-type closed collision between North China plate and South China plate from east to west in Permian, and the evolution of paleotopography and provenance system caused by this.
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[Objective] The Dagushi Formation of the Mesoproterozoic Xiong 'er Group comprises the earliest sedimentary unit covering on the metamorphic crystalline basement in the southern margin of the North China Craton. Studies on depositional environment and processes of this formation are of great significance for understanding the breakup of the Columbia supercontinent and the sedimentary environment and tectonic setting of the early Xiong'er Group. However, systematic sedimentary provenance and paleoenvironmental research on the Dagushi Formation is still lacking. [Methods] Based on the major and trace element analysis of the Dagushi Formation in the Xiong’er Group, Xiaogoubei area, Jiyuan of Henan Province, the provenance characteristics, sedimentary environment and tectonic setting of the Dagushi Formation are discussed. [Results] Major element results show that the fine-grained clastic rocks of the Dagushi Formation are close to provenance and the compositional maturity gradually decreases from bottom to top. The sediments are mainly eroded from the mixture of mafic and felsic rocks, and gradually shifted from granites to felsic volcanic rocks, and then to intermediate rocks from bottom to top. The composition of ancient sediments in the upper member gradually increases. The Dagushi Formation was deposited in a warm and humid climate with several climatic fluctuations. Trace elements and REE analysis show that the lower Dagushi Formation were formed in a relatively stable tectonic setting, while the middle and upper segments were formed in an active tectonic setting. [Conclusion] Based on previous studies, we conclude that the transition of sediment source, climate and tectonic environment during the deposition of the Dagushi Formation of the Xiong'er Group is associated with crust activation and associated tectono-thermal events. Mantle plume caused the uplifting and activation of the crust, thus the southern margin of the North China Craton gradually turned into an active tectonic setting. The deposition of the Dagushi Formation was located in a local depression. The early volcanism of the Xiong'er Group has developed and provided sedimentary provenance for the Dagushi Formation. This study provides new evidence for better understanding of the early Mesoproterozoic tectonic-deposition evolution of the North China Craton.
[Objective] The Dagushi Formation of the Mesoproterozoic Xiong 'er Group comprises the earliest sedimentary unit covering on the metamorphic crystalline basement in the southern margin of the North China Craton. Studies on depositional environment and processes of this formation are of great significance for understanding the breakup of the Columbia supercontinent and the sedimentary environment and tectonic setting of the early Xiong'er Group. However, systematic sedimentary provenance and paleoenvironmental research on the Dagushi Formation is still lacking. [Methods] Based on the major and trace element analysis of the Dagushi Formation in the Xiong’er Group, Xiaogoubei area, Jiyuan of Henan Province, the provenance characteristics, sedimentary environment and tectonic setting of the Dagushi Formation are discussed. [Results] Major element results show that the fine-grained clastic rocks of the Dagushi Formation are close to provenance and the compositional maturity gradually decreases from bottom to top. The sediments are mainly eroded from the mixture of mafic and felsic rocks, and gradually shifted from granites to felsic volcanic rocks, and then to intermediate rocks from bottom to top. The composition of ancient sediments in the upper member gradually increases. The Dagushi Formation was deposited in a warm and humid climate with several climatic fluctuations. Trace elements and REE analysis show that the lower Dagushi Formation were formed in a relatively stable tectonic setting, while the middle and upper segments were formed in an active tectonic setting. [Conclusion] Based on previous studies, we conclude that the transition of sediment source, climate and tectonic environment during the deposition of the Dagushi Formation of the Xiong'er Group is associated with crust activation and associated tectono-thermal events. Mantle plume caused the uplifting and activation of the crust, thus the southern margin of the North China Craton gradually turned into an active tectonic setting. The deposition of the Dagushi Formation was located in a local depression. The early volcanism of the Xiong'er Group has developed and provided sedimentary provenance for the Dagushi Formation. This study provides new evidence for better understanding of the early Mesoproterozoic tectonic-deposition evolution of the North China Craton.
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[Objective] The Chinese Loess Plateau (CLP) preserves the most widely distributed, thickest, and continuous aeolian dust deposits in the world. Studying the evolution of loess provenance is of great significance for deducing climate change in inland Asia. Predecessors have made a series of achievements,but the Quaternary climate changed quickly during the glacial-interglacial period, this made the alternation of winter and summer monsoon. Therefore, the source of loess is likely to change with the monsoon, however, there is still some controversy about the change of loess sources in the glacial-interglacial period due to the lack of evidence of continuous strata. [Methods] Therefore, in this paper, we collected nine loess-paleosol layers from Luochuan (S0, L1, L2, L2, S2 ) and Lingtai (S0, L1, S1, L2, S2) for detrital zircon U-Pb dating study. Zircon U-Pb ages were determined at the State Key Laboratory of Continental Dynamics, Northwest University. The U-Pb ages of detrital zircons of the samples are displayed in PDP, KDE,and CAD diagrams. By comparing the zircon age combinations between the different layers and the potential source regions, and also use the MDS technology to analyse data correlation. [Results and Discussions] According to the analysis results, the correlation analysis of the data using MDS shows that 9 samples in this paper have better correlation with the sediments includes the Ruoshui river, Western Mu Us Desert, Yellow River, Songpan and Qaidam basins. However, we find some differences in the KDE and PDP diagrams, it is found that the main age distribution of the sample is 200-600 Ma, and the secondary age distribution is between 900-1200 Ma,1800-2100 Ma and >2700 Ma.The U-Pb age characteristics of Lingtai and Luochuan samples are more similar to those of Songpan,Ruoshui River,Western Mu Us Desert and Yellow River samples.The Qaidam basins and Eastern Mu Us Desert show different age characteristics with our samples.Thus ,the Qaidam basins and Eastern Mu Us Desert are not the main source area of loess, so we conclude that the dust material of loess is mainly derived from the northwest mixture source, includes northeast of the Tibetan Plateau,Alxa region and the Western Mu Us Desert. Also, no significant difference was found between the loess-palsoil layers during the glacial-interglacial period . In order to avoid errors caused by data volume, we divide the sample data into two units, namely loess-paleosol, for analysis. The cumulative growth trend of the sample age was analyzed by using the CAD diagram, and the results showed that there are no enough data difference,which means the provenance kept stable between the glacial and the interglacial. [Conclusions] Based on the above research and analysis, we draw the following conclusions :(1) Affected by Asian climate drought and Tibetan Plateau uplift, the dust material of loess is mainly derived from the northwest mixture source, includes northeast of the Tibetan Plateau,Alxa region and the Western Mu Us Desert; (2) The source of loess indicating the glacial-interglacial period did not change significantly.
[Objective] The Chinese Loess Plateau (CLP) preserves the most widely distributed, thickest, and continuous aeolian dust deposits in the world. Studying the evolution of loess provenance is of great significance for deducing climate change in inland Asia. Predecessors have made a series of achievements,but the Quaternary climate changed quickly during the glacial-interglacial period, this made the alternation of winter and summer monsoon. Therefore, the source of loess is likely to change with the monsoon, however, there is still some controversy about the change of loess sources in the glacial-interglacial period due to the lack of evidence of continuous strata. [Methods] Therefore, in this paper, we collected nine loess-paleosol layers from Luochuan (S0, L1, L2, L2, S2 ) and Lingtai (S0, L1, S1, L2, S2) for detrital zircon U-Pb dating study. Zircon U-Pb ages were determined at the State Key Laboratory of Continental Dynamics, Northwest University. The U-Pb ages of detrital zircons of the samples are displayed in PDP, KDE,and CAD diagrams. By comparing the zircon age combinations between the different layers and the potential source regions, and also use the MDS technology to analyse data correlation. [Results and Discussions] According to the analysis results, the correlation analysis of the data using MDS shows that 9 samples in this paper have better correlation with the sediments includes the Ruoshui river, Western Mu Us Desert, Yellow River, Songpan and Qaidam basins. However, we find some differences in the KDE and PDP diagrams, it is found that the main age distribution of the sample is 200-600 Ma, and the secondary age distribution is between 900-1200 Ma,1800-2100 Ma and >2700 Ma.The U-Pb age characteristics of Lingtai and Luochuan samples are more similar to those of Songpan,Ruoshui River,Western Mu Us Desert and Yellow River samples.The Qaidam basins and Eastern Mu Us Desert show different age characteristics with our samples.Thus ,the Qaidam basins and Eastern Mu Us Desert are not the main source area of loess, so we conclude that the dust material of loess is mainly derived from the northwest mixture source, includes northeast of the Tibetan Plateau,Alxa region and the Western Mu Us Desert. Also, no significant difference was found between the loess-palsoil layers during the glacial-interglacial period . In order to avoid errors caused by data volume, we divide the sample data into two units, namely loess-paleosol, for analysis. The cumulative growth trend of the sample age was analyzed by using the CAD diagram, and the results showed that there are no enough data difference,which means the provenance kept stable between the glacial and the interglacial. [Conclusions] Based on the above research and analysis, we draw the following conclusions :(1) Affected by Asian climate drought and Tibetan Plateau uplift, the dust material of loess is mainly derived from the northwest mixture source, includes northeast of the Tibetan Plateau,Alxa region and the Western Mu Us Desert; (2) The source of loess indicating the glacial-interglacial period did not change significantly.
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Fine-grained sedimentary varves is the most basic sedimentary unit structure that can be distinguished in the inner bed of semi-deep lake-deep basin. The thickness of the single varve is generally less than 10mm. Its material composition, continuity and geometry play an important role in the restoration of paleo-environmental changes and sedimentary mechanism. With the development of unconventional oil and gas revolution, many scholars have found that lacustrine varve have an significant impact on shale oil and gas enrichment, development and production effects, but rich in types, complex formation mechanisms and various controlled factors. By systematically combing the research results of domestic and foreign scholars, the genetic mechanisms of clay mineral varve, felsic varve, calcareous varve and organic varve were determined respectively, and the fine flocculation reaction was the main hot theory of varve deposition mechanism in recent years. Then influencing factors of varve deposition were classified into four categories: paleoclimatic factors, palaeogeographic conditions, palaeogeological events and other factors,and the corresponding coupling relationship between different environmental conditions and preferential varve was summarized. Finally, it is proposed that the establishment of varve mechanism model including the combination of multiple factors and the accurate inversion of varve formation by using the perfect model are the main research directions in the future stage, which will provide guidance for the further study of the varve structure of fine-grained sedimentary rocks and the research and application of unconventional oil and gas.
Fine-grained sedimentary varves is the most basic sedimentary unit structure that can be distinguished in the inner bed of semi-deep lake-deep basin. The thickness of the single varve is generally less than 10mm. Its material composition, continuity and geometry play an important role in the restoration of paleo-environmental changes and sedimentary mechanism. With the development of unconventional oil and gas revolution, many scholars have found that lacustrine varve have an significant impact on shale oil and gas enrichment, development and production effects, but rich in types, complex formation mechanisms and various controlled factors. By systematically combing the research results of domestic and foreign scholars, the genetic mechanisms of clay mineral varve, felsic varve, calcareous varve and organic varve were determined respectively, and the fine flocculation reaction was the main hot theory of varve deposition mechanism in recent years. Then influencing factors of varve deposition were classified into four categories: paleoclimatic factors, palaeogeographic conditions, palaeogeological events and other factors,and the corresponding coupling relationship between different environmental conditions and preferential varve was summarized. Finally, it is proposed that the establishment of varve mechanism model including the combination of multiple factors and the accurate inversion of varve formation by using the perfect model are the main research directions in the future stage, which will provide guidance for the further study of the varve structure of fine-grained sedimentary rocks and the research and application of unconventional oil and gas.
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Abstract:
The research on avulsion has been fully applied in geology, geomorphology, hydrology and other fields, but it has not received sufficient attention from domestic sedimentologists. On the basis of sorting out the relevant controversial issues, the key issues concerning the concept, genesis, evolution, identification and application of avulsion are reviewed and discussed. The main results include :(1) the concept of avulsion, the similarities and differences between avulsion, crevasse splay and diversion, and the narrow definition of avulsion are suggested to explain large-scale river diversion. (2) Clear slope ratio is the main control factor of avulsion, and the anti-flood property of natural embankments (sandy natural embankments or muddy natural embankments) and the geomorphic characteristics of flood plains (surface vegetation, water level, drainage condition, abandoned river) are the secondary control factors of avulsion. (3) The evolution model and identification criteria of avulsion are summarized, and a classification scheme suitable for reservoir sedimentology is proposed. It is suggested that sedimentologists in China should identify different channel types and evolution modes by using the pre-deposition type and the reoccupation type of abandoned channel, or use the classification scheme of stratigraphic transitional type and stratigraphic abrupt type to distinguish the superposition relationship between channels. (4) The application prospect of avulsion in current hot issues such as reservoir configuration and river transformation is discussed. It is suggested that the concept of avulsion should be introduced to improve the evolution of five-level configurations in the field of reservoir architecture, the establishment of geological knowledge base of large-scale watercourse system, and the influence of heterocyclic cycles on reservoir architecture. Sedimentary model of intertransformation between large single channel and network channel in supplementary fluvial transformation. The review and discussion on avulsion not only enrich the current domestic theory of fluvial facies deposition, but also provide more scientific basis for reservoir sedimentologists to restore the evolution mode of ancient channels and establish more accurate geological models.
The research on avulsion has been fully applied in geology, geomorphology, hydrology and other fields, but it has not received sufficient attention from domestic sedimentologists. On the basis of sorting out the relevant controversial issues, the key issues concerning the concept, genesis, evolution, identification and application of avulsion are reviewed and discussed. The main results include :(1) the concept of avulsion, the similarities and differences between avulsion, crevasse splay and diversion, and the narrow definition of avulsion are suggested to explain large-scale river diversion. (2) Clear slope ratio is the main control factor of avulsion, and the anti-flood property of natural embankments (sandy natural embankments or muddy natural embankments) and the geomorphic characteristics of flood plains (surface vegetation, water level, drainage condition, abandoned river) are the secondary control factors of avulsion. (3) The evolution model and identification criteria of avulsion are summarized, and a classification scheme suitable for reservoir sedimentology is proposed. It is suggested that sedimentologists in China should identify different channel types and evolution modes by using the pre-deposition type and the reoccupation type of abandoned channel, or use the classification scheme of stratigraphic transitional type and stratigraphic abrupt type to distinguish the superposition relationship between channels. (4) The application prospect of avulsion in current hot issues such as reservoir configuration and river transformation is discussed. It is suggested that the concept of avulsion should be introduced to improve the evolution of five-level configurations in the field of reservoir architecture, the establishment of geological knowledge base of large-scale watercourse system, and the influence of heterocyclic cycles on reservoir architecture. Sedimentary model of intertransformation between large single channel and network channel in supplementary fluvial transformation. The review and discussion on avulsion not only enrich the current domestic theory of fluvial facies deposition, but also provide more scientific basis for reservoir sedimentologists to restore the evolution mode of ancient channels and establish more accurate geological models.
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Abstract:
The lacustrine fine-grained sedimentary rocks in Dongying Sag have great prospects for unconventional oil and gas resources. However, due to the difficulties of small grain size, rapid phase transition and difficult identification of sequence interface, the traditional sequence stratigraphy cannot accurately divide and contrast the strata. At present, the understanding of organic matter enrichment modle is unclear, which limits the progress of unconventional oil and gas exploration Cyclostratigraphy can divide high-frequency sequences and conduct fine stratigraphic correlation. On the other hand, it explores the process of fine-grained rock deposition driven by astronomical cycles.In order to establish the organic matter enrichment model and predict the sweet spot of shale oil, taking Well LY1 in Dongying Sag, Bohai Bay Basin as an example, the cyclostratigraphy of lacustrine fine-grained sedimentary rocks in the lower Es3(Es3l) and upper Es4(Es4u) submember was analyzed based on core, geochemical analysis and natural gamma logging data.The results show that this set of strata records good astronomical period signals, the Es3l is mainly controlled by eccentricity and precession period, and the Es4u is mainly controlled by eccentricity and obliquity period.An absolute astronomical time scale was established using a stable 405 kyr long eccentricity astronomical tuning, with the top age of the Es3l at 39.40 Ma as the anchor point.The filter curves of long eccentricity, short eccentricity and obliquity were used as the reference curves for the fourth, fifth and sixth order sequence division, and 10 fourth-order sequences and 40 fifth-order sequences were divided.Further, the long eccentricity with significant regional contrast characteristics was used as the scale for linking well correlation, and the high precision isochronous stratigraphic framework of the whole area was established. By discussing the response of fine-grained sedimentary rocks to eccentricity and precession period, we proposed the organic matter enrichment model under warm and wet climate, dry and cold climate conditions, and considered that the maximum eccentricity value is beneficial to organic matter enrichment.
The lacustrine fine-grained sedimentary rocks in Dongying Sag have great prospects for unconventional oil and gas resources. However, due to the difficulties of small grain size, rapid phase transition and difficult identification of sequence interface, the traditional sequence stratigraphy cannot accurately divide and contrast the strata. At present, the understanding of organic matter enrichment modle is unclear, which limits the progress of unconventional oil and gas exploration Cyclostratigraphy can divide high-frequency sequences and conduct fine stratigraphic correlation. On the other hand, it explores the process of fine-grained rock deposition driven by astronomical cycles.In order to establish the organic matter enrichment model and predict the sweet spot of shale oil, taking Well LY1 in Dongying Sag, Bohai Bay Basin as an example, the cyclostratigraphy of lacustrine fine-grained sedimentary rocks in the lower Es3(Es3l) and upper Es4(Es4u) submember was analyzed based on core, geochemical analysis and natural gamma logging data.The results show that this set of strata records good astronomical period signals, the Es3l is mainly controlled by eccentricity and precession period, and the Es4u is mainly controlled by eccentricity and obliquity period.An absolute astronomical time scale was established using a stable 405 kyr long eccentricity astronomical tuning, with the top age of the Es3l at 39.40 Ma as the anchor point.The filter curves of long eccentricity, short eccentricity and obliquity were used as the reference curves for the fourth, fifth and sixth order sequence division, and 10 fourth-order sequences and 40 fifth-order sequences were divided.Further, the long eccentricity with significant regional contrast characteristics was used as the scale for linking well correlation, and the high precision isochronous stratigraphic framework of the whole area was established. By discussing the response of fine-grained sedimentary rocks to eccentricity and precession period, we proposed the organic matter enrichment model under warm and wet climate, dry and cold climate conditions, and considered that the maximum eccentricity value is beneficial to organic matter enrichment.
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Abstract:
With the deepening of exploration from conventional oil and gas to unconventional oil and gas, tight sandstone gas has gradually become a hot spot of exploration. The tight sandstone reservoirs of the second and fourth members of Xujiahe Formation in Xinchang area of Western Sichuan Depression are the main gas producing layers of Xujiahe Formation. There are obvious differences in the mineral composition of sandstone under the influence of different provenance, resulting in significant differences in diagenetic evolution and reservoir properties. Firstly, the provenance direction of the second and fourth member of Xujiahe Formation in Xinchang area was systematically studied through multi-parameter analysis of sandstone distribution, lithic distribution, composition maturity, heavy mineral assemblage and quartz cathode luminescence characteristics. Secondly, the influence of provenance on reservoir characteristics is explored through reservoir petrology characteristics, physical properties, reservoir space characteristics and reservoir diagenesis types. Finally, the comprehensive research results are used to study the differences in reservoir characteristics of the second and fourth member of Xujiahe Formation under Longmen Mountain provenance and Micang Mountain-Daba Mountain provenance. The results show that : (1) the main source area of the second member of Xujiahe Formation is Micang Mountain-Daba Mountain, and the main source area of the fourth member of Xujiahe Formation is Longmen Mountain ;(2)The diagenesis characteristics of reservoirs controlled by different provenance at the same layer are different. In the second member of Xujiahe Formation, Micang Mountain-Daba Mountain provenance has stronger compaction effect than Longmen Mountain provenance, chlorite film is developed, carbonate cementation and siliceous cementation are weak. In the fourth member of Xujiahe Formation, carbonate cuttings of the reservoir controlled by Longmen Mountain provenance greatly improve the anti-compaction ability of the reservoir. The feldspar dissolution of the reservoir controlled by Micang Mountain-Daba Mountain provenance is obvious, and the calcite cementation is slightly stronger than that of the reservoir controlled Longmen Mountain provenance.(3)The characteristics of reservoir diagenesis under different provenance control have obvious differences. Under Longmen Mountain provenance, the chlorite cementation and feldspar dissolution of the second member of Xujiahe Formation mainly change the reservoir physical properties. Carbonate cementation and siliceous cementation are the key factors for reservoir densification. The dissolution of the fourth member is more obvious than that of the second member, and the compaction effect is relatively weak. Under the provenance of Micang Mountain-Daba Mountain, feldspar dissolution and dolomite cementation of the second member of Xujiahe Formation are obvious, and siliceous cementation is the key factor for reservoir densification. The dissolution of the fourth member of Xujiahe Formation and the anti-compaction ability of carbonate debris are the main factors for improving reservoir physical properties and pore development, and carbonate cementation is obvious.
With the deepening of exploration from conventional oil and gas to unconventional oil and gas, tight sandstone gas has gradually become a hot spot of exploration. The tight sandstone reservoirs of the second and fourth members of Xujiahe Formation in Xinchang area of Western Sichuan Depression are the main gas producing layers of Xujiahe Formation. There are obvious differences in the mineral composition of sandstone under the influence of different provenance, resulting in significant differences in diagenetic evolution and reservoir properties. Firstly, the provenance direction of the second and fourth member of Xujiahe Formation in Xinchang area was systematically studied through multi-parameter analysis of sandstone distribution, lithic distribution, composition maturity, heavy mineral assemblage and quartz cathode luminescence characteristics. Secondly, the influence of provenance on reservoir characteristics is explored through reservoir petrology characteristics, physical properties, reservoir space characteristics and reservoir diagenesis types. Finally, the comprehensive research results are used to study the differences in reservoir characteristics of the second and fourth member of Xujiahe Formation under Longmen Mountain provenance and Micang Mountain-Daba Mountain provenance. The results show that : (1) the main source area of the second member of Xujiahe Formation is Micang Mountain-Daba Mountain, and the main source area of the fourth member of Xujiahe Formation is Longmen Mountain ;(2)The diagenesis characteristics of reservoirs controlled by different provenance at the same layer are different. In the second member of Xujiahe Formation, Micang Mountain-Daba Mountain provenance has stronger compaction effect than Longmen Mountain provenance, chlorite film is developed, carbonate cementation and siliceous cementation are weak. In the fourth member of Xujiahe Formation, carbonate cuttings of the reservoir controlled by Longmen Mountain provenance greatly improve the anti-compaction ability of the reservoir. The feldspar dissolution of the reservoir controlled by Micang Mountain-Daba Mountain provenance is obvious, and the calcite cementation is slightly stronger than that of the reservoir controlled Longmen Mountain provenance.(3)The characteristics of reservoir diagenesis under different provenance control have obvious differences. Under Longmen Mountain provenance, the chlorite cementation and feldspar dissolution of the second member of Xujiahe Formation mainly change the reservoir physical properties. Carbonate cementation and siliceous cementation are the key factors for reservoir densification. The dissolution of the fourth member is more obvious than that of the second member, and the compaction effect is relatively weak. Under the provenance of Micang Mountain-Daba Mountain, feldspar dissolution and dolomite cementation of the second member of Xujiahe Formation are obvious, and siliceous cementation is the key factor for reservoir densification. The dissolution of the fourth member of Xujiahe Formation and the anti-compaction ability of carbonate debris are the main factors for improving reservoir physical properties and pore development, and carbonate cementation is obvious.
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Abstract:
The mixed siliciclastic-carbonate sediments (MSS) contain both carbonate and detrital components that can concurrently carry aqueous and provenance signatures in composition. During the early Cambrian, the MSS were widely distributed in the Hannan-Micangshan area, western Yangtze Craton but the factors influencing their development have not been well known. In this study, we performed a combined petrological and sedimentological analysis on the compositions of MSS in the Xiannüdong Formation of the Zhujiaba section, southern Shaanxi. The results indicate that the MSS were formed from the middle to the inner ramp settings in a regressive depositional cycle and the distribution of MSS appears to be more focused on the middle part of each upward-shoaling sequence. Accordingly, detritus- and carbonate-dominated sediments are respectively concentrated in the lower and upper parts of the sequence. It is inferred that detrital sediments and a few low-relief reefs developed in the middle ramp environment and other fine-grained carbonate fractions were mainly transported from shallow-water carbonate depositional settings. In contrast, ooid shoals and reefs are supposed to develop in inner ramp environments with a small quantality of terrigenous sand-sized particles (quartz and lithic fragment). In addition, the petrological evidence indicates that transported (dolomitized) carbonate grains and fine-grained detritus were mixed in the lagoon setting at that time. The development of early Cambrian MSS in the study area may be related to high carbonate productivity of shallow-water environments and active onshore-to-offshore transportation mainly induced by storm currents. This study may provide a case for understanding the factors influencing the development of the deep-time MSS and a reference for oil and gas exploration of Cambrian MSS of the western Yangtze area.
The mixed siliciclastic-carbonate sediments (MSS) contain both carbonate and detrital components that can concurrently carry aqueous and provenance signatures in composition. During the early Cambrian, the MSS were widely distributed in the Hannan-Micangshan area, western Yangtze Craton but the factors influencing their development have not been well known. In this study, we performed a combined petrological and sedimentological analysis on the compositions of MSS in the Xiannüdong Formation of the Zhujiaba section, southern Shaanxi. The results indicate that the MSS were formed from the middle to the inner ramp settings in a regressive depositional cycle and the distribution of MSS appears to be more focused on the middle part of each upward-shoaling sequence. Accordingly, detritus- and carbonate-dominated sediments are respectively concentrated in the lower and upper parts of the sequence. It is inferred that detrital sediments and a few low-relief reefs developed in the middle ramp environment and other fine-grained carbonate fractions were mainly transported from shallow-water carbonate depositional settings. In contrast, ooid shoals and reefs are supposed to develop in inner ramp environments with a small quantality of terrigenous sand-sized particles (quartz and lithic fragment). In addition, the petrological evidence indicates that transported (dolomitized) carbonate grains and fine-grained detritus were mixed in the lagoon setting at that time. The development of early Cambrian MSS in the study area may be related to high carbonate productivity of shallow-water environments and active onshore-to-offshore transportation mainly induced by storm currents. This study may provide a case for understanding the factors influencing the development of the deep-time MSS and a reference for oil and gas exploration of Cambrian MSS of the western Yangtze area.
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Abstract:
In the Early Permian, Junggar Basin was an intracontinental successor rift basin formed after the closure of the Paleo-Asian Ocean. During the syn-rifting stage, the most important source rock, the Lower Permian Fengcheng Formation alkaline lake source rock, was filled in the Mahu Sag on the northwestern margin of the Junggar Basin, but the exact depositional age is still unclear. A detailed petrological analysis of a piece of tuffaceous lithic sandstone was carried out by scanning electron microscopy and energy dispersive analysis, and the results showed that the sample contained a large amount of tuffaceous clasts and volcanic glass (52%), intermediate-felsic lithic clasts (38%), and a small amount of quartz, feldspar and hornblende minerals (10%). The published LA-ICP-MS zircon U-Pb dating of this sample shows that the average age of the five youngest detrital zircons and the youngest age peak are consistent, with an age of 282±4 Ma, suggesting that the early Permian syn-sedimentary volcanic rocks are the major source area, and the mountains in West Junggar and Zhongguai-Luliang uplifts also have been source areas. Combined with the published zircon U-Pb results of two tuffaceous samples at the bottom and top of the alkaline lake deposition, the average age of the five youngest detrital zircon is 284±4 Ma and 279±4 Ma, respectively. The age gradually becomes younger from the bottom to the top, which is the syn-sedimentary record of episodic volcanic eruptions in the syn-rift stage of a rift basin, indicating that the sedimentary age of the Lower Permian Fengcheng Formation alkaline lake is 284-279? Ma.
In the Early Permian, Junggar Basin was an intracontinental successor rift basin formed after the closure of the Paleo-Asian Ocean. During the syn-rifting stage, the most important source rock, the Lower Permian Fengcheng Formation alkaline lake source rock, was filled in the Mahu Sag on the northwestern margin of the Junggar Basin, but the exact depositional age is still unclear. A detailed petrological analysis of a piece of tuffaceous lithic sandstone was carried out by scanning electron microscopy and energy dispersive analysis, and the results showed that the sample contained a large amount of tuffaceous clasts and volcanic glass (52%), intermediate-felsic lithic clasts (38%), and a small amount of quartz, feldspar and hornblende minerals (10%). The published LA-ICP-MS zircon U-Pb dating of this sample shows that the average age of the five youngest detrital zircons and the youngest age peak are consistent, with an age of 282±4 Ma, suggesting that the early Permian syn-sedimentary volcanic rocks are the major source area, and the mountains in West Junggar and Zhongguai-Luliang uplifts also have been source areas. Combined with the published zircon U-Pb results of two tuffaceous samples at the bottom and top of the alkaline lake deposition, the average age of the five youngest detrital zircon is 284±4 Ma and 279±4 Ma, respectively. The age gradually becomes younger from the bottom to the top, which is the syn-sedimentary record of episodic volcanic eruptions in the syn-rift stage of a rift basin, indicating that the sedimentary age of the Lower Permian Fengcheng Formation alkaline lake is 284-279? Ma.
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Abstract:
The Ordos Basin is located in the west of North China Craton, which is at the junction between the stable area of eastern China and the active belt of western China. The provenance system of Ordos Basin is the key to understand the basin-mountain evolution. However, the Early Jurassic provenance system in the northeastern Ordos Basin is still unclear. To address this scientific question, we carried out this study on the Yulin Anya section in the northern Ordos Basin. In this study, the geochemical characteristics of the Lower Jurassic Fuxian Formation sandstones are investigated, and the provenance system of the Fuxian Formation sandstones is discussed using petrological methods and the characteristics of the study area and the adjacent ancient land in terms of Rare Earth Elements (REEs). The findings demonstrate that the Fuxian Formation in the studied area originates from a single provenance area, and that the provenance materials were mainly formed in the recycling orogenic belt. The lithology of the parent rock is granite and a small amount of basic igneous rocks. The distribution of REE exhibits a "Lean slowly to the right" pattern and is generally flat; this pattern is similar to that of the source rocks in the Yinshan orogenic belt and suggests that the Yinshan orogenic belt is the main provenance area for the Fuxian Formation in the northeastern Ordos Basin. The collision of the North China block and the Mongolian block, which occurred from the Permian to Triassic, resulted in the intrusion of numerous granites into the Yinshan orogenic belt. These granites were weathered and denuded during the Early to Middle Jurassic, and they were then transported to the northeastern Ordos Basin for deposition.
The Ordos Basin is located in the west of North China Craton, which is at the junction between the stable area of eastern China and the active belt of western China. The provenance system of Ordos Basin is the key to understand the basin-mountain evolution. However, the Early Jurassic provenance system in the northeastern Ordos Basin is still unclear. To address this scientific question, we carried out this study on the Yulin Anya section in the northern Ordos Basin. In this study, the geochemical characteristics of the Lower Jurassic Fuxian Formation sandstones are investigated, and the provenance system of the Fuxian Formation sandstones is discussed using petrological methods and the characteristics of the study area and the adjacent ancient land in terms of Rare Earth Elements (REEs). The findings demonstrate that the Fuxian Formation in the studied area originates from a single provenance area, and that the provenance materials were mainly formed in the recycling orogenic belt. The lithology of the parent rock is granite and a small amount of basic igneous rocks. The distribution of REE exhibits a "Lean slowly to the right" pattern and is generally flat; this pattern is similar to that of the source rocks in the Yinshan orogenic belt and suggests that the Yinshan orogenic belt is the main provenance area for the Fuxian Formation in the northeastern Ordos Basin. The collision of the North China block and the Mongolian block, which occurred from the Permian to Triassic, resulted in the intrusion of numerous granites into the Yinshan orogenic belt. These granites were weathered and denuded during the Early to Middle Jurassic, and they were then transported to the northeastern Ordos Basin for deposition.
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Abstract:
In the oil-gas exploration of glutenite bodies in Jiyang depression, the complex sand distribution and differential accumulation of oil and water have led us to ponder over and explore the existing deposition filling pattern of nearshore subaqueous fan. Based on the flume simulation experiment and further analysis of the sedimentation filling process, it is considered that the nearshore subaqueous fan in steep slope zone of fault-depressed lacustrine basin can be divided into four sedimentary subfacies, namely, fan-root, fan-middle, fan-inter and fan-terminal, including nine sedimentary microfacies. Compared with the past, the microfacies of slope accumulation lobes in fan-middle and lateral migrating lobes in fan-inter are established. The slope accumulation lobes mostly overlie the early fan body with an external form of "concave bottom and convex top", and its longitudinal cycle presents a unique reverse rhythm. The lateral migrating lobes are characterized by positive rhythm medium and fine sandstones, with remarkable sedimentary filling characteristics. Both of them are in close contact with the semi and deep lake mudstones, fan-terminal mudstones and fan-inter mudstones, which is conducive to forming lithologic traps. In the steep slope zone of Jiyang depression, many wells with the exploration targets of slope accumulation lobes and lateral migrating lobes have successively obtained high and stable industrial oil-gas currents. This has verified the new sedimentary understandings of nearshore subaqueous fan in the oil-gas exploration practice, and broadened a new exploration space of glutenite bodies in the fault-depressed lacustrine basin.
In the oil-gas exploration of glutenite bodies in Jiyang depression, the complex sand distribution and differential accumulation of oil and water have led us to ponder over and explore the existing deposition filling pattern of nearshore subaqueous fan. Based on the flume simulation experiment and further analysis of the sedimentation filling process, it is considered that the nearshore subaqueous fan in steep slope zone of fault-depressed lacustrine basin can be divided into four sedimentary subfacies, namely, fan-root, fan-middle, fan-inter and fan-terminal, including nine sedimentary microfacies. Compared with the past, the microfacies of slope accumulation lobes in fan-middle and lateral migrating lobes in fan-inter are established. The slope accumulation lobes mostly overlie the early fan body with an external form of "concave bottom and convex top", and its longitudinal cycle presents a unique reverse rhythm. The lateral migrating lobes are characterized by positive rhythm medium and fine sandstones, with remarkable sedimentary filling characteristics. Both of them are in close contact with the semi and deep lake mudstones, fan-terminal mudstones and fan-inter mudstones, which is conducive to forming lithologic traps. In the steep slope zone of Jiyang depression, many wells with the exploration targets of slope accumulation lobes and lateral migrating lobes have successively obtained high and stable industrial oil-gas currents. This has verified the new sedimentary understandings of nearshore subaqueous fan in the oil-gas exploration practice, and broadened a new exploration space of glutenite bodies in the fault-depressed lacustrine basin.
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Abstract:
The Mangshan loess deposits located at central China Plain, to the southeastern Chinese Loess Plateau (CLP), preserve high-resolution records of paleoclimatic and paleoenvironmental variations at glacial-interglacial scale due to their large thickness and rapid accumulation rate.In order to explore the mechanism of Mangshan loess formation, in this study, sixteen samples including 4202 detrital zircon particles are analyzed for U-Pb dating from the Mangshan loess-paleosol sequence of the last glacial-interglacial cycle, the results reveal that the main age spectrum peaked at 240 Ma, 440 Ma, 800-1000 Ma, 1800-2000 Ma and 2500 Ma, which indicate that the provenances of Mangshan loess were mainly located at the northeastern Qinghai-Tibetan Plateau and North China Craton. During the last glacial period, denudation materials from the upper reaches of the Yellow River in the northeastern Tibetan Plateau were increased, the eroded sediments were carried by fluvial runoff to the lower reaches of the Yellow River, closing to the Manshan loess deposit site; while during the interglacial period, the contribution of the proximal source materials to the Mangshan loess deposits were intensified and the contribution is increased by 10%. Investigation of provenance of Mangshan loess can help to better understand the late Quaternary sedimentary environment in central China, the coupling processes between tectonics and climate as well as the Yellow River evolution during the Pleistocene.
The Mangshan loess deposits located at central China Plain, to the southeastern Chinese Loess Plateau (CLP), preserve high-resolution records of paleoclimatic and paleoenvironmental variations at glacial-interglacial scale due to their large thickness and rapid accumulation rate.In order to explore the mechanism of Mangshan loess formation, in this study, sixteen samples including 4202 detrital zircon particles are analyzed for U-Pb dating from the Mangshan loess-paleosol sequence of the last glacial-interglacial cycle, the results reveal that the main age spectrum peaked at 240 Ma, 440 Ma, 800-1000 Ma, 1800-2000 Ma and 2500 Ma, which indicate that the provenances of Mangshan loess were mainly located at the northeastern Qinghai-Tibetan Plateau and North China Craton. During the last glacial period, denudation materials from the upper reaches of the Yellow River in the northeastern Tibetan Plateau were increased, the eroded sediments were carried by fluvial runoff to the lower reaches of the Yellow River, closing to the Manshan loess deposit site; while during the interglacial period, the contribution of the proximal source materials to the Mangshan loess deposits were intensified and the contribution is increased by 10%. Investigation of provenance of Mangshan loess can help to better understand the late Quaternary sedimentary environment in central China, the coupling processes between tectonics and climate as well as the Yellow River evolution during the Pleistocene.
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Abstract:
The Carboniferous Yanghugou Formation in the western margin of Ordos Basin has rich exploration potential for oil and gas resources, but due to its complex tectonic activities, its filling process from source to sink and paleogeographic pattern are still controversial. Combined with previous research data, through the analysis of the characteristics of light and heavy minerals, lithic assemblages and rare earth elements, four source sink systems are divided: Alxa in the northwest, Yinshan in the Northeast, North Qilian in the southwest and North Qinling in the southeast. In the Shizuishan-Tudong 4 well area in the northern part of the study area, there is a mixed provenance area between Yinshan and Alxa source-sink system.The tectonic background of the source area of Alxa source sink system is mainly active continental margin, and the other three source sink systems are mainly passive continental margin. The source areas of Alashan, Yinshan and North Qinling source sink systems are mainly felsic, and the North Qilian source sink system is ancient sediments. Based on the division of the source and sink system, the paleogeographic pattern was reconstructed: (1) The source-sink system in Alxa has a long distance for sediment transport and relatively shallow water bodies, and the river-controlled deltas sedimentary system of the marine-land transitional facies develops; (2) The detrital sediments of the Yinshan source-sink system are widely distributed and transported far away. The water body is relatively shallow, and the tidal-controlled deltas sedimentary system of the marine-land transitional facies develops; (3) The source and sink system of the Northern Qilian basin is deep, and Marine shallow shelf sedimentary system is developed in the deep water part, and small river-controlled deltas developed near the shore; (4) The source sink system of the North Qinling has a short sediment transport distance and shallow water body, and developed a barrier island coastal sedimentary system of marine-land transitional facies.The research results are of great significance to guide oil and gas exploration and enrich the theory of source sink system in the western margin of Ordos Basin.
The Carboniferous Yanghugou Formation in the western margin of Ordos Basin has rich exploration potential for oil and gas resources, but due to its complex tectonic activities, its filling process from source to sink and paleogeographic pattern are still controversial. Combined with previous research data, through the analysis of the characteristics of light and heavy minerals, lithic assemblages and rare earth elements, four source sink systems are divided: Alxa in the northwest, Yinshan in the Northeast, North Qilian in the southwest and North Qinling in the southeast. In the Shizuishan-Tudong 4 well area in the northern part of the study area, there is a mixed provenance area between Yinshan and Alxa source-sink system.The tectonic background of the source area of Alxa source sink system is mainly active continental margin, and the other three source sink systems are mainly passive continental margin. The source areas of Alashan, Yinshan and North Qinling source sink systems are mainly felsic, and the North Qilian source sink system is ancient sediments. Based on the division of the source and sink system, the paleogeographic pattern was reconstructed: (1) The source-sink system in Alxa has a long distance for sediment transport and relatively shallow water bodies, and the river-controlled deltas sedimentary system of the marine-land transitional facies develops; (2) The detrital sediments of the Yinshan source-sink system are widely distributed and transported far away. The water body is relatively shallow, and the tidal-controlled deltas sedimentary system of the marine-land transitional facies develops; (3) The source and sink system of the Northern Qilian basin is deep, and Marine shallow shelf sedimentary system is developed in the deep water part, and small river-controlled deltas developed near the shore; (4) The source sink system of the North Qinling has a short sediment transport distance and shallow water body, and developed a barrier island coastal sedimentary system of marine-land transitional facies.The research results are of great significance to guide oil and gas exploration and enrich the theory of source sink system in the western margin of Ordos Basin.
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Abstract:
[Objective] The paleoclimate and environment have changed significantly across the Norian-Rhaetian transition (NRT, Late Triassic), as demonstrated by carbon-isotope fluctuations and biological extinction events. However, the causes of climate perturbations and biotic crises during the NRT remain controversial. It is believed that the eruption of contemporaneous volcanisms (e.g., the Angayucham Large Igneous Province) was the main cause of paleoenvironmental changes during the NRT. The large-scale volcanic activity released a large amount of greenhouse gases, which will result in global temperature rise, carbon-isotope perturbation and biological crisis during the NRT. At present, the majority of NRT studies have focused on the shallow marine strata in the Tethys region, but knowledge on the changes in terrestrial paleoclimate and paleoenvironment and their driving mechanism during the NRT is extremely limited. Studies have shown that terrestrial strata can also faithfully record paleoclimatic and paleoenvironmental changes during geological events, such as the end-Permian mass extinction. However, previous studies mainly focused on paleobotany, sedimentology, organic carbon isotopes and wildfires during the NRT in the Sichuan Basin, but lacked element geochemical evidence, limiting the accurate understanding of the climatic changes in this time interval and the comparison between different research methods. [Methods] In order to tackle this scientific question, we focus on the Norian-Rhaetian section (Xujiahe section) which is located 4.5 km NE of Guangyuan City, northwest Sichuan Basin. Thirty-four samples were collected at a resolution of 10 cm to 2 m in the Xujiahe section for major and trace element compositions. The surface dust and weathered parts of samples were removed with a rasper and then washed with deionized water. After eight hours of oven drying at 50°C, samples were ground into powder using agate mortars. Sample preparations were completed in the School of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology. Analysis of major and trace elements in samples was completed at the Institute of Earth Environment, Chinese Academy of Sciences, Xi 'an. A glass bead was created by fusing 0.6 g of the powdered sample with 6 g of dry lithium tetraborate (Li2B4O7) for 5 minutes at 1000 °C. The glass bead was further scanned by X-ray fluorescence spectrometer (WD-XRF; PANalytical, Ea Almelo, The Netherlands). The analytical accuracy was better than 2%. [Results] The analyzed samples have high Chemical Index of Alteration (CIA) values and Rb/Sr ratios at 105.5 m, 110.2~122.5 m, 119 m, 123.4~123.45 m, 137.7 m of the Xujiahe section, and low CIA values and Rb/Sr ratios at 107 m, 109.5 m, 115.5~116.5 m, 121.5 m and 127~135m of the Xujiahe section. The uppermost part of Upper Norian successions (105.5~129.5m) have CIA values ranging from 59 to 82, with a mean of 73; Rb/Sr ratios ranging from 0.2 to 2.6, with a mean of 1.2; R values ranging from 3.8 to 16.9, with a mean of 8.2. The Norian-Rhaetian boundary interval (NRB, 129.5~135m), CIA values range from 59 to 63, with a mean of 60; Rb/Sr ratios range from 0.5 to 0.6, with a mean of 0.5; R values range from 13.1 to 13.9, with a mean of 13.5. [Conclusions] Results show that the climate fluctuated frequently during the NRT of Xujiahe section in the Sichuan Basin. Late Norian is dominated by warm and humid climate which is interrupted by a short-term cooling event close to the NRB. The prevailing megamonsoon in Pangaea during the Late Triassic may be the main trigger for the frequent climate change and NRB cooling events in the Xujiahe section, but the influence of volcanic activity and wildfire events on the paleoclimate system cannot be ruled out in this time period. To figure out the precise timing of volcanic eruptions and wildfires during the NRT and how they contributed to climate change, more research is needed.
[Objective] The paleoclimate and environment have changed significantly across the Norian-Rhaetian transition (NRT, Late Triassic), as demonstrated by carbon-isotope fluctuations and biological extinction events. However, the causes of climate perturbations and biotic crises during the NRT remain controversial. It is believed that the eruption of contemporaneous volcanisms (e.g., the Angayucham Large Igneous Province) was the main cause of paleoenvironmental changes during the NRT. The large-scale volcanic activity released a large amount of greenhouse gases, which will result in global temperature rise, carbon-isotope perturbation and biological crisis during the NRT. At present, the majority of NRT studies have focused on the shallow marine strata in the Tethys region, but knowledge on the changes in terrestrial paleoclimate and paleoenvironment and their driving mechanism during the NRT is extremely limited. Studies have shown that terrestrial strata can also faithfully record paleoclimatic and paleoenvironmental changes during geological events, such as the end-Permian mass extinction. However, previous studies mainly focused on paleobotany, sedimentology, organic carbon isotopes and wildfires during the NRT in the Sichuan Basin, but lacked element geochemical evidence, limiting the accurate understanding of the climatic changes in this time interval and the comparison between different research methods. [Methods] In order to tackle this scientific question, we focus on the Norian-Rhaetian section (Xujiahe section) which is located 4.5 km NE of Guangyuan City, northwest Sichuan Basin. Thirty-four samples were collected at a resolution of 10 cm to 2 m in the Xujiahe section for major and trace element compositions. The surface dust and weathered parts of samples were removed with a rasper and then washed with deionized water. After eight hours of oven drying at 50°C, samples were ground into powder using agate mortars. Sample preparations were completed in the School of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology. Analysis of major and trace elements in samples was completed at the Institute of Earth Environment, Chinese Academy of Sciences, Xi 'an. A glass bead was created by fusing 0.6 g of the powdered sample with 6 g of dry lithium tetraborate (Li2B4O7) for 5 minutes at 1000 °C. The glass bead was further scanned by X-ray fluorescence spectrometer (WD-XRF; PANalytical, Ea Almelo, The Netherlands). The analytical accuracy was better than 2%. [Results] The analyzed samples have high Chemical Index of Alteration (CIA) values and Rb/Sr ratios at 105.5 m, 110.2~122.5 m, 119 m, 123.4~123.45 m, 137.7 m of the Xujiahe section, and low CIA values and Rb/Sr ratios at 107 m, 109.5 m, 115.5~116.5 m, 121.5 m and 127~135m of the Xujiahe section. The uppermost part of Upper Norian successions (105.5~129.5m) have CIA values ranging from 59 to 82, with a mean of 73; Rb/Sr ratios ranging from 0.2 to 2.6, with a mean of 1.2; R values ranging from 3.8 to 16.9, with a mean of 8.2. The Norian-Rhaetian boundary interval (NRB, 129.5~135m), CIA values range from 59 to 63, with a mean of 60; Rb/Sr ratios range from 0.5 to 0.6, with a mean of 0.5; R values range from 13.1 to 13.9, with a mean of 13.5. [Conclusions] Results show that the climate fluctuated frequently during the NRT of Xujiahe section in the Sichuan Basin. Late Norian is dominated by warm and humid climate which is interrupted by a short-term cooling event close to the NRB. The prevailing megamonsoon in Pangaea during the Late Triassic may be the main trigger for the frequent climate change and NRB cooling events in the Xujiahe section, but the influence of volcanic activity and wildfire events on the paleoclimate system cannot be ruled out in this time period. To figure out the precise timing of volcanic eruptions and wildfires during the NRT and how they contributed to climate change, more research is needed.
The composition and distribution characteristics of biological traces in the Pearl River Delta Front
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Abstract:
The study aims to expound the Pearl River Delta Front in the composition and distribution characteristics of modern biological traces. Through field observation, sampling and laboratory research methods (grain size analysis, CT scanning and three-dimensional reconstruction), the sedimentary environment characteristics of the micro environment of the Pearl River Delta Front, such as the estuary sandbar, underwater branch, subtidal zone and interdistributary bay, were studied. The sedimentary environment in the study area is complex, and the modern biological traces are mainly distributed in the underwater branch and interdistributary bay. The main trace organisms include crabs, ragworms and mudskippers. The main trace organisms in the subtidal zone and the foreslope include sand clams, crabs, and hermit crabs. The traces of crabs and ragworms were mainly trackways (trawl tracks), excretion tracks, dwelling tracks on the layer, and the morphology of burrows in the layer (L-shaped, Y-shaped, U-shaped and I-shaped). Mudskipper traces are mainly trackways and dwelling tracks on the layer. Hermit crab traces are trackways (trawl tracks) on the layer. The composition and distribution characteristics of biological traces in the Pearl River Delta Front will provide a modern empirical basis and basis for the paleoichnology of the Delta front and the reconstruction of the paleo-sedimentary environment of the Delta front.
The study aims to expound the Pearl River Delta Front in the composition and distribution characteristics of modern biological traces. Through field observation, sampling and laboratory research methods (grain size analysis, CT scanning and three-dimensional reconstruction), the sedimentary environment characteristics of the micro environment of the Pearl River Delta Front, such as the estuary sandbar, underwater branch, subtidal zone and interdistributary bay, were studied. The sedimentary environment in the study area is complex, and the modern biological traces are mainly distributed in the underwater branch and interdistributary bay. The main trace organisms include crabs, ragworms and mudskippers. The main trace organisms in the subtidal zone and the foreslope include sand clams, crabs, and hermit crabs. The traces of crabs and ragworms were mainly trackways (trawl tracks), excretion tracks, dwelling tracks on the layer, and the morphology of burrows in the layer (L-shaped, Y-shaped, U-shaped and I-shaped). Mudskipper traces are mainly trackways and dwelling tracks on the layer. Hermit crab traces are trackways (trawl tracks) on the layer. The composition and distribution characteristics of biological traces in the Pearl River Delta Front will provide a modern empirical basis and basis for the paleoichnology of the Delta front and the reconstruction of the paleo-sedimentary environment of the Delta front.
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Abstract:
[Objective] Clinoform growth is generally found in lacustrine or marine basins, and its growth mode can reveal the changes of sediment supply, lake level and deep-water sand delivery pattern. The typical clinoform growth styles are identified in middle-upper parts of the Yanchang Formation based on newly obtained 3D seismic data in southwestern Ordos Basin. This discovery has changed the traditional understanding of “flat-filling” deposition of the Yanchang Formation, provided a new idea for analyzing the distribution of sandstone and reservoir prediction from delta to deep-water area. [Methods] Based on the 3D seismic and drilling data from the Qingcheng area in southwestern Ordos Basin, the middle-upper parts of the Yanchang Formation can be divided into 6 clinothems named F1-F6 respectively, guided by the clinoform growth theory. The characteristics of the clinothems of F1-F4 were described quantitatively, which have a relatively complete slope form. [Results] Firstly, the result shows that the four clinothems have the similar morphological characteristics accroding to the representative seismic profiles in the study area. All of the four clinothems have lenticular external morphology and S-shaped internal reflection structure. Secondly, the sedimentary time span of one clinothem is about 4 to 6 million years. Thirdly, The clinothems of F1-F4 can be quantitatively divided into two types, including “thick-topset and thin-foreset” and “thin-topset and thick-foreset” based on the strata thickness. The clinothem of F1 belongs to the former type, while the other three clinothems belong to the latter type. Fourthly, two types of shoreline trajectories were identified in this paper, including flat of 0-0.5° and slightly rising of 0.5-1°. The trajectory angle of F2 is 0.366-0.489° and the angle of F3 is 0.256-0.275°. While the trajectory angle of F4 is 0.475-0.673°, which has a slight increase compared with the previous period of F2 and F3. Moreover, the shoreline trajectories of F2 and F3 are flat, while the shoreline trajectories of F4 are slightly rising. [Conclusions] The F1 period is under the largest lake basin stage and aggradation dominated clinothems were formed with the sandstone concentrated in the topset within poor sediment. Since the poor sediment supply in the F1 period, the thickness of F1 is thinner than the other three clinothems. As the enhancement of sediment supply and the overall decline of lake level, progradation dominated clinothems were formed during the F2-F3 period. The clinothems of F2 and F3 are both progradation dominated clinothems with abundant sandstone in the deep water, which have flat shoreline trajectories. While in the F4 period, the clinothems were controlled by aggradation-progradation. The clinothem of F4 has slightly rising shoreline trajectories because of the rising lake level. And sandstone is abundant in the topset and deep-water area during the period of F4. It is concluded that the sediment supply and lake level change are the main controlling factors of clinoform growth and distribution of sandstone in the study area. With the gradual abundance of sediment supply and the overall regression of lake level, the type of clinothems changed from aggradation dominated to progradation dominated and the sandstone in deep lake area gradually enriched.
[Objective] Clinoform growth is generally found in lacustrine or marine basins, and its growth mode can reveal the changes of sediment supply, lake level and deep-water sand delivery pattern. The typical clinoform growth styles are identified in middle-upper parts of the Yanchang Formation based on newly obtained 3D seismic data in southwestern Ordos Basin. This discovery has changed the traditional understanding of “flat-filling” deposition of the Yanchang Formation, provided a new idea for analyzing the distribution of sandstone and reservoir prediction from delta to deep-water area. [Methods] Based on the 3D seismic and drilling data from the Qingcheng area in southwestern Ordos Basin, the middle-upper parts of the Yanchang Formation can be divided into 6 clinothems named F1-F6 respectively, guided by the clinoform growth theory. The characteristics of the clinothems of F1-F4 were described quantitatively, which have a relatively complete slope form. [Results] Firstly, the result shows that the four clinothems have the similar morphological characteristics accroding to the representative seismic profiles in the study area. All of the four clinothems have lenticular external morphology and S-shaped internal reflection structure. Secondly, the sedimentary time span of one clinothem is about 4 to 6 million years. Thirdly, The clinothems of F1-F4 can be quantitatively divided into two types, including “thick-topset and thin-foreset” and “thin-topset and thick-foreset” based on the strata thickness. The clinothem of F1 belongs to the former type, while the other three clinothems belong to the latter type. Fourthly, two types of shoreline trajectories were identified in this paper, including flat of 0-0.5° and slightly rising of 0.5-1°. The trajectory angle of F2 is 0.366-0.489° and the angle of F3 is 0.256-0.275°. While the trajectory angle of F4 is 0.475-0.673°, which has a slight increase compared with the previous period of F2 and F3. Moreover, the shoreline trajectories of F2 and F3 are flat, while the shoreline trajectories of F4 are slightly rising. [Conclusions] The F1 period is under the largest lake basin stage and aggradation dominated clinothems were formed with the sandstone concentrated in the topset within poor sediment. Since the poor sediment supply in the F1 period, the thickness of F1 is thinner than the other three clinothems. As the enhancement of sediment supply and the overall decline of lake level, progradation dominated clinothems were formed during the F2-F3 period. The clinothems of F2 and F3 are both progradation dominated clinothems with abundant sandstone in the deep water, which have flat shoreline trajectories. While in the F4 period, the clinothems were controlled by aggradation-progradation. The clinothem of F4 has slightly rising shoreline trajectories because of the rising lake level. And sandstone is abundant in the topset and deep-water area during the period of F4. It is concluded that the sediment supply and lake level change are the main controlling factors of clinoform growth and distribution of sandstone in the study area. With the gradual abundance of sediment supply and the overall regression of lake level, the type of clinothems changed from aggradation dominated to progradation dominated and the sandstone in deep lake area gradually enriched.
, Available online
Abstract:
[Objective] Multi-types of shore-parallel sandstone bodies are ubiquitous in the delta to shallow water area on the shelf, and their morphologies, scales, and spatial-temporal patterns comprehensively responded to hydrodynamic processes, sediment supply, and climate changes, thus recording plenty of geological information. Meanwhile, they are favorable reservoir sandstone bodies for stratigraphic trap exploration. This study intended to finely interpret the high amplitude and wedge-shaped shore-parallel sandstone bodies of the Huizhou area in the Pearl River Mouth Basin of the South China Sea and discuss their controlling evolutionary factors. [Methods] Based on well and seismic data, detailed studies were conducted on the high-resolution stratigraphic framework of the Hanjiang and Zhujiang Formations, Lower-Middle Miocene, and wedge-shaped shore-parallel sandstone bodies were identified in the forced regressive systems tracts within several sequences. Combined with 3D seismic interpretation, spectral decomposition, and other analysis tools of seismic sedimentology, analysis based on core and log data, and comparisons with modern deposits, the characteristics of the shelf-parallel sandstone bodies were discussed in detail. [Results and Discussions] According to basic principles of sequence stratigraphy, the interval of interest strata could be divided into 15 sequences by 16 sequence boundaries. Other surfaces like the maximum flooding surfaces, the maximum regressive surfaces, and the basal surfaces of forced regression can also be identified in most sequences. The shore-parallel sandstone bodies could be identified as mainly ridge-shaped on seismic sections and primarily composed of three recognizable seismic reflections, including a high-amplitude seismic reflection in the head, high-angle shingling progradational reflections in the middle, and low-amplitude reflections in the tail. Meanwhile, these shelf-parallel sandstone bodies tended to widen from northeast to southwest, with significant densely arranged striated internal structures. Combining seismic, well-log, and core data, it is deduced that these sandstone bodies were mainly ancient beach ridges. Closely spaced, sharply outlined beach ridges in zone2 may be related to continuous progradation, and greater spacing beach ridges in zone3 may be related to discontinuous progradation. According to pieces of evidence such as toplap contact relationship in the seismic section, the existence of sharp-based coarsening-upward sandstones, irregular variation of sandstone bodies' thickness in depositional-dip direction, and wave erosion surface in the core, it was conducted that the development of these ancient beach ridges was mainly controlled by forced regression and stable high sediment supply. [Conclusions] In conclusion, the pattern of beach ridges in the study area was as follows: in the early stage of forced regression, broad spacing beach ridges in zone3 formed with low progradation rates; in the later stage of the forced regression, sharply outlined and narrow beach ridges in zone2 formed with high progradation rates; at the end of forced regression, gently sloping with continuous internal structures of zone1 formed with low progradation rates and pinched out seaward. Based on the analysis of ancient ridge planar distribution characteristics, it was speculated that its formation and evolution might be controlled by the southwest-oriented paleocurrent environment of the study area. Moreover, according to the earliest ancient beach ridge development time, it was proposed that the southwest-oriented paleocurrent should exist since ca. 21 Ma and affected the development of the Pearl River delta.
[Objective] Multi-types of shore-parallel sandstone bodies are ubiquitous in the delta to shallow water area on the shelf, and their morphologies, scales, and spatial-temporal patterns comprehensively responded to hydrodynamic processes, sediment supply, and climate changes, thus recording plenty of geological information. Meanwhile, they are favorable reservoir sandstone bodies for stratigraphic trap exploration. This study intended to finely interpret the high amplitude and wedge-shaped shore-parallel sandstone bodies of the Huizhou area in the Pearl River Mouth Basin of the South China Sea and discuss their controlling evolutionary factors. [Methods] Based on well and seismic data, detailed studies were conducted on the high-resolution stratigraphic framework of the Hanjiang and Zhujiang Formations, Lower-Middle Miocene, and wedge-shaped shore-parallel sandstone bodies were identified in the forced regressive systems tracts within several sequences. Combined with 3D seismic interpretation, spectral decomposition, and other analysis tools of seismic sedimentology, analysis based on core and log data, and comparisons with modern deposits, the characteristics of the shelf-parallel sandstone bodies were discussed in detail. [Results and Discussions] According to basic principles of sequence stratigraphy, the interval of interest strata could be divided into 15 sequences by 16 sequence boundaries. Other surfaces like the maximum flooding surfaces, the maximum regressive surfaces, and the basal surfaces of forced regression can also be identified in most sequences. The shore-parallel sandstone bodies could be identified as mainly ridge-shaped on seismic sections and primarily composed of three recognizable seismic reflections, including a high-amplitude seismic reflection in the head, high-angle shingling progradational reflections in the middle, and low-amplitude reflections in the tail. Meanwhile, these shelf-parallel sandstone bodies tended to widen from northeast to southwest, with significant densely arranged striated internal structures. Combining seismic, well-log, and core data, it is deduced that these sandstone bodies were mainly ancient beach ridges. Closely spaced, sharply outlined beach ridges in zone2 may be related to continuous progradation, and greater spacing beach ridges in zone3 may be related to discontinuous progradation. According to pieces of evidence such as toplap contact relationship in the seismic section, the existence of sharp-based coarsening-upward sandstones, irregular variation of sandstone bodies' thickness in depositional-dip direction, and wave erosion surface in the core, it was conducted that the development of these ancient beach ridges was mainly controlled by forced regression and stable high sediment supply. [Conclusions] In conclusion, the pattern of beach ridges in the study area was as follows: in the early stage of forced regression, broad spacing beach ridges in zone3 formed with low progradation rates; in the later stage of the forced regression, sharply outlined and narrow beach ridges in zone2 formed with high progradation rates; at the end of forced regression, gently sloping with continuous internal structures of zone1 formed with low progradation rates and pinched out seaward. Based on the analysis of ancient ridge planar distribution characteristics, it was speculated that its formation and evolution might be controlled by the southwest-oriented paleocurrent environment of the study area. Moreover, according to the earliest ancient beach ridge development time, it was proposed that the southwest-oriented paleocurrent should exist since ca. 21 Ma and affected the development of the Pearl River delta.
, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.064
Abstract:
[Objective] The latest 3D seismic data displays a large number of strong reflections seismic events progradation in Yanchang Formation, which is quite different from the traditional stratigraphic scheme of "flat rise flat fall and equal thickness distribution". This difference provides a new perspective for re-understanding the stratigraphic framework of Yanchang Formation. [Methods] The seismic facies, sequence stratigraphy and sedimentary system in Longdong area of Ordos Basin are systematically studied through core observation, well seismic calibration and 3D seismic interpretation combined with seismic inversion technology. [Results] The continuous seismic events of strong reflections in Yanchang Formation can indicate the deposition of condensed layers during lake flooding. The seismic facies along provenance and across provenance are quite different. The seismic profiles along the provenance can be divided into three types: sub-parallel structures with medium amplitude and medium continuity, progradational reflections with strong amplitude and strong continuity, and disordered structures with low amplitude and low continuity, among which the progradational type are most obvious. The seismic profiles across the provenance can be divided into three types: parallel structures with strong amplitude and strong continuity, mound structure with medium-strong amplitude and strong continuity, disordered structures with low amplitude and low continuity. The lake basin evolution of Yanchang Formation in Longdong area with some rapid lake transgression and slow lake regression fluctuating processes can be divided into a third-order sequence unit consisting of multi-stage transgressive-regressive (T-R) system tracts. The sequence units prograde and overlapped as the form of wedges toward the center of the lake, and develop the sedimentary sequence of "slope rich in mudstone and both top-set and bottom-set rich in sand bodies". [Conclusion] The conclusion of this paper is quite different from the traditional sedimentary model, which is manifested in three aspects. First, the mudstone marker layer has not changed and the corresponding relationship between individual wells has changed. Second, the extent of lake in Yanchang Formation has not changed, however, the evolution process of basin filling has changed. Third, the overall distribution of sandstone has not changed, while the connectivity between sand layers has changed.
[Objective] The latest 3D seismic data displays a large number of strong reflections seismic events progradation in Yanchang Formation, which is quite different from the traditional stratigraphic scheme of "flat rise flat fall and equal thickness distribution". This difference provides a new perspective for re-understanding the stratigraphic framework of Yanchang Formation. [Methods] The seismic facies, sequence stratigraphy and sedimentary system in Longdong area of Ordos Basin are systematically studied through core observation, well seismic calibration and 3D seismic interpretation combined with seismic inversion technology. [Results] The continuous seismic events of strong reflections in Yanchang Formation can indicate the deposition of condensed layers during lake flooding. The seismic facies along provenance and across provenance are quite different. The seismic profiles along the provenance can be divided into three types: sub-parallel structures with medium amplitude and medium continuity, progradational reflections with strong amplitude and strong continuity, and disordered structures with low amplitude and low continuity, among which the progradational type are most obvious. The seismic profiles across the provenance can be divided into three types: parallel structures with strong amplitude and strong continuity, mound structure with medium-strong amplitude and strong continuity, disordered structures with low amplitude and low continuity. The lake basin evolution of Yanchang Formation in Longdong area with some rapid lake transgression and slow lake regression fluctuating processes can be divided into a third-order sequence unit consisting of multi-stage transgressive-regressive (T-R) system tracts. The sequence units prograde and overlapped as the form of wedges toward the center of the lake, and develop the sedimentary sequence of "slope rich in mudstone and both top-set and bottom-set rich in sand bodies". [Conclusion] The conclusion of this paper is quite different from the traditional sedimentary model, which is manifested in three aspects. First, the mudstone marker layer has not changed and the corresponding relationship between individual wells has changed. Second, the extent of lake in Yanchang Formation has not changed, however, the evolution process of basin filling has changed. Third, the overall distribution of sandstone has not changed, while the connectivity between sand layers has changed.
, Available online
Abstract:
Large scale lacustrine carbonate sediments were developed in the upper fourth member of Shahejie Formation (Es4s) in the western Dongying Depression, whereas its development pattern and depositional model is still controversial. Based on analysis of cores, thin-sections and well logging data, rock types, sedimentary microfacies and their spatiotemporal distribution of the Es4s carbonates in the Dongying Depression were detailedly studied. The results are as follows: (1) There are mainly eight rock types of lacustrine carbonates in the study area. Based on their lithological associations, four sedimentary microfacies were recognized, namely reef-shoal, shoal-intershoal, mixed to muddy-lime flat and storm-gravity flow. (2) The study area was macroscopically characterized by a small structural platform during the period of lacustrine carbonate deposition, and the development and spatial distribution of microfacies were mainly controlled by two factors, i.e. paleo-geomorphology and paleo-wind field. The paleo-geomorphology determined developing types of sedimentary microfacies and their distribution. On the top of the platform, high-energy facies belts composed of reef-shoal and shoal microfacies developed in the direction of broad lake basin, while mixed-mud flat deposited in the landward direction. On the east and south slope of the platform, storm-gravity flows were well developed. In addition, hydrodynamic differences between windward and leeward sides caused by the prevailing southeast wind affected the sedimentary distribution, which facilitated the formation of reef-shoal complex and large shallow shoal facies belt, affected the main high-hydrodynamic facies NE-SW-direction distribution vertically to wind and wave movement and becoming contiguous belt, and promoted the gradual expansion of these high-hydrodynamic facies southward and eastward. It is proposed that the deposition model was like a wind-wave and geomorphology integratedly controlled carbonate platform, which can provide significant guidance for the further oil and gas exploration and prediction of favorable phase zones in lacustrine carbonates.
Large scale lacustrine carbonate sediments were developed in the upper fourth member of Shahejie Formation (Es4s) in the western Dongying Depression, whereas its development pattern and depositional model is still controversial. Based on analysis of cores, thin-sections and well logging data, rock types, sedimentary microfacies and their spatiotemporal distribution of the Es4s carbonates in the Dongying Depression were detailedly studied. The results are as follows: (1) There are mainly eight rock types of lacustrine carbonates in the study area. Based on their lithological associations, four sedimentary microfacies were recognized, namely reef-shoal, shoal-intershoal, mixed to muddy-lime flat and storm-gravity flow. (2) The study area was macroscopically characterized by a small structural platform during the period of lacustrine carbonate deposition, and the development and spatial distribution of microfacies were mainly controlled by two factors, i.e. paleo-geomorphology and paleo-wind field. The paleo-geomorphology determined developing types of sedimentary microfacies and their distribution. On the top of the platform, high-energy facies belts composed of reef-shoal and shoal microfacies developed in the direction of broad lake basin, while mixed-mud flat deposited in the landward direction. On the east and south slope of the platform, storm-gravity flows were well developed. In addition, hydrodynamic differences between windward and leeward sides caused by the prevailing southeast wind affected the sedimentary distribution, which facilitated the formation of reef-shoal complex and large shallow shoal facies belt, affected the main high-hydrodynamic facies NE-SW-direction distribution vertically to wind and wave movement and becoming contiguous belt, and promoted the gradual expansion of these high-hydrodynamic facies southward and eastward. It is proposed that the deposition model was like a wind-wave and geomorphology integratedly controlled carbonate platform, which can provide significant guidance for the further oil and gas exploration and prediction of favorable phase zones in lacustrine carbonates.
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Abstract:
The study of hyperpycnal flow deposits has important theoretical and practical significance for scientific research of sedimentary geology, prevention and control of geological disasters, oil and gas exploration and development, etc. It has thus become one of the research hotspots in geology. On the basis of previous research results, the concept, research and development course, formation conditions, evolution process and sedimentary characteristics of hyperpycnal flow are systematically expounded combining with examples from different basins. The formation of hyperpycnal flow will be influenced by climate, structure, topography, material supply and other factors, which are interrelated. There are two kinds of transport modes of sediment by hyperpycnal flow: suspended load and bed load. The couplets of inverse grain beddings and positive grain beddings can be used as one of the identification marks of hyperpycnal flow deposits. But the identification marks of hyperpycnal flow deposits (hyperpycnites) should also be comprehensively analyzed based on their sedimentary background, sedimentary position, sedimentary structure, rock structure, sedimentary sequence, paleontological fossils and many other characteristics. Even if it is a complete deposition process of hyperpycnal flow, its deposition characteristics and identification marks are not unique under different deposition positions and backgrounds, so it is difficult to use a single scale to measure hyperpycnal flow deposition under different conditions. The grain size and thickness of hyperpycnal flow deposits decrease from the near (distributary) estuary to the far fan end of hyperpycnal flow deposits. The erosion and filling of the proximal main channels are the main factors, forming subaqueous channels; The middle part is a transitional area, and sedimentary units such as undercut channel, natural dike, channel side edge, branch channel and leafy body will be formed in turn. The distant lobes are characterized by fine-grained deposition and thin layers. Looking forward to the future, in-depth research can be carried out in the improvement of hyperpycnal flow deposits theory, identification of ancient hyperpycnal flow deposits characteristics, study of hyperpycnal flow deposits characteristics of terrestrial lake basin, study of hyperpycnites formation, hyperpycnites reservoir prediction, geochemical element analysis, etc.; innovative research can also be carried out in hyperpycnal flow deposits flume experiment, underwater observation, numerical simulation and other research methods.
The study of hyperpycnal flow deposits has important theoretical and practical significance for scientific research of sedimentary geology, prevention and control of geological disasters, oil and gas exploration and development, etc. It has thus become one of the research hotspots in geology. On the basis of previous research results, the concept, research and development course, formation conditions, evolution process and sedimentary characteristics of hyperpycnal flow are systematically expounded combining with examples from different basins. The formation of hyperpycnal flow will be influenced by climate, structure, topography, material supply and other factors, which are interrelated. There are two kinds of transport modes of sediment by hyperpycnal flow: suspended load and bed load. The couplets of inverse grain beddings and positive grain beddings can be used as one of the identification marks of hyperpycnal flow deposits. But the identification marks of hyperpycnal flow deposits (hyperpycnites) should also be comprehensively analyzed based on their sedimentary background, sedimentary position, sedimentary structure, rock structure, sedimentary sequence, paleontological fossils and many other characteristics. Even if it is a complete deposition process of hyperpycnal flow, its deposition characteristics and identification marks are not unique under different deposition positions and backgrounds, so it is difficult to use a single scale to measure hyperpycnal flow deposition under different conditions. The grain size and thickness of hyperpycnal flow deposits decrease from the near (distributary) estuary to the far fan end of hyperpycnal flow deposits. The erosion and filling of the proximal main channels are the main factors, forming subaqueous channels; The middle part is a transitional area, and sedimentary units such as undercut channel, natural dike, channel side edge, branch channel and leafy body will be formed in turn. The distant lobes are characterized by fine-grained deposition and thin layers. Looking forward to the future, in-depth research can be carried out in the improvement of hyperpycnal flow deposits theory, identification of ancient hyperpycnal flow deposits characteristics, study of hyperpycnal flow deposits characteristics of terrestrial lake basin, study of hyperpycnites formation, hyperpycnites reservoir prediction, geochemical element analysis, etc.; innovative research can also be carried out in hyperpycnal flow deposits flume experiment, underwater observation, numerical simulation and other research methods.
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Abstract:
Based on the observation and identification of cores, cast thin sections and cathode luminescence, using image recognition software to obtain quantitative data of the content of rock components and pore parameters etc, and the pore characteristics, genesis and evolution models of different lithological pores in the first member of Canglangpu Formation of Cambrian Terreneuvian in central and northern Sichuan are studied. The results show that: the pore type of the first member of Canglangpu Formation is mainly intragranular dissolved pore, which has the best positive correlation with the total face rate, followed by intergranular dissolved pore. The higher oolite/terrigenous sand content ratio is an important material basis for pore development, and dissolution is the most favorable factor for pore development. Because the selective dissolution of atmospheric water in the syngenetic period is the key to the Formation of the most important dissolution pores in oolitic in the first member of Canglangpu Formation, while the dolomitization in the quasi syngenetic and burial period enhances the compression resistance of rocks, reduces the solid volume and increases the pores, and the dissolution in the burial period is along the fractures by tectonic disruption and early pores to expand. terrigenous sand, cementation, compaction and pressure dissolution are not conducive to the development of pores in the first member of Canglangpu Formation. Therefore, favorable carbonate components and subsequent diagenesis and tectonism have affected the development and evolution of pores, and formed the lithologic sequence characteristics of decreasing pore face rate in turn: bright crystal oolitic dolomite, oolitic dolomite with sandy, sandy oolitic dolomite, fine-grained lithic sandstone, limestone etc.
Based on the observation and identification of cores, cast thin sections and cathode luminescence, using image recognition software to obtain quantitative data of the content of rock components and pore parameters etc, and the pore characteristics, genesis and evolution models of different lithological pores in the first member of Canglangpu Formation of Cambrian Terreneuvian in central and northern Sichuan are studied. The results show that: the pore type of the first member of Canglangpu Formation is mainly intragranular dissolved pore, which has the best positive correlation with the total face rate, followed by intergranular dissolved pore. The higher oolite/terrigenous sand content ratio is an important material basis for pore development, and dissolution is the most favorable factor for pore development. Because the selective dissolution of atmospheric water in the syngenetic period is the key to the Formation of the most important dissolution pores in oolitic in the first member of Canglangpu Formation, while the dolomitization in the quasi syngenetic and burial period enhances the compression resistance of rocks, reduces the solid volume and increases the pores, and the dissolution in the burial period is along the fractures by tectonic disruption and early pores to expand. terrigenous sand, cementation, compaction and pressure dissolution are not conducive to the development of pores in the first member of Canglangpu Formation. Therefore, favorable carbonate components and subsequent diagenesis and tectonism have affected the development and evolution of pores, and formed the lithologic sequence characteristics of decreasing pore face rate in turn: bright crystal oolitic dolomite, oolitic dolomite with sandy, sandy oolitic dolomite, fine-grained lithic sandstone, limestone etc.
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Abstract:
The distributions and compositions of various biomarkers in the crude oils from the Yingxi area in the western Qaidam Basin were analyzed by GC-MS and GC-MS-MS so as to determine their maturity and origin. The analytical results demonstrate that these oils have some common geochemical characteristics such as an even carbon predominance at nC20 and nC22 in the normal alkane series, lower Pr/Ph ratio (<0.60), higher Ph/nC18 ratio (>1.30) and higher gammacerane index (0.90-1.36), consistent with the geological background of saline depositional environment during Paleogene in the western Qaidam Basin. Based on the distribution and relative abundance of extended tricyclic terpanes in different crude oils in the studied area, they could be classified into two types. One of them from the well Shi 62 and Shixi 58-1 has unusually abundant C19-49 tricyclic terpanes, such as C19-30T/C27-35H>1.60 and C23T/C30H>1.40, accompanied by higher steranes/hopanes ratio (>4.50) and higher β-carotane/nC37 ratio (>3.20), suggesting that algae are their main contributor. The other one from the well Shi 57 and Shi 61 has moderate extended C19-30 tricyclic terpanes because of lower C19-30T/C27-35H ratio (<0.50), C23T/C30H ratio (<0.55), steranes/hopanes ratio (<2.0) and β-carotane/nC37 ratio (<1.50), demonstrating that the algae biological input is relatively low compared to the first kind of crude oils. Based on the maturity parameters of steranes, terpanes and diamondoid hydrocarbons, the maturity of these oils from the Yingxi area is similar and their Ro values are about 1.1%-1.3%, suggesting that they were generated after the hydrocarbon generation peak but before condensates stage. In other words, it is that biological input, not maturity, is a main factor to affect the relative abundance of extended tricyclic terpanes in different oils from the Yingxi area. Therefore, two kinds of crude oils in the studied area have their own sources, and much more attention should be paid to them in next exploration.
The distributions and compositions of various biomarkers in the crude oils from the Yingxi area in the western Qaidam Basin were analyzed by GC-MS and GC-MS-MS so as to determine their maturity and origin. The analytical results demonstrate that these oils have some common geochemical characteristics such as an even carbon predominance at nC20 and nC22 in the normal alkane series, lower Pr/Ph ratio (<0.60), higher Ph/nC18 ratio (>1.30) and higher gammacerane index (0.90-1.36), consistent with the geological background of saline depositional environment during Paleogene in the western Qaidam Basin. Based on the distribution and relative abundance of extended tricyclic terpanes in different crude oils in the studied area, they could be classified into two types. One of them from the well Shi 62 and Shixi 58-1 has unusually abundant C19-49 tricyclic terpanes, such as C19-30T/C27-35H>1.60 and C23T/C30H>1.40, accompanied by higher steranes/hopanes ratio (>4.50) and higher β-carotane/nC37 ratio (>3.20), suggesting that algae are their main contributor. The other one from the well Shi 57 and Shi 61 has moderate extended C19-30 tricyclic terpanes because of lower C19-30T/C27-35H ratio (<0.50), C23T/C30H ratio (<0.55), steranes/hopanes ratio (<2.0) and β-carotane/nC37 ratio (<1.50), demonstrating that the algae biological input is relatively low compared to the first kind of crude oils. Based on the maturity parameters of steranes, terpanes and diamondoid hydrocarbons, the maturity of these oils from the Yingxi area is similar and their Ro values are about 1.1%-1.3%, suggesting that they were generated after the hydrocarbon generation peak but before condensates stage. In other words, it is that biological input, not maturity, is a main factor to affect the relative abundance of extended tricyclic terpanes in different oils from the Yingxi area. Therefore, two kinds of crude oils in the studied area have their own sources, and much more attention should be paid to them in next exploration.
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Abstract:
Oil sands are imperative mineral resources. With the expanding request for oil and gas, oil sands and other unconventional oil and gas resources have made up the energy crevice in later a long time. The oil sands within the Cretaceous McMurray Formation are plenteous in Athabasca of Alberta Basin. In any case, research on the Athabasca oil sands not only has few comprehensive analysis of the McMurray Formation oil sands in the Mackay River area, but the source of the oil sands is still controversial. [Methods]There are 25 oil sand samples from the Cretaceous McMurray Formation in the Mackay River of Athabasca in Alberta Basin are explored by precise geochemical investigation. Soluble organic matter extraction, family component separation, saturated hydrocarbon gas chromatography, saturated hydrocarbon and aromatic hydrocarbon chromatography and mass spectrometry were performed on the 25 samples. The sedimentary environment, biological origin and maturity of organic matter in the bituminous source rocks of the oil sands of the McMurray Formation are identified based on the analysis results of the family components and biomarker parameters of these samples. [Results and Discussions] The results showed that the n-alkanes were completely consumed, the content of acyclic isoprene was lower than the detection limit, and there were a lot of iso-alkanes and unresolved compounds in the samples. Hopanes endure destruction, and a small amount of 25-norhopanes was identified. The steranes were destroyed continuously, the abundance of pregnane and homopregnane was higher, the regular steranes suffered a loss, and the content of C27 regular steranes was relatively high. The tricyclic terpenes were intact, and the baseline was slightly raised, showing high content of C23 tricyclic terpenes. The characteristic peaks of the triaromatic steranes are obvious and easy to identify. The distribution of each sample of the McMurray Formation oil sands asphalt is concentrated in the C26-C27-C28 triangular diagram triangle and C19+20-C21-C23 tricyclic terpenes triangular diagram, and all have the advantages of C23 tricyclic terpenes and C27 regular steranes and C28 triaromatic steranes, indicating that the oil sands of the McMurray Formation have the same origin. In addition, these characteristics indicate that the hydrocarbons in the oil sands are derived from lower aquatic organisms and algae deposited in Marine facies sedimentary source rock. The equivalent vitrinite reflectance calculated by MPI and MDR extending from 0.55% to 0.77% illustrates low oil sand maturity. The McMurray Formation tar sands have high non-hydrocarbon and asphaltene content, low API ratio, high relative density and viscosity. [Conclusions] The characteristics of physical properties and biomarkers indicate that the oil sands of the McMurray Formation are caused by serious biodegradation, and the biodegradation level of the samples is inferred to PM 7 according to the scheme proposed by Peters and Moldowan. Based on the comparative analysis of biomarker composition characteristics of source rocks in the study area, it is speculated that the McMurray Formation oil sands asphalt may be contributed by one of the following three groups of source rocks: The Lower Jurassic Nordegg/Cordondale Formation, the Keg River Formation of the Middle Devonian Elk Point Group, and the Lodgepole Formation of the Upper Devonian Series are the Mississippian.
Oil sands are imperative mineral resources. With the expanding request for oil and gas, oil sands and other unconventional oil and gas resources have made up the energy crevice in later a long time. The oil sands within the Cretaceous McMurray Formation are plenteous in Athabasca of Alberta Basin. In any case, research on the Athabasca oil sands not only has few comprehensive analysis of the McMurray Formation oil sands in the Mackay River area, but the source of the oil sands is still controversial. [Methods]There are 25 oil sand samples from the Cretaceous McMurray Formation in the Mackay River of Athabasca in Alberta Basin are explored by precise geochemical investigation. Soluble organic matter extraction, family component separation, saturated hydrocarbon gas chromatography, saturated hydrocarbon and aromatic hydrocarbon chromatography and mass spectrometry were performed on the 25 samples. The sedimentary environment, biological origin and maturity of organic matter in the bituminous source rocks of the oil sands of the McMurray Formation are identified based on the analysis results of the family components and biomarker parameters of these samples. [Results and Discussions] The results showed that the n-alkanes were completely consumed, the content of acyclic isoprene was lower than the detection limit, and there were a lot of iso-alkanes and unresolved compounds in the samples. Hopanes endure destruction, and a small amount of 25-norhopanes was identified. The steranes were destroyed continuously, the abundance of pregnane and homopregnane was higher, the regular steranes suffered a loss, and the content of C27 regular steranes was relatively high. The tricyclic terpenes were intact, and the baseline was slightly raised, showing high content of C23 tricyclic terpenes. The characteristic peaks of the triaromatic steranes are obvious and easy to identify. The distribution of each sample of the McMurray Formation oil sands asphalt is concentrated in the C26-C27-C28 triangular diagram triangle and C19+20-C21-C23 tricyclic terpenes triangular diagram, and all have the advantages of C23 tricyclic terpenes and C27 regular steranes and C28 triaromatic steranes, indicating that the oil sands of the McMurray Formation have the same origin. In addition, these characteristics indicate that the hydrocarbons in the oil sands are derived from lower aquatic organisms and algae deposited in Marine facies sedimentary source rock. The equivalent vitrinite reflectance calculated by MPI and MDR extending from 0.55% to 0.77% illustrates low oil sand maturity. The McMurray Formation tar sands have high non-hydrocarbon and asphaltene content, low API ratio, high relative density and viscosity. [Conclusions] The characteristics of physical properties and biomarkers indicate that the oil sands of the McMurray Formation are caused by serious biodegradation, and the biodegradation level of the samples is inferred to PM 7 according to the scheme proposed by Peters and Moldowan. Based on the comparative analysis of biomarker composition characteristics of source rocks in the study area, it is speculated that the McMurray Formation oil sands asphalt may be contributed by one of the following three groups of source rocks: The Lower Jurassic Nordegg/Cordondale Formation, the Keg River Formation of the Middle Devonian Elk Point Group, and the Lodgepole Formation of the Upper Devonian Series are the Mississippian.
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Abstract:
Abstract: [Objective] Crevasse splay deposits are an important component of river delta depositional systems, which is conducive to the enrichment of remaining oil and gas. However, the study on the way and extent of crevasse splay deposition connecting distributary channel sand bodies in the delta plain subfacies is relatively weak at present. Therefore, the purpose of this study was to determine the quantitative impact of crevasse splay deposits on the connectivity of sand body in delta plain subfacies. [Methods] To determine the influence of crevasse splay sedimentation on the connectivity of sand body in delta plain subfacies, the Putaohua oil layer of the Lower Cretaceous Yaojia Formation in the Weixing oilfield of Songliao Basin is selected as the research object. The core, logging, and production data of 5 development blocks of the Putaohua oil layer in the Weixing oilfield were used in our study. At first, the quantitative characterization of the crevasse splay sedimentary structures is carried out, focusing on the identification of sedimentary facies markers, characterization of sand body geometric parameters, an analysis of the sand body drilling ratio, and analysuis of the connection mode of the sand bodies. Based on the results, the connectivity of the delta plain sand body subfacies is quantitatively characterized by 3D random geological modeling technology, and the influence of crevasse splay deposition on the connectivity of sand body in the delta plain subfacies is quantitatively analyzed. [Results and Discussions] The results of the study show that: (1) The lengths of the crevasse splay sand bodies are 50–3000 m, and the widths are 50–2500 m, and the thicknesses are 0.2–5 m, the length to width of the sand body is about 1.2, and the width to thickness of the sand body is 400–600. The ratio of well drilling in crevasse splays is 2%–38%, negatively correlated with that in delta distributary channels. (2) The connection mode of sand bodies between crevasse splays and delta distributary channels can be divided into 5 types: the crevasse splay sand body is not connected with the distributary channel, i.e., an isolated crevasse splay; the crevasse splay sand body is connected with a single distributary channel, which is genetically related to the formation of crevasse splay sand body; the crevasse splay sand body is connected with a single distributary channel, which has no genetic relationship with the formation of the crevasse splay sand body; the crevasse splay sand body is connected with two different distributary channel sand bodies, and the two distributary channels belong to the same sedimentary period; and, the crevasse splay sand body is connected with two different distributary channel sand bodies, however, the two distributary channels belong to different sedimentary periods. (3) Crevasse splay sedimentation has an obvious influence on the connectivity of sand bodies in medium and small delta plain subfacies, especially when the net-to-gross ratio of the delta plain subfacies is less than 30%. [Conclusions] This study is helpful to the deployment and design of well patterns in the middle and late stages of oil and gas field development, and can effectively guide the efficient extraction of any remaining oil and gas, thus reducing the cost of oil and gas exploration and development.
Abstract: [Objective] Crevasse splay deposits are an important component of river delta depositional systems, which is conducive to the enrichment of remaining oil and gas. However, the study on the way and extent of crevasse splay deposition connecting distributary channel sand bodies in the delta plain subfacies is relatively weak at present. Therefore, the purpose of this study was to determine the quantitative impact of crevasse splay deposits on the connectivity of sand body in delta plain subfacies. [Methods] To determine the influence of crevasse splay sedimentation on the connectivity of sand body in delta plain subfacies, the Putaohua oil layer of the Lower Cretaceous Yaojia Formation in the Weixing oilfield of Songliao Basin is selected as the research object. The core, logging, and production data of 5 development blocks of the Putaohua oil layer in the Weixing oilfield were used in our study. At first, the quantitative characterization of the crevasse splay sedimentary structures is carried out, focusing on the identification of sedimentary facies markers, characterization of sand body geometric parameters, an analysis of the sand body drilling ratio, and analysuis of the connection mode of the sand bodies. Based on the results, the connectivity of the delta plain sand body subfacies is quantitatively characterized by 3D random geological modeling technology, and the influence of crevasse splay deposition on the connectivity of sand body in the delta plain subfacies is quantitatively analyzed. [Results and Discussions] The results of the study show that: (1) The lengths of the crevasse splay sand bodies are 50–3000 m, and the widths are 50–2500 m, and the thicknesses are 0.2–5 m, the length to width of the sand body is about 1.2, and the width to thickness of the sand body is 400–600. The ratio of well drilling in crevasse splays is 2%–38%, negatively correlated with that in delta distributary channels. (2) The connection mode of sand bodies between crevasse splays and delta distributary channels can be divided into 5 types: the crevasse splay sand body is not connected with the distributary channel, i.e., an isolated crevasse splay; the crevasse splay sand body is connected with a single distributary channel, which is genetically related to the formation of crevasse splay sand body; the crevasse splay sand body is connected with a single distributary channel, which has no genetic relationship with the formation of the crevasse splay sand body; the crevasse splay sand body is connected with two different distributary channel sand bodies, and the two distributary channels belong to the same sedimentary period; and, the crevasse splay sand body is connected with two different distributary channel sand bodies, however, the two distributary channels belong to different sedimentary periods. (3) Crevasse splay sedimentation has an obvious influence on the connectivity of sand bodies in medium and small delta plain subfacies, especially when the net-to-gross ratio of the delta plain subfacies is less than 30%. [Conclusions] This study is helpful to the deployment and design of well patterns in the middle and late stages of oil and gas field development, and can effectively guide the efficient extraction of any remaining oil and gas, thus reducing the cost of oil and gas exploration and development.
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Abstract:
[Objective] River sediments record abundant source information, which is of great significance for exploring weathering, transport-sedimentation cycle and parent rock composition in the source region of the basin. Different from large watersheds that integrate different weathering mechanisms and contain complex rock types, small rivers have similar climatic and lithologic backgrounds, which is of great value for studying sediment composition. [Methods] In order to explore the influence of fluvial processes on sediment composition, we obtained eight samples from the upper and lower Breland of the Balan River for granular processing (<63 μm, 63-125 μm, 125-250 μm). The samples <63 μm were subjected to geochemical testing (major, trace, rare earth and Sr-Nd isotopes), 63-125 μm and 125-250 μm samples were tested for heavy minerals. [Results and Discussions] The results show that the sediments of Balan River have undergone low chemical weathering, low maturity, and are in the primary cycle of deposition, and the provenance is mainly from felsic parent rock. The provenance indices (La/Sc, Co/Th, Cr/Th, Th/Sc) and Sr-Nd isotopic compositions did not change much on the whole, which could represent the overall characteristics of the Balan River basin. [Conclusions] The Baran River samples showed consistent chemical weathering, maturity, recycling characteristics, and host rock characteristics, indicating that the river process did not significantly affect the geochemical composition of the Balan sediments. The heavy minerals were diluted and mixed after river transport, and the heavy minerals of different river reaches and different grain size fractions showed obviously different content compositions, indicating that it was difficult to evenly distribute heavy minerals to different grain size fractions by short distance transport. Therefore, when studying river source-sink systems, a few samples are difficult to represent the heavy mineral composition of the entire basin, even in small rivers. This study also emphasizes that the combination of Sr-Nd isotope and inactive element ratio can be used effectively for river provenance tracing.
[Objective] River sediments record abundant source information, which is of great significance for exploring weathering, transport-sedimentation cycle and parent rock composition in the source region of the basin. Different from large watersheds that integrate different weathering mechanisms and contain complex rock types, small rivers have similar climatic and lithologic backgrounds, which is of great value for studying sediment composition. [Methods] In order to explore the influence of fluvial processes on sediment composition, we obtained eight samples from the upper and lower Breland of the Balan River for granular processing (<63 μm, 63-125 μm, 125-250 μm). The samples <63 μm were subjected to geochemical testing (major, trace, rare earth and Sr-Nd isotopes), 63-125 μm and 125-250 μm samples were tested for heavy minerals. [Results and Discussions] The results show that the sediments of Balan River have undergone low chemical weathering, low maturity, and are in the primary cycle of deposition, and the provenance is mainly from felsic parent rock. The provenance indices (La/Sc, Co/Th, Cr/Th, Th/Sc) and Sr-Nd isotopic compositions did not change much on the whole, which could represent the overall characteristics of the Balan River basin. [Conclusions] The Baran River samples showed consistent chemical weathering, maturity, recycling characteristics, and host rock characteristics, indicating that the river process did not significantly affect the geochemical composition of the Balan sediments. The heavy minerals were diluted and mixed after river transport, and the heavy minerals of different river reaches and different grain size fractions showed obviously different content compositions, indicating that it was difficult to evenly distribute heavy minerals to different grain size fractions by short distance transport. Therefore, when studying river source-sink systems, a few samples are difficult to represent the heavy mineral composition of the entire basin, even in small rivers. This study also emphasizes that the combination of Sr-Nd isotope and inactive element ratio can be used effectively for river provenance tracing.
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Abstract:
[Objective] To determine the origin of micro-nano quartz in Qiongzhusi black shales, the source of silica and the cause of its differential development with regions. [Methods] 36 black shale samples were collected from the bottom of Qiongzhusi Formation at different sections in the study area. Bulk mineralogy was determined by X-ray diffraction (XRD); the lithology, bulk rock mineral composition and microstructure of the black shales were determined by light microscopy and field-emission scanning electron (FE-SEM). The microstructure, occurrence of the micro-nano quartz in the shales were determined by FE-SEM. The cathodoluminescence features of minerals in the shales were determined by SEM-based cathodoluminescence imaging (SEM-CL). The total organic content were determined by the combustion method. [Results] Qiongzhusi black shales in the study area are lithologically variable (they are mainly siltstone in Majinzi and Well Z1, however they are mainly mudstone in Songlin). The micro-nano quartz in Qiongzhusi black shales, which are generally several hundred nanometers to 2μm (a few are more than 2μm) in diameter, have an idiomorphic to allomorphic shape, and are low to non-luminescent. Micro-nano quartz crystals in the shales are either intergrown in clusters or isolated. The content of micro-nano quartz in the black shales varies vertically or by regions. In general, it is higher in the black shales in the east (Songlin) than that in the west (Majinzi, Well Z1), and in the lower section of the black shale than that in the upper section. [Conclusions] The micro-nano quartz were authigenic, and its silica were from multiple sources. While the large number of intergrown micro-nano quartz in the black shales may be mainly from reprecipitation of hydrothermal silica. The content of micro-nano quartz in Qiongzhusi black shales in the study area are indicative to upwelling: a relatively high content of micro-nano quartz indicates an upwelling sedimentary environment or sedimentary environment in which there were hydrothermal activities, while a low content of micro-nano quartz may indicate an euxinic and anoxic sedimentary environment (or sedimentary environment that were weakly affected by upwelling).
[Objective] To determine the origin of micro-nano quartz in Qiongzhusi black shales, the source of silica and the cause of its differential development with regions. [Methods] 36 black shale samples were collected from the bottom of Qiongzhusi Formation at different sections in the study area. Bulk mineralogy was determined by X-ray diffraction (XRD); the lithology, bulk rock mineral composition and microstructure of the black shales were determined by light microscopy and field-emission scanning electron (FE-SEM). The microstructure, occurrence of the micro-nano quartz in the shales were determined by FE-SEM. The cathodoluminescence features of minerals in the shales were determined by SEM-based cathodoluminescence imaging (SEM-CL). The total organic content were determined by the combustion method. [Results] Qiongzhusi black shales in the study area are lithologically variable (they are mainly siltstone in Majinzi and Well Z1, however they are mainly mudstone in Songlin). The micro-nano quartz in Qiongzhusi black shales, which are generally several hundred nanometers to 2μm (a few are more than 2μm) in diameter, have an idiomorphic to allomorphic shape, and are low to non-luminescent. Micro-nano quartz crystals in the shales are either intergrown in clusters or isolated. The content of micro-nano quartz in the black shales varies vertically or by regions. In general, it is higher in the black shales in the east (Songlin) than that in the west (Majinzi, Well Z1), and in the lower section of the black shale than that in the upper section. [Conclusions] The micro-nano quartz were authigenic, and its silica were from multiple sources. While the large number of intergrown micro-nano quartz in the black shales may be mainly from reprecipitation of hydrothermal silica. The content of micro-nano quartz in Qiongzhusi black shales in the study area are indicative to upwelling: a relatively high content of micro-nano quartz indicates an upwelling sedimentary environment or sedimentary environment in which there were hydrothermal activities, while a low content of micro-nano quartz may indicate an euxinic and anoxic sedimentary environment (or sedimentary environment that were weakly affected by upwelling).
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Abstract:
The Carboniferous deposists are developed in the north margin of Qaidam Basin, which records the history of the transition from Proto-Tethyan to Paleo-Tethyan Ocean. However, the high metamorphism of the Carboniferous system restricts the understanding of the regional tectonic setting, material source and sedimentary environment. The chemical properties of rare earth elements are stable, so the outcrop of Lower Carboniferous Huaitoutala Formation (C1h) in Xiaosaishiteng Shan is selected to reconstruct the tectono-sedimentary pattern of early Carboniferous based on REE geochemical characteristics of argillaceous rocks. The clastic rocks in the middle and lower part of C1h have higher ∑REE values and normal or weak negative Ce anomalies, while the argillaceous interlayers in the top carbonate rocks have relatively lower ∑REE values and obvious negative Ce anomalies. During the period of C1h, the Xiaosaishiteng Shan area was affected by the subduction of the Southern Kunlun ocean crust to the north, and was located between the local highland composed of the Qaidam block and the subduction collision zone in the northern margin and the western extension zone of the Zongwulong continental rift, showing an overall palaeogeomorphic pattern of "high in the south and low in the north, from land to sea". The orogenic belt extending west of the subduction collision zone in the north margin of Qaidam to the southeast of Xiaosaishiteng Shan was the important provenance area, which provided the weathered detrital materials of parent rocks composed of granite, alkaline basalt and sedimentary rock to the study area during the period of C1h clastic section. With the weakening of regional tectonic intensity and the decrease of terrigenous clastic material supply, the clastic materials of the argillaceous interlayers may come from the re-transport of the preexisting sediments. The sedimentary paleo-water of C1h overall showed a trend of shallow to deep and to shallow again. The clastic shale was formed in a relatively anoxic environment, while the mudstone interlayers in carbonate rocks was in oxidized environment. The phase sequence of “platform edge shoal – platform front slope – shelf edge – platform front slope – platform edge organic reef” was developed successively. These results provide a basis for the reconstruction of regional paleogeographic pattern and the understanding of the temporal and spatial evolution of the Proto-Tethys oceans.
The Carboniferous deposists are developed in the north margin of Qaidam Basin, which records the history of the transition from Proto-Tethyan to Paleo-Tethyan Ocean. However, the high metamorphism of the Carboniferous system restricts the understanding of the regional tectonic setting, material source and sedimentary environment. The chemical properties of rare earth elements are stable, so the outcrop of Lower Carboniferous Huaitoutala Formation (C1h) in Xiaosaishiteng Shan is selected to reconstruct the tectono-sedimentary pattern of early Carboniferous based on REE geochemical characteristics of argillaceous rocks. The clastic rocks in the middle and lower part of C1h have higher ∑REE values and normal or weak negative Ce anomalies, while the argillaceous interlayers in the top carbonate rocks have relatively lower ∑REE values and obvious negative Ce anomalies. During the period of C1h, the Xiaosaishiteng Shan area was affected by the subduction of the Southern Kunlun ocean crust to the north, and was located between the local highland composed of the Qaidam block and the subduction collision zone in the northern margin and the western extension zone of the Zongwulong continental rift, showing an overall palaeogeomorphic pattern of "high in the south and low in the north, from land to sea". The orogenic belt extending west of the subduction collision zone in the north margin of Qaidam to the southeast of Xiaosaishiteng Shan was the important provenance area, which provided the weathered detrital materials of parent rocks composed of granite, alkaline basalt and sedimentary rock to the study area during the period of C1h clastic section. With the weakening of regional tectonic intensity and the decrease of terrigenous clastic material supply, the clastic materials of the argillaceous interlayers may come from the re-transport of the preexisting sediments. The sedimentary paleo-water of C1h overall showed a trend of shallow to deep and to shallow again. The clastic shale was formed in a relatively anoxic environment, while the mudstone interlayers in carbonate rocks was in oxidized environment. The phase sequence of “platform edge shoal – platform front slope – shelf edge – platform front slope – platform edge organic reef” was developed successively. These results provide a basis for the reconstruction of regional paleogeographic pattern and the understanding of the temporal and spatial evolution of the Proto-Tethys oceans.
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Abstract:
Eogenetic karstification is an important factor for the formation and improvement of carbonate reservoirs, but the distribution and controlling factors of the eogenetic karst reservoirs in mound-shoal complex are unclear. Taking the fourth member of The Dengying Formation in central Sichuan Basin as an example, we studied karst facies, distribution and control factors of karst reservoirs in mound-shoal complex using Formation Micro-Scanner Image (FMI) data, cores, thin-sections and conventional well-logging data. According to the image characteristics of FMI, the fourth member of The Dengying Formation are divided into seven types of karst facies, including fracture and cave facies (F1), cave-filling facies (F2), breccia facies (F3), lamination-related vugs facies (F4), scattered vugs facies (F5), etc. The distribution of karst facies and favorable reservoirs are closely related to the structure of high-frequency sequences. The vug reservoirs (F4 and F5) are mainly developed in mound-shoal complex deposits in the upper part of the high-frequency sequence, and the thick fracture and cave reservoirs (F1~F4) are developed in thick mound-shoal complex at the top of the Dengying Formation. The development of eogenetic karst reservoirs is primarily controlled by sedimentary facies and high-frequency sequence. Mound-shoal complex is the material basis for karst development. The high-frequency sequence boundary controls the scale of karst reservoirs, and the sedimentary micro-geomorphology further controls the quality of karst reservoirs. The karst slope is superior to the karst highland in terms of total reservoir thickness, reservoir type and, net reservoir index. The results can promote the understanding of the development mechanism of eogenetic karstification reservoirs, and provide a basis for the prediction of favorable reservoirs in the study area.
Eogenetic karstification is an important factor for the formation and improvement of carbonate reservoirs, but the distribution and controlling factors of the eogenetic karst reservoirs in mound-shoal complex are unclear. Taking the fourth member of The Dengying Formation in central Sichuan Basin as an example, we studied karst facies, distribution and control factors of karst reservoirs in mound-shoal complex using Formation Micro-Scanner Image (FMI) data, cores, thin-sections and conventional well-logging data. According to the image characteristics of FMI, the fourth member of The Dengying Formation are divided into seven types of karst facies, including fracture and cave facies (F1), cave-filling facies (F2), breccia facies (F3), lamination-related vugs facies (F4), scattered vugs facies (F5), etc. The distribution of karst facies and favorable reservoirs are closely related to the structure of high-frequency sequences. The vug reservoirs (F4 and F5) are mainly developed in mound-shoal complex deposits in the upper part of the high-frequency sequence, and the thick fracture and cave reservoirs (F1~F4) are developed in thick mound-shoal complex at the top of the Dengying Formation. The development of eogenetic karst reservoirs is primarily controlled by sedimentary facies and high-frequency sequence. Mound-shoal complex is the material basis for karst development. The high-frequency sequence boundary controls the scale of karst reservoirs, and the sedimentary micro-geomorphology further controls the quality of karst reservoirs. The karst slope is superior to the karst highland in terms of total reservoir thickness, reservoir type and, net reservoir index. The results can promote the understanding of the development mechanism of eogenetic karstification reservoirs, and provide a basis for the prediction of favorable reservoirs in the study area.
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The extremely low grade metamorphism is in the evolution stage of petroleum, wet gas, dry gas and peat, bituminous coal and anthracite, and is closely related to paleotemperature. Therefore, the study of extremely low grade metamorphism and paleotemperature is of great practical significance for the exploration of energy resources such as oil, gas and coal. Compared with Longmaxi Formation shale gas which has made exploration breakthrough, the Lower Cambrian Qiongzhusi Formation shale has higher organic matter abundance, brittleness, thermal evolution and more developed fractures in the Upper Yangtze region. At the same time, Qiongzhusi Formation has a larger sedimentary thickness and a wider distribution area compared with Longmaxi Formation, therefore has huge shale gas exploration potential. It is another key shale gas exploration and development layer in China. In the past, researches on Qiongzhusi Formation mainly focused on organic matter type, pore and fracture structure of reservoir, and sedimentary facies. There is no systematic study on the extremely low grade metamorphism and paleotemperature of the Qiongzhusi Formation source rocks with high maturity. Based on the profile measurements in this paper, the study on the ultralow grade metamorphism and paleotemperature of Qiongzhusi Formation in northeast Yunnan was carried out for the first time with the mineral structure order degree, crystallinity degree of illite and vitrinite reflectance of source rocks. It is concluded that :(1) The illite content in the illite/Mongolian mixed layer is 95%. The crystallinity of illite in authigenic illite and Illite/Mengzi mixed layer minerals ranges from 0.24 to 0.35. The vitreous reflectance (Ro) of source rocks calculated by bitumen reflectance is between 2.22%-2.65%, lower than that of the southeast margin of the Yangtze region (the vitrinite reflectance Ro in this area calculated by asphalt reflectance between 3.18%-3.43%) and the upper limit of maturity for marine kerogen gas generation (vitrinite reflectance Ro3%).; (2) The maximum palaeotemperature of Qiongzhusi Formation in northeastern Yunnan was found to be from 200℃ to 227.57℃, which was lower than that of the southeastern margin of the Yangtze River (211℃ - 246℃) and the maximum hydrocarbon death temperature (230℃-300℃). The paleotemperature gradient from Early Cretaceous to Neogene maximum burial depth is 2.53℃/100m to 2.91℃/100m, which is close to the southeast margin of the Yangtze; (3) According to comprehensive classification standard and scheme of metamorphism, Qiongzhusi Formation in the northeast of Yunnan belonged to the very lower metamorphic zone A-B, near metamorphic zone, lower near metamorphic zone to high near metamorphic zone, and belonged to the Vitiite-chlorospar facies. Qiongzhusi stage in northeast Yunnan Province was in the favorable direction of transition from sedimentary sag to uplift. Qiongzhusi Formation experienced lower highest paleotemperature and maturity. In addition, the maturity of organic matter in Qiongzhusi Formation in northeast Yunnan Province was lower than that in other parts of Yangtze region, and had hydrocarbon formation conditions and material basis. At present, no paleooil reservoir was found, and the structural preservation conditions were good. The oil and gas prospect of Qiongzhusi Formation in northeast Yunnan should be paid attention to.
The extremely low grade metamorphism is in the evolution stage of petroleum, wet gas, dry gas and peat, bituminous coal and anthracite, and is closely related to paleotemperature. Therefore, the study of extremely low grade metamorphism and paleotemperature is of great practical significance for the exploration of energy resources such as oil, gas and coal. Compared with Longmaxi Formation shale gas which has made exploration breakthrough, the Lower Cambrian Qiongzhusi Formation shale has higher organic matter abundance, brittleness, thermal evolution and more developed fractures in the Upper Yangtze region. At the same time, Qiongzhusi Formation has a larger sedimentary thickness and a wider distribution area compared with Longmaxi Formation, therefore has huge shale gas exploration potential. It is another key shale gas exploration and development layer in China. In the past, researches on Qiongzhusi Formation mainly focused on organic matter type, pore and fracture structure of reservoir, and sedimentary facies. There is no systematic study on the extremely low grade metamorphism and paleotemperature of the Qiongzhusi Formation source rocks with high maturity. Based on the profile measurements in this paper, the study on the ultralow grade metamorphism and paleotemperature of Qiongzhusi Formation in northeast Yunnan was carried out for the first time with the mineral structure order degree, crystallinity degree of illite and vitrinite reflectance of source rocks. It is concluded that :(1) The illite content in the illite/Mongolian mixed layer is 95%. The crystallinity of illite in authigenic illite and Illite/Mengzi mixed layer minerals ranges from 0.24 to 0.35. The vitreous reflectance (Ro) of source rocks calculated by bitumen reflectance is between 2.22%-2.65%, lower than that of the southeast margin of the Yangtze region (the vitrinite reflectance Ro in this area calculated by asphalt reflectance between 3.18%-3.43%) and the upper limit of maturity for marine kerogen gas generation (vitrinite reflectance Ro3%).; (2) The maximum palaeotemperature of Qiongzhusi Formation in northeastern Yunnan was found to be from 200℃ to 227.57℃, which was lower than that of the southeastern margin of the Yangtze River (211℃ - 246℃) and the maximum hydrocarbon death temperature (230℃-300℃). The paleotemperature gradient from Early Cretaceous to Neogene maximum burial depth is 2.53℃/100m to 2.91℃/100m, which is close to the southeast margin of the Yangtze; (3) According to comprehensive classification standard and scheme of metamorphism, Qiongzhusi Formation in the northeast of Yunnan belonged to the very lower metamorphic zone A-B, near metamorphic zone, lower near metamorphic zone to high near metamorphic zone, and belonged to the Vitiite-chlorospar facies. Qiongzhusi stage in northeast Yunnan Province was in the favorable direction of transition from sedimentary sag to uplift. Qiongzhusi Formation experienced lower highest paleotemperature and maturity. In addition, the maturity of organic matter in Qiongzhusi Formation in northeast Yunnan Province was lower than that in other parts of Yangtze region, and had hydrocarbon formation conditions and material basis. At present, no paleooil reservoir was found, and the structural preservation conditions were good. The oil and gas prospect of Qiongzhusi Formation in northeast Yunnan should be paid attention to.
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Abstract:
[Objective] In this study, we clarified the difference and development rule of clastic reservoirs in the middle and deep layers of the No. 4 structural belt in the Nanpu Sag and explored the key factors affecting the quality of middle and deep reservoirs. [Methods] We used scanning electron microscopy, casting thin section, mercury, injection analysis and other techniques, combined with the empirical calculation formula of diagenetic strength. Reservoir petrology, porosity and permeability, pore structure, and the reason of reservoir quality difference were analyzed in a stratified system. [Results] The study shows that the sandstones of different strata are similar in lithology, mainly composed of lithic feldspar sandstone and feldspar lithic sandstone, but the reservoir quality obviously differs between layers, showing the "abnormal" phenomenon that the reservoir quality of the second member of Dongying Formation (Ed2) and the third member of Dongying Formation (Ed3) decreases rapidly with the increase of burial depth. However, the reservoir quality of the first member of the Shahejie Formation (Es1), which is the underlying member, improves with depth. From Ed2 to Es1, the average porosity and permeability increased from 12.96 % and 3.39 ×10-3μm2 to 16.61 % and 9.58 ×10-3μm2, respectively. Based on the analysis of the high-pressure mercury injection experiment, the study area can be divided into three types of mercury injection curves. The proportions of types Ⅰ, Ⅱ, and Ⅲ in Es1 were 43.75 %, 25 %, and 31.25 %, respectively. The types of mercury injection curves in Ed3 were 28.57 %, 64.29 %, and 7.14 %, respectively. The types of mercury injection curves in Ed2 accounted for 36.36 %, 45.45 %, and 18.18 %, respectively. In general, Es1 has both type Ⅰ and high-quality pore-throat and type Ⅲ with small pore-throat radius, and its physical properties are better than those of other strata. Furthermore, through the calculation of the difference of diagenetic strength, differences are discovered in the diagenesis of different reservoirs. The compaction intensity of Es1 is the weakest (COPL-P= 38.13 %), and the dissolution intensity is the strongest (CRPI-P= 46.47 %). The reservoirs are well reformed and have good physical properties. Ed3 has the strongest compaction (COPL-P= 53.30 %), the weakest dissolution (CRPI-P= 26.03 %), and poor physical properties. [Conclusions] The difference of sedimentary facies and diagenesis under the control of tectonic evolution and burial is the fundamental reason for the "anomaly" of reservoir quality layers. From Es1 to Ed3 and Ed2, the rifting activity was enhanced, topography steepened, meander river delta evolved into braided river delta, reservoir grain size became coarser, sandstone composition and structure maturity was reduced, sandstone compressive ability decreased, and compaction porosity reduction rate increased, resulting in better preservation of primary pores in Es1. In addition, the rate of dissolution and porosity increase at depth, and high pressure of the formation further increased the interlayer "anomaly" of reservoir quality.
[Objective] In this study, we clarified the difference and development rule of clastic reservoirs in the middle and deep layers of the No. 4 structural belt in the Nanpu Sag and explored the key factors affecting the quality of middle and deep reservoirs. [Methods] We used scanning electron microscopy, casting thin section, mercury, injection analysis and other techniques, combined with the empirical calculation formula of diagenetic strength. Reservoir petrology, porosity and permeability, pore structure, and the reason of reservoir quality difference were analyzed in a stratified system. [Results] The study shows that the sandstones of different strata are similar in lithology, mainly composed of lithic feldspar sandstone and feldspar lithic sandstone, but the reservoir quality obviously differs between layers, showing the "abnormal" phenomenon that the reservoir quality of the second member of Dongying Formation (Ed2) and the third member of Dongying Formation (Ed3) decreases rapidly with the increase of burial depth. However, the reservoir quality of the first member of the Shahejie Formation (Es1), which is the underlying member, improves with depth. From Ed2 to Es1, the average porosity and permeability increased from 12.96 % and 3.39 ×10-3μm2 to 16.61 % and 9.58 ×10-3μm2, respectively. Based on the analysis of the high-pressure mercury injection experiment, the study area can be divided into three types of mercury injection curves. The proportions of types Ⅰ, Ⅱ, and Ⅲ in Es1 were 43.75 %, 25 %, and 31.25 %, respectively. The types of mercury injection curves in Ed3 were 28.57 %, 64.29 %, and 7.14 %, respectively. The types of mercury injection curves in Ed2 accounted for 36.36 %, 45.45 %, and 18.18 %, respectively. In general, Es1 has both type Ⅰ and high-quality pore-throat and type Ⅲ with small pore-throat radius, and its physical properties are better than those of other strata. Furthermore, through the calculation of the difference of diagenetic strength, differences are discovered in the diagenesis of different reservoirs. The compaction intensity of Es1 is the weakest (COPL-P= 38.13 %), and the dissolution intensity is the strongest (CRPI-P= 46.47 %). The reservoirs are well reformed and have good physical properties. Ed3 has the strongest compaction (COPL-P= 53.30 %), the weakest dissolution (CRPI-P= 26.03 %), and poor physical properties. [Conclusions] The difference of sedimentary facies and diagenesis under the control of tectonic evolution and burial is the fundamental reason for the "anomaly" of reservoir quality layers. From Es1 to Ed3 and Ed2, the rifting activity was enhanced, topography steepened, meander river delta evolved into braided river delta, reservoir grain size became coarser, sandstone composition and structure maturity was reduced, sandstone compressive ability decreased, and compaction porosity reduction rate increased, resulting in better preservation of primary pores in Es1. In addition, the rate of dissolution and porosity increase at depth, and high pressure of the formation further increased the interlayer "anomaly" of reservoir quality.
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Abstract:
In order to clarify the multi-stage dolomitization of the Lower-Middle Ordovician carbonate rocks in the Maigaiti Slope, on the basis of lithofacies analysis and in-situ trace and rare earth element (REEs) tests using LA-ICP-MS, we analyzed the origin of dolomites and its control on the reservoir. The Lower-Middle Ordovician dolomites mainly include silt-crystalline dolomite, grain dolomite, calcite dolomite, medium-crystalline dolomite, and dolomite cement in fractures and vugs. The sedimentary environment is interpreted as shoal and tidal flat in a restricted platform. The composition and patterns of REEs of dolomites and abundant Na content indicate that the dolomitization fluid are seawater origin and locally influenced by hydrothermal fluid. The dolomitization of the Lower-Middle Ordovician carbonates is characterized by multi-stage process. During the deposition of the Penglaiba Formation, penecontemporaneous dolomitization caused tidal deposits to form silt-crystalline dolomite, and seepage-reflux dolomitization caused shoal deposits to form grain dolomite. During the deposition of the Yingshan Formation, burial dolomitization produced continuous growth of dolomite crystals, and grain-supported textures were partially destroyed and resulted in medium-crystalline dolomite. Besides, fractures and vugs were continuously filled with dolomite. Lime-grainstones in the Yingshan Formation was partially dolomitized during burial, result in patchy distribution of dolomite crystals. Multi-stage dolomitization controls the quality of Lower-Middle Ordovician dolomite reservoirs in the study area. In the shoal and tidal flat system in a restricted platform, the favorable type of reservoir is the grain dolomite formed by seepage-reflux dolomitization during the early-stage diagenesis.
In order to clarify the multi-stage dolomitization of the Lower-Middle Ordovician carbonate rocks in the Maigaiti Slope, on the basis of lithofacies analysis and in-situ trace and rare earth element (REEs) tests using LA-ICP-MS, we analyzed the origin of dolomites and its control on the reservoir. The Lower-Middle Ordovician dolomites mainly include silt-crystalline dolomite, grain dolomite, calcite dolomite, medium-crystalline dolomite, and dolomite cement in fractures and vugs. The sedimentary environment is interpreted as shoal and tidal flat in a restricted platform. The composition and patterns of REEs of dolomites and abundant Na content indicate that the dolomitization fluid are seawater origin and locally influenced by hydrothermal fluid. The dolomitization of the Lower-Middle Ordovician carbonates is characterized by multi-stage process. During the deposition of the Penglaiba Formation, penecontemporaneous dolomitization caused tidal deposits to form silt-crystalline dolomite, and seepage-reflux dolomitization caused shoal deposits to form grain dolomite. During the deposition of the Yingshan Formation, burial dolomitization produced continuous growth of dolomite crystals, and grain-supported textures were partially destroyed and resulted in medium-crystalline dolomite. Besides, fractures and vugs were continuously filled with dolomite. Lime-grainstones in the Yingshan Formation was partially dolomitized during burial, result in patchy distribution of dolomite crystals. Multi-stage dolomitization controls the quality of Lower-Middle Ordovician dolomite reservoirs in the study area. In the shoal and tidal flat system in a restricted platform, the favorable type of reservoir is the grain dolomite formed by seepage-reflux dolomitization during the early-stage diagenesis.
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Abstract:
The Milankovitch cycle affects the Earth's climate system and organic carbon burial by regulating the Earth's astronomical orbital parameters. In addition to the conventional astronomical cycles that regulate the climate system through linear processes, there are also "unconventional" astronomical cycles that regulate the climate system through a series of "non-linear" positive or negative feedback processes, such as the 170-kyr obliquity amplitude modulation(AM) cycle. Previous studies have demonstrated the modulating effect of the 170-kyr cycle on organic carbon burial in the middle to high latitudes of the Earth during the Mesozoic-Cenozoic. However, due to the lack of accurate astronomical solutions and high-resolution geological records, the 170-kyr cycle has rarely been reported in the Paleozoic. In this study, the total organic carbon content and natural gamma logging data of the Early Permian Luchaogou Formation in the Junggar Basin were analyzed with cyclostratigraphy, which concluded that the Luchaogou Formation has preserved short eccentricity, obliquity, and precession cycles. The astronomical tuning results based on the short eccentricity cycle show that the deposition duration of the Lucaogou Formation is ~2.8 Myr and the sedimentary rate is estimated to be 9.1 cm / kyr. In addition to conventional astronomical cycles, the 170-kyr cycle were also found in detrended data series and their obliquity AM series, which is the first systematic exploration of the 170-kyr cycle in Paleozoic terrestrial basin. Based on the strong obliquity signals, it is hypothesized that this 170-kyr cycle originates from the s3-s6 obliquity AM cycle. It can affect organic carbon burial by modulating water circulation processes in the middle to high latitude of the earth during Early Permian. And the threshold response effect in sedimentary basins amplifies the 170-kyr AM cycle in the obliquity cycle and appears in the geological record.
The Milankovitch cycle affects the Earth's climate system and organic carbon burial by regulating the Earth's astronomical orbital parameters. In addition to the conventional astronomical cycles that regulate the climate system through linear processes, there are also "unconventional" astronomical cycles that regulate the climate system through a series of "non-linear" positive or negative feedback processes, such as the 170-kyr obliquity amplitude modulation(AM) cycle. Previous studies have demonstrated the modulating effect of the 170-kyr cycle on organic carbon burial in the middle to high latitudes of the Earth during the Mesozoic-Cenozoic. However, due to the lack of accurate astronomical solutions and high-resolution geological records, the 170-kyr cycle has rarely been reported in the Paleozoic. In this study, the total organic carbon content and natural gamma logging data of the Early Permian Luchaogou Formation in the Junggar Basin were analyzed with cyclostratigraphy, which concluded that the Luchaogou Formation has preserved short eccentricity, obliquity, and precession cycles. The astronomical tuning results based on the short eccentricity cycle show that the deposition duration of the Lucaogou Formation is ~2.8 Myr and the sedimentary rate is estimated to be 9.1 cm / kyr. In addition to conventional astronomical cycles, the 170-kyr cycle were also found in detrended data series and their obliquity AM series, which is the first systematic exploration of the 170-kyr cycle in Paleozoic terrestrial basin. Based on the strong obliquity signals, it is hypothesized that this 170-kyr cycle originates from the s3-s6 obliquity AM cycle. It can affect organic carbon burial by modulating water circulation processes in the middle to high latitude of the earth during Early Permian. And the threshold response effect in sedimentary basins amplifies the 170-kyr AM cycle in the obliquity cycle and appears in the geological record.
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Grain-size parameter play a vital role in characterizing the basic features of the sediments, and also a crucial reference for distinguishing sedimentary environment. For a long time, particle size Φ and particle size parameters based on the equal ratio system and negative logarithm conversion have been widely used in the field of geology and Marine science, and even become the national standard. Among them, the mathematical connotation of the sorting coefficient is closely related to the standard deviation, so whether the sorting coefficient has the same dimension as the particle size, whether the sorting coefficient should use the unit, with what unit, has become a controversial issue. In order to clarify this problem, this paper reviewed the introduction of Udden-Wentworth equal ratio system, the origin of Φ value and the modification of the calculation formula, as well as the evolution process of the calculation formula of particle size parameters such as sorting coefficient in the in the graphic and the moment methods, and analyzed the usage habits of terms and units of sorting coefficient of Chinese scholars since 1970. (1) In 1963, McManus modified the calculation formula of Φ value and established Φ value as a dimensionless parameter, making Φ value a convenient index to express the size of particle size, but it does not have the inherent property of a unit of measurement, and cannot be used as a unit of length dimension (i.e., particle size). (2) Although the sorting coefficient is derived from the statistical standard deviation, it has been independently developed as an important parameter to describe the sorting of detrital sediments, which is parallel with the skewness coefficient and kurtosis coefficient, etc. It is recommended that units should not be added when used, because there are still units in the results of the existing sorting coefficient calculation formula. Therefore, the formula of sorting coefficient is improved by referring to McManus' method of removing dimension. (3) The results of literature statistics show that most domestic scholars tend to use the term "sorting coefficient" rather than the statistical term "standard deviation", and do not use units when describing the sorting results. The proportion of this situation in all statistical kinds of literature shows an increasing trend with the shortening of time from now. (4) The current national standard GB/T 12763.8-2007 provides that the unit of the sorting coefficient is Φ, and there is a print proofreading error in the description of the particle size parameter calculation formula, which is suggested to correct when revising the standard. In this paper, the origin and evolution of Φ and the existing commonly used sorting coefficient calculation formulas are reviewed and based on various definitions, the current situation of the use of terms and units of sorting coefficient in China is analyzed. Finally, on the basis of previous studies, some suggestions are put forward to modify the sorting coefficient calculation formula. The above work can provide suggestions for the revision and improvement of Marine investigation norms, and provide suggestions for promoting the unification and standardization of terms.
Grain-size parameter play a vital role in characterizing the basic features of the sediments, and also a crucial reference for distinguishing sedimentary environment. For a long time, particle size Φ and particle size parameters based on the equal ratio system and negative logarithm conversion have been widely used in the field of geology and Marine science, and even become the national standard. Among them, the mathematical connotation of the sorting coefficient is closely related to the standard deviation, so whether the sorting coefficient has the same dimension as the particle size, whether the sorting coefficient should use the unit, with what unit, has become a controversial issue. In order to clarify this problem, this paper reviewed the introduction of Udden-Wentworth equal ratio system, the origin of Φ value and the modification of the calculation formula, as well as the evolution process of the calculation formula of particle size parameters such as sorting coefficient in the in the graphic and the moment methods, and analyzed the usage habits of terms and units of sorting coefficient of Chinese scholars since 1970. (1) In 1963, McManus modified the calculation formula of Φ value and established Φ value as a dimensionless parameter, making Φ value a convenient index to express the size of particle size, but it does not have the inherent property of a unit of measurement, and cannot be used as a unit of length dimension (i.e., particle size). (2) Although the sorting coefficient is derived from the statistical standard deviation, it has been independently developed as an important parameter to describe the sorting of detrital sediments, which is parallel with the skewness coefficient and kurtosis coefficient, etc. It is recommended that units should not be added when used, because there are still units in the results of the existing sorting coefficient calculation formula. Therefore, the formula of sorting coefficient is improved by referring to McManus' method of removing dimension. (3) The results of literature statistics show that most domestic scholars tend to use the term "sorting coefficient" rather than the statistical term "standard deviation", and do not use units when describing the sorting results. The proportion of this situation in all statistical kinds of literature shows an increasing trend with the shortening of time from now. (4) The current national standard GB/T 12763.8-2007 provides that the unit of the sorting coefficient is Φ, and there is a print proofreading error in the description of the particle size parameter calculation formula, which is suggested to correct when revising the standard. In this paper, the origin and evolution of Φ and the existing commonly used sorting coefficient calculation formulas are reviewed and based on various definitions, the current situation of the use of terms and units of sorting coefficient in China is analyzed. Finally, on the basis of previous studies, some suggestions are put forward to modify the sorting coefficient calculation formula. The above work can provide suggestions for the revision and improvement of Marine investigation norms, and provide suggestions for promoting the unification and standardization of terms.
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[Objective]The East China Sea Bridge is located in the important passage for the exchange of water and suspended sediment between Hangzhou Bay and the Yangtze River estuary, which has a significant impact on the distribution and transportation of the suspended sediment in the adjacent area. Therefore, the variation characteristics of suspended sediment concentration (SSC) on both sides of the East China Sea Bridge under the scales of tidal cycle, seasonal and interannual are studied. [Methods]Based on 26 days of high-quality GOCI images with 8 continuous tidal hour per day from 2011 to 2020, the inversion equation was established to transfer remote sensing reflectance to SSC in the adjacent waters around the East Sea Bridge. And combined with the ideal numerical model and the observation data of seabed sediment, the influence of the East China Sea Bridge on the changes of suspended sediment and seabed sediment distribution at different time scales were studied. [Results]The results show that the SSC on both sides of the East China Sea Bridge presents an obvious gradient distribution, with the higher value on the lee side and lower value on the upstream face of the bridge both during the flood and ebb periods. The SSC difference is up to 300%, which is related to the vertical movement caused by the lower water level in the lee side of the bridge and strengthened disturbance induced by the vortex behind the piers. During the ebb and flood maximum time, the difference in SSC between the two sides of the bridge is the largest, and the difference between the two sides at the flood slack and fall is the smallest. During the ebb period, the difference of SSC on both sides of the bridge is obviously greater than that of high tide. The gradient distribution of SSC on the two sides of the bridge is not much different during the ebb and flood periods in different seasons, but the concentration difference is different. The difference of SSC on both sides of the bridge in winter is less than 300 mg/L, which is less than the value in summer that is up to 500 mg/L. Spring is the transition season, and the difference of SSC on both sides of the bridge is between winter and summer. From the changes over the years, the SSC gradient on both sides of the East China Sea Bridge has little changed. Comparing the grain size changes of seabed sediments near the bridge after 11 years of bridge construction, the seabed sediments in the adjacent waters tend to become finer, which may be related to the weakening of the current velocity due to the water blockage effect by the bridge. [Conclusion] This study concludes SSC gradient distribution between the two sides of the bridge with higher value in the leeside while lower value in the upstream face, which does not vary seasonally or annually. This study is of great significance to improve the research on the impact of cross sea bridges on the marine environment at different time scales.
[Objective]The East China Sea Bridge is located in the important passage for the exchange of water and suspended sediment between Hangzhou Bay and the Yangtze River estuary, which has a significant impact on the distribution and transportation of the suspended sediment in the adjacent area. Therefore, the variation characteristics of suspended sediment concentration (SSC) on both sides of the East China Sea Bridge under the scales of tidal cycle, seasonal and interannual are studied. [Methods]Based on 26 days of high-quality GOCI images with 8 continuous tidal hour per day from 2011 to 2020, the inversion equation was established to transfer remote sensing reflectance to SSC in the adjacent waters around the East Sea Bridge. And combined with the ideal numerical model and the observation data of seabed sediment, the influence of the East China Sea Bridge on the changes of suspended sediment and seabed sediment distribution at different time scales were studied. [Results]The results show that the SSC on both sides of the East China Sea Bridge presents an obvious gradient distribution, with the higher value on the lee side and lower value on the upstream face of the bridge both during the flood and ebb periods. The SSC difference is up to 300%, which is related to the vertical movement caused by the lower water level in the lee side of the bridge and strengthened disturbance induced by the vortex behind the piers. During the ebb and flood maximum time, the difference in SSC between the two sides of the bridge is the largest, and the difference between the two sides at the flood slack and fall is the smallest. During the ebb period, the difference of SSC on both sides of the bridge is obviously greater than that of high tide. The gradient distribution of SSC on the two sides of the bridge is not much different during the ebb and flood periods in different seasons, but the concentration difference is different. The difference of SSC on both sides of the bridge in winter is less than 300 mg/L, which is less than the value in summer that is up to 500 mg/L. Spring is the transition season, and the difference of SSC on both sides of the bridge is between winter and summer. From the changes over the years, the SSC gradient on both sides of the East China Sea Bridge has little changed. Comparing the grain size changes of seabed sediments near the bridge after 11 years of bridge construction, the seabed sediments in the adjacent waters tend to become finer, which may be related to the weakening of the current velocity due to the water blockage effect by the bridge. [Conclusion] This study concludes SSC gradient distribution between the two sides of the bridge with higher value in the leeside while lower value in the upstream face, which does not vary seasonally or annually. This study is of great significance to improve the research on the impact of cross sea bridges on the marine environment at different time scales.
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In order to clarify the controlling effect of paleogeomorphology, paleo-provenance and paleosedimentary environment on sedimentary facies, fully understand the plane distribution characteristics of sedimentary facies, and optimize the next exploration field, taking the Triassic Karamay formation in midwest of Taibei sag as an example, the paleogeomorphology was restored by impression method, the paleo-source analysis was carried out by heavy mineral combination method, and the paleo-sedimentary environment analysis was carried out by trace elements. Combined with rock facies, single well facies and profile facies marks, glutenite thickness and sand-ground ratio, the plane distribution characteristics of sedimentary facies of Triassic Karamay formation in midwest of Taibei sag were determined. Finally, multi-factor comprehensive classification and evaluation of reservoirs were carried out according to fuzzy mathematics evaluation method. The results show that during the sedimentary period of the Karamay Formation, the overall paleotopography of the midwest of Taibei Sag was relatively slow, the paleocurrent was relatively slow, and the hydrodynamics was relatively weak. The widely-covered braided river delta deposits were developed. The Karamay Formation is a braided river delta front deposit, which is sheet-like distributed along the basin margin. Sediment source is mainly derived from the southern ancient convex, sedimentary environment is semi-humid, anaerobic reduction of salt lake environment. According to fuzzy evaluation, the front edge of braided river delta bulge is a favorable sedimentary facies belt of high-quality reservoir in Karamay formation. It is a favorable oil and gas exploration zone with good formation, migration and accumulation conditions.
In order to clarify the controlling effect of paleogeomorphology, paleo-provenance and paleosedimentary environment on sedimentary facies, fully understand the plane distribution characteristics of sedimentary facies, and optimize the next exploration field, taking the Triassic Karamay formation in midwest of Taibei sag as an example, the paleogeomorphology was restored by impression method, the paleo-source analysis was carried out by heavy mineral combination method, and the paleo-sedimentary environment analysis was carried out by trace elements. Combined with rock facies, single well facies and profile facies marks, glutenite thickness and sand-ground ratio, the plane distribution characteristics of sedimentary facies of Triassic Karamay formation in midwest of Taibei sag were determined. Finally, multi-factor comprehensive classification and evaluation of reservoirs were carried out according to fuzzy mathematics evaluation method. The results show that during the sedimentary period of the Karamay Formation, the overall paleotopography of the midwest of Taibei Sag was relatively slow, the paleocurrent was relatively slow, and the hydrodynamics was relatively weak. The widely-covered braided river delta deposits were developed. The Karamay Formation is a braided river delta front deposit, which is sheet-like distributed along the basin margin. Sediment source is mainly derived from the southern ancient convex, sedimentary environment is semi-humid, anaerobic reduction of salt lake environment. According to fuzzy evaluation, the front edge of braided river delta bulge is a favorable sedimentary facies belt of high-quality reservoir in Karamay formation. It is a favorable oil and gas exploration zone with good formation, migration and accumulation conditions.
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Sichuan Basin is rich in oil and gas resources. The breakthroughs of Sinian Dengying Formation and Cambrian Longwangmiao Formation have revealed the great exploration potential of deep oil and gas resources in the Sichuan Basin. The study and exploration degree of Cambrian Gaotai Formation in eastern Sichuan Basin are generally low. The basic geological research on sequence stratigraphy, sedimentary characteristics and distribution of Gaotai Formation can provide a basis for the next oil and gas exploration deployment. Based on the data of drilling, logging, outcrop profile, core and seismic data, the sequence lithofacies paleogeography of the Cambrian Gaotai Formation in the eastern Sichuan Basin is studied comprehensively. The results show that: Tower group is divided into three sequence from bottom to top, 6 level 4 sequence (SSQ1 - SSQ6), the main development of carbonate platform sedimentary environment, from west to east, in turn, develop mix of tidal flat, restricted platform, product quality, and the tidal flat, open platform facies, the restricted platform is the main type of the sedimentary facies, tidal flat, the beach, three sedimentary subfacies such as lagoons; The Gaotai Formation has developed silk-fine crystal dolomite reservoirs, which are characterized by "medium-low porosity and low permeability", with strong heterogeneity and thin thickness. Combined with the characteristics of deposition and reservoir development, favorable exploration zones in the east and west of the study area are predicted.
Sichuan Basin is rich in oil and gas resources. The breakthroughs of Sinian Dengying Formation and Cambrian Longwangmiao Formation have revealed the great exploration potential of deep oil and gas resources in the Sichuan Basin. The study and exploration degree of Cambrian Gaotai Formation in eastern Sichuan Basin are generally low. The basic geological research on sequence stratigraphy, sedimentary characteristics and distribution of Gaotai Formation can provide a basis for the next oil and gas exploration deployment. Based on the data of drilling, logging, outcrop profile, core and seismic data, the sequence lithofacies paleogeography of the Cambrian Gaotai Formation in the eastern Sichuan Basin is studied comprehensively. The results show that: Tower group is divided into three sequence from bottom to top, 6 level 4 sequence (SSQ1 - SSQ6), the main development of carbonate platform sedimentary environment, from west to east, in turn, develop mix of tidal flat, restricted platform, product quality, and the tidal flat, open platform facies, the restricted platform is the main type of the sedimentary facies, tidal flat, the beach, three sedimentary subfacies such as lagoons; The Gaotai Formation has developed silk-fine crystal dolomite reservoirs, which are characterized by "medium-low porosity and low permeability", with strong heterogeneity and thin thickness. Combined with the characteristics of deposition and reservoir development, favorable exploration zones in the east and west of the study area are predicted.
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[Significance] As the most extensive sediment transport systems on Earth, submarine channels shaped by turbidity currents transport billions of tonnes of sediment to the deep sea. The internal structure, sedimentary architecture and hydrodynamics of turbidity currents are revealed by summarizing the advances of depositional dynamics in submarine channel. [Progress] 1) The definitions and flow properties (Re, Fr and Ri number) of gravity current are provided. The general anatomy and structure of turbidity currents are shown by head and body of the current, and structure of velocity, density and turbulence. 2) A review of the related literature describing sediment transport for uniform and non-uniform sediment beds and bedform development associated with open channel flow is provided. It is meaningful to research the hydrodynamics of the turbidity current in submarine channel in order to reveal the morphology and geometry, overspilling, sediments distribution and the reservoir architecture, as well as guide the deep-water hydrocarbon exploration. 3) Three main methods (field observations, experimental modelling and numerical modelling) for studying the depositional dynamics in submarine channels are introduced. [Prospects]4) The exploring frontier areas and controversial topics in current research on depositional dynamics in submarine channels are discussed.
[Significance] As the most extensive sediment transport systems on Earth, submarine channels shaped by turbidity currents transport billions of tonnes of sediment to the deep sea. The internal structure, sedimentary architecture and hydrodynamics of turbidity currents are revealed by summarizing the advances of depositional dynamics in submarine channel. [Progress] 1) The definitions and flow properties (Re, Fr and Ri number) of gravity current are provided. The general anatomy and structure of turbidity currents are shown by head and body of the current, and structure of velocity, density and turbulence. 2) A review of the related literature describing sediment transport for uniform and non-uniform sediment beds and bedform development associated with open channel flow is provided. It is meaningful to research the hydrodynamics of the turbidity current in submarine channel in order to reveal the morphology and geometry, overspilling, sediments distribution and the reservoir architecture, as well as guide the deep-water hydrocarbon exploration. 3) Three main methods (field observations, experimental modelling and numerical modelling) for studying the depositional dynamics in submarine channels are introduced. [Prospects]4) The exploring frontier areas and controversial topics in current research on depositional dynamics in submarine channels are discussed.
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The PLB boundary at the turn of the Middle Late Permian is a difficult problem for geoscientists to study for a long time. In this paper, the late Guadalupian strata of seven profiles, including Sandui Town, Wangjiagou and Daliangxiang in the north of Sichuan Basin, are taken as the research object to explore the relationship between biological extinction and geological events by means of lithostratigraphy, biostratigraphy, major, trace and rare earth element analysis. Display: from J. postserrata to C Dukouensis zone can be divided into four lithologic sections, namely, bioclastic limestone (containing dolomite), siliceous rock (argillaceous limestone), coal seam and marl bearing limestone, representing three stages of sea level stabilization, decline and rise, J A set of black rock series was deposited on altudaensis belt under the background of tensile stress. The paleo exposed surface, lithologic abrupt change surface and C Based on the first appearance of dukouensis conodont, the location of PLB boundary can be identified. The regional geochemical data are listed in J.postserra-J Shannoni zone and J.altudaensis-J The xuanhanensis belt recorded two regression events, resulting in synchronous negative bias of Sr/Ba and Y/Ho values and relative enrichment of LREs. Emeishan large igneous province started to move in the J. altudaensis belt, and the total amount of regional rare earth elements increased sharply due to the input of hydrothermal solution. The biological population began to be affected by the extinction event in the J. postserrata zone, and the event continued until the PLB boundary.
The PLB boundary at the turn of the Middle Late Permian is a difficult problem for geoscientists to study for a long time. In this paper, the late Guadalupian strata of seven profiles, including Sandui Town, Wangjiagou and Daliangxiang in the north of Sichuan Basin, are taken as the research object to explore the relationship between biological extinction and geological events by means of lithostratigraphy, biostratigraphy, major, trace and rare earth element analysis. Display: from J. postserrata to C Dukouensis zone can be divided into four lithologic sections, namely, bioclastic limestone (containing dolomite), siliceous rock (argillaceous limestone), coal seam and marl bearing limestone, representing three stages of sea level stabilization, decline and rise, J A set of black rock series was deposited on altudaensis belt under the background of tensile stress. The paleo exposed surface, lithologic abrupt change surface and C Based on the first appearance of dukouensis conodont, the location of PLB boundary can be identified. The regional geochemical data are listed in J.postserra-J Shannoni zone and J.altudaensis-J The xuanhanensis belt recorded two regression events, resulting in synchronous negative bias of Sr/Ba and Y/Ho values and relative enrichment of LREs. Emeishan large igneous province started to move in the J. altudaensis belt, and the total amount of regional rare earth elements increased sharply due to the input of hydrothermal solution. The biological population began to be affected by the extinction event in the J. postserrata zone, and the event continued until the PLB boundary.
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The Middle–Upper Ordovician Saergan Formation in the Tarim Basin represents as an important hydrocarbon source rock deposited in marine environment. However, the model of the deposition of the Saergan Formation remains nebulous. High-precision geochronologic constraint may shed new light on deposition history of the Saergan Formation. The identification of Milankovitch cycles, in particular, the 405 kyr long orbital eccentricity cycle can be used to construct precise time scales for the sedimentary succession of the Paleozoic Era. The magnetic susceptibility (MS) is a measure of the degree of magnetization of a material in response to an applied magnetic field and it can be a powerful tool for cyclostratigraphy and paleoclimate studies. Here, a total of 701 MS data from the 9 m Saergan Formation in Subashigou section of the Kalpin area, Aksu City, Xinjiang were obtained to conduct cyclostratigraphic analysis, including the multitaper method spectral analysis, the evolutive harmonic analysis and the bandpass filtering. Spectral analyses show significant peaks at 0.74–1.28 m, 0.2–0.27 m, 0.057–0.071 m, and 0.035–0.039 m with the ratio of 21.14: 7.71: 5.71: 1.86: 1.11: 1, which is close to that of the Middle–Late Ordovician astronomical cycles. Although there is no reliable astronomical solution for the Ordovician period, astronomical calibration can be achieved using stable 405 kyr eccentricity cycle. After 405-kyr long eccentricity calibration, the spectral analysis shows periods with 100 kyr (short eccentricity), 30.6–31.2 kyr (obliquity), and 20–21.8 kyr (precession), respectively. Ten eccentricity cycles were obtained using bandpass filtering and a " floating " astronomical time scale with a duration of ~3.9 Myr was established for the Saergan Formation of the Subashigou section. Amplitude modulation (AM) envelope of the interpreted 30.6 kyr band of the 405 kyr-calibrated MS time series reveals long-term cycles with a period of ~1.2 Myr for the Ordovician, which is identical with that at present. The first appearance datum (FAD) of the graptolite Nemagraptus. gracilis was used as a tie point for building the correlation between the Subashigou section and Dawangou section (Global Stratotype Section and Point auxiliary Stratotype of the Sandbian). The result shows that the initiation of deposition of the Saergan Formation in the Subashigou section was ~1.03 Myr later than that at Dawangou section. It supports that the Saergan black shales developed during the strong sea-level transgression process, which drowned the platform, and organic-rich, sediments have been deposited on the carbonate platform. Further comparison among the MS series, 1.2 Myr obliquity cycle and global sea-level curve during the Middle–Late Ordovician, we suggested that 1.2 Myr long obliquity cycle may control the sea-level changes during a time of Saergan Formation deposition. Ice accumulation at the million-year scale can be explained by a sustained reduction of ice melting in cool high-latitude summers during an interval of a series of reduced obliquity variations (minima of the long term obliquity cycle). In sum, the orbitally forced formation of the Saergan Formation was confirmed and the possible model of the deposition process of the Saergan Shale was proposed based on the high-resolution cyclostratigraphy study in this study.
The Middle–Upper Ordovician Saergan Formation in the Tarim Basin represents as an important hydrocarbon source rock deposited in marine environment. However, the model of the deposition of the Saergan Formation remains nebulous. High-precision geochronologic constraint may shed new light on deposition history of the Saergan Formation. The identification of Milankovitch cycles, in particular, the 405 kyr long orbital eccentricity cycle can be used to construct precise time scales for the sedimentary succession of the Paleozoic Era. The magnetic susceptibility (MS) is a measure of the degree of magnetization of a material in response to an applied magnetic field and it can be a powerful tool for cyclostratigraphy and paleoclimate studies. Here, a total of 701 MS data from the 9 m Saergan Formation in Subashigou section of the Kalpin area, Aksu City, Xinjiang were obtained to conduct cyclostratigraphic analysis, including the multitaper method spectral analysis, the evolutive harmonic analysis and the bandpass filtering. Spectral analyses show significant peaks at 0.74–1.28 m, 0.2–0.27 m, 0.057–0.071 m, and 0.035–0.039 m with the ratio of 21.14: 7.71: 5.71: 1.86: 1.11: 1, which is close to that of the Middle–Late Ordovician astronomical cycles. Although there is no reliable astronomical solution for the Ordovician period, astronomical calibration can be achieved using stable 405 kyr eccentricity cycle. After 405-kyr long eccentricity calibration, the spectral analysis shows periods with 100 kyr (short eccentricity), 30.6–31.2 kyr (obliquity), and 20–21.8 kyr (precession), respectively. Ten eccentricity cycles were obtained using bandpass filtering and a " floating " astronomical time scale with a duration of ~3.9 Myr was established for the Saergan Formation of the Subashigou section. Amplitude modulation (AM) envelope of the interpreted 30.6 kyr band of the 405 kyr-calibrated MS time series reveals long-term cycles with a period of ~1.2 Myr for the Ordovician, which is identical with that at present. The first appearance datum (FAD) of the graptolite Nemagraptus. gracilis was used as a tie point for building the correlation between the Subashigou section and Dawangou section (Global Stratotype Section and Point auxiliary Stratotype of the Sandbian). The result shows that the initiation of deposition of the Saergan Formation in the Subashigou section was ~1.03 Myr later than that at Dawangou section. It supports that the Saergan black shales developed during the strong sea-level transgression process, which drowned the platform, and organic-rich, sediments have been deposited on the carbonate platform. Further comparison among the MS series, 1.2 Myr obliquity cycle and global sea-level curve during the Middle–Late Ordovician, we suggested that 1.2 Myr long obliquity cycle may control the sea-level changes during a time of Saergan Formation deposition. Ice accumulation at the million-year scale can be explained by a sustained reduction of ice melting in cool high-latitude summers during an interval of a series of reduced obliquity variations (minima of the long term obliquity cycle). In sum, the orbitally forced formation of the Saergan Formation was confirmed and the possible model of the deposition process of the Saergan Shale was proposed based on the high-resolution cyclostratigraphy study in this study.
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doi: 10.14027/j.issn.1000-0550.2023.073
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As an important component of unconventional oil and gas resources, the basic research of shale oil and gas resources has gradually attracted attention. Microstructures of clay sediments have an impact on shale foliation and lamination structure, thus influencing the shale reservoir capacity and development effect. In addition to being affected by physical action, clay particles also undergo chemical adsorption and flocculation to form floccules with varying degrees. The basic unit of floccule is tabular particles or domains, further forming flocs or chains, and finally forming a card house structure under the action of electric charge. In the sedimentary stage, the physical and chemical factors affecting the flocculation include particle size, particle content, external hydrodynamic strength and flow properties, climate, electrolyte concentration, ion type, pH value, organic matter, etc. By studying the physical and chemical factors affecting the microstructures of clay sediments and analyzing the other components of mudstone composite particles such as volcanic rock fragments, shale lithics, muddy intraclasts and fecal pellets, the sedimentary environments of mudstone and shale can be identified and described. This study is still in its infancy and a perfect geological model has not been established; The quantitative research of floccules and other components of mudstone composite particles is insufficient, and big data technology has not been used well; The study on the sedimentary micro-environment and internal association characteristics of marine black shale in western China needs to be deepened; The research technology and method are slightly single. Based on the qualitative and quantitative description of microstructures of clay sediments and demonstration of sedimentary environments of mudstone composite particles, it can achieve fine description of complex and changeable sedimentary micro-environment, deepen understanding of the differentiation characteristics of sedimentary environments of shale such as lakes and seas, and further reveal the differences in shale reservoir quality within the high-precision range, laying a foundation for the selection and development of geology and engineering "desserts" in shale.
As an important component of unconventional oil and gas resources, the basic research of shale oil and gas resources has gradually attracted attention. Microstructures of clay sediments have an impact on shale foliation and lamination structure, thus influencing the shale reservoir capacity and development effect. In addition to being affected by physical action, clay particles also undergo chemical adsorption and flocculation to form floccules with varying degrees. The basic unit of floccule is tabular particles or domains, further forming flocs or chains, and finally forming a card house structure under the action of electric charge. In the sedimentary stage, the physical and chemical factors affecting the flocculation include particle size, particle content, external hydrodynamic strength and flow properties, climate, electrolyte concentration, ion type, pH value, organic matter, etc. By studying the physical and chemical factors affecting the microstructures of clay sediments and analyzing the other components of mudstone composite particles such as volcanic rock fragments, shale lithics, muddy intraclasts and fecal pellets, the sedimentary environments of mudstone and shale can be identified and described. This study is still in its infancy and a perfect geological model has not been established; The quantitative research of floccules and other components of mudstone composite particles is insufficient, and big data technology has not been used well; The study on the sedimentary micro-environment and internal association characteristics of marine black shale in western China needs to be deepened; The research technology and method are slightly single. Based on the qualitative and quantitative description of microstructures of clay sediments and demonstration of sedimentary environments of mudstone composite particles, it can achieve fine description of complex and changeable sedimentary micro-environment, deepen understanding of the differentiation characteristics of sedimentary environments of shale such as lakes and seas, and further reveal the differences in shale reservoir quality within the high-precision range, laying a foundation for the selection and development of geology and engineering "desserts" in shale.
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Abstract:
[Objective]Marine carbonates of Permian Wujiaping Formation are commonly inserted by tuffs in northwest Sichuan. The tuff beds are changeable in thicknesses and advantage in capacities in natural gas storage capacity. The Wujiaping Formation at the Daping section is 45.02m thick, and subdivided into two members. Individual thicknesses of tuff beds are 5-55cm, We conduct measurements on geochemical parameters on tuff samples with special references on their reservoir types. [Methods]Synthetic database on microfacies, XRD, scanning electron microscopy, major and trace elements and zircon U-Pb are obtained. [Results] The tuffs are mainly volcanic dust, which are composed of glass chips with particles size less than 0.05mm. The mineral compositions of tuffs are mainly illite and illite mixed montmorillonite, with few amount of quartz and gypsum are less in contains. They are high ratio of Al2O3/TiO2(23.36-34.56), low ratio of SiO2/Al2O3(1.84-2.75), the obvious negative anomaly of Eu, Ba, Sr and Ti elements in the Wu 1 Member, The Wu 2 Member geochemical characteristic with high ratio of Al2O3/TiO2(21.14-53.049), low ratio of SiO2/Al2O3(1.829-2.682), moderate negative anomaly of Eu, depletion of high fleld strength elements such as Nb and Ti. [Conclusion] Such profiles show that Volcanic debris were undergone strong alteration secondary. The tuffs were sourced from multiple acid volcanic eruptions in Emeishan Large Igneous Province, and were formed in the intraplate extensional environment and the Wu 2 Member tuffs is affected by crust-mantle mixed. Reservior space types in tuffs include caves, irregular dissolution pores, intragranular dissolution pores, organic matter pores, intergranular dissolution pores, fractures, etc, the U-Pb age of hydrothermal zircon is dated as (132.37±0.53) Ma. The reservoir in tuffs was influenced by various factors such as the early Cretaceous hydrothermal fluid, tectonic activity.
[Objective]Marine carbonates of Permian Wujiaping Formation are commonly inserted by tuffs in northwest Sichuan. The tuff beds are changeable in thicknesses and advantage in capacities in natural gas storage capacity. The Wujiaping Formation at the Daping section is 45.02m thick, and subdivided into two members. Individual thicknesses of tuff beds are 5-55cm, We conduct measurements on geochemical parameters on tuff samples with special references on their reservoir types. [Methods]Synthetic database on microfacies, XRD, scanning electron microscopy, major and trace elements and zircon U-Pb are obtained. [Results] The tuffs are mainly volcanic dust, which are composed of glass chips with particles size less than 0.05mm. The mineral compositions of tuffs are mainly illite and illite mixed montmorillonite, with few amount of quartz and gypsum are less in contains. They are high ratio of Al2O3/TiO2(23.36-34.56), low ratio of SiO2/Al2O3(1.84-2.75), the obvious negative anomaly of Eu, Ba, Sr and Ti elements in the Wu 1 Member, The Wu 2 Member geochemical characteristic with high ratio of Al2O3/TiO2(21.14-53.049), low ratio of SiO2/Al2O3(1.829-2.682), moderate negative anomaly of Eu, depletion of high fleld strength elements such as Nb and Ti. [Conclusion] Such profiles show that Volcanic debris were undergone strong alteration secondary. The tuffs were sourced from multiple acid volcanic eruptions in Emeishan Large Igneous Province, and were formed in the intraplate extensional environment and the Wu 2 Member tuffs is affected by crust-mantle mixed. Reservior space types in tuffs include caves, irregular dissolution pores, intragranular dissolution pores, organic matter pores, intergranular dissolution pores, fractures, etc, the U-Pb age of hydrothermal zircon is dated as (132.37±0.53) Ma. The reservoir in tuffs was influenced by various factors such as the early Cretaceous hydrothermal fluid, tectonic activity.
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Abstract:
【Objective】To enrich the quantitative evaluation method of shale natural fracture development degree and clarify the main controlling factors of fracture development.【Methods】Taking the Wufeng-Longmaxi Formation shale in Luzhou region as an example, the classification, development index evaluation and control factors of natural fractures in shale reservoirs were systematically studied by means of fine core description, organic geochemical test, triaxial rock mechanics experiment and logging mechanics interpretation.【Results】The results show that there are three genetic categories of developed structural fracture, diagenetic fracture and abnormal high pressure fracture in the Wufeng Formation- S1?11 sub-member shale in Luzhou region, which are subdivided into six types of fractures : shear fractures, tensile fractures, bedding detachment fractures, interlayer bedding fractures, dissolution fractures and abnormal high pressure fractures.The evaluation method of natural fracture development index coupling fracture linear density, filling type and dip angle type is innovatively established, and the quantitative characterization of fracture development degree is realized. It’s clarity that the fracture development degree controlled by structural position: anticline > slope > syncline. The comprehensive analysis of the main controlling factors of fracture development shows that the factors affecting the development degree of natural fractures in shale cores of Wufeng Formation - S1?11 sub-member in Luzhou area from large to small are : tectonic action, rock mechanical properties, sedimentary diagenesis. 【Conclusion】The relevant understanding can provide reference and new ideas for the quantitative evaluation of natural fractures and differential fracturing engineering design in marine shale reservoirs.
【Objective】To enrich the quantitative evaluation method of shale natural fracture development degree and clarify the main controlling factors of fracture development.【Methods】Taking the Wufeng-Longmaxi Formation shale in Luzhou region as an example, the classification, development index evaluation and control factors of natural fractures in shale reservoirs were systematically studied by means of fine core description, organic geochemical test, triaxial rock mechanics experiment and logging mechanics interpretation.【Results】The results show that there are three genetic categories of developed structural fracture, diagenetic fracture and abnormal high pressure fracture in the Wufeng Formation- S1?11 sub-member shale in Luzhou region, which are subdivided into six types of fractures : shear fractures, tensile fractures, bedding detachment fractures, interlayer bedding fractures, dissolution fractures and abnormal high pressure fractures.The evaluation method of natural fracture development index coupling fracture linear density, filling type and dip angle type is innovatively established, and the quantitative characterization of fracture development degree is realized. It’s clarity that the fracture development degree controlled by structural position: anticline > slope > syncline. The comprehensive analysis of the main controlling factors of fracture development shows that the factors affecting the development degree of natural fractures in shale cores of Wufeng Formation - S1?11 sub-member in Luzhou area from large to small are : tectonic action, rock mechanical properties, sedimentary diagenesis. 【Conclusion】The relevant understanding can provide reference and new ideas for the quantitative evaluation of natural fractures and differential fracturing engineering design in marine shale reservoirs.
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Abstract:
[Objective]The study of sedimentology, geochemistry and zircon U-Pb dating of sand-gravel sediments is of great significance to stratigraphic division, river system evolution, revealing mountain tectonic uplift history and regional tectono-magmatic events. However, the weak understanding of the Hulun Buir Bayan Tara sand gravel profile limits its stratigraphic division and in-depth understanding of the regional surface process. [Methods]For this reason, sedimentological, heavy mineral, geochemical (macronutrients, trace and rare earth elements) and zircon U-Pb chronology analyses were performed on this section to analyze the chemical weathering characteristics and sedimentary cycles of the sediments as well as the material sources, and to explore the stratigraphic delineation attribution as well as the tectonic context and indication of regional magmatic-tectonic events. It provides a new basis for discussing the characteristic areas of sedimentary environment and stratigraphic division and correlation. [Results and Discussions]The results show that: (1) The gravels are poorly sorted and rounded, and have undergone a non-weak degree of weathering, with quartzaceous (61.2%) and tuff (34.9%) dominating the gravel composition, followed by terrigenous clastic (2.6%) and rhyolite (1.3%). The heavy mineral composition is absolutely dominated by albite (32.54%) and ilmenite (33.01%), followed by magnetite (12.11%), zircon (5.98%), hematite (5.47%) and anatase (1.34%), with less than 1% chlorite, rutile and garnet. There are no or very few unstable minerals, indicating that the sediments have experienced strong chemical weathering. Combined with geochemical characteristics and geomorphological evidence, the comprehensive analysis shows that the sediment maturity of Bayan Tara sand gravel profile is low and belongs to the product of the first cycle, and the sediment has experienced moderate chemical weathering after accumulation. And compared with the age spectrum of detrital zircons in the northern section of the Greater Khingan Mountains, it is further proved that the provenance area comes from the northern section of the Greater Khingan Mountains. (2) Combined with macro and micro perspectives (heavy minerals and geochemical indicators, etc.), it is considered that the sediments of Bayan Tala sand gravel profile are alluvial-proluvial deposits formed under warm and dry oxidation environment. Combined with new research results, various methods were integrated and analyzed such as sedimentology, mineral petrology and geochronology, and compared with the standard sections of the Baitushan Formation in Longjiang County and Pingan Town at the eastern foot of the Greater Khingan Mountains, its stratigraphic units can be divided into Baitushan Group (3) The discrimination diagram of the tectonic background shows that the tectonic background is a passive continental margin, which is consistent with the fact that the Greater Khingan Mountains are located within the plate and the structure is relatively stable. The peak ages of U-Pb ages of clastic zircons at 100~200Ma and 250~350Ma record the multi-stage magmatic tectonic events triggered by the closure of the Paleo-Asian Ocean and the subduction and retrogression of the Paleo-Pacific Ocean in the northern segment of the Greater Khingan Mountains. [Conclusions]The above studies are of great significance to the division of Quaternary strata and the reconstruction of surface processes in the early Pleistocene in the Greater Khingan Mountains area, and it provides a new indication for a better understanding of the tectonic evolution of the Hulun Buir Bayan Tala sandy gravel section and its surrounding areas.
[Objective]The study of sedimentology, geochemistry and zircon U-Pb dating of sand-gravel sediments is of great significance to stratigraphic division, river system evolution, revealing mountain tectonic uplift history and regional tectono-magmatic events. However, the weak understanding of the Hulun Buir Bayan Tara sand gravel profile limits its stratigraphic division and in-depth understanding of the regional surface process. [Methods]For this reason, sedimentological, heavy mineral, geochemical (macronutrients, trace and rare earth elements) and zircon U-Pb chronology analyses were performed on this section to analyze the chemical weathering characteristics and sedimentary cycles of the sediments as well as the material sources, and to explore the stratigraphic delineation attribution as well as the tectonic context and indication of regional magmatic-tectonic events. It provides a new basis for discussing the characteristic areas of sedimentary environment and stratigraphic division and correlation. [Results and Discussions]The results show that: (1) The gravels are poorly sorted and rounded, and have undergone a non-weak degree of weathering, with quartzaceous (61.2%) and tuff (34.9%) dominating the gravel composition, followed by terrigenous clastic (2.6%) and rhyolite (1.3%). The heavy mineral composition is absolutely dominated by albite (32.54%) and ilmenite (33.01%), followed by magnetite (12.11%), zircon (5.98%), hematite (5.47%) and anatase (1.34%), with less than 1% chlorite, rutile and garnet. There are no or very few unstable minerals, indicating that the sediments have experienced strong chemical weathering. Combined with geochemical characteristics and geomorphological evidence, the comprehensive analysis shows that the sediment maturity of Bayan Tara sand gravel profile is low and belongs to the product of the first cycle, and the sediment has experienced moderate chemical weathering after accumulation. And compared with the age spectrum of detrital zircons in the northern section of the Greater Khingan Mountains, it is further proved that the provenance area comes from the northern section of the Greater Khingan Mountains. (2) Combined with macro and micro perspectives (heavy minerals and geochemical indicators, etc.), it is considered that the sediments of Bayan Tala sand gravel profile are alluvial-proluvial deposits formed under warm and dry oxidation environment. Combined with new research results, various methods were integrated and analyzed such as sedimentology, mineral petrology and geochronology, and compared with the standard sections of the Baitushan Formation in Longjiang County and Pingan Town at the eastern foot of the Greater Khingan Mountains, its stratigraphic units can be divided into Baitushan Group (3) The discrimination diagram of the tectonic background shows that the tectonic background is a passive continental margin, which is consistent with the fact that the Greater Khingan Mountains are located within the plate and the structure is relatively stable. The peak ages of U-Pb ages of clastic zircons at 100~200Ma and 250~350Ma record the multi-stage magmatic tectonic events triggered by the closure of the Paleo-Asian Ocean and the subduction and retrogression of the Paleo-Pacific Ocean in the northern segment of the Greater Khingan Mountains. [Conclusions]The above studies are of great significance to the division of Quaternary strata and the reconstruction of surface processes in the early Pleistocene in the Greater Khingan Mountains area, and it provides a new indication for a better understanding of the tectonic evolution of the Hulun Buir Bayan Tala sandy gravel section and its surrounding areas.
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Abstract:
The hydrothermal activity in early Cambrian in northwest Hunan take great influence on the sedimentary strata at that time. But the specific influence and extent of the hydrothermal activity on the surrounding area are not very clear. This study systematically revealed the differences in sedimentary geochemical characteristics and the specific influence based on comprehensively analyzing total organic carbon (TOC), X-ray diffraction (XRD), major and trace elements in Huaye1 (HY1), Xiangan1 (XA1) and Xiangji1 (XJ1). Research shows that the wells were far away from the hydrothermal activities, but some indicators showed both normal and hydrothermal deposition characteristics in the bottom of Niutitang formation black shales. XJ1 was the most affected by the hydrothermal activity, XA1 was basically unaffected, and HY1 lies somewhere in between. Co/Zn, LaN/CeN, ∑REE and ∑LREE/∑HREE are well indicators for showing the hydrothermal activity. Ba, Mo, Ni, U, V are highly enriched in the stratum, and their enrichment is the result of combining the hydrothermal activities, strong reducing environment, biological activities and organic matter etc. The sedimentary environment of strong reducing or vulcanization may be the main factor for the enrichment of elements. The abundance of organic matter within a certain range has a positive correlation with the enrichment degree of the different elements. XJ1, HY1 and XA1, which are far away from hydrothermal activities in turn, have certain differences on the response of sedimentary geochemistry characteristics. XA1, which in the deep-sea basin is more dependent on the supply from the deep internal source of the remote debris. The hydrothermal activities provide a material basis rich in these elements, and strengthen the reducibility of the surrounding sedimentary environment at the same time, which is conducive to the further enrichment of these elements and organic matter. Furthermore, this influence gradually decreases with the increase of the distance from the hydrothermal activities.
The hydrothermal activity in early Cambrian in northwest Hunan take great influence on the sedimentary strata at that time. But the specific influence and extent of the hydrothermal activity on the surrounding area are not very clear. This study systematically revealed the differences in sedimentary geochemical characteristics and the specific influence based on comprehensively analyzing total organic carbon (TOC), X-ray diffraction (XRD), major and trace elements in Huaye1 (HY1), Xiangan1 (XA1) and Xiangji1 (XJ1). Research shows that the wells were far away from the hydrothermal activities, but some indicators showed both normal and hydrothermal deposition characteristics in the bottom of Niutitang formation black shales. XJ1 was the most affected by the hydrothermal activity, XA1 was basically unaffected, and HY1 lies somewhere in between. Co/Zn, LaN/CeN, ∑REE and ∑LREE/∑HREE are well indicators for showing the hydrothermal activity. Ba, Mo, Ni, U, V are highly enriched in the stratum, and their enrichment is the result of combining the hydrothermal activities, strong reducing environment, biological activities and organic matter etc. The sedimentary environment of strong reducing or vulcanization may be the main factor for the enrichment of elements. The abundance of organic matter within a certain range has a positive correlation with the enrichment degree of the different elements. XJ1, HY1 and XA1, which are far away from hydrothermal activities in turn, have certain differences on the response of sedimentary geochemistry characteristics. XA1, which in the deep-sea basin is more dependent on the supply from the deep internal source of the remote debris. The hydrothermal activities provide a material basis rich in these elements, and strengthen the reducibility of the surrounding sedimentary environment at the same time, which is conducive to the further enrichment of these elements and organic matter. Furthermore, this influence gradually decreases with the increase of the distance from the hydrothermal activities.
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Abstract:
Based on a stalagmite δ13C record from Yongxing Cave, Hubei Province in the middle reaches of the Yangtze River, we reconstruct a history of local paleoclimate and environment during the period of 1044 ~ 1954 A.D. The δ13C record shows two completely different states during the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA), with the lower δ13C values charactering the MCA period, while the higher δ13C values the LIA. This phenomenon indicates a regime shift from a strong to weak state for the vegetation respiration activity and precipitation variation. This variation is consistent with many stalagmites δ13C records in southwest China and middle reaches of the Yangtze River. This variation is attributed to both climate deterioration and human influences, which lead to the reduction of vegetation cover at that time. Here our stalagmite δ13C record shows that the shift of the vegetation cover was rapid from the MCA to LIA. A Rampfit analysis shows that the shift occurred between 1434 A.D. and 1460 A.D., lasting 26 years. This rapid shift helps to clearly and accurately constrain the timing boundary between the MCA and LIA in the middle reaches of the Yangtze River. On the other hand, the Yongxing δ13C record is correlated with changes in the total solar radiation, intertropical convergence zone, Chinese temperature and ENSO on the MCA and LIA event scales. This correlation indicates that the changes of the hydrological circulation and vegetation cover in the middle reaches of the Yangtze River have a dynamic relation with the regional and global climate change during the past millennium，and the impacts of human activities on surface vegetation may be related to the background of regional or global climate change.
Based on a stalagmite δ13C record from Yongxing Cave, Hubei Province in the middle reaches of the Yangtze River, we reconstruct a history of local paleoclimate and environment during the period of 1044 ~ 1954 A.D. The δ13C record shows two completely different states during the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA), with the lower δ13C values charactering the MCA period, while the higher δ13C values the LIA. This phenomenon indicates a regime shift from a strong to weak state for the vegetation respiration activity and precipitation variation. This variation is consistent with many stalagmites δ13C records in southwest China and middle reaches of the Yangtze River. This variation is attributed to both climate deterioration and human influences, which lead to the reduction of vegetation cover at that time. Here our stalagmite δ13C record shows that the shift of the vegetation cover was rapid from the MCA to LIA. A Rampfit analysis shows that the shift occurred between 1434 A.D. and 1460 A.D., lasting 26 years. This rapid shift helps to clearly and accurately constrain the timing boundary between the MCA and LIA in the middle reaches of the Yangtze River. On the other hand, the Yongxing δ13C record is correlated with changes in the total solar radiation, intertropical convergence zone, Chinese temperature and ENSO on the MCA and LIA event scales. This correlation indicates that the changes of the hydrological circulation and vegetation cover in the middle reaches of the Yangtze River have a dynamic relation with the regional and global climate change during the past millennium，and the impacts of human activities on surface vegetation may be related to the background of regional or global climate change.
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Abstract:
[Objective] The Wutonggou Formation of the Upper Permian in Lukeqin area of the Turpan-Hami Basin has good oil and gas exploration potential and thus is the key deep exploration target in the Turpan-Hami Basin. Diagenetic analysis shows that calcite cement is one of the main authigenic minerals developed in the reservoir of Wutonggou Formation in this area, but more work on the precise analysis is still recommended to better understand its genetic period and how it affects the reservoir quality. Since the calcite cement is one of the abundant authigenic cements in most clastic rocks. It is also the product of fluid rock interaction during diagenesis, which its relative content, occurrence type, occurrence state and formation mechanism would likely exert huge impacts on reservoir quality. [Methods] Combining with the previous study with the conclusion that mechanical compaction and cementation under deep burial conditions are the two main factors affecting the quality of Wutonggou Formation sandstone reservoir in Lukeqin area, here we present the thin section identification, physical property analysis, scanning electron microscopy, cathodoluminescence and other testing methods of the Wutonggou Formation of the Upper Permian in Lukeqin area of the Turpan-Hami Basin. We systematically investigated the period and genesis of calcite cements commonly existing in the deep sandstone reservoir of this period, and discussed the influence of calcite cement on reservoir quality. [Results and Discussions] The photomicrographs and statistics show an obvious positive correlation between the porosity and permeability, indicating that the sandstone reservoir of Wutonggou Formation is a porous reservoir; The calcite cement area content most favorable for reservoir development of the Wutonggou Formation reservoir in Lukeqin area is 1-8%; More than 8.0% samples show that the primary pores are almost filled with calcite, while less than 1.0% samples present that the compaction is too strong and therefore unfavorable for reservoir development; Photomicrographs also exhibit a filling relationship that indicates three stages of calcite cement and the first stage is argillaceous calcite, which is the origin of alkaline lake water sedimentation in the quasi contemporaneous stage; The second stage is calcite cemented by continuous crystal, which is the origin of active Ca2+ rich pore water precipitation in the open diagenetic system with shallow burial of early diagenesis; Stage Ⅲ is calcite filled with feldspar and other intragranular solution pores, namely the iron calcite that formed by the transformation of clay minerals such as montmorillonite in the deep burial environment of middle diagenesis. There is no obvious positive or negative correlation between calcite cement and physical properties, which indicates that it is mainly belongs to retentive diagenesis and appears in the form of pore filling, which could occupy the remaining intergranular pores while enhance the ability to resist compaction of the clastic particle skeleton. This is also consistent with a large number of earlier studies that the calcite cement formed in the early diagenetic stage before the main compaction can preserve the primary pores in the sandstone, which may further dissolve and release the secondary pores to improve the reservoir quality in the later diagenetic process. [Conclusion] Therefore, we suggest that the calcite cement is the key factor for the development of deep sandstone reservoirs of the Wutonggou Formation in Lukeqin area.
[Objective] The Wutonggou Formation of the Upper Permian in Lukeqin area of the Turpan-Hami Basin has good oil and gas exploration potential and thus is the key deep exploration target in the Turpan-Hami Basin. Diagenetic analysis shows that calcite cement is one of the main authigenic minerals developed in the reservoir of Wutonggou Formation in this area, but more work on the precise analysis is still recommended to better understand its genetic period and how it affects the reservoir quality. Since the calcite cement is one of the abundant authigenic cements in most clastic rocks. It is also the product of fluid rock interaction during diagenesis, which its relative content, occurrence type, occurrence state and formation mechanism would likely exert huge impacts on reservoir quality. [Methods] Combining with the previous study with the conclusion that mechanical compaction and cementation under deep burial conditions are the two main factors affecting the quality of Wutonggou Formation sandstone reservoir in Lukeqin area, here we present the thin section identification, physical property analysis, scanning electron microscopy, cathodoluminescence and other testing methods of the Wutonggou Formation of the Upper Permian in Lukeqin area of the Turpan-Hami Basin. We systematically investigated the period and genesis of calcite cements commonly existing in the deep sandstone reservoir of this period, and discussed the influence of calcite cement on reservoir quality. [Results and Discussions] The photomicrographs and statistics show an obvious positive correlation between the porosity and permeability, indicating that the sandstone reservoir of Wutonggou Formation is a porous reservoir; The calcite cement area content most favorable for reservoir development of the Wutonggou Formation reservoir in Lukeqin area is 1-8%; More than 8.0% samples show that the primary pores are almost filled with calcite, while less than 1.0% samples present that the compaction is too strong and therefore unfavorable for reservoir development; Photomicrographs also exhibit a filling relationship that indicates three stages of calcite cement and the first stage is argillaceous calcite, which is the origin of alkaline lake water sedimentation in the quasi contemporaneous stage; The second stage is calcite cemented by continuous crystal, which is the origin of active Ca2+ rich pore water precipitation in the open diagenetic system with shallow burial of early diagenesis; Stage Ⅲ is calcite filled with feldspar and other intragranular solution pores, namely the iron calcite that formed by the transformation of clay minerals such as montmorillonite in the deep burial environment of middle diagenesis. There is no obvious positive or negative correlation between calcite cement and physical properties, which indicates that it is mainly belongs to retentive diagenesis and appears in the form of pore filling, which could occupy the remaining intergranular pores while enhance the ability to resist compaction of the clastic particle skeleton. This is also consistent with a large number of earlier studies that the calcite cement formed in the early diagenetic stage before the main compaction can preserve the primary pores in the sandstone, which may further dissolve and release the secondary pores to improve the reservoir quality in the later diagenetic process. [Conclusion] Therefore, we suggest that the calcite cement is the key factor for the development of deep sandstone reservoirs of the Wutonggou Formation in Lukeqin area.
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Abstract:
[Objective] In the lower Yangtze area, thick Early Paleozoic carbonates are potential reservoirs for oil, gas and geothermal resources. In 2021, Well Sure1, drilled by the Geological Survey of Jiangsu Province in the Subei Basin, successfully detected high-temperature hot-dry rock geothermal resources in the Early Paleozoic carbonates, bringing the Early Paleozoic carbonate sedimentary microfacies and environmental evolution widespread academic attention. [Method] A detailed microfacies analysis was conducted on Well Sure 1 in Subei Basin and three field outcrops in the Ningzhen Mountains to reconstruct the sedimentary environmental evolution of the Early Paleozoic carbonates in the lower Yangtze area and provide key basic geological information for the exploration of hot-dry rock geothermal resources in the study area. [Result] Thirteen microfacies, corresponding to peritidal and shoal environments in an inner carbonate platform setting with no significant change in paleowater depth, were identified by integrating sedimentological and paleontological observations. The Cambrian Mufushan and Guanyintai formations and Early Ordovician Lunshan Formation are mainly silty dolomites with micrite (MF1), silty dolomite (MF2), laminated silty dolomite (MF3), scarce fenestrae bonded dolomite (MF4), fine crystalline dolomite (MF5), fine crystalline dolomite with micrite (MF7). and breccia dolomite (MF8). These strata lack fossils, but laminations, birdeyes, and fenestral structures indicate upper intertidal to lower supratidal environments. The Early Ordovician Honghuayuan Formation is mainly dolomitized peloidal limestone (MF6), intraclastic dolomite (MF9), dolomitized oolitic limestone (MF10), oolitic dolomite (MF11), intraclastic limestone (MF12), and oolitic limestone with echinoderm fragments (MF13), indicating a high-energy shoal environment. [Conclusion] The Cambrian Mufushan, Paotaishan, and Guanyintai formations were dominated by an intertidal environment, while the lower part of the Early Ordovician Lunshan Formation and the Honghuayuan Formation were dominated by a shoal environment, and the ancient water depth was relatively deeper. The Cambrian Guanyintai Formation in the Lower Yangtze region is a favorable target for future exploration of hot and dry rock reservoirs.
[Objective] In the lower Yangtze area, thick Early Paleozoic carbonates are potential reservoirs for oil, gas and geothermal resources. In 2021, Well Sure1, drilled by the Geological Survey of Jiangsu Province in the Subei Basin, successfully detected high-temperature hot-dry rock geothermal resources in the Early Paleozoic carbonates, bringing the Early Paleozoic carbonate sedimentary microfacies and environmental evolution widespread academic attention. [Method] A detailed microfacies analysis was conducted on Well Sure 1 in Subei Basin and three field outcrops in the Ningzhen Mountains to reconstruct the sedimentary environmental evolution of the Early Paleozoic carbonates in the lower Yangtze area and provide key basic geological information for the exploration of hot-dry rock geothermal resources in the study area. [Result] Thirteen microfacies, corresponding to peritidal and shoal environments in an inner carbonate platform setting with no significant change in paleowater depth, were identified by integrating sedimentological and paleontological observations. The Cambrian Mufushan and Guanyintai formations and Early Ordovician Lunshan Formation are mainly silty dolomites with micrite (MF1), silty dolomite (MF2), laminated silty dolomite (MF3), scarce fenestrae bonded dolomite (MF4), fine crystalline dolomite (MF5), fine crystalline dolomite with micrite (MF7). and breccia dolomite (MF8). These strata lack fossils, but laminations, birdeyes, and fenestral structures indicate upper intertidal to lower supratidal environments. The Early Ordovician Honghuayuan Formation is mainly dolomitized peloidal limestone (MF6), intraclastic dolomite (MF9), dolomitized oolitic limestone (MF10), oolitic dolomite (MF11), intraclastic limestone (MF12), and oolitic limestone with echinoderm fragments (MF13), indicating a high-energy shoal environment. [Conclusion] The Cambrian Mufushan, Paotaishan, and Guanyintai formations were dominated by an intertidal environment, while the lower part of the Early Ordovician Lunshan Formation and the Honghuayuan Formation were dominated by a shoal environment, and the ancient water depth was relatively deeper. The Cambrian Guanyintai Formation in the Lower Yangtze region is a favorable target for future exploration of hot and dry rock reservoirs.
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Abstract:
[Objective] The offshore Indus Basin was located in the equatorial region during the Paleo-Eocene period, and large-scale carbonate platform was developed. However, limited by the quality and quantity of 2D seismic data, the sedimentary characteristics and evolution of carbonate platform are not clear, and the internal structure of platform is not depicted sufficiently, which further restricts the deepening of oil and gas exploration in this area. [Method] Through the collection of previous and newly acquired 2D seismic and drilling data, the seismic facies identification of the Paleo-Eocene carbonate platform in the offshore Indus Basin was carried out, the internal plane and vertical distribution characteristics of the platform in different periods were depicted, the sedimentary evolution history of the platform was discussed, and the main controlling factors affecting the development of the platform were summarized. [Results] Based on the systematic analysis of seismic data, 6 types of seismic facies have been identified. Among them, mound or lenticular shape-medium weak amplitude-medium low continuous-medium low frequency corresponds to reef sedimentary subfacies, with good reservoir physical properties. On the basis of seismic facies analysis, the carbonate platform in the study area is divided into four sedimentary evolution stages, including initial development stage, prosperity stage, recession stage and inundation stage. The initial stage is dominated by platform lagoon facies, mainly showing vertical growth and limited sedimentary thickness. In the prosperity stage, large-scale carbonate rocks were deposited on the early thin carbonate platform, and the thickness of reef shoal facies was significantly increased. In the recession stage, the platform edge obviously retreats, the area decreases, and the platforms are isolated. In the inundation stage, the range of the platform is further reduced, and the reef and shoal facies are mainly deposited, and the platform is gradually inundated by seawater in the late stage. Based on the analysis of the background of regional tectonic evolution, sea level rise and fall, and paleoclimate evolution, combined with the space-time distribution characteristics of the carbonate platform, it is believed that the pre ancient highland terrain formed by magma intrusion limits the spatial distribution, shape, and scale of the carbonate platform in the Paleo Eocene period, and sea level rise and fall and paleoclimate evolution affect the platform shape. In the petroleum accumulation process of reef reservoir in the study area, the distribution of effective hydrocarbon source rocks, migration pathways, and the spatial distribution of reef and carbonate reservoirs are the three most important control factors. The isolated platform in the middle of the study area is far away from the source rock, and the oil and gas filling is insufficient, which has been confirmed in the drilling. There are many reefs in the south of the study area with different scales. In addition, a large number of NE trending faults are developed in the area, which connect the Paleogene and Neogene, and are good channels for oil and gas migration. The study provides a basis for revealing regional sea level changes and driving mechanisms, and provides support for oil and gas exploration in the region.
[Objective] The offshore Indus Basin was located in the equatorial region during the Paleo-Eocene period, and large-scale carbonate platform was developed. However, limited by the quality and quantity of 2D seismic data, the sedimentary characteristics and evolution of carbonate platform are not clear, and the internal structure of platform is not depicted sufficiently, which further restricts the deepening of oil and gas exploration in this area. [Method] Through the collection of previous and newly acquired 2D seismic and drilling data, the seismic facies identification of the Paleo-Eocene carbonate platform in the offshore Indus Basin was carried out, the internal plane and vertical distribution characteristics of the platform in different periods were depicted, the sedimentary evolution history of the platform was discussed, and the main controlling factors affecting the development of the platform were summarized. [Results] Based on the systematic analysis of seismic data, 6 types of seismic facies have been identified. Among them, mound or lenticular shape-medium weak amplitude-medium low continuous-medium low frequency corresponds to reef sedimentary subfacies, with good reservoir physical properties. On the basis of seismic facies analysis, the carbonate platform in the study area is divided into four sedimentary evolution stages, including initial development stage, prosperity stage, recession stage and inundation stage. The initial stage is dominated by platform lagoon facies, mainly showing vertical growth and limited sedimentary thickness. In the prosperity stage, large-scale carbonate rocks were deposited on the early thin carbonate platform, and the thickness of reef shoal facies was significantly increased. In the recession stage, the platform edge obviously retreats, the area decreases, and the platforms are isolated. In the inundation stage, the range of the platform is further reduced, and the reef and shoal facies are mainly deposited, and the platform is gradually inundated by seawater in the late stage. Based on the analysis of the background of regional tectonic evolution, sea level rise and fall, and paleoclimate evolution, combined with the space-time distribution characteristics of the carbonate platform, it is believed that the pre ancient highland terrain formed by magma intrusion limits the spatial distribution, shape, and scale of the carbonate platform in the Paleo Eocene period, and sea level rise and fall and paleoclimate evolution affect the platform shape. In the petroleum accumulation process of reef reservoir in the study area, the distribution of effective hydrocarbon source rocks, migration pathways, and the spatial distribution of reef and carbonate reservoirs are the three most important control factors. The isolated platform in the middle of the study area is far away from the source rock, and the oil and gas filling is insufficient, which has been confirmed in the drilling. There are many reefs in the south of the study area with different scales. In addition, a large number of NE trending faults are developed in the area, which connect the Paleogene and Neogene, and are good channels for oil and gas migration. The study provides a basis for revealing regional sea level changes and driving mechanisms, and provides support for oil and gas exploration in the region.
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Abstract:
[Objective] The thin-layered shale and shell-limestone are beneficial for tight shale-oil reservoir of the Dongyuemiao Member of Ziliujing Formation (Lower Jurassic) in northern of Sichuan Basin，and developing various types of fractures，calcite veins and dissolution. To decipher the burial and diagenetic sequence of shell-limestone interlayers，and discuss the relations of hydrocarbon accumulation with formation of calcite and reservoir densification. [Methods] detailed core observation, microscopic section observation，electron probe composition，trace elements and paragenetic minerals are conducted. [Results and Discussions] The results show that seven types of calcite occur in the organic-rich shale of Dongyuemiao Member according to morphology, staining and occurrence condition，such as (1) Recrystallized fine-medium crystalline calcite (C1) which constituting shell-limestone, (2) Noddle-lenticular fibrous calcite which along the edge of shell-limestone (C2), (3) Micro-sparry calcite which occurs along the edge of shell limestone (C3), (4) Fibrous calcite in the shell-mudstone (C4), (5) Microcrystalline granular calcite in argillaceous-shell limestone (C5), (6) Microcrystalline granular calcite in muddy shell-limestone (C6) and sparry calcite in pores and/ or fractures (C7). Besides, the microfractures in the shell-limestone are developed, which can be obviously divided into F1, F2 and F3. The formation sequence of minerals such as fractures and calcite is: C1+pyrite → F1 → F2→ C2/C4 → C3→ quartz+ kaolinite → F3→ C5/C6+ asphalt → C7. The major elements in calcite and the division of phases indicate that C1 to C3 calcite which have low content of FeO and high content of SrO may formed in the early diagenetic stage, The contact relationship between C2 and interlayer fracture (F2) caused by fluid overpressure indicates that calcite C2 belongs to the first phase of fluid overpressure cement. Calcite C3 is mainly derived from the dissolution and re-precipitation of C1 and C2, and is formed during the second phase cementation. Calcite C4 is mainly developed at the edge of the shell mudstone; the incomplete fibrous crystal morphology and obvious dissolution at the edge imply that C4 should be the product of ion exchange and recrystallization of calcite from the first phase of fluid overpressure. Furthermore, Calcite C5, C6 and C7 have high content of MnO, FeO and low content of SrO, which inferred products of the middle and late stage of diagenesis and belong to the fourth stage cement. Precipitation models of various types of calcite are elucidated by the integration of regional burial history, diagenetic evolution sequence and tectonic- thermal evolution history, and four models are pointed out: (1) Recrystallization of shell-sediments; (2) Fibrous calcite formed during Stage B of early diagenesis by hydrocarbon generation and expulsion from organic rich shale；(3) Calcite formed during Stage A of middle diagenesis by dissolution and re-precipitation；(4) Block-sparry calcite formed during Stage B of middle diagenesis. The element content of Fe，Mn and Sr in the calcite is closely related to its formation time and stage. [Conclusions] Muti-cementation of calcite is crucial to densification of limestone reservoir. Fibrous calcite veins triggered by fluid overpressure led to densification as well as foundation for late dissolution. However，the precipitation of calcite during middle diagenesis eventually decreased pores. Overall，the precipitation of various types of calcite constrained the distribution of shale-oil in densified reservoir.
[Objective] The thin-layered shale and shell-limestone are beneficial for tight shale-oil reservoir of the Dongyuemiao Member of Ziliujing Formation (Lower Jurassic) in northern of Sichuan Basin，and developing various types of fractures，calcite veins and dissolution. To decipher the burial and diagenetic sequence of shell-limestone interlayers，and discuss the relations of hydrocarbon accumulation with formation of calcite and reservoir densification. [Methods] detailed core observation, microscopic section observation，electron probe composition，trace elements and paragenetic minerals are conducted. [Results and Discussions] The results show that seven types of calcite occur in the organic-rich shale of Dongyuemiao Member according to morphology, staining and occurrence condition，such as (1) Recrystallized fine-medium crystalline calcite (C1) which constituting shell-limestone, (2) Noddle-lenticular fibrous calcite which along the edge of shell-limestone (C2), (3) Micro-sparry calcite which occurs along the edge of shell limestone (C3), (4) Fibrous calcite in the shell-mudstone (C4), (5) Microcrystalline granular calcite in argillaceous-shell limestone (C5), (6) Microcrystalline granular calcite in muddy shell-limestone (C6) and sparry calcite in pores and/ or fractures (C7). Besides, the microfractures in the shell-limestone are developed, which can be obviously divided into F1, F2 and F3. The formation sequence of minerals such as fractures and calcite is: C1+pyrite → F1 → F2→ C2/C4 → C3→ quartz+ kaolinite → F3→ C5/C6+ asphalt → C7. The major elements in calcite and the division of phases indicate that C1 to C3 calcite which have low content of FeO and high content of SrO may formed in the early diagenetic stage, The contact relationship between C2 and interlayer fracture (F2) caused by fluid overpressure indicates that calcite C2 belongs to the first phase of fluid overpressure cement. Calcite C3 is mainly derived from the dissolution and re-precipitation of C1 and C2, and is formed during the second phase cementation. Calcite C4 is mainly developed at the edge of the shell mudstone; the incomplete fibrous crystal morphology and obvious dissolution at the edge imply that C4 should be the product of ion exchange and recrystallization of calcite from the first phase of fluid overpressure. Furthermore, Calcite C5, C6 and C7 have high content of MnO, FeO and low content of SrO, which inferred products of the middle and late stage of diagenesis and belong to the fourth stage cement. Precipitation models of various types of calcite are elucidated by the integration of regional burial history, diagenetic evolution sequence and tectonic- thermal evolution history, and four models are pointed out: (1) Recrystallization of shell-sediments; (2) Fibrous calcite formed during Stage B of early diagenesis by hydrocarbon generation and expulsion from organic rich shale；(3) Calcite formed during Stage A of middle diagenesis by dissolution and re-precipitation；(4) Block-sparry calcite formed during Stage B of middle diagenesis. The element content of Fe，Mn and Sr in the calcite is closely related to its formation time and stage. [Conclusions] Muti-cementation of calcite is crucial to densification of limestone reservoir. Fibrous calcite veins triggered by fluid overpressure led to densification as well as foundation for late dissolution. However，the precipitation of calcite during middle diagenesis eventually decreased pores. Overall，the precipitation of various types of calcite constrained the distribution of shale-oil in densified reservoir.
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Abstract:
[Objective] Benxi Formation in the central and eastern part of Ordos Basin is rich in natural gas resources and has exploration potential, but the sedimentary complex sand body changes laterally, the continuity of fast gas reservoir is poor, and the origin is unclear. Discussion on the genetic types and development of sand bodies in this period provides useful reference for oil and gas exploration and paleogeographic reconstruction in this area.[Methods] On the basis of field outcrop and core observation, combined with rock thin section grain size and logging data system, the characteristics of lithofacies and lithofacies association of Benxi Formation are studied, the genetic types of sand bodies of Benxi Formation are discussed, the distribution law and sedimentary evolution of sand bodies are revealed, and the sedimentation of Benxi Formation is established. [Results and Conclusion] The study shows that there are 12 lithofacies types in Benxi Formation in the central and eastern Ordos Basin during the sedimentary period. The genetic types of sand bodies are mainly six types: underwater distributary channel, tidal channel, tidal flat (sand flat-mixed flat), tidal bar, barrier bar, tidal storm and shelf. Among them, the north and south ends of North China plate were in the initial collision and splicing stage of small landmasses during the sedimentary period of Hutian section, and the provenance supplied weak and undeveloped sand bodies; The eastern part of the study area was covered by seawater, and the north-south provenance system basin was reformed by the tidal action mainly based on the background of spring tide difference. The sand bodies are mainly tidal bar sand bodies, small-scale underwater distributary channel sand bodies, tidal channel sand bodies and tidal flat (sand flat-mixed flat) sand bodies; During the sedimentary period of Jinci section, the orogeny in the north and south directions was enhanced. In the north of the study area, the source supply was sufficient, and the delta system was developed continuously into the basin. The delta sand body was reformed by tidal action dominated by medium and small tidal range background, but it was mainly reformed by underwater distributary channel sand body in the south-central part, mainly developed tidal bar sand body in the west, which was relatively shallow near paleowater body, and was reformed by tidal action dominated by medium and small tidal range background. Barrier bar sand body, tidal channel sand body and tidal flat (sand flat-mixed flat) sand body were developed.
[Objective] Benxi Formation in the central and eastern part of Ordos Basin is rich in natural gas resources and has exploration potential, but the sedimentary complex sand body changes laterally, the continuity of fast gas reservoir is poor, and the origin is unclear. Discussion on the genetic types and development of sand bodies in this period provides useful reference for oil and gas exploration and paleogeographic reconstruction in this area.[Methods] On the basis of field outcrop and core observation, combined with rock thin section grain size and logging data system, the characteristics of lithofacies and lithofacies association of Benxi Formation are studied, the genetic types of sand bodies of Benxi Formation are discussed, the distribution law and sedimentary evolution of sand bodies are revealed, and the sedimentation of Benxi Formation is established. [Results and Conclusion] The study shows that there are 12 lithofacies types in Benxi Formation in the central and eastern Ordos Basin during the sedimentary period. The genetic types of sand bodies are mainly six types: underwater distributary channel, tidal channel, tidal flat (sand flat-mixed flat), tidal bar, barrier bar, tidal storm and shelf. Among them, the north and south ends of North China plate were in the initial collision and splicing stage of small landmasses during the sedimentary period of Hutian section, and the provenance supplied weak and undeveloped sand bodies; The eastern part of the study area was covered by seawater, and the north-south provenance system basin was reformed by the tidal action mainly based on the background of spring tide difference. The sand bodies are mainly tidal bar sand bodies, small-scale underwater distributary channel sand bodies, tidal channel sand bodies and tidal flat (sand flat-mixed flat) sand bodies; During the sedimentary period of Jinci section, the orogeny in the north and south directions was enhanced. In the north of the study area, the source supply was sufficient, and the delta system was developed continuously into the basin. The delta sand body was reformed by tidal action dominated by medium and small tidal range background, but it was mainly reformed by underwater distributary channel sand body in the south-central part, mainly developed tidal bar sand body in the west, which was relatively shallow near paleowater body, and was reformed by tidal action dominated by medium and small tidal range background. Barrier bar sand body, tidal channel sand body and tidal flat (sand flat-mixed flat) sand body were developed.
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Abstract:
The carbonate rocks from the Sinian Dengying Formation in the northern Sichuan Basin experienced multi-stage fluid alternation, which has exerted a significant influence on the quality of the reservoir. Laser in-situ carbon and oxygen isotope, micro-area strontium isotope, petrography and cathodoluminescence were used to systematically analyze the petrology, and diagenetic evolution of dolomite in Dengying Formation. Based on these researches, we clarified the diagenesis process of different diagenetic fluids and its influence on reservoir. The results indicate that: (1) The dolomite can be divided into three different lithofacies, such as microbial dolomite, granular dolomite, and crystalline dolomite. Growth-framework porosity of carbonates is the fundamental factor to develop high-quality reservoir, therefore, laminated dolomites, stromatolite dolomites and clotted dolomites that developed large number of primary pores can be regarded as high-quality reservoir rocks. (2) Four diagenetic environments associated with the development of high-quality reservoir in the 4th member of Dengying formation are identified, including evaporated seawater environment, shallow buried “trapped” seawater environment, medium-deep buried organic acid migration environment and hydrothermal environment. By means of researching on the relationship between diagenetic fluid properties and high-quality reservoir alteration in the 4th member of Dengying Formation, we proved that the dissolution of buried organic acid and hydrothermal fluid has greatly improved the reservoir property. (3) The development of high-quality reservoir in the 4th member of Dengying Formation in northern Sichuan is controlled and restricted by sedimentary environment, diagenetic evolution and tectonic movement. Among these, the favorable sedimentary facies belt is the fundamental character, multi-stage fluids dissolution is the key factor, and the faults formed by tectonic movement provide favorable the deep fluid fluxion. The study of the identification and quantitative reformation degree of high-quality reservoir in the 4th member of Dengying formation provides a theoretical basis for sedimentary-diagenesis for the predicting of oil and gas exploration targets in this area.
The carbonate rocks from the Sinian Dengying Formation in the northern Sichuan Basin experienced multi-stage fluid alternation, which has exerted a significant influence on the quality of the reservoir. Laser in-situ carbon and oxygen isotope, micro-area strontium isotope, petrography and cathodoluminescence were used to systematically analyze the petrology, and diagenetic evolution of dolomite in Dengying Formation. Based on these researches, we clarified the diagenesis process of different diagenetic fluids and its influence on reservoir. The results indicate that: (1) The dolomite can be divided into three different lithofacies, such as microbial dolomite, granular dolomite, and crystalline dolomite. Growth-framework porosity of carbonates is the fundamental factor to develop high-quality reservoir, therefore, laminated dolomites, stromatolite dolomites and clotted dolomites that developed large number of primary pores can be regarded as high-quality reservoir rocks. (2) Four diagenetic environments associated with the development of high-quality reservoir in the 4th member of Dengying formation are identified, including evaporated seawater environment, shallow buried “trapped” seawater environment, medium-deep buried organic acid migration environment and hydrothermal environment. By means of researching on the relationship between diagenetic fluid properties and high-quality reservoir alteration in the 4th member of Dengying Formation, we proved that the dissolution of buried organic acid and hydrothermal fluid has greatly improved the reservoir property. (3) The development of high-quality reservoir in the 4th member of Dengying Formation in northern Sichuan is controlled and restricted by sedimentary environment, diagenetic evolution and tectonic movement. Among these, the favorable sedimentary facies belt is the fundamental character, multi-stage fluids dissolution is the key factor, and the faults formed by tectonic movement provide favorable the deep fluid fluxion. The study of the identification and quantitative reformation degree of high-quality reservoir in the 4th member of Dengying formation provides a theoretical basis for sedimentary-diagenesis for the predicting of oil and gas exploration targets in this area.
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[Objective] Due to favorable hydrocarbon accumulation conditions, terrigenous Marine source rocks are widely developed in the transitional facies delta sedimentary system, and terrigenous organic matter is the main source material. In order to investigate the sedimentary characteristics and influencing factors of terrigenous organic matter in the transitional deltaic sedimentary system, a simulation experiment of terrigenous organic matter deposition was carried out. [Methods] The dynamic quantitative characterization of terrigenous organic matter transport and deposition process under experimental conditions was realized by using carbon and sulfur analyzer to detect organic carbon content and 3D laser scanning technology. [Results] The results show the following. At the first point. In the delta plain, terrigenous organic matter mainly accumulates locally in the overflow areas of river channels, abandoned river channels and the flow surface behind sandbar. In the profile, the distribution of terrigenous organic matter is mainly lens-type, discontinuous type and interbedded type. In the delta front and foredelta, the organic matter is distributed in sheet shape on the plane, and it is distributed in strips with large thickness in the profile. In the second point. The transport distance of terrigenous organic matter in the gentle slope delta system is relatively long. With the gradual increase of the sediment thickness of the delta, the influence of the initial slope of the delta has decreased on the transport distance of terrigenous organic matter. In the third point. Hydrodynamic strength and waves are important factors affecting the transport distance of organic matter. The weaker the hydrodynamic force, the more favorable the deposition of organic matter. Waves prevent organic matter from moving forward and form multiple sand bars in the delta front. Organic matter is deposited in annular bands in the grooves between the bars. In the fourth point. In the transitional facies delta depositional system, the organic carbon content gradually increases from the delta plain to the delta front-pre-delta area, and then decreases as the transport distance continues to increase. [Conclusion] The influence factors and enrichment sites of terrigenous organic matter has deeply established, and the sedimentary model of terrigenous organic matter under the flume experiment model is established, which provides an important reference for oil and gas exploration and development in the transitional facies delta depositional system.
[Objective] Due to favorable hydrocarbon accumulation conditions, terrigenous Marine source rocks are widely developed in the transitional facies delta sedimentary system, and terrigenous organic matter is the main source material. In order to investigate the sedimentary characteristics and influencing factors of terrigenous organic matter in the transitional deltaic sedimentary system, a simulation experiment of terrigenous organic matter deposition was carried out. [Methods] The dynamic quantitative characterization of terrigenous organic matter transport and deposition process under experimental conditions was realized by using carbon and sulfur analyzer to detect organic carbon content and 3D laser scanning technology. [Results] The results show the following. At the first point. In the delta plain, terrigenous organic matter mainly accumulates locally in the overflow areas of river channels, abandoned river channels and the flow surface behind sandbar. In the profile, the distribution of terrigenous organic matter is mainly lens-type, discontinuous type and interbedded type. In the delta front and foredelta, the organic matter is distributed in sheet shape on the plane, and it is distributed in strips with large thickness in the profile. In the second point. The transport distance of terrigenous organic matter in the gentle slope delta system is relatively long. With the gradual increase of the sediment thickness of the delta, the influence of the initial slope of the delta has decreased on the transport distance of terrigenous organic matter. In the third point. Hydrodynamic strength and waves are important factors affecting the transport distance of organic matter. The weaker the hydrodynamic force, the more favorable the deposition of organic matter. Waves prevent organic matter from moving forward and form multiple sand bars in the delta front. Organic matter is deposited in annular bands in the grooves between the bars. In the fourth point. In the transitional facies delta depositional system, the organic carbon content gradually increases from the delta plain to the delta front-pre-delta area, and then decreases as the transport distance continues to increase. [Conclusion] The influence factors and enrichment sites of terrigenous organic matter has deeply established, and the sedimentary model of terrigenous organic matter under the flume experiment model is established, which provides an important reference for oil and gas exploration and development in the transitional facies delta depositional system.
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Abstract:
[Objective]The Yaha gas reservoir in the Kuqa Depression is one of the condensate gas reservoirs with the earliest development time and the most mature development technology in my country. Its main producing interval is the bottom sandstone interval of the Paleogene Suweiyi Formation. The block is dominated by fine sandstone. The occurrence states of gypsum in sandstone are various, and the development period, hydrodynamic conditions, depositional environment and physical properties of gypsum of different occurrence states are different. [Methods]Based on the data of drilling cores, field profiles, and rock thin sections in the bottom sandstone section of the Paleogene Suweiyi Formation in the Yaha Gas Field, the occurrence state and deposition process of gypsum were discussed. [Results]The results show that: (1) the different occurrence states of gypsum in the study area are caused by the differences in depositional environment, depositional process and diagenetic environment. The sedimentary gypsum of Paleogene bottom sandstone in the study area can be divided into allogeneic gypsum and in-situ gypsum. (2) The gypsum masses deposited in different places are mainly transported by flowing water, and the transport distances from near to far are as follows: ① Irregular gypsum: irregular gypsum masses with a particle size of 8-10cm; (2) gypsum in the shape of a cloud: the cloud shape gypsum mass with 4-8 cm, angular; (3) crumby structure gypsum: the particle size is 2-5cm, nearly round gypsum mass, the roundness is good; (4) Directional arranged gypsum: 0.5-2cm in diameter, with parallel bedding structure; The gypsum deposited in situ includes the uniformly distributed spot-shaped gypsum formed by evaporation concentration and the oolitic gypsum with core and no concentric ring structure formed by flowing water agitation.[Conclusion]Gypsum in different occurrence states represents different paleoenvironment, paleoclimate and paleohydrodynamic conditions, which can provide new ideas for the study of the sedimentary process of seasonal river salt lake delta under the arid climate of Suwei Formation.
[Objective]The Yaha gas reservoir in the Kuqa Depression is one of the condensate gas reservoirs with the earliest development time and the most mature development technology in my country. Its main producing interval is the bottom sandstone interval of the Paleogene Suweiyi Formation. The block is dominated by fine sandstone. The occurrence states of gypsum in sandstone are various, and the development period, hydrodynamic conditions, depositional environment and physical properties of gypsum of different occurrence states are different. [Methods]Based on the data of drilling cores, field profiles, and rock thin sections in the bottom sandstone section of the Paleogene Suweiyi Formation in the Yaha Gas Field, the occurrence state and deposition process of gypsum were discussed. [Results]The results show that: (1) the different occurrence states of gypsum in the study area are caused by the differences in depositional environment, depositional process and diagenetic environment. The sedimentary gypsum of Paleogene bottom sandstone in the study area can be divided into allogeneic gypsum and in-situ gypsum. (2) The gypsum masses deposited in different places are mainly transported by flowing water, and the transport distances from near to far are as follows: ① Irregular gypsum: irregular gypsum masses with a particle size of 8-10cm; (2) gypsum in the shape of a cloud: the cloud shape gypsum mass with 4-8 cm, angular; (3) crumby structure gypsum: the particle size is 2-5cm, nearly round gypsum mass, the roundness is good; (4) Directional arranged gypsum: 0.5-2cm in diameter, with parallel bedding structure; The gypsum deposited in situ includes the uniformly distributed spot-shaped gypsum formed by evaporation concentration and the oolitic gypsum with core and no concentric ring structure formed by flowing water agitation.[Conclusion]Gypsum in different occurrence states represents different paleoenvironment, paleoclimate and paleohydrodynamic conditions, which can provide new ideas for the study of the sedimentary process of seasonal river salt lake delta under the arid climate of Suwei Formation.
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[Objective] As an important part of the continental-margin strata, mass-transport deposits (MTDs) attract considerable attention from foreigner and domestic researchers. However, previous studies rarely related the development of mass-transport deposits to the building of depositional sequences. This study takes SQ4 and SQ5 on the late-Quaternary Pearl River margin as the study objects to investigate the influence of different sequence-building background on the development of mass-transport deposits. [Methods] Through the integrated method of seismic interpretation and numerical stratigraphic forward modelling, it is observed that mass-transport deposits are mainly occurred in the deep-water reach of SQ4, whereas in the deep-water part of SQ5, they are rarely occurred. Around the shelf-slope break, recognizing of different systems tracts suggests that highstand system tracts in SQ4 are highly developed compared with their counterparts in SQ5. According to such real condition of the late-Quaternary Pearl River margin, totally 45 modelling experiments that have different relative sea-level changes are designed in Software DionisosFlow 2016 to investigate the development of mass-transport deposits under different backgrounds of depositional sequence building. [Results] The results prove that under the scenario of high sediment supply (with sediment discharge being 5000km3/My and water discharge being 1200m3/s) and high amplitude of relative sea-level changes (up to 250 m), the development of mass transport deposits is indeed sensitive to the development of highstand systems tracts during the building of sequences; under the background of highstand systems tracts being longer and going through sufficient development, mass-transport deposits in deep-water areas are easily formed, which is in consistent with the real condition of mass-transport deposits within SQ4 and SQ5. [Conclusions] Moreover, the model experiment respectively representing SQ4 and SQ5 (Model C8 and Model E5) further explains the occurrence mechanism of mass-transport deposits. During the building of SQ4, highstand system tracts are fully developed (with the duration of highstand systems tracts accounting for 65% of the elapsed model run) and the associated delta-shoreline systems overreach the shelf break, causing delta fronts merge onto the continental slope and forming clinothems with high relieves and high slopes; those clinothems are highly unstable and tend to drive the occurrence of mass wasting processes, leading to the deposition of mass-transport deposits in deep water. During the building of SQ5, the development of highstand systems tracts is limited (with the duration of highstand systems tracts accounting for 40% of the elapsed model run) and the associated delta-shoreline systems prograde to the outer shelf but do not overreach the pre-existing shelf-slope break , forming clinothems with low relieves and low slopes, which disfavor the occurrence of mass wasting processes and the development of mass-transport deposits in deep water. Those controls of different sequence-building backgrounds on the formation of mass-transport deposits in deep water provide a useful method to predict the type of submarine depositional elements, which in turn is of great significance for the hydrocarbon exploration and development in the future.
[Objective] As an important part of the continental-margin strata, mass-transport deposits (MTDs) attract considerable attention from foreigner and domestic researchers. However, previous studies rarely related the development of mass-transport deposits to the building of depositional sequences. This study takes SQ4 and SQ5 on the late-Quaternary Pearl River margin as the study objects to investigate the influence of different sequence-building background on the development of mass-transport deposits. [Methods] Through the integrated method of seismic interpretation and numerical stratigraphic forward modelling, it is observed that mass-transport deposits are mainly occurred in the deep-water reach of SQ4, whereas in the deep-water part of SQ5, they are rarely occurred. Around the shelf-slope break, recognizing of different systems tracts suggests that highstand system tracts in SQ4 are highly developed compared with their counterparts in SQ5. According to such real condition of the late-Quaternary Pearl River margin, totally 45 modelling experiments that have different relative sea-level changes are designed in Software DionisosFlow 2016 to investigate the development of mass-transport deposits under different backgrounds of depositional sequence building. [Results] The results prove that under the scenario of high sediment supply (with sediment discharge being 5000km3/My and water discharge being 1200m3/s) and high amplitude of relative sea-level changes (up to 250 m), the development of mass transport deposits is indeed sensitive to the development of highstand systems tracts during the building of sequences; under the background of highstand systems tracts being longer and going through sufficient development, mass-transport deposits in deep-water areas are easily formed, which is in consistent with the real condition of mass-transport deposits within SQ4 and SQ5. [Conclusions] Moreover, the model experiment respectively representing SQ4 and SQ5 (Model C8 and Model E5) further explains the occurrence mechanism of mass-transport deposits. During the building of SQ4, highstand system tracts are fully developed (with the duration of highstand systems tracts accounting for 65% of the elapsed model run) and the associated delta-shoreline systems overreach the shelf break, causing delta fronts merge onto the continental slope and forming clinothems with high relieves and high slopes; those clinothems are highly unstable and tend to drive the occurrence of mass wasting processes, leading to the deposition of mass-transport deposits in deep water. During the building of SQ5, the development of highstand systems tracts is limited (with the duration of highstand systems tracts accounting for 40% of the elapsed model run) and the associated delta-shoreline systems prograde to the outer shelf but do not overreach the pre-existing shelf-slope break , forming clinothems with low relieves and low slopes, which disfavor the occurrence of mass wasting processes and the development of mass-transport deposits in deep water. Those controls of different sequence-building backgrounds on the formation of mass-transport deposits in deep water provide a useful method to predict the type of submarine depositional elements, which in turn is of great significance for the hydrocarbon exploration and development in the future.
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Abstract:
We analyzed the sedimentary environment of manganese ore in the Datangpo Formation of the Nanhua System in the Guzhang area, northwest Hunan Province.[Methods] Based on the geochemical analysis of major and trace elements, rare earth elements and carbon and oxygen isotopes, the oxidation-reduction environment and the source of ore-forming materials during the deposition of manganese ore in the Datangpo Formation were studied. [Results and Discussions] (1) There is a positive correlation between SiO2, TiO2, K2O, and Al2O3, weak negative correlation with MgO and CaO, and weak correlation with MnO, Na2O, TFe, and P2O5 for the main elements of manganese ore in the Guzhang area. The deposit is similar to the Gucheng Manganese ore in Hubei, Xiangtan Manganese ore in Hunan, and Zhaodong Manganese ore in Hunan, with an overall high Si, low Fe, and P-bearing manganese ore. (2) The redox-sensitive elemental indicators, Fe/Mn<1, 20.57, Ni/Co<5, and U / Th<0.75, of the depositional environment indicate that the water column was in a normoxic-poor environment when the manganese ore was formed in the Datangpo Formation. The enrichment pattern of the medium rare earth elements, depletion of light and heavy rare earth elements, and the weak positive Ce anomaly indicate that Mn was first precipitated in the form of manganese oxides or hydroxides and then changed into Mn carbonate during digenesis. (3) A variety of metallogenic material source identification indicators, SiO2/Al2O3>3.6, Y/Ho close to that of the hydrothermal fluid on the seafloor, results of Fe-Mn- (Ni+Cu+Co) ×10 triangulation, and Co/Zn- (Cu+Ni+Co) diagrammatic show that the formation of Mn elements from the Manganese ores in the Datangpo Formation in the Guzhang area is closely related to submarine hydrothermal action and has characteristics of hot-water deposition. [Conclusions] The manganese ore of the Datangpo Formation was formed in a normoxic-poor environment in the Guzhang area, northwest Hunan Province. The formation of manganese is closely related to submarine hydrothermal action.
We analyzed the sedimentary environment of manganese ore in the Datangpo Formation of the Nanhua System in the Guzhang area, northwest Hunan Province.[Methods] Based on the geochemical analysis of major and trace elements, rare earth elements and carbon and oxygen isotopes, the oxidation-reduction environment and the source of ore-forming materials during the deposition of manganese ore in the Datangpo Formation were studied. [Results and Discussions] (1) There is a positive correlation between SiO2, TiO2, K2O, and Al2O3, weak negative correlation with MgO and CaO, and weak correlation with MnO, Na2O, TFe, and P2O5 for the main elements of manganese ore in the Guzhang area. The deposit is similar to the Gucheng Manganese ore in Hubei, Xiangtan Manganese ore in Hunan, and Zhaodong Manganese ore in Hunan, with an overall high Si, low Fe, and P-bearing manganese ore. (2) The redox-sensitive elemental indicators, Fe/Mn<1, 2
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In order to explore the influence of the intensity and occurrence time of overpressure on the development of high-quality reservoirs, based on restoring the formation pressure of sandy-conglomerate reservoirs in the third member of Shahejie Formation in the steep slope zone of Chezhen sag using the inclusion PVTx method, the logging curve combination and the acoustic velocity-density crossplot methods are conducted to analyze the origin of overpressure in mudstones. Then, the occurrence time of overpressure and oil saturation were synthetically used to analyze the origin of overpressure in reservoirs, and compare the differences in reservoir space and diagenesis among different reservoirs with inconsistent histories of pressure evolution. The mudstones in the third member of the Shahejie Formation in the steep slope of the Chezhen sag generally develop medium-strong overpressure, which are mainly caused by hydrocarbon generation pressurization. The overpressures, undergoing two periods of supercharging, in the conglomerate reservoirs are mainly caused by the pressure transition from the overpressure in the source rocks from the third member of Shahejie Formation. The first and second phases exactly correspond to the oil emplacements in yellow and blue fluorescent, respectively. But, there were differences in different regions. The sandstones and conglomerates in the third member of the Shahejie Formation in the steep slope belt of the Dawangbei sag underwent two periods of pressurization. The first period occurred at 28.3 Ma-27.8 Ma, and the coeval formation pressure coefficient was 1.34-1.35. The second period occurred at 11.6 Ma-9 Ma, and the coeval formation pressure coefficient is 1.56. The current formation pressure coefficient is 0.8-1.2. The conglomerate reservoirs in the third member of the Shahejie Formation in the steep slope zone of the Chexi sag experienced only one period of pressurization, occurring from 6 Ma to the present, with a coeval formation pressure coefficient of 1.2-1.4 and the present-day formation pressure coefficient of 1.0-1.3. The sandstones and conglomerates in the third member of the Shahejie Formation in the steep slope of the Taoerhe sag experienced two periods of pressurization, the first period occurred at 35.7 Ma-27.2 Ma, and the formation pressure coefficient is 1.54-2.08, while the second period occurred from 12.9 Ma to the present, the formation pressure coefficient is 1.57-2.1, and the current formation pressure coefficient is 1.2-2.1. The development of high-quality clastic rock reservoirs in the middle and deep layers are not only controlled by the overpressure strength in the current formations, but also closely related to the occurrence time and the strength of ancient overpressure. Obviously, the earlier and stronger overpressure develops, the more significant inhibitions of compaction and cementation occur, and the better the reservoir physical property is. The weaker compaction and carbonate cementation and more primary pores and better physical properties can be identified in the conglomerate reservoirs in the steep slope belt of Dawangbei sag with normal pressure-weak overpressure rather than in the Chexi sag with normal pressure-medium overpressure. The main reason is likely that two periods of paleo-overpressure with higher intensity occurred in the Dawangbei sag, while only one period of paleo-overpressure with relatively low intensity occurred in the Chexi sag.
In order to explore the influence of the intensity and occurrence time of overpressure on the development of high-quality reservoirs, based on restoring the formation pressure of sandy-conglomerate reservoirs in the third member of Shahejie Formation in the steep slope zone of Chezhen sag using the inclusion PVTx method, the logging curve combination and the acoustic velocity-density crossplot methods are conducted to analyze the origin of overpressure in mudstones. Then, the occurrence time of overpressure and oil saturation were synthetically used to analyze the origin of overpressure in reservoirs, and compare the differences in reservoir space and diagenesis among different reservoirs with inconsistent histories of pressure evolution. The mudstones in the third member of the Shahejie Formation in the steep slope of the Chezhen sag generally develop medium-strong overpressure, which are mainly caused by hydrocarbon generation pressurization. The overpressures, undergoing two periods of supercharging, in the conglomerate reservoirs are mainly caused by the pressure transition from the overpressure in the source rocks from the third member of Shahejie Formation. The first and second phases exactly correspond to the oil emplacements in yellow and blue fluorescent, respectively. But, there were differences in different regions. The sandstones and conglomerates in the third member of the Shahejie Formation in the steep slope belt of the Dawangbei sag underwent two periods of pressurization. The first period occurred at 28.3 Ma-27.8 Ma, and the coeval formation pressure coefficient was 1.34-1.35. The second period occurred at 11.6 Ma-9 Ma, and the coeval formation pressure coefficient is 1.56. The current formation pressure coefficient is 0.8-1.2. The conglomerate reservoirs in the third member of the Shahejie Formation in the steep slope zone of the Chexi sag experienced only one period of pressurization, occurring from 6 Ma to the present, with a coeval formation pressure coefficient of 1.2-1.4 and the present-day formation pressure coefficient of 1.0-1.3. The sandstones and conglomerates in the third member of the Shahejie Formation in the steep slope of the Taoerhe sag experienced two periods of pressurization, the first period occurred at 35.7 Ma-27.2 Ma, and the formation pressure coefficient is 1.54-2.08, while the second period occurred from 12.9 Ma to the present, the formation pressure coefficient is 1.57-2.1, and the current formation pressure coefficient is 1.2-2.1. The development of high-quality clastic rock reservoirs in the middle and deep layers are not only controlled by the overpressure strength in the current formations, but also closely related to the occurrence time and the strength of ancient overpressure. Obviously, the earlier and stronger overpressure develops, the more significant inhibitions of compaction and cementation occur, and the better the reservoir physical property is. The weaker compaction and carbonate cementation and more primary pores and better physical properties can be identified in the conglomerate reservoirs in the steep slope belt of Dawangbei sag with normal pressure-weak overpressure rather than in the Chexi sag with normal pressure-medium overpressure. The main reason is likely that two periods of paleo-overpressure with higher intensity occurred in the Dawangbei sag, while only one period of paleo-overpressure with relatively low intensity occurred in the Chexi sag.
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Abstract:
[Objective] The widely developed clay minerals in sedimentary rocks link up the whole geological process of tectonism, sedimentation and diagenesis, and record the interaction information of water-rock-hydrocarbon on the whole basin and multiple scales. Systematic investigation on the formation, growth and transformation of clay minerals in sandstone reservoirs is not only of great academic significance to perfect the diagenesis framework, but also provides powerful support for tight sandstone reservoirs exploration and development from the perspective of pore-throat evolution and pore-permeability response. [Method] Focusing on this theme, the basic characteristics, material bases and growing environments of montmorillonite, kaolinite, illite, chlorite and other mixed layer clay minerals are discussed in detail. On the basis of summing up the previous classical views and the latest progress, the key scientific issues and research hotspots are sorted out. [Result] The results show that there is obvious spatial coupling relationship between clay minerals, parent rocks and sedimentary microfacies. Mechanical percolation and biological induction mechanisms may exist in the formation of the internal clay coating, which need to be further clarified in the follow-up research. Under the dominance of diagenetic environment, the growth of the outer clay coating and other geological fluid-rock interactions have the relationship of material dependence and space competition, and affect the fluid medium in reverse. In petroliferous basins, clay minerals play an absolutely negative and relatively positive role in reservoir quality by changing the pore-throat structure and diagenetic process. Micro-zone in-situ analysis technology is used to accurately reveal the growth process of clay minerals and its control on reservoirs at the whole basin scale, which not only meets the realistic demand of petroleum exploration and development, but also promotes the study of geological fluid-rock interaction. [Conclusion] Technical innovation drives the deepening of geological understanding and gradually improves it in the practical exploration, providing a theoretical basis for increasing petroleum storage and production.
[Objective] The widely developed clay minerals in sedimentary rocks link up the whole geological process of tectonism, sedimentation and diagenesis, and record the interaction information of water-rock-hydrocarbon on the whole basin and multiple scales. Systematic investigation on the formation, growth and transformation of clay minerals in sandstone reservoirs is not only of great academic significance to perfect the diagenesis framework, but also provides powerful support for tight sandstone reservoirs exploration and development from the perspective of pore-throat evolution and pore-permeability response. [Method] Focusing on this theme, the basic characteristics, material bases and growing environments of montmorillonite, kaolinite, illite, chlorite and other mixed layer clay minerals are discussed in detail. On the basis of summing up the previous classical views and the latest progress, the key scientific issues and research hotspots are sorted out. [Result] The results show that there is obvious spatial coupling relationship between clay minerals, parent rocks and sedimentary microfacies. Mechanical percolation and biological induction mechanisms may exist in the formation of the internal clay coating, which need to be further clarified in the follow-up research. Under the dominance of diagenetic environment, the growth of the outer clay coating and other geological fluid-rock interactions have the relationship of material dependence and space competition, and affect the fluid medium in reverse. In petroliferous basins, clay minerals play an absolutely negative and relatively positive role in reservoir quality by changing the pore-throat structure and diagenetic process. Micro-zone in-situ analysis technology is used to accurately reveal the growth process of clay minerals and its control on reservoirs at the whole basin scale, which not only meets the realistic demand of petroleum exploration and development, but also promotes the study of geological fluid-rock interaction. [Conclusion] Technical innovation drives the deepening of geological understanding and gradually improves it in the practical exploration, providing a theoretical basis for increasing petroleum storage and production.
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[Objective] In order to find out the mineral composition and element content in the aluminiferous rock series of Taiyuan Formation in Longdong area of Ordos Basin, this paper selects the aluminiferous rock series in this area as the research object. [Methods] To uses the automatic mineral analysis system TIMA of Czech Tesken Electron Microscopy Company, combining with thin section observation and other means to study the mineralogical characteristics of the aluminiferous rock series, we try to find out the mineral composition and its occurrence state, determine the element types and contents of minerals in the ore in detail, discuss its mineral genesis, and summarize the mineral evolution sequence. [Results and Discussions] The study shows that the main mineral components of the aluminiferous rock series in Longdong include diaspore, kaolinite, illite, oolitic chlorite, anatase, siderite and pyrite. The main body of illite is the product of fluid alteration process, the early sedimentary kaolinite is the product of weathering process, and the late diagenetic kaolinite is formed by silicification of later diaspore. The simultaneous crystallization of anatase and diaspore was formed in a reducing environment. The early oolitic chlorite was formed in a certain karst environment and migrated to the ore site after a certain distance. The late oolitic chlorite formation is related to the dissolution of siderite. The formation and evolution of minerals in bauxite rocks in this area can be summarized as the following three stages: surface weathering stage, metallogenic stage and epigenetic stage. [Conclusions] TIMA based on scanning electron microscopy and energy spectrum analysis can quickly and effectively identify the mineral composition of aluminiferous rock series, obtain mineral content and element information, and identify the symbiosis between different minerals.
[Objective] In order to find out the mineral composition and element content in the aluminiferous rock series of Taiyuan Formation in Longdong area of Ordos Basin, this paper selects the aluminiferous rock series in this area as the research object. [Methods] To uses the automatic mineral analysis system TIMA of Czech Tesken Electron Microscopy Company, combining with thin section observation and other means to study the mineralogical characteristics of the aluminiferous rock series, we try to find out the mineral composition and its occurrence state, determine the element types and contents of minerals in the ore in detail, discuss its mineral genesis, and summarize the mineral evolution sequence. [Results and Discussions] The study shows that the main mineral components of the aluminiferous rock series in Longdong include diaspore, kaolinite, illite, oolitic chlorite, anatase, siderite and pyrite. The main body of illite is the product of fluid alteration process, the early sedimentary kaolinite is the product of weathering process, and the late diagenetic kaolinite is formed by silicification of later diaspore. The simultaneous crystallization of anatase and diaspore was formed in a reducing environment. The early oolitic chlorite was formed in a certain karst environment and migrated to the ore site after a certain distance. The late oolitic chlorite formation is related to the dissolution of siderite. The formation and evolution of minerals in bauxite rocks in this area can be summarized as the following three stages: surface weathering stage, metallogenic stage and epigenetic stage. [Conclusions] TIMA based on scanning electron microscopy and energy spectrum analysis can quickly and effectively identify the mineral composition of aluminiferous rock series, obtain mineral content and element information, and identify the symbiosis between different minerals.
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[Objective] The Yanchang Formation comprises the most important source rock and reservoirs in the Ordos Basin. Recent 3D seismic exploration shows that progradational reflection is widely developed in delta-deepwater transition zone of the Yanchang Formation, which means that the previous "thousand-layer pie-like" and near equal-thickness stratigraphic division and correlation scheme would cause stratigraphic "diachronism" correlation in clinoform development area. The aims of this paper are to explore the establishment of isochronal division and correlation scheme of the Yanchang Formation under the clinoform pattern, and to explore the connection and correlation relationship between it and the traditional stratigraphic division scheme. [Methods] Based on the 3D seismic data from the study area, the seismic profiles are carefully interpreted to obtain the understanding of the shape type, migration superposition relationship and internal structure of the clinothem, guided by the theories of sequence stratigraphy and sedimentology. Then, under the pattern of the clinoform, through well-seismic mutual calibration (drilling calibration of seismic horizon, seismic calibration of horizontal correlation of drilling profile strata), combined with the constraints of core facies marks, a new isochronous stratigraphic division and correlation scheme is established, which is about the middle and upper part of the Yanchang Formation in the southwestern Ordos Basin. The mid-upper part of the Yanchang Formation is divided into six stages of clinothems (F1-F6) in Qingcheng, Heshui area. And the mid-upper part of the Yanchang Formation is divided into five stages of clinothems (F1-F5) in Huanxian area. In the topsets, they correspond to the traditionally stratified Chang 7-Chang 1 oil layers respectively. [Results and Discussions] The differences of the stratigraphic division results under different schemes are mainly reflected in the foreset and the bottomset areas. In the foreset area, the strata in each clinothem are generally thickened compared with the traditional schemes. In the deep water area, the strata thickness of the newly determined F2 and F3 is significantly reduced compared with the traditional ones, while the thickness of F5-F6 is dramatically increased. On the plane, the isochronous stratigraphic units of each clinothem show a NW-SE zonation. And from the southwest to the northeast of the study area, they show a thin-thick-thin NW-SE zonal distribution pattern in turn. Under the pattern of clinoform, there are isochronous and intrinsic genetic relationships of the tracking and correlation relationship between stratigraphic division and sandstone bodies. The connection relationship of sandstone bodies is closer to the real situation of the underground reservoir, which is conducive to the reasonable layout of oilfield development well pattern and the determination of water injection horizon. The foresets indicated by the thicker stratum continue to advance toward the basin depocenter, indicating the contraction and filling process of the lacustrine basin. [Conclusions] This study proposes the method of "natural extension tracking of the topsets, marker bed constraint, and 3-D space closure test", and establishes the isochronous correlation between the middle and upper Yanchang Formation in the progradation development area, southwest of Ordos Basin. It provides important implication for re-understanding the stratigraphic division and correlation in the delta-deepwater areas of the Yanchang Formation, and also provides new insights for better understanding of the connectivity and spatial distribution of sandstone bodies, and the sedimentary filling process of the basin.
[Objective] The Yanchang Formation comprises the most important source rock and reservoirs in the Ordos Basin. Recent 3D seismic exploration shows that progradational reflection is widely developed in delta-deepwater transition zone of the Yanchang Formation, which means that the previous "thousand-layer pie-like" and near equal-thickness stratigraphic division and correlation scheme would cause stratigraphic "diachronism" correlation in clinoform development area. The aims of this paper are to explore the establishment of isochronal division and correlation scheme of the Yanchang Formation under the clinoform pattern, and to explore the connection and correlation relationship between it and the traditional stratigraphic division scheme. [Methods] Based on the 3D seismic data from the study area, the seismic profiles are carefully interpreted to obtain the understanding of the shape type, migration superposition relationship and internal structure of the clinothem, guided by the theories of sequence stratigraphy and sedimentology. Then, under the pattern of the clinoform, through well-seismic mutual calibration (drilling calibration of seismic horizon, seismic calibration of horizontal correlation of drilling profile strata), combined with the constraints of core facies marks, a new isochronous stratigraphic division and correlation scheme is established, which is about the middle and upper part of the Yanchang Formation in the southwestern Ordos Basin. The mid-upper part of the Yanchang Formation is divided into six stages of clinothems (F1-F6) in Qingcheng, Heshui area. And the mid-upper part of the Yanchang Formation is divided into five stages of clinothems (F1-F5) in Huanxian area. In the topsets, they correspond to the traditionally stratified Chang 7-Chang 1 oil layers respectively. [Results and Discussions] The differences of the stratigraphic division results under different schemes are mainly reflected in the foreset and the bottomset areas. In the foreset area, the strata in each clinothem are generally thickened compared with the traditional schemes. In the deep water area, the strata thickness of the newly determined F2 and F3 is significantly reduced compared with the traditional ones, while the thickness of F5-F6 is dramatically increased. On the plane, the isochronous stratigraphic units of each clinothem show a NW-SE zonation. And from the southwest to the northeast of the study area, they show a thin-thick-thin NW-SE zonal distribution pattern in turn. Under the pattern of clinoform, there are isochronous and intrinsic genetic relationships of the tracking and correlation relationship between stratigraphic division and sandstone bodies. The connection relationship of sandstone bodies is closer to the real situation of the underground reservoir, which is conducive to the reasonable layout of oilfield development well pattern and the determination of water injection horizon. The foresets indicated by the thicker stratum continue to advance toward the basin depocenter, indicating the contraction and filling process of the lacustrine basin. [Conclusions] This study proposes the method of "natural extension tracking of the topsets, marker bed constraint, and 3-D space closure test", and establishes the isochronous correlation between the middle and upper Yanchang Formation in the progradation development area, southwest of Ordos Basin. It provides important implication for re-understanding the stratigraphic division and correlation in the delta-deepwater areas of the Yanchang Formation, and also provides new insights for better understanding of the connectivity and spatial distribution of sandstone bodies, and the sedimentary filling process of the basin.
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Abstract:
The study of C and S isotopic fractionation process in the paleo-ocean is always a difficult point, and there are few reports on the study of C and S isotopic fractionation process in the study area. The kinetic model of C and S isotope fractionation is established in the late Ordovician to early Silurian in Sichuan Basin . The simulation results show that (1) the carbon and sulfur isotope fractionation model shows when the burial flux of organic carbon increases to 1.5 ~ 2.0 times of the original in the time of 0.5 myr ~ 1.5 Myr, the buried flux of pyrite increases to 1.5 ~ 3.0 times of the original. And the positive deviation of C and S isotopes occurs when superimposed on the small decrease of the input flux. The higher primary productivity and the existence of iron anoxic water make the organic carbon in the water can be buried in a short time, and cause the positive migration of δ13Corg gradually. with the continuous decrease of sea level, the oxygen content of water body gradually increases, and the rate of organic carbon burial decreases greatly, at which time δ13Corg reaches the maximum value and gradually negative deviation during the sedimentary period of Guanyinqiao Formation. The enhanced volcanism at the end of Hernandez period promoted the δ13Corg migration and shortened the time needed to recover to the initial state. (2) According to the variation of sulfate parameters under the condition of 5mM, the concentration of sulfate iron in water during non-glacial period should be 5mM, the first part of the Hernand Ice Age, with the development of anoxic water and the relatively strong Fpy, the concentration of seawater sulfate gradually decreased from 5 mM to 3 mM. Under the influence of increasing Fpy, the sulfate concentration decreased again, and the sulfur isotope fractionation became positive, and reached its peak during the sedimentary period of the Guanyinqiao Formation, the sea level rose rapidly, the input of land weathering increased, the fractionation of sulfur isotope decreased, and the concentration of sulfate gradually recovered to 5mM in the non-glacial period. The results show that the buried fluxes of organic carbon and pyrite control the positive deviation of C and S, and the validity of the model is verified by other profiles.
The study of C and S isotopic fractionation process in the paleo-ocean is always a difficult point, and there are few reports on the study of C and S isotopic fractionation process in the study area. The kinetic model of C and S isotope fractionation is established in the late Ordovician to early Silurian in Sichuan Basin . The simulation results show that (1) the carbon and sulfur isotope fractionation model shows when the burial flux of organic carbon increases to 1.5 ~ 2.0 times of the original in the time of 0.5 myr ~ 1.5 Myr, the buried flux of pyrite increases to 1.5 ~ 3.0 times of the original. And the positive deviation of C and S isotopes occurs when superimposed on the small decrease of the input flux. The higher primary productivity and the existence of iron anoxic water make the organic carbon in the water can be buried in a short time, and cause the positive migration of δ13Corg gradually. with the continuous decrease of sea level, the oxygen content of water body gradually increases, and the rate of organic carbon burial decreases greatly, at which time δ13Corg reaches the maximum value and gradually negative deviation during the sedimentary period of Guanyinqiao Formation. The enhanced volcanism at the end of Hernandez period promoted the δ13Corg migration and shortened the time needed to recover to the initial state. (2) According to the variation of sulfate parameters under the condition of 5mM, the concentration of sulfate iron in water during non-glacial period should be 5mM, the first part of the Hernand Ice Age, with the development of anoxic water and the relatively strong Fpy, the concentration of seawater sulfate gradually decreased from 5 mM to 3 mM. Under the influence of increasing Fpy, the sulfate concentration decreased again, and the sulfur isotope fractionation became positive, and reached its peak during the sedimentary period of the Guanyinqiao Formation, the sea level rose rapidly, the input of land weathering increased, the fractionation of sulfur isotope decreased, and the concentration of sulfate gradually recovered to 5mM in the non-glacial period. The results show that the buried fluxes of organic carbon and pyrite control the positive deviation of C and S, and the validity of the model is verified by other profiles.
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Abstract:
Mixed siliciclastic-carbonate reservoir is currently being a new target as potential reservoirs in the context of hydrocarbon exploration,but are prone to the puzzle of heterogeneities. Previous studies focused mainly on understanding such puzzle in “strata mixing” sediments, however little attention has been paid to the “compositional mixing” type. In recent years, typical “compositional mixing” sedimentation has been discovered in a medium-deep depth of the Paleogene of the Bohai Sea with breakthroughs in oil and gas exploration, which provide ideal research materials to explore the heterogeneity issue within “compositional mixing” deposits. Core and logging data were used for detailed studies on characteristics and main controlling factors of heterogeneities associated with “compositional mixing” in the Bohai Sea area. Two principal facies associations are recognized in this study, that include biological mixing shore and debris-flows mixing shore. The two different facies associations of "compositional mixing " have significant heterogeneities in spatial distribution due to a complex interplay of controlling factors. The biological mixing shore association tends to be distributed in the flanks of detrital deposition that controlled by paleoclimate and provenance and different genetic facies within this facis association were vertically stacked which may be attributed to lake-level changes. In the view of the debris-flows mixing shoal association, it is a restriction of later distribution on proximal area of nearby uplift because this association can be controlled by interplay of paleoclimate and paleo water-depth and the vertical patterns are heterolithic that are related to variational hydrodynamic strength of gravity-driven depositional processes. Afterward, the results of the current study also show complex heterogeneity on the aspect of reservoir physical properties and pore structure. The results further reveal that the differences of clastic components supply, selective dissolution, dolomitization, cement type and quantity complex structure and connectivity of pore networks within the reservoir would widely control heterogeneities of the reservoir ability. Therefore, a formation model of “compositional mixing” heterogeneity during the depositional and diagenetic processes during depositional and diagenetic processes were finally built up, which has important enlightenment significance for the further reservoir prediction and evaluation of mixed sediments reservoirs worldwide.
Mixed siliciclastic-carbonate reservoir is currently being a new target as potential reservoirs in the context of hydrocarbon exploration,but are prone to the puzzle of heterogeneities. Previous studies focused mainly on understanding such puzzle in “strata mixing” sediments, however little attention has been paid to the “compositional mixing” type. In recent years, typical “compositional mixing” sedimentation has been discovered in a medium-deep depth of the Paleogene of the Bohai Sea with breakthroughs in oil and gas exploration, which provide ideal research materials to explore the heterogeneity issue within “compositional mixing” deposits. Core and logging data were used for detailed studies on characteristics and main controlling factors of heterogeneities associated with “compositional mixing” in the Bohai Sea area. Two principal facies associations are recognized in this study, that include biological mixing shore and debris-flows mixing shore. The two different facies associations of "compositional mixing " have significant heterogeneities in spatial distribution due to a complex interplay of controlling factors. The biological mixing shore association tends to be distributed in the flanks of detrital deposition that controlled by paleoclimate and provenance and different genetic facies within this facis association were vertically stacked which may be attributed to lake-level changes. In the view of the debris-flows mixing shoal association, it is a restriction of later distribution on proximal area of nearby uplift because this association can be controlled by interplay of paleoclimate and paleo water-depth and the vertical patterns are heterolithic that are related to variational hydrodynamic strength of gravity-driven depositional processes. Afterward, the results of the current study also show complex heterogeneity on the aspect of reservoir physical properties and pore structure. The results further reveal that the differences of clastic components supply, selective dissolution, dolomitization, cement type and quantity complex structure and connectivity of pore networks within the reservoir would widely control heterogeneities of the reservoir ability. Therefore, a formation model of “compositional mixing” heterogeneity during the depositional and diagenetic processes during depositional and diagenetic processes were finally built up, which has important enlightenment significance for the further reservoir prediction and evaluation of mixed sediments reservoirs worldwide.
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Abstract:
[Objective] In recent years, more and more scholars have paid attention to the deep-water deposition, which can form coarse clastic sand bodies and fine-grained sediments in submarine slopes, abyssal plains and abyssal lakes. However, the understanding of its development law and sedimentary model is still controversial. [Methods] Taking the Lower Cretaceous Laiyang Formation in the Lingshan Island of Riqingwei Basin as an example, with the help of core observation of Well LK-1, thin-section microscopic identification and outcrop exploration, the deep-water sedimentary process was discussed from the aspects of lithofacies assemblage, sedimentary types, genetic mechanism, fluid evolution characteristics and sedimentary model. [Results] The results show that: 1) The early Cretaceous deep-water sedimentary lithofacies in the study area can be divided into 9 types: layered shale facies, deformed structural mudstone facies, deformed structural argillaceous siltstone facies, parallel bedding siltstone facies, argillaceous clastic siltstone facies, sequence-bedding fine sandstone facies, massive bedding fine sandstone facies, cross-bedding fine sandstone facies, and massive bedding pebbled sandstone facies. Five types of lithofacies association are summarized according to the development situation. 2) Based on the types of lithofacies assemblages, 6 sedimentary types were identified, including slump deposits, sandy debris flow deposits, turbidity current deposits, hybrid event bed deposits, bottom current deposits and deep-water suspended deposits. 3) On the premise of fully considering the tectonic setting of the basin, the distribution law of deep-water sediments and the triggering mechanism of gravity flow, it is found that gravity flow presents the evolution characteristics of sandy debris flow to sandy debris flow-turbidity flow and then to turbidity flow from the continental slope to the basin floor. Based on this, the Early Cretaceous deep-water sedimentary model dominated by deep-water gravity flow in the Lingshan Island was established. [Conclusion] The research results not only provide a new understanding of the formation process and fluid evolution mechanism of deep-water fine-grained sediments in the Laiyang Formation of Lingshan Island, but also provide sedimentary evidence for the reconstruction of paleoenvironment and paleogeography during the Early Cretaceous period in this area.
[Objective] In recent years, more and more scholars have paid attention to the deep-water deposition, which can form coarse clastic sand bodies and fine-grained sediments in submarine slopes, abyssal plains and abyssal lakes. However, the understanding of its development law and sedimentary model is still controversial. [Methods] Taking the Lower Cretaceous Laiyang Formation in the Lingshan Island of Riqingwei Basin as an example, with the help of core observation of Well LK-1, thin-section microscopic identification and outcrop exploration, the deep-water sedimentary process was discussed from the aspects of lithofacies assemblage, sedimentary types, genetic mechanism, fluid evolution characteristics and sedimentary model. [Results] The results show that: 1) The early Cretaceous deep-water sedimentary lithofacies in the study area can be divided into 9 types: layered shale facies, deformed structural mudstone facies, deformed structural argillaceous siltstone facies, parallel bedding siltstone facies, argillaceous clastic siltstone facies, sequence-bedding fine sandstone facies, massive bedding fine sandstone facies, cross-bedding fine sandstone facies, and massive bedding pebbled sandstone facies. Five types of lithofacies association are summarized according to the development situation. 2) Based on the types of lithofacies assemblages, 6 sedimentary types were identified, including slump deposits, sandy debris flow deposits, turbidity current deposits, hybrid event bed deposits, bottom current deposits and deep-water suspended deposits. 3) On the premise of fully considering the tectonic setting of the basin, the distribution law of deep-water sediments and the triggering mechanism of gravity flow, it is found that gravity flow presents the evolution characteristics of sandy debris flow to sandy debris flow-turbidity flow and then to turbidity flow from the continental slope to the basin floor. Based on this, the Early Cretaceous deep-water sedimentary model dominated by deep-water gravity flow in the Lingshan Island was established. [Conclusion] The research results not only provide a new understanding of the formation process and fluid evolution mechanism of deep-water fine-grained sediments in the Laiyang Formation of Lingshan Island, but also provide sedimentary evidence for the reconstruction of paleoenvironment and paleogeography during the Early Cretaceous period in this area.
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Abstract:
Kerogen is the most abundant source of natural organic matter in the world. It is of great significance to study the pyrolysis of kerogen for the exploitation and utilization of oil shale. The traditional pyrolysis experiment is difficult to deeply reveal the mechanism of kerogen pyrolysis, but the molecular simulation method can expose the microscopic mechanism of kerogen pyrolysis at the atomic and molecular level, which is an important research method. In this paper, the research progress of molecular simulation of kerogen pyrolysis was systematically investigated. Combined with the experimental results, the effects of temperature, heating rate, water, pressure and shale mineral composition on kerogen pyrolysis were described. Compared with the experimental results, it is found that molecular simulation has great advantages in quantitative description, whereas it lacks systematic understanding in qualitative description. Molecular simulation usually uses the method of increasing the simulation temperature to shorten the reaction time to make up for the geological thermal evolution time, which is one of the shortcomings of molecular simulation at present. In addition, the high temperature simulation of kerogen will produce a large amount of C2H4, which is not consistent with the experimental facts and geological situation, which is also the deficiency of the current molecular simulation. In a word, the thermal simulation of kerogen is a multi-factor process. In the future research work, we should focus on constructing multi-scale and complex kerogen models rich in shale mineral components, water, organic acids and inorganic salts. Moreover, combined with the actual geological situation, the mechanism of kerogen pyrolysis to generate hydrocarbon at low temperature should be explored, so as to bridge the gap between experiment, geology and theory, and provide important reference information and theoretical guidance for the exploration and development of shale oil and gas.
Kerogen is the most abundant source of natural organic matter in the world. It is of great significance to study the pyrolysis of kerogen for the exploitation and utilization of oil shale. The traditional pyrolysis experiment is difficult to deeply reveal the mechanism of kerogen pyrolysis, but the molecular simulation method can expose the microscopic mechanism of kerogen pyrolysis at the atomic and molecular level, which is an important research method. In this paper, the research progress of molecular simulation of kerogen pyrolysis was systematically investigated. Combined with the experimental results, the effects of temperature, heating rate, water, pressure and shale mineral composition on kerogen pyrolysis were described. Compared with the experimental results, it is found that molecular simulation has great advantages in quantitative description, whereas it lacks systematic understanding in qualitative description. Molecular simulation usually uses the method of increasing the simulation temperature to shorten the reaction time to make up for the geological thermal evolution time, which is one of the shortcomings of molecular simulation at present. In addition, the high temperature simulation of kerogen will produce a large amount of C2H4, which is not consistent with the experimental facts and geological situation, which is also the deficiency of the current molecular simulation. In a word, the thermal simulation of kerogen is a multi-factor process. In the future research work, we should focus on constructing multi-scale and complex kerogen models rich in shale mineral components, water, organic acids and inorganic salts. Moreover, combined with the actual geological situation, the mechanism of kerogen pyrolysis to generate hydrocarbon at low temperature should be explored, so as to bridge the gap between experiment, geology and theory, and provide important reference information and theoretical guidance for the exploration and development of shale oil and gas.
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Abstract:
[Objective] The Lower Paleozoic Qiongzhusi Formation and Longmaxi Formation are the key strata for shale gas exploration and development. However, there has been a lack of systematic comparative study on the environmental control factors of organic matter enrichment in the two sets of shales. [Methods] Based on the comparative analysis of the sedimentary and geochemical characteristics (Terrigenous input, Paleo-redox conditions, Paleoproductivity levels, Degree of water stagnation and upwelling current) of the two sets of shales in the passive continental margin and craton depression in the western part of the Middle Yangtze, the main controlling factors and formation models of organic matter differential enrichment were discussed. [Results] The results show that the high TOC sections of the two sets of shales are located at the bottom (The mean values of the two formations in the passive continental margin and cratonic depression are 5.7% and 4.1%, 4.7% and 3.5%, respectively), formed in an environment with low terrestrial input, high paleoproductivity level and good preservation conditions, and the paleoproductivity level and bottom water reduction degree at the bottom of the Qiongzhusi Formation are higher, resulting in higher TOC content. Since then, the tensional rifting in the Qiongzhusi period continued to weaken, and the foreland flexural-migration gradually increased in the Longmaxi period. With the continuous decline of sea level, both sets of shales showed the characteristics of increased terrestrial input and poor preservation conditions, but the changes in paleoproductivity levels were quite different : in the Qiongzhusi period, ocean current activity weakened with the decline of sea level, and the level of paleoproductivity decreased. In the Longmaxi period, the flexural-migration led to the gradual opening of the northern barrier opening in the Yangtze Basin, and the scale of ocean current influx gradually expanded. Weakly affected by sea level decline, the level of paleoproductivity increased. Therefore, vertically, the decrease of TOC content in Qiongzhusi Formation is mainly controlled by the decrease of paleoproductivity, the deterioration of preservation conditions and the increase of terrestrial input, while Longmaxi Formation is mainly controlled by the latter two factors. Horizontally, the two sets of shales transited from the passive continental margin to the craton depression, and the sea level height and ocean current activity showed a decreasing trend. The preservation conditions and paleoproductivity levels deteriorated at the same time, and the TOC content decreased. Under this control, the focus of shale gas exploration and development in the Qiongzhusi Formation should be implemented to the southwest, while the Longmaxi Formation should be turned to the northwest. During the Qiongzhusi period, the organic matter enrichment environment gradually improved towards the southwest direction, and the thickness of organic rich shale increased near the center of the extensional rift. However, during the Longmaxi period, the organic matter enrichment environment improved towards the northwest direction. At the same time, under the control of foreland flexure migration, the sedimentary center gradually migrated towards the northwest direction, and the thickness of organic rich shale increased accordingly. It is difficult to take into account both. [Conclusions] This study has positive significance for further exploring the accumulation mechanism of organic matter in Lower Paleozoic Marine shale and guiding shale gas exploration practice.
[Objective] The Lower Paleozoic Qiongzhusi Formation and Longmaxi Formation are the key strata for shale gas exploration and development. However, there has been a lack of systematic comparative study on the environmental control factors of organic matter enrichment in the two sets of shales. [Methods] Based on the comparative analysis of the sedimentary and geochemical characteristics (Terrigenous input, Paleo-redox conditions, Paleoproductivity levels, Degree of water stagnation and upwelling current) of the two sets of shales in the passive continental margin and craton depression in the western part of the Middle Yangtze, the main controlling factors and formation models of organic matter differential enrichment were discussed. [Results] The results show that the high TOC sections of the two sets of shales are located at the bottom (The mean values of the two formations in the passive continental margin and cratonic depression are 5.7% and 4.1%, 4.7% and 3.5%, respectively), formed in an environment with low terrestrial input, high paleoproductivity level and good preservation conditions, and the paleoproductivity level and bottom water reduction degree at the bottom of the Qiongzhusi Formation are higher, resulting in higher TOC content. Since then, the tensional rifting in the Qiongzhusi period continued to weaken, and the foreland flexural-migration gradually increased in the Longmaxi period. With the continuous decline of sea level, both sets of shales showed the characteristics of increased terrestrial input and poor preservation conditions, but the changes in paleoproductivity levels were quite different : in the Qiongzhusi period, ocean current activity weakened with the decline of sea level, and the level of paleoproductivity decreased. In the Longmaxi period, the flexural-migration led to the gradual opening of the northern barrier opening in the Yangtze Basin, and the scale of ocean current influx gradually expanded. Weakly affected by sea level decline, the level of paleoproductivity increased. Therefore, vertically, the decrease of TOC content in Qiongzhusi Formation is mainly controlled by the decrease of paleoproductivity, the deterioration of preservation conditions and the increase of terrestrial input, while Longmaxi Formation is mainly controlled by the latter two factors. Horizontally, the two sets of shales transited from the passive continental margin to the craton depression, and the sea level height and ocean current activity showed a decreasing trend. The preservation conditions and paleoproductivity levels deteriorated at the same time, and the TOC content decreased. Under this control, the focus of shale gas exploration and development in the Qiongzhusi Formation should be implemented to the southwest, while the Longmaxi Formation should be turned to the northwest. During the Qiongzhusi period, the organic matter enrichment environment gradually improved towards the southwest direction, and the thickness of organic rich shale increased near the center of the extensional rift. However, during the Longmaxi period, the organic matter enrichment environment improved towards the northwest direction. At the same time, under the control of foreland flexure migration, the sedimentary center gradually migrated towards the northwest direction, and the thickness of organic rich shale increased accordingly. It is difficult to take into account both. [Conclusions] This study has positive significance for further exploring the accumulation mechanism of organic matter in Lower Paleozoic Marine shale and guiding shale gas exploration practice.
, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.060
Abstract:
In order to deeply analyze the sedimentary environment of organic matter enrichment in the shale of Wufeng-Longmaxi Formation in Sichuan Basin, this paper studies the spatial and temporal distribution characteristics of shale and its organic matter by comparing the metallogenic model of coal, combining the spatial distribution of primary productivity and carbon fixation rate of different water bodies, as well as the characteristics of sedimentary facies, paleogeomorphology, fossil development, etc. The study found that the shallower and more closed the water body, the higher the primary productivity and carbon fixation rate; Oil-bearing shale is developed in the restricted desalinated shallow water environment, which has low energy, stagnant water and strong reduction environment, and can develop type I organic matter; Shale oil and gas have a similar pattern with coal seams. The Mawei pattern, the closer to the land, the richer the organic matter is, and is associated with coal, evaporite, etc; The carbon and nitrogen sources in the water body are mainly exogenous. The development of sapropelic shale and stone coal from Proterozoic to Early Paleozoic is suitable for the lack of terrestrial higher plants that produce humus at this time; The open shelf or bay environment has low primary productivity, and the seabed is a high hydrodynamic environment affected by ocean currents, which is not conducive to the development of shale and preservation of organic matter; Marine transgression or high water deposition periods are not conducive to organic matter enrichment. It is concluded that the shale of the Wufeng Formation - Longmaxi Formation is developed in a regressive environment, which is a shallow sea-land transitional environment such as lagoon and relatively closed bay restricted by ancient land and underwater low uplift, and has the characteristics of near land and far water; Finally, a two-dimensional table of water depth and closure is established to describe the enrichment law of organic matter in detail. It is proposed that the sufficient condition for the enrichment of organic matter in marine shale is a closed water body, and the necessary condition is a shallow water body (<40 m).
In order to deeply analyze the sedimentary environment of organic matter enrichment in the shale of Wufeng-Longmaxi Formation in Sichuan Basin, this paper studies the spatial and temporal distribution characteristics of shale and its organic matter by comparing the metallogenic model of coal, combining the spatial distribution of primary productivity and carbon fixation rate of different water bodies, as well as the characteristics of sedimentary facies, paleogeomorphology, fossil development, etc. The study found that the shallower and more closed the water body, the higher the primary productivity and carbon fixation rate; Oil-bearing shale is developed in the restricted desalinated shallow water environment, which has low energy, stagnant water and strong reduction environment, and can develop type I organic matter; Shale oil and gas have a similar pattern with coal seams. The Mawei pattern, the closer to the land, the richer the organic matter is, and is associated with coal, evaporite, etc; The carbon and nitrogen sources in the water body are mainly exogenous. The development of sapropelic shale and stone coal from Proterozoic to Early Paleozoic is suitable for the lack of terrestrial higher plants that produce humus at this time; The open shelf or bay environment has low primary productivity, and the seabed is a high hydrodynamic environment affected by ocean currents, which is not conducive to the development of shale and preservation of organic matter; Marine transgression or high water deposition periods are not conducive to organic matter enrichment. It is concluded that the shale of the Wufeng Formation - Longmaxi Formation is developed in a regressive environment, which is a shallow sea-land transitional environment such as lagoon and relatively closed bay restricted by ancient land and underwater low uplift, and has the characteristics of near land and far water; Finally, a two-dimensional table of water depth and closure is established to describe the enrichment law of organic matter in detail. It is proposed that the sufficient condition for the enrichment of organic matter in marine shale is a closed water body, and the necessary condition is a shallow water body (<40 m).
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Abstract:
The sedimentary micro-environment, sedimentary microfacies, sedimentary characteristics and sedimentary mechanism of mixed fine-grained rocks is not clear. Using the data of core, outcrop, logging, XRF element logging, analytical testing, oil testing and production are integrated by lithofacies, sedimentary facies coupling analysis and dynamic static combination. The sedimentary micro-environment, microfacies classification, sedimentary model and its controlling on dessert were studied. The results show that: (1) According to the core, 8 types of sedimentary structures are identified, including wave cross bedding, horizontal bedding, syngenetic deformation structure, pyrite, calcite strip, birds-eye structure and nodule, suture structure, biological fossil and dolomite dissolution hole and so on. The sub-facies are divided into semi deep lacustrine to deep lacustrine, mixed shallow lacustrine and clastic shallow lacustrine, which are subdivided into six microfacies: semi deep lacustrine mud, dolomitic flat, mixed beach bar, mixed shallow lacustrine mud, shallow lacustrine sand bar and clastic shallow lacustrine mud. The sedimentary characteristics and sedimentary mechanism of different microfacies are obviously different. (2) A sedimentary microfacies model of mixed fine-grained rocks in saline lakes has been established. No.1Member of Lucaogou Formation evolves from deep lacustrine to semi deep lacustrine to shallow lacustrine from bottom to top. Typical reservoir microfacies are developed in different layers, including shallow lacustrine sand bar, mixed beach bar and dolomitic flat. Among them, dolomitic flat is more in continuous and large-scale sheet shape, mixed beach bar is more in potato shape, which with highly developed and different scales. The shallow lacustrine sand bar is intermittent and scale limited, and vertically in the superposition of thin reservoir microfacies and thick mudstone. Lucaogou Formation No.2 Member is dominated by shallow lacustrine facies. The reservoir microfacies are similar to No.1, but the architecture style is quite different. The development quantity and scale of dolomitic flat and mixed beach bars are greatly reduced, and shallow lacustrine sand bars were developed, showing large-scale scattered potato shape, and thick layer superposition vertically. The profile shows that the stacking style of microfacies is change at different positions of the plane. (3) the deposition of the target layer is a transition environment from dry and hot brackish water to salt water, and highly of the paleo-productivity level; The Lower Dessert Section is deposited in oxygen enriched environment, but the Upper dessert section is deposited in anaerobic sub reduction to reduction environment. (4) Sedimentary microfacies control dessert distribution and oilfield development strategy. Mixed beach bar microfacies is type I sweet spot reservoir has high development degree, weak heterogeneity and the best production effect. Large scale deployment of horizontal well platform operation is adopted for benefit development. Dolomitic flat microfacies is type III sweet spot reservoir being developed, with strong heterogeneity and general development effect. It is a follow-up replacement oil and gas resource. Shallow lacustrine sand bar is type II sweet spot reservoir being developed, with overall dispersion, poor continuity, strong heterogeneity and good production effect. After the detailed study of the spatial distribution of sedimentary microfacies, the horizontal well development is deployed with reference to the parameters of NMR curve.
The sedimentary micro-environment, sedimentary microfacies, sedimentary characteristics and sedimentary mechanism of mixed fine-grained rocks is not clear. Using the data of core, outcrop, logging, XRF element logging, analytical testing, oil testing and production are integrated by lithofacies, sedimentary facies coupling analysis and dynamic static combination. The sedimentary micro-environment, microfacies classification, sedimentary model and its controlling on dessert were studied. The results show that: (1) According to the core, 8 types of sedimentary structures are identified, including wave cross bedding, horizontal bedding, syngenetic deformation structure, pyrite, calcite strip, birds-eye structure and nodule, suture structure, biological fossil and dolomite dissolution hole and so on. The sub-facies are divided into semi deep lacustrine to deep lacustrine, mixed shallow lacustrine and clastic shallow lacustrine, which are subdivided into six microfacies: semi deep lacustrine mud, dolomitic flat, mixed beach bar, mixed shallow lacustrine mud, shallow lacustrine sand bar and clastic shallow lacustrine mud. The sedimentary characteristics and sedimentary mechanism of different microfacies are obviously different. (2) A sedimentary microfacies model of mixed fine-grained rocks in saline lakes has been established. No.1Member of Lucaogou Formation evolves from deep lacustrine to semi deep lacustrine to shallow lacustrine from bottom to top. Typical reservoir microfacies are developed in different layers, including shallow lacustrine sand bar, mixed beach bar and dolomitic flat. Among them, dolomitic flat is more in continuous and large-scale sheet shape, mixed beach bar is more in potato shape, which with highly developed and different scales. The shallow lacustrine sand bar is intermittent and scale limited, and vertically in the superposition of thin reservoir microfacies and thick mudstone. Lucaogou Formation No.2 Member is dominated by shallow lacustrine facies. The reservoir microfacies are similar to No.1, but the architecture style is quite different. The development quantity and scale of dolomitic flat and mixed beach bars are greatly reduced, and shallow lacustrine sand bars were developed, showing large-scale scattered potato shape, and thick layer superposition vertically. The profile shows that the stacking style of microfacies is change at different positions of the plane. (3) the deposition of the target layer is a transition environment from dry and hot brackish water to salt water, and highly of the paleo-productivity level; The Lower Dessert Section is deposited in oxygen enriched environment, but the Upper dessert section is deposited in anaerobic sub reduction to reduction environment. (4) Sedimentary microfacies control dessert distribution and oilfield development strategy. Mixed beach bar microfacies is type I sweet spot reservoir has high development degree, weak heterogeneity and the best production effect. Large scale deployment of horizontal well platform operation is adopted for benefit development. Dolomitic flat microfacies is type III sweet spot reservoir being developed, with strong heterogeneity and general development effect. It is a follow-up replacement oil and gas resource. Shallow lacustrine sand bar is type II sweet spot reservoir being developed, with overall dispersion, poor continuity, strong heterogeneity and good production effect. After the detailed study of the spatial distribution of sedimentary microfacies, the horizontal well development is deployed with reference to the parameters of NMR curve.
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Abstract:
Multiple layer storm deposits distributed in the Lower Permian Taiyuan Formation carbonate rocks located at Gancaoshan zone of Xiangning county on the eastern margin of the Ordos Basin, which is mainly distributed in the limestone beds L2, L3 and L4. Based on the research of lithology, sedimentary structure, trace fossils and sedimentary sequence, this paper discusses in detail the main characteristics of the deposit sequence made up of the eroded basement structure and bioclastic lags, graded bedding, laminated unit, bioturbation structures (trace fossils) and marl or argillaceous limestone unit in carbonate rocks. According to the vertical component features of storm deposits sequence in different limestone beds,, five types of tempestite deposit sequences were identified: Type A is comprised of the wavy bottom erosion surface and graded bedding, developing mainly in near shore zone above the fair weather wave base. Type B consists of the wavy bottom erosion surface, graded bedding, and hummocky cross-bedding, generating in the subtidal zone, namely the upper zone between the fair weather wave base and the storm wave base. Type C is composed of the wavy bottom erosion surface, graded bedding, hummocky and concave cross-bedding and marlstone unit, forming in the lower zone between the fair weather wave base and storm wave base. Type D is made up the wavy bottom erosionsurface with bioclastic lags, graded bedding and bioturbation structure and marlstone unit, appearing mainly near the storm wave base. Type E consists of the slight fluctuation bottom erosion surface, thin-bedded graded bedding, ichnofossils-bearing unit and marlstone unit, occurring in outer shelf environment near/below the storm wave base. This result not only provides new understanding of the Lower Permian Taiyuan Formation carbonate rocks and their sedimentary environment in Ordos Basin，but also it can provide evidence of sedimentary environment analysis and palaeogeographic reconstruction for the exploration and development of oil and gas resources in this stratum.
Multiple layer storm deposits distributed in the Lower Permian Taiyuan Formation carbonate rocks located at Gancaoshan zone of Xiangning county on the eastern margin of the Ordos Basin, which is mainly distributed in the limestone beds L2, L3 and L4. Based on the research of lithology, sedimentary structure, trace fossils and sedimentary sequence, this paper discusses in detail the main characteristics of the deposit sequence made up of the eroded basement structure and bioclastic lags, graded bedding, laminated unit, bioturbation structures (trace fossils) and marl or argillaceous limestone unit in carbonate rocks. According to the vertical component features of storm deposits sequence in different limestone beds,, five types of tempestite deposit sequences were identified: Type A is comprised of the wavy bottom erosion surface and graded bedding, developing mainly in near shore zone above the fair weather wave base. Type B consists of the wavy bottom erosion surface, graded bedding, and hummocky cross-bedding, generating in the subtidal zone, namely the upper zone between the fair weather wave base and the storm wave base. Type C is composed of the wavy bottom erosion surface, graded bedding, hummocky and concave cross-bedding and marlstone unit, forming in the lower zone between the fair weather wave base and storm wave base. Type D is made up the wavy bottom erosionsurface with bioclastic lags, graded bedding and bioturbation structure and marlstone unit, appearing mainly near the storm wave base. Type E consists of the slight fluctuation bottom erosion surface, thin-bedded graded bedding, ichnofossils-bearing unit and marlstone unit, occurring in outer shelf environment near/below the storm wave base. This result not only provides new understanding of the Lower Permian Taiyuan Formation carbonate rocks and their sedimentary environment in Ordos Basin，but also it can provide evidence of sedimentary environment analysis and palaeogeographic reconstruction for the exploration and development of oil and gas resources in this stratum.
, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.065
Abstract:
Formation of lacustrine laminae result from water stratification and slow rates of deposition of fine-grained sediments. Carbonate laminae are sensitive to changes in water salinity, alkalinity, and biological activity and can provide important implications for paleoclimate and paleohydrology, which have, however, not received enough attention yet. Here, we take the Oligocene Shangganchaigou Formation of the Xichagou Section, SW Qaidam Basin as an example to study the formation mechanisms of lacustrine laminae, the origins of different carbonate mineral phases in saline lake basins, and their climatic and hydrological significances by observation of conventional thin section, fluorescence thin section and scanning electron microscope, and analysis of X-ray powder diffraction (XRD) and stable carbon and oxygen isotopes. Results show that the Shangganchaigou Formation of the Xichagou Section in the SW Qaidam Basin consist of three kinds of carbonate minerals: aragonite, dolomite, and calcite, all of which show a close association with algal residues. Carbon isotopic values of samples with high contents of aragonite are positive and samples containing rich dolomite show relatively higher δ18O values than those of other samples, indicating that the preservation of aragonite in Oligocene strata was related to algal bloom and dolomite formation resulted from high water salinity. The differed distributions of different carbonate mineral phases reflect a dynamic lake evolving from an early clastic-rich brackish lake to a later saline lake, controlled by early Oligocene humid climate and late Oligocene semi-arid climate.
Formation of lacustrine laminae result from water stratification and slow rates of deposition of fine-grained sediments. Carbonate laminae are sensitive to changes in water salinity, alkalinity, and biological activity and can provide important implications for paleoclimate and paleohydrology, which have, however, not received enough attention yet. Here, we take the Oligocene Shangganchaigou Formation of the Xichagou Section, SW Qaidam Basin as an example to study the formation mechanisms of lacustrine laminae, the origins of different carbonate mineral phases in saline lake basins, and their climatic and hydrological significances by observation of conventional thin section, fluorescence thin section and scanning electron microscope, and analysis of X-ray powder diffraction (XRD) and stable carbon and oxygen isotopes. Results show that the Shangganchaigou Formation of the Xichagou Section in the SW Qaidam Basin consist of three kinds of carbonate minerals: aragonite, dolomite, and calcite, all of which show a close association with algal residues. Carbon isotopic values of samples with high contents of aragonite are positive and samples containing rich dolomite show relatively higher δ18O values than those of other samples, indicating that the preservation of aragonite in Oligocene strata was related to algal bloom and dolomite formation resulted from high water salinity. The differed distributions of different carbonate mineral phases reflect a dynamic lake evolving from an early clastic-rich brackish lake to a later saline lake, controlled by early Oligocene humid climate and late Oligocene semi-arid climate.
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Abstract:
Shelf-marginal sea, under land-sea interaction, is a key region with important information about climate, sea-level change, biogeochemical cycles and human activities. Based on the analysis of the dating results, total organic carbon (TOC) and stable carbon isotope composition of the core H12 in the eastern side of Central South Yellow Sea Mud, this study discussed the phased characteristics and the influencing factors of organic carbon burial in the background of sedimentary environment evolution since the last deglaciation. The results showed that the hard clay layer developed during the period of relatively low sea level (17~12.6 ka B.P.) with relatively high TOC content and TOC-MAR mainly contributed by terrigenous organic matter. During the transgression period (12.6~7.8 ka B.P.), affected by dynamic effects such as tidal current erosion, TOC originated from mixed terrestrial and marine sources. The terrigenous organic carbon flux shows a significantly high value around 8 ka B.P., similar to the obviously increasing sedimentation rate, the East Asian Winter Monsoon intensification and global cooling events, which may be related to the change of sediment transport mode driven by monsoon. During the high sea level period (since 7.8 ka B.P.), the organic carbon was mainly composed of marine organic carbon. Especially during 5~2 ka B.P., the relative variation amplitude of TOC content on the centennial scale was large, consistent with the weakening stage of Kuroshio Current and the strong period of East Asian Winter Monsoon, which may reflect the changes of marine primary productivity and water environment caused by the strengthening of Yellow Sea Warm Current driven by East Asian Winter Monsoon. Furthermore, the burial characteristics of TOC are affected. Since about 2 ka B.P., The variation amplitude of TOC content was decreased and contribution of organic matter from marine sources has increased, which may be related to the strengthening of ENSO activities. In conclusion, sea level change is the main controlling factor of organic carbon burial in the Central South Yellow Sea since the last deglaciation. The significant change of TOC sedimentary records since high sea level may be related to the changes of Yellow Sea Warm Current under the influence of East Asian Winter Monsoon and ENSO activities.
Shelf-marginal sea, under land-sea interaction, is a key region with important information about climate, sea-level change, biogeochemical cycles and human activities. Based on the analysis of the dating results, total organic carbon (TOC) and stable carbon isotope composition of the core H12 in the eastern side of Central South Yellow Sea Mud, this study discussed the phased characteristics and the influencing factors of organic carbon burial in the background of sedimentary environment evolution since the last deglaciation. The results showed that the hard clay layer developed during the period of relatively low sea level (17~12.6 ka B.P.) with relatively high TOC content and TOC-MAR mainly contributed by terrigenous organic matter. During the transgression period (12.6~7.8 ka B.P.), affected by dynamic effects such as tidal current erosion, TOC originated from mixed terrestrial and marine sources. The terrigenous organic carbon flux shows a significantly high value around 8 ka B.P., similar to the obviously increasing sedimentation rate, the East Asian Winter Monsoon intensification and global cooling events, which may be related to the change of sediment transport mode driven by monsoon. During the high sea level period (since 7.8 ka B.P.), the organic carbon was mainly composed of marine organic carbon. Especially during 5~2 ka B.P., the relative variation amplitude of TOC content on the centennial scale was large, consistent with the weakening stage of Kuroshio Current and the strong period of East Asian Winter Monsoon, which may reflect the changes of marine primary productivity and water environment caused by the strengthening of Yellow Sea Warm Current driven by East Asian Winter Monsoon. Furthermore, the burial characteristics of TOC are affected. Since about 2 ka B.P., The variation amplitude of TOC content was decreased and contribution of organic matter from marine sources has increased, which may be related to the strengthening of ENSO activities. In conclusion, sea level change is the main controlling factor of organic carbon burial in the Central South Yellow Sea since the last deglaciation. The significant change of TOC sedimentary records since high sea level may be related to the changes of Yellow Sea Warm Current under the influence of East Asian Winter Monsoon and ENSO activities.
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Abstract:
[Objective] During the Early Permian, shallow water carbonate platforms were widely developed in Ziyun area, southern Guizhou, which is a significant region for studying the characteristics of bioconstructions and the implications to palaeoenvironment. [Methods] The methods of paleontology and sedimentary petrology were systematically used to study the Gaozhai coral reef in Zongdi Town, Ziyun County, Guizhou Province. The Gaozahi coral reef was meticulously measured in the field. The lithology, sedimentary structures, bed thickness and components were documented in detail. [Results] Based on field observations, the Gaozhai coral reef is exposed with a thickness of approximately 3.0 m and a lateral exposure of nearly 23.6 m. A total of 10 species in 8 genera fusulinids were recognized: Eoparafusulina parashengi，E. pararegularis，Mccloudia contracta，Pseudofusulina cf. wulungensis，Rugosofusulina paragregariformis，Triticites daaoziensis，Zellia ex. gr. crassialveola，Sphaeroschwagerina borealis，S. sp. indet., Boultonia wills. The fusulinids collected from the reef indicate an Early–Middle Sakmarian age. The Gaozhai coral reef is primarily composed of the in suit colonial rugose coral Fomichevella. A small quantity of solitary rugose coral Bothrophyllum, Timania and colonial rugose coral Kepingophyllum are also recognized. The coral framework is predominantly built by the branching colonial rugose coral Fomichevella preserved in situ. The great majority of corals are well-preserved, and the fragments are rare. The growth mechanism of Fomichevella is mostly attached to each other with asexual budding structure in branching forms and mostly occupies as much space as possible. The associated biotic compositions of the coral reef, including foraminifera, fusulinids, brachiopods, bryozoans, crinoids, ooids and calcareous algae, are abundant and spatially diverse. The differences in the composition of coral reef-dwellers reflect the temporal and spatial changes in the biotic constitutions of the coral reef. Four microfacies types have been identified, including bioclastic grainstone, bioclastic packstone, coral framestone and bioclastic wackestone. In the substrate of the Gaozhai coral reef, the microfacies types are predominantly characterized by bioclastic grainstone and bioclastic packstone, including the bioclasts of foraminifers, brachiopods, bryozoans and calcareous algae. In the core of the coral reef, the microfacies types are dominated by the coral framestone. Bioclastic wackestone is common in the interior of this coral reef, filling the spaces between coral skeletons. Bioclastic packstone is predominant in the cap of the coral reef. [Conclusion] Fasciculate corals have the highest growth rates among rugose corals, which can occupy ecologic niches much quicker than other forms and become relatively dominant at times. The dominance of the fasciculate colonial coral Fomichevella is more adaptable to the environment and could build a strong coral framework in the development of the reef. According to the growth of the reef-builder (corals) and microfacies analyses, relative sea-level changes are interpreted to control the development of the Gaozhai coral reef，which provides compelling evidence for the response of the reef evolution to the Late Palaeozoic glaciation at low latitudes. The development of the Gaozhai coral reef in South China was strongly coupled to the relative global deglaciation episode and associated sea-level rise during the Sakmarian.
[Objective] During the Early Permian, shallow water carbonate platforms were widely developed in Ziyun area, southern Guizhou, which is a significant region for studying the characteristics of bioconstructions and the implications to palaeoenvironment. [Methods] The methods of paleontology and sedimentary petrology were systematically used to study the Gaozhai coral reef in Zongdi Town, Ziyun County, Guizhou Province. The Gaozahi coral reef was meticulously measured in the field. The lithology, sedimentary structures, bed thickness and components were documented in detail. [Results] Based on field observations, the Gaozhai coral reef is exposed with a thickness of approximately 3.0 m and a lateral exposure of nearly 23.6 m. A total of 10 species in 8 genera fusulinids were recognized: Eoparafusulina parashengi，E. pararegularis，Mccloudia contracta，Pseudofusulina cf. wulungensis，Rugosofusulina paragregariformis，Triticites daaoziensis，Zellia ex. gr. crassialveola，Sphaeroschwagerina borealis，S. sp. indet., Boultonia wills. The fusulinids collected from the reef indicate an Early–Middle Sakmarian age. The Gaozhai coral reef is primarily composed of the in suit colonial rugose coral Fomichevella. A small quantity of solitary rugose coral Bothrophyllum, Timania and colonial rugose coral Kepingophyllum are also recognized. The coral framework is predominantly built by the branching colonial rugose coral Fomichevella preserved in situ. The great majority of corals are well-preserved, and the fragments are rare. The growth mechanism of Fomichevella is mostly attached to each other with asexual budding structure in branching forms and mostly occupies as much space as possible. The associated biotic compositions of the coral reef, including foraminifera, fusulinids, brachiopods, bryozoans, crinoids, ooids and calcareous algae, are abundant and spatially diverse. The differences in the composition of coral reef-dwellers reflect the temporal and spatial changes in the biotic constitutions of the coral reef. Four microfacies types have been identified, including bioclastic grainstone, bioclastic packstone, coral framestone and bioclastic wackestone. In the substrate of the Gaozhai coral reef, the microfacies types are predominantly characterized by bioclastic grainstone and bioclastic packstone, including the bioclasts of foraminifers, brachiopods, bryozoans and calcareous algae. In the core of the coral reef, the microfacies types are dominated by the coral framestone. Bioclastic wackestone is common in the interior of this coral reef, filling the spaces between coral skeletons. Bioclastic packstone is predominant in the cap of the coral reef. [Conclusion] Fasciculate corals have the highest growth rates among rugose corals, which can occupy ecologic niches much quicker than other forms and become relatively dominant at times. The dominance of the fasciculate colonial coral Fomichevella is more adaptable to the environment and could build a strong coral framework in the development of the reef. According to the growth of the reef-builder (corals) and microfacies analyses, relative sea-level changes are interpreted to control the development of the Gaozhai coral reef，which provides compelling evidence for the response of the reef evolution to the Late Palaeozoic glaciation at low latitudes. The development of the Gaozhai coral reef in South China was strongly coupled to the relative global deglaciation episode and associated sea-level rise during the Sakmarian.
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Abstract:
Permeability is a key factor that determines the seepage capacity of tight sandstone reservoirs and ultimately determines productivity. Due to the complex pore structure and strong heterogeneity of tight sandstone reservoirs, the permeability has a wide range of variation and is difficult to predict. Thus, it is urgent to develop a permeability prediction model suitable for tight sandstone. Taking the Cretaceous Bashijiqike tight sandstone in the Keshen2 gas reservoir of the Kuqa Depression of the Tarim Basin as the research object, by integrating routine physical analysis, microscopic observation based on thin section and scanning electron microscope, high-pressure mercury injection, nuclear magnetic resonance and fractal theory, we qualitatively and quantitatively characterized the pore structure of tight sandstone. Based on fractal theory, by fully considering the influence of pore structure heterogeneity on permeability, two novel tight sandstone permeability prediction models based on fractal theory were proposed. Compared with the rapex permeability prediction model, the permeability prediction accuracy of the r20 fractal model and the SDR(>40) fractal model increased by 42% and 20%, respectively.
Permeability is a key factor that determines the seepage capacity of tight sandstone reservoirs and ultimately determines productivity. Due to the complex pore structure and strong heterogeneity of tight sandstone reservoirs, the permeability has a wide range of variation and is difficult to predict. Thus, it is urgent to develop a permeability prediction model suitable for tight sandstone. Taking the Cretaceous Bashijiqike tight sandstone in the Keshen2 gas reservoir of the Kuqa Depression of the Tarim Basin as the research object, by integrating routine physical analysis, microscopic observation based on thin section and scanning electron microscope, high-pressure mercury injection, nuclear magnetic resonance and fractal theory, we qualitatively and quantitatively characterized the pore structure of tight sandstone. Based on fractal theory, by fully considering the influence of pore structure heterogeneity on permeability, two novel tight sandstone permeability prediction models based on fractal theory were proposed. Compared with the rapex permeability prediction model, the permeability prediction accuracy of the r20 fractal model and the SDR(>40) fractal model increased by 42% and 20%, respectively.
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Abstract:
[Objective] There were long-term and extensive glaciation that occurred during the Late Carboniferous-Early Permian. In this period, the Baoshan Block, as a part of the Gondwana continental margin, had experienced several transgressive-regressive cycle events, preserving important information on the expansion or depletion of glaciers. This study focuses on the Xiyi, Dongshanpo, and Woniusi sections in the Baoshan area of western Yunnan, explores the paleo-ocean redox environment from the Middle Carboniferous-early Permian, and analyzes the mechanism of anoxic events and the relationship with glaciation. [Methods] Pyrite framboid is widely utilized to reconstruct paleo-ocean redox conditions, given its different formation mechanisms in oxic and euxinic environments. The specific methods employed include statistical analysis of the size data of pyrite framboids through box-whisker plots, scatter plots of mean-standard deviation, and scatter plots of mean-skewness. [Results] The results indicate four distinct episodes of redox conditions: Interval Ⅰ, the late Tournaisian redox conditions varied rapidly from euxinic-anoxic to dysoxic-oxic. Interval Ⅱ, the Visean redox conditions changed from euxinic-anoxic to dysoxic-oxic. Interval Ⅲ, the middle Sakmarian to early Artinskian redox conditions experienced mainly oxic and dysoxic but punctuated by short anoxic-dysoxic episodes. Interval Ⅳ, the early Kungurian to the middle Roadian experienced the same trace to Interval Ⅲ. In genral, the redox environment of the paleo-ocean in Baoshan area showed a trend of euxinic → anoxic → dysoxic → oxic. The Early Carboniferous was dominated by anoxic- dysoxic environment. But the Early-Middle Permian was dominated by dysoxic - oxic environment. [Conclusions] Euxinic-anoxic events from the late Tournaisian to the early Visean are obviously positively correlated with the positive drift of δ13Ccard and the decrease of biomass. The other pieces of evidence also indicated an anoxic environment during the early Carboniferous, and the euxinic-anoxic event of the early Carboniferous in the Baoshan block was probably a response to the prelude of the late Paleozoic ice age. The redox condition of the early and middle Permian was more oxidizable than the early Carboniferous, which might be related to the sea level falls caused by glacial events and the temperature falling resulting from the paleogeographic evolution of the Cimmerian region. Furthermore, this change may have played a key role in promoting the biotic recovery of the early Permian in the study area.
[Objective] There were long-term and extensive glaciation that occurred during the Late Carboniferous-Early Permian. In this period, the Baoshan Block, as a part of the Gondwana continental margin, had experienced several transgressive-regressive cycle events, preserving important information on the expansion or depletion of glaciers. This study focuses on the Xiyi, Dongshanpo, and Woniusi sections in the Baoshan area of western Yunnan, explores the paleo-ocean redox environment from the Middle Carboniferous-early Permian, and analyzes the mechanism of anoxic events and the relationship with glaciation. [Methods] Pyrite framboid is widely utilized to reconstruct paleo-ocean redox conditions, given its different formation mechanisms in oxic and euxinic environments. The specific methods employed include statistical analysis of the size data of pyrite framboids through box-whisker plots, scatter plots of mean-standard deviation, and scatter plots of mean-skewness. [Results] The results indicate four distinct episodes of redox conditions: Interval Ⅰ, the late Tournaisian redox conditions varied rapidly from euxinic-anoxic to dysoxic-oxic. Interval Ⅱ, the Visean redox conditions changed from euxinic-anoxic to dysoxic-oxic. Interval Ⅲ, the middle Sakmarian to early Artinskian redox conditions experienced mainly oxic and dysoxic but punctuated by short anoxic-dysoxic episodes. Interval Ⅳ, the early Kungurian to the middle Roadian experienced the same trace to Interval Ⅲ. In genral, the redox environment of the paleo-ocean in Baoshan area showed a trend of euxinic → anoxic → dysoxic → oxic. The Early Carboniferous was dominated by anoxic- dysoxic environment. But the Early-Middle Permian was dominated by dysoxic - oxic environment. [Conclusions] Euxinic-anoxic events from the late Tournaisian to the early Visean are obviously positively correlated with the positive drift of δ13Ccard and the decrease of biomass. The other pieces of evidence also indicated an anoxic environment during the early Carboniferous, and the euxinic-anoxic event of the early Carboniferous in the Baoshan block was probably a response to the prelude of the late Paleozoic ice age. The redox condition of the early and middle Permian was more oxidizable than the early Carboniferous, which might be related to the sea level falls caused by glacial events and the temperature falling resulting from the paleogeographic evolution of the Cimmerian region. Furthermore, this change may have played a key role in promoting the biotic recovery of the early Permian in the study area.
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Abstract: In sedimentological studies, how to effectively distinguish the aeolian and hydrogenic deposits has long been the focus of academic attention, which is the difficult point as well. Although some macro-scale sedimentary features (such as wind-ripple marks, wind-ripple strata and pin strip laminated, etc.) can provide favorable support for the identification of aeolian deposits, due to the differences in outcrops exposure conditions, the features mentioned above are difficult to be accurately recognized. In contrast, the characteristic of microtextures of aeolian deposits , such as high composition and structural maturity, stable mineral surface morphology, etc., is not limited by outcrop conditions, which provides us with an effective way to identify aeolian deposits. In this study, taking late Jurassic eolian and hydrogenic deposits from the Ningwu-Jingle basin of Shanxi Province as an example, a comparative study has been carried out in terms of thin section analysis, grain size analysis, scanning electron microscopy and energy spectrum analysis. Based on the comprehensive analysis of microscopic identification criteria of eolian sediments, it is proposed that the dished pits on the surface of mineral particles and the wind-ripple strata with inverse grain size grading can be used as the unique identification indicators of eolian deposits. In view of the explanatory ambiguity of the microscopic characteristics of most aeolian deposits, it is recommended to adopt multi-index combined way to analyze the genesis of aeolian deposits.
Abstract: In sedimentological studies, how to effectively distinguish the aeolian and hydrogenic deposits has long been the focus of academic attention, which is the difficult point as well. Although some macro-scale sedimentary features (such as wind-ripple marks, wind-ripple strata and pin strip laminated, etc.) can provide favorable support for the identification of aeolian deposits, due to the differences in outcrops exposure conditions, the features mentioned above are difficult to be accurately recognized. In contrast, the characteristic of microtextures of aeolian deposits , such as high composition and structural maturity, stable mineral surface morphology, etc., is not limited by outcrop conditions, which provides us with an effective way to identify aeolian deposits. In this study, taking late Jurassic eolian and hydrogenic deposits from the Ningwu-Jingle basin of Shanxi Province as an example, a comparative study has been carried out in terms of thin section analysis, grain size analysis, scanning electron microscopy and energy spectrum analysis. Based on the comprehensive analysis of microscopic identification criteria of eolian sediments, it is proposed that the dished pits on the surface of mineral particles and the wind-ripple strata with inverse grain size grading can be used as the unique identification indicators of eolian deposits. In view of the explanatory ambiguity of the microscopic characteristics of most aeolian deposits, it is recommended to adopt multi-index combined way to analyze the genesis of aeolian deposits.
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Abstract:
[Objective] The reticulated laterite in southern China is of great significance for the reconstruction of the Quaternary climatic environment in the south, but micro recognition of the understanding of reticulated laterite process is still relatively weak.[Methods] Combines micro-area analysis techniques with geostatistical analysis and factor analysis to conduct element geochemical analysis on the white vein micro-area and the transition micro-area of red vein and white vein profile in Langxi（30°58′24″N，119°7′43″E）. [Results] Results indicate that:(1)From the perspective of element content,The content of iron group elements such as Fe2O3 (5.77~13.02%), Mn (253~2277ppm) and Co (7~140ppm) showed a trend of low value area in the center of the vein and high value area in the periphery, and gradually increased from the center to the periphery. However, K2O(1.11-1.51%), MgO (0.23-0.37%) and other constant elements, as well as Ti (4950-6544ppm), Zr(354-371ppm) and other elements are basically different from the distribution trend. (2)The common feature of factors in the white vein micro-area and the red-white transition micro-area is that they are mainly factor 1, which mainly reflects the leaching migration of iron and iron group elements in the white vein, as well as the relative enrichment process of soluble constant elements such as K, Ca, Mg and stable elements such as Ti and Zr, while factor 2 may be mainly related to the deposition process of iron. In addition, there may be adsorption processes of iron oxides on Cu, Zn, etc. [Conclusion]Through the microarea technical method and factor analysis, the interior of the white area is not homogeneous, and there is actually a gradual change from the center of the vein to the periphery. The variation of element content from white vein to red vein also showed a gradual change, which was similar to that in white vein micro-area.Reticulation is a continuous developmental process.?During the process of reticulation, the leaching migration of iron and iron elements dominates, the deposition and leaching migration of iron and iron group elements coexist, the reticulation process is relatively complicated.
[Objective] The reticulated laterite in southern China is of great significance for the reconstruction of the Quaternary climatic environment in the south, but micro recognition of the understanding of reticulated laterite process is still relatively weak.[Methods] Combines micro-area analysis techniques with geostatistical analysis and factor analysis to conduct element geochemical analysis on the white vein micro-area and the transition micro-area of red vein and white vein profile in Langxi（30°58′24″N，119°7′43″E）. [Results] Results indicate that:(1)From the perspective of element content,The content of iron group elements such as Fe2O3 (5.77~13.02%), Mn (253~2277ppm) and Co (7~140ppm) showed a trend of low value area in the center of the vein and high value area in the periphery, and gradually increased from the center to the periphery. However, K2O(1.11-1.51%), MgO (0.23-0.37%) and other constant elements, as well as Ti (4950-6544ppm), Zr(354-371ppm) and other elements are basically different from the distribution trend. (2)The common feature of factors in the white vein micro-area and the red-white transition micro-area is that they are mainly factor 1, which mainly reflects the leaching migration of iron and iron group elements in the white vein, as well as the relative enrichment process of soluble constant elements such as K, Ca, Mg and stable elements such as Ti and Zr, while factor 2 may be mainly related to the deposition process of iron. In addition, there may be adsorption processes of iron oxides on Cu, Zn, etc. [Conclusion]Through the microarea technical method and factor analysis, the interior of the white area is not homogeneous, and there is actually a gradual change from the center of the vein to the periphery. The variation of element content from white vein to red vein also showed a gradual change, which was similar to that in white vein micro-area.Reticulation is a continuous developmental process.?During the process of reticulation, the leaching migration of iron and iron elements dominates, the deposition and leaching migration of iron and iron group elements coexist, the reticulation process is relatively complicated.
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Abstract:
[Objective]Aiming at the problems of large difference in paleoenvironment characteristics of Jurassic Da 'anzhai period and unclear distribution law of shale source and reservoir in Sichuan Basin, [Methods]based on the geological data of drilling core and field section of Jurassic Da 'anzhai member in central and eastern Sichuan Basin, study the lithology and sedimentary paleoenvironment of Da 'anzhai Member.Through geochemical analysis of elements to recovery and comparative analysis the Paleo-climate, the Paleo-redox conditions and the Paleo-salinity in Da 'anzhai Period.[Results]The results show that the Da 'anzhai Member can be divided into shale, shell shale, mudstone, silty mudstone, argillaceous siltstone, shell limestone and argillaceous shell limestone.The paleoenvironment of different sub-member in the Da 'anzhai Member is different to some extent.During the sedimentation period of the third sub-member of Daanzhai, the climate was dry to semi dry, and the water environment was fresh to semi saline under sub reducing conditions, located in a shallow to semi deep lake environment.During the sedimentation period of the second sub-member of Daanzhai, the climate was semi dry to semi humid, with more precipitation and lower temperatures, and the water environment was fresh water with sub reducing conditions, and it was in a semi deep lake environment.During the sedimentation period of the first sub-member of Daanzhai, the climate was dry to semi dry, and the water environment was semi saline to saline under oxidation sub reduction conditions, located in a lakeside shallow lake environment.Both well RA1 and well YT1 have the same rule in Da 'anzhai period that the climate was dry→wet→dry, the precipitation was less→more→less, the temperature was high→low→high, the reducibility of water was weak→strong→weak, the paleosalinity was high→low→high.From the sedimentation period of the third sub-member of Da 'anzhai to the early sedimentation period of the second sub-member of Da 'anzhai, the lacustrine basin depositional center migrated from the eastern Sichuan Basin to the central Sichuan Basin.The middle sedimentation period of the second sub-member of Da 'anzhai was a transitional stage in which the migration direction of the lake basin depositional center changed.From the late sedimentation period of the second sub-member of Da 'anzhai to the sedimentation period of the first sub-member of Da 'anzhai, the lacustrine basin depositional center migrated from the central Sichuan Basin to the eastern Sichuan Basin.The average TOC of the second sub-member of Daanzhai is 1.70%, and the average porosity is 4.93%,which are significantly higher than the first sub-member and the third sub-member of Da 'anzhai,and the fluorescence display is strong, it is the main source and reservoir of shale oil in the Daanzhai section.The Paleoenvironmental factors have great influence on the source and reservoir configuration. The more humid climate, more precipitation, lower temperature, stronger reducibility and lower salinity are conducive to shale deposition, organic matter enrichment and pore development.[Conclusions]The study on the paleoenvironment of Da 'anzhai Member in central-eastern Sichuan Basin is of great significance to the regularity of shale deposition, organic matter enrichment and pore development degree, and provides a theoretical basis for shale oil exploration in Sichuan Basin.
[Objective]Aiming at the problems of large difference in paleoenvironment characteristics of Jurassic Da 'anzhai period and unclear distribution law of shale source and reservoir in Sichuan Basin, [Methods]based on the geological data of drilling core and field section of Jurassic Da 'anzhai member in central and eastern Sichuan Basin, study the lithology and sedimentary paleoenvironment of Da 'anzhai Member.Through geochemical analysis of elements to recovery and comparative analysis the Paleo-climate, the Paleo-redox conditions and the Paleo-salinity in Da 'anzhai Period.[Results]The results show that the Da 'anzhai Member can be divided into shale, shell shale, mudstone, silty mudstone, argillaceous siltstone, shell limestone and argillaceous shell limestone.The paleoenvironment of different sub-member in the Da 'anzhai Member is different to some extent.During the sedimentation period of the third sub-member of Daanzhai, the climate was dry to semi dry, and the water environment was fresh to semi saline under sub reducing conditions, located in a shallow to semi deep lake environment.During the sedimentation period of the second sub-member of Daanzhai, the climate was semi dry to semi humid, with more precipitation and lower temperatures, and the water environment was fresh water with sub reducing conditions, and it was in a semi deep lake environment.During the sedimentation period of the first sub-member of Daanzhai, the climate was dry to semi dry, and the water environment was semi saline to saline under oxidation sub reduction conditions, located in a lakeside shallow lake environment.Both well RA1 and well YT1 have the same rule in Da 'anzhai period that the climate was dry→wet→dry, the precipitation was less→more→less, the temperature was high→low→high, the reducibility of water was weak→strong→weak, the paleosalinity was high→low→high.From the sedimentation period of the third sub-member of Da 'anzhai to the early sedimentation period of the second sub-member of Da 'anzhai, the lacustrine basin depositional center migrated from the eastern Sichuan Basin to the central Sichuan Basin.The middle sedimentation period of the second sub-member of Da 'anzhai was a transitional stage in which the migration direction of the lake basin depositional center changed.From the late sedimentation period of the second sub-member of Da 'anzhai to the sedimentation period of the first sub-member of Da 'anzhai, the lacustrine basin depositional center migrated from the central Sichuan Basin to the eastern Sichuan Basin.The average TOC of the second sub-member of Daanzhai is 1.70%, and the average porosity is 4.93%,which are significantly higher than the first sub-member and the third sub-member of Da 'anzhai,and the fluorescence display is strong, it is the main source and reservoir of shale oil in the Daanzhai section.The Paleoenvironmental factors have great influence on the source and reservoir configuration. The more humid climate, more precipitation, lower temperature, stronger reducibility and lower salinity are conducive to shale deposition, organic matter enrichment and pore development.[Conclusions]The study on the paleoenvironment of Da 'anzhai Member in central-eastern Sichuan Basin is of great significance to the regularity of shale deposition, organic matter enrichment and pore development degree, and provides a theoretical basis for shale oil exploration in Sichuan Basin.
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Abstract:
Deep-ultra-deep carbonate rocks have great potential in oil and gas exploration, and their reservoirs are characterized by strong heterogeneity and difficult prediction, which is, at least, partly related to their complex diagenetic alterations. Therefore, clarifying the beneficial diagenetic processes in reservoir development, that is, profitable diagenetic path and reservoir formation efficiency, is the key to revealing the genesis of deep carbonate reservoirs. We have systematically compared the geochemical parameters, porosity and permeability of the Sinian to Lower Cambrian dolostone from the Sichuan Basin and the Tarim Basin (including a small amount of data from the Oman Basin and the Siberian Platform), which including: carbon and oxygen isotopes (n=617), strontium isotope (n=189), rare earth elements (n=106), fluid inclusion homogenization temperature (n=161), cluster isotope temperature (n=117) and porosity and permeability (n=1557). The geochemical feature templates of dolomite and late calcite of different origins in the two strata reservoirs were established. The results show that the geochemical characteristics of diagenetic minerals in the two reservoirs are generally quite similar, and both have undergone constructive diagenetic alterations such as dolomitization, meteoric water, fracturing, and hydrothermal fluids. Compared with the Lower Cambrian dolostone reservoirs, the highest-quality reservoirs in the area (the Dengying Formation) have experienced stronger seepage-reflux dolomitization, and especially the more intense hydrothermal alternations, suggesting differential effective diagenetic alterations is the key to good carbonate reservoir formation. Based on the above characteristics, the development of Sinian-Cambrian high-quality dolostone reservoirs in the Sichuan Basin and Tarim Basin is jointly controlled by the development of evaporite facies in the depositional period and the development of late structural hydrothermal fluids. The above understanding thus has important enlightenment significance for deep-ultra-deep carbonate oil and gas exploration.
Deep-ultra-deep carbonate rocks have great potential in oil and gas exploration, and their reservoirs are characterized by strong heterogeneity and difficult prediction, which is, at least, partly related to their complex diagenetic alterations. Therefore, clarifying the beneficial diagenetic processes in reservoir development, that is, profitable diagenetic path and reservoir formation efficiency, is the key to revealing the genesis of deep carbonate reservoirs. We have systematically compared the geochemical parameters, porosity and permeability of the Sinian to Lower Cambrian dolostone from the Sichuan Basin and the Tarim Basin (including a small amount of data from the Oman Basin and the Siberian Platform), which including: carbon and oxygen isotopes (n=617), strontium isotope (n=189), rare earth elements (n=106), fluid inclusion homogenization temperature (n=161), cluster isotope temperature (n=117) and porosity and permeability (n=1557). The geochemical feature templates of dolomite and late calcite of different origins in the two strata reservoirs were established. The results show that the geochemical characteristics of diagenetic minerals in the two reservoirs are generally quite similar, and both have undergone constructive diagenetic alterations such as dolomitization, meteoric water, fracturing, and hydrothermal fluids. Compared with the Lower Cambrian dolostone reservoirs, the highest-quality reservoirs in the area (the Dengying Formation) have experienced stronger seepage-reflux dolomitization, and especially the more intense hydrothermal alternations, suggesting differential effective diagenetic alterations is the key to good carbonate reservoir formation. Based on the above characteristics, the development of Sinian-Cambrian high-quality dolostone reservoirs in the Sichuan Basin and Tarim Basin is jointly controlled by the development of evaporite facies in the depositional period and the development of late structural hydrothermal fluids. The above understanding thus has important enlightenment significance for deep-ultra-deep carbonate oil and gas exploration.
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Abstract:
[Objective] Solid bitumen is commonly distributed in the petroliferous basins all over the world and it has been widely applied in the oil and gas exploration. Solid bitumen is especially important for the oil and gas exploration in the deep and ultra-deep carbonate reservoirs. However, some problems also exist during the concrete application of solid bitumen in the oil and gas exploration such as its reflectance is hard to determine under the microscope and the applicability of oil/gas-source correlation parameters of solid bitumen is constrained by its genesis type. if these problems are not properly dealt with, wrong results may be achieved. As a result, it is very important to effectively analyze and summarize the multiple application of solid bitumen in the oil and gas exploration. [Methods] Based on the extensive literature research in both Chinese and English, the morphological characteristics and genetic types of solid bitumen which are closely related to its application in the oil and gas exploration are systematic analyzed, and then the multiple applications of solid bitumen in the oil and gas exploration are summarized. In the end, the advantages and disadvantages of the applications of solid bitumen in the oil and gas exploration are pointed out. [Results] The results are as follows. Solid bitumen is characterized by complex and diverse optical structures, such as isotropic, fine-grained mosaic, medium-grained mosaic, coarse-grained mosaic, coarse flow mosaic, domain and fibrous optical structures, which are mainly controlled by the factors such as formation environment and parent material composition. Solid bitumen also have complex and diverse ultramicroscopic morphology, such as massive, finger-like, vesicular, warty, sheet-like, thin-skinned globular, botryoidalis and vermicular ultramicroscopic morphology, which may be affected by the factors such as migration and the generation and escalation of natural gas. Solid bitumen owns multiple genetic types, such as thermal chemical alteration, anaerobic or aerobic biodegradation, deasphalting and thermochemical sulfate reduction, which have great differences in the organic element composition, carbon and sulfur isotope values, and biomarker composition. At the same time, solid bitumen can be used to indicate the generation, migration and accumulation of oil and gas, and its reflectivity and laser Raman parameters can be used to reflect the thermal evolution maturity. In addition, the carbon isotopes, biomarkers, trace and rare earth elements, as well as rhenium and osmium isotopes of soild bitumen can be applied to trace the origins of oil and gas. However, due to the various formation mechanisms, the geochemical characteristics of solid bitumen with different genetic types derived from same parent rock will turn different, which will result to the significant differences in the applicability of the oil/gas-source correlation parameters for the solid bitumen with different genetic types. As a result, it is of great necessity to determine the genetic types of solid bitumen prior to the application of its oil/gas-source correlation parameters. [Conclusion] This study can provide a strong support for the effective application of solid bitumen in the oil and gas exploration, and will play an important guiding role in the deep and ultra-deep oil and gas exploration.
[Objective] Solid bitumen is commonly distributed in the petroliferous basins all over the world and it has been widely applied in the oil and gas exploration. Solid bitumen is especially important for the oil and gas exploration in the deep and ultra-deep carbonate reservoirs. However, some problems also exist during the concrete application of solid bitumen in the oil and gas exploration such as its reflectance is hard to determine under the microscope and the applicability of oil/gas-source correlation parameters of solid bitumen is constrained by its genesis type. if these problems are not properly dealt with, wrong results may be achieved. As a result, it is very important to effectively analyze and summarize the multiple application of solid bitumen in the oil and gas exploration. [Methods] Based on the extensive literature research in both Chinese and English, the morphological characteristics and genetic types of solid bitumen which are closely related to its application in the oil and gas exploration are systematic analyzed, and then the multiple applications of solid bitumen in the oil and gas exploration are summarized. In the end, the advantages and disadvantages of the applications of solid bitumen in the oil and gas exploration are pointed out. [Results] The results are as follows. Solid bitumen is characterized by complex and diverse optical structures, such as isotropic, fine-grained mosaic, medium-grained mosaic, coarse-grained mosaic, coarse flow mosaic, domain and fibrous optical structures, which are mainly controlled by the factors such as formation environment and parent material composition. Solid bitumen also have complex and diverse ultramicroscopic morphology, such as massive, finger-like, vesicular, warty, sheet-like, thin-skinned globular, botryoidalis and vermicular ultramicroscopic morphology, which may be affected by the factors such as migration and the generation and escalation of natural gas. Solid bitumen owns multiple genetic types, such as thermal chemical alteration, anaerobic or aerobic biodegradation, deasphalting and thermochemical sulfate reduction, which have great differences in the organic element composition, carbon and sulfur isotope values, and biomarker composition. At the same time, solid bitumen can be used to indicate the generation, migration and accumulation of oil and gas, and its reflectivity and laser Raman parameters can be used to reflect the thermal evolution maturity. In addition, the carbon isotopes, biomarkers, trace and rare earth elements, as well as rhenium and osmium isotopes of soild bitumen can be applied to trace the origins of oil and gas. However, due to the various formation mechanisms, the geochemical characteristics of solid bitumen with different genetic types derived from same parent rock will turn different, which will result to the significant differences in the applicability of the oil/gas-source correlation parameters for the solid bitumen with different genetic types. As a result, it is of great necessity to determine the genetic types of solid bitumen prior to the application of its oil/gas-source correlation parameters. [Conclusion] This study can provide a strong support for the effective application of solid bitumen in the oil and gas exploration, and will play an important guiding role in the deep and ultra-deep oil and gas exploration.
, Available online
Abstract:
[Objective] Sandy conglomerates, significantly contributing to gravity flow sedimentation studies, have become prime targets for oil, gas, and groundwater exploration, thanks to their advantageous reservoir conditions. However, their complex depositional attributes, heterogeneous composition, and intricate pore structures pose challenges, markedly affecting the elastic response of seismic waves. This complexity can compromise the reliability of fluid inversion methodologies and the outcomes of fluid identification processes. Consequently, a comprehensive understanding of the interrelationship between reservoir lithology, its physical properties, involved fluids, and seismic attributes is vital. Such understanding, attainable through petrophysical experiments, is critical for accurately deciphering the petrophysical response characteristics of sandy conglomerates. [Method] We undertook multi-frequency-band measurements (employing seismic frequencies at 1-100 Hz and ultrasonic frequency at 1MHz) on the elastic parameters of sandy conglomerate from the Dongying Sag in the Bohai Bay Basin. Initially, we selected series of samples from each grain level for porosity and permeability tests, followed by classification and analysis of the samples' rock types and physical properties. We then measured the P- and S-wave ultrasonic velocities in samples saturated with varying fluids, assessing the effects of fluid, lithology, and pressure on velocities. This led to the determination of the relationship between pressure and velocity by evaluating different water-saturated samples, followed by calculation of indicative factors to identify rock types and fluid sensitivity parameters. Furthermore, we measured the Young’s modulus and Poisson’s ratio to calculate the P-wave and S-wave velocities at seismic band. Lastly, we computed the crack density and soft porosity using ultrasonic velocity, and compared the velocity dispersion with the seismic frequency band measurements. [Results] Our results suggest that: 1) sensitive parameters ρ，K, λ, λρ, λ? enable us to distinguish sandy conglomerate from shale and conglomerate, albeit not from sandstone. For fluids, gas-water can be separated through υ, ρV_P/V_S, ρv, λv, whereas oil and water cannot; 2) at in-situ reservoir pressure, sandy conglomerate demonstrates larger P-wave velocity dispersion, crack density, and corresponding closure pressure compared to sandstone, conglomerate, and mudstone; 3) the dispersion can be explained by the "squirt flow" mechanism, aligning with a crack aspect ratio distribution that mirrors the actual scenario. The velocity dispersion range of oil-saturated samples falls in lower frequencies, with a larger dispersion span, thus positioning seismic band dispersion range as a sensitive parameter to differentiate between oil and water, overcoming the limitations of traditional sensitive parameters. [Conclusion] This study offers insights into lithology and fluid-sensitive parameters via ultrasonic experiments and explores the pronounced velocity dispersion characteristics of sandy conglomerate under in-situ reservoir conditions through seismic frequency band experimental results, thereby identifying the key dispersion physical mechanism in sandy conglomerate. We assert that the fractured sandy conglomerate possesses excellent reservoir properties, exhibiting velocity dispersion characteristics markedly different from marl with fluid sensitivity. This s the consideration of frequency effects in fluid identification for traditional inversion methods. Our work systematically encapsulates the petrophysical response characteristics of sandy conglomerate bodies, establishing a theoretical groundwork for studying seismic wave response and identifying fluids in sandy conglomerate reservoirs. This could enhance reservoir prediction accuracy and effectively guide the geophysical exploration of sandy conglomerate reservoirs.
[Objective] Sandy conglomerates, significantly contributing to gravity flow sedimentation studies, have become prime targets for oil, gas, and groundwater exploration, thanks to their advantageous reservoir conditions. However, their complex depositional attributes, heterogeneous composition, and intricate pore structures pose challenges, markedly affecting the elastic response of seismic waves. This complexity can compromise the reliability of fluid inversion methodologies and the outcomes of fluid identification processes. Consequently, a comprehensive understanding of the interrelationship between reservoir lithology, its physical properties, involved fluids, and seismic attributes is vital. Such understanding, attainable through petrophysical experiments, is critical for accurately deciphering the petrophysical response characteristics of sandy conglomerates. [Method] We undertook multi-frequency-band measurements (employing seismic frequencies at 1-100 Hz and ultrasonic frequency at 1MHz) on the elastic parameters of sandy conglomerate from the Dongying Sag in the Bohai Bay Basin. Initially, we selected series of samples from each grain level for porosity and permeability tests, followed by classification and analysis of the samples' rock types and physical properties. We then measured the P- and S-wave ultrasonic velocities in samples saturated with varying fluids, assessing the effects of fluid, lithology, and pressure on velocities. This led to the determination of the relationship between pressure and velocity by evaluating different water-saturated samples, followed by calculation of indicative factors to identify rock types and fluid sensitivity parameters. Furthermore, we measured the Young’s modulus and Poisson’s ratio to calculate the P-wave and S-wave velocities at seismic band. Lastly, we computed the crack density and soft porosity using ultrasonic velocity, and compared the velocity dispersion with the seismic frequency band measurements. [Results] Our results suggest that: 1) sensitive parameters ρ，K, λ, λρ, λ? enable us to distinguish sandy conglomerate from shale and conglomerate, albeit not from sandstone. For fluids, gas-water can be separated through υ, ρV_P/V_S, ρv, λv, whereas oil and water cannot; 2) at in-situ reservoir pressure, sandy conglomerate demonstrates larger P-wave velocity dispersion, crack density, and corresponding closure pressure compared to sandstone, conglomerate, and mudstone; 3) the dispersion can be explained by the "squirt flow" mechanism, aligning with a crack aspect ratio distribution that mirrors the actual scenario. The velocity dispersion range of oil-saturated samples falls in lower frequencies, with a larger dispersion span, thus positioning seismic band dispersion range as a sensitive parameter to differentiate between oil and water, overcoming the limitations of traditional sensitive parameters. [Conclusion] This study offers insights into lithology and fluid-sensitive parameters via ultrasonic experiments and explores the pronounced velocity dispersion characteristics of sandy conglomerate under in-situ reservoir conditions through seismic frequency band experimental results, thereby identifying the key dispersion physical mechanism in sandy conglomerate. We assert that the fractured sandy conglomerate possesses excellent reservoir properties, exhibiting velocity dispersion characteristics markedly different from marl with fluid sensitivity. This s the consideration of frequency effects in fluid identification for traditional inversion methods. Our work systematically encapsulates the petrophysical response characteristics of sandy conglomerate bodies, establishing a theoretical groundwork for studying seismic wave response and identifying fluids in sandy conglomerate reservoirs. This could enhance reservoir prediction accuracy and effectively guide the geophysical exploration of sandy conglomerate reservoirs.
, Available online
Abstract:
The Otindag sandland, located at the boundary of the East Asian monsoon region in east-central Inner Mongolia, is an ideal area for studying climate change since the Last Glacial Maximum due to its unique geographical environment and the extensive development of aeolian sand stratigraphy. Previous studies on the chronology of the Otindag sandland have focused on the Holocene, and relatively few studies have been conducted since the Last Glacial Maximum due to the lack of a systematic stratigraphic chronology framework. In this paper, two aeolian sand sedimentary sequences in the southern edge of Otindag sandland, Lanqi South (LQS) and Baleng Mountain (BLS), were studied, and the stratigraphic chronology framework was determined by using the single-aliquot regenerative-dose (SAR) method in the optical stimulated luminescence (OSL) dating method. Combined with the sedimentary characteristics, grain size and quartz grain surface morphological features were integrated for analysis, the results indicate that, aeolian sand and sandy loess interstratification were mainly developed, with a cold and dry climate, strong sandstorm activity, and millennial-scale climate fluctuations from 18 to 11.5 ka in the sandland. Between 11.5 and 8.2 ka, the temperature fluctuated and increased, with a relatively dry and cold climate, and mostly developed aeolian sands with sandy paleosols. During the period of 8.2 to 2.7 ka, the climate was the warmest and wettest, and sandy palaeosol were developed in both profiles. From 2.7 ka to the present, the climate is mild and dry, and weak sandy palaeosol are developed. In general, the rapid climate change since the Last Glacial Maximum in Otindag sandland has global and universal characteristics so that is a regional response to global climate change, which is closely related to the East Asian monsoon, driven by solar radiation and global ice volume together.
The Otindag sandland, located at the boundary of the East Asian monsoon region in east-central Inner Mongolia, is an ideal area for studying climate change since the Last Glacial Maximum due to its unique geographical environment and the extensive development of aeolian sand stratigraphy. Previous studies on the chronology of the Otindag sandland have focused on the Holocene, and relatively few studies have been conducted since the Last Glacial Maximum due to the lack of a systematic stratigraphic chronology framework. In this paper, two aeolian sand sedimentary sequences in the southern edge of Otindag sandland, Lanqi South (LQS) and Baleng Mountain (BLS), were studied, and the stratigraphic chronology framework was determined by using the single-aliquot regenerative-dose (SAR) method in the optical stimulated luminescence (OSL) dating method. Combined with the sedimentary characteristics, grain size and quartz grain surface morphological features were integrated for analysis, the results indicate that, aeolian sand and sandy loess interstratification were mainly developed, with a cold and dry climate, strong sandstorm activity, and millennial-scale climate fluctuations from 18 to 11.5 ka in the sandland. Between 11.5 and 8.2 ka, the temperature fluctuated and increased, with a relatively dry and cold climate, and mostly developed aeolian sands with sandy paleosols. During the period of 8.2 to 2.7 ka, the climate was the warmest and wettest, and sandy palaeosol were developed in both profiles. From 2.7 ka to the present, the climate is mild and dry, and weak sandy palaeosol are developed. In general, the rapid climate change since the Last Glacial Maximum in Otindag sandland has global and universal characteristics so that is a regional response to global climate change, which is closely related to the East Asian monsoon, driven by solar radiation and global ice volume together.
, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.066
Abstract:
The Shizigou anticline structure is located in the west of the Qaidam Basin.There are abundant brine resources in the upper part of the Paleogene Lower Ganchaigou Formation, and the content of K, B and Li in brine is high, which has development prospects. In this paper, through the detection of major, trace elements and strontium isotope of the brine, it is found that: The content of K+ in the brine in the study area is 1.058~15.87g/L, of which 70% exceeds 3g/L ; the chemical type of brine is mainly chloride type; By calculating the characteristic coefficient of brine and analyzing the phase diagram of water-salt system, it is considered that the leaching salt layer is the main cause of the high salinity brine. At the same time, the relationship between strontium isotope characteristics of brine and salt layer and the correlation between K+ and Li+ reflect that the source of deep thermal fluid K also has a certain contribution. Through analysis, the metallogenic model of brine potassium in the study area is preliminarily established: During the Paleogene Xiaganchaigou period, the Shizigou area was in a weak extensional environment, and the sedimentary environment was relatively stable. The halite and potassium-magnesium salt deposits of the upper member of the Xiaganchaigou Formation in the late Eocene were deposited. In the later period, the tectonic activity intensified, and the potassium-rich thermal fluid rose into the lake along the tensile fault, providing some deep material source K, and causing the dissolution of the existing potassium-magnesium salt and some halite deposits, which in turn provided another important source of dissolved potassium for the brine in this area.
The Shizigou anticline structure is located in the west of the Qaidam Basin.There are abundant brine resources in the upper part of the Paleogene Lower Ganchaigou Formation, and the content of K, B and Li in brine is high, which has development prospects. In this paper, through the detection of major, trace elements and strontium isotope of the brine, it is found that: The content of K+ in the brine in the study area is 1.058~15.87g/L, of which 70% exceeds 3g/L ; the chemical type of brine is mainly chloride type; By calculating the characteristic coefficient of brine and analyzing the phase diagram of water-salt system, it is considered that the leaching salt layer is the main cause of the high salinity brine. At the same time, the relationship between strontium isotope characteristics of brine and salt layer and the correlation between K+ and Li+ reflect that the source of deep thermal fluid K also has a certain contribution. Through analysis, the metallogenic model of brine potassium in the study area is preliminarily established: During the Paleogene Xiaganchaigou period, the Shizigou area was in a weak extensional environment, and the sedimentary environment was relatively stable. The halite and potassium-magnesium salt deposits of the upper member of the Xiaganchaigou Formation in the late Eocene were deposited. In the later period, the tectonic activity intensified, and the potassium-rich thermal fluid rose into the lake along the tensile fault, providing some deep material source K, and causing the dissolution of the existing potassium-magnesium salt and some halite deposits, which in turn provided another important source of dissolved potassium for the brine in this area.
, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.061
Abstract:
[Objective] To study the evolution of river patterns in the distributive fluvial system, establish a database of corresponding parameters, and provide a data basis for predicting the distribution of sedimentary systems within the forecast basin, [Methods] Using modern geographic information software such as Google Earth and Global Mapper, the channel sinuosity was measured according to the grid of equal proportions, analyzes the variation of the channel sinuosity along the course, and establishes the depositional mode of the evolution of the Golmud fluvial fan. [Results and Discussions] A total of 2989 channel sinuosity data were measured, and according to the characteristics of the sinuosity of the Golmud fluvial fan, the Golmud fluvial fan can be divided into four parts: "braided river section", "braided-meander coexistence section", "large high-sinuosity meandering river section" and "small low-sinuosity meandering river section": 1) The slope of the braid river section was 0.7%, the development of the straight river and the braided river with low sinuosity, the braided belt width was large, the channel sinuosity was 1.01-1.43, the average sinuosity was 1.08, and the microfacies such as braided river, abandoned river and flood plain were mainly developed; 2) The slope of the braided-meander coexistence section was 0.63%, which developed both braided river and meandering river, and the development degree and river sinuosity of braided river and meandering river in different positions were different, the channel sinuosity was 1.08-5, and the average sinuosity was 1.52, and microfacies such as braided river, meandering river, abandoned river, crevasse splay, sand dunes and flood plain were mainly developed; 3) The slope of the large high-sinuosity meandering river section was 0.29%, mainly developed large meandering river, the channel was wide, the river bend swing was large, the channel sinuosity was 1.12-5, the average sinuosity was 1.83, and the microfacies such as meandering river, abandoned river, sand dunes and flood plain were mainly developed; 4) The slope of the small low-sinuosity meandering river section was 0.08%, mainly developed small bifurcated meandering river, narrow channel, small river bend swing, the channel sinuosity was 1.07-3.13, the average sinuosity was 1.51, and microfacies such as meandering river, abandoned river, crevasse splay, sand dunes and flood plain were mainly developed. [Conclusions] The depositional model of river-type evolution of macroDFS was established, which provided new knowledge base information for the prediction of the distribution of underground sedimentary systems.
[Objective] To study the evolution of river patterns in the distributive fluvial system, establish a database of corresponding parameters, and provide a data basis for predicting the distribution of sedimentary systems within the forecast basin, [Methods] Using modern geographic information software such as Google Earth and Global Mapper, the channel sinuosity was measured according to the grid of equal proportions, analyzes the variation of the channel sinuosity along the course, and establishes the depositional mode of the evolution of the Golmud fluvial fan. [Results and Discussions] A total of 2989 channel sinuosity data were measured, and according to the characteristics of the sinuosity of the Golmud fluvial fan, the Golmud fluvial fan can be divided into four parts: "braided river section", "braided-meander coexistence section", "large high-sinuosity meandering river section" and "small low-sinuosity meandering river section": 1) The slope of the braid river section was 0.7%, the development of the straight river and the braided river with low sinuosity, the braided belt width was large, the channel sinuosity was 1.01-1.43, the average sinuosity was 1.08, and the microfacies such as braided river, abandoned river and flood plain were mainly developed; 2) The slope of the braided-meander coexistence section was 0.63%, which developed both braided river and meandering river, and the development degree and river sinuosity of braided river and meandering river in different positions were different, the channel sinuosity was 1.08-5, and the average sinuosity was 1.52, and microfacies such as braided river, meandering river, abandoned river, crevasse splay, sand dunes and flood plain were mainly developed; 3) The slope of the large high-sinuosity meandering river section was 0.29%, mainly developed large meandering river, the channel was wide, the river bend swing was large, the channel sinuosity was 1.12-5, the average sinuosity was 1.83, and the microfacies such as meandering river, abandoned river, sand dunes and flood plain were mainly developed; 4) The slope of the small low-sinuosity meandering river section was 0.08%, mainly developed small bifurcated meandering river, narrow channel, small river bend swing, the channel sinuosity was 1.07-3.13, the average sinuosity was 1.51, and microfacies such as meandering river, abandoned river, crevasse splay, sand dunes and flood plain were mainly developed. [Conclusions] The depositional model of river-type evolution of macroDFS was established, which provided new knowledge base information for the prediction of the distribution of underground sedimentary systems.
, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.072
Abstract:
[Objective] Statistics of published literature and analysis of previous research results show that the reservoir physical properties and oil and gas enrichment of laminar fine-grained sedimentary rocks are obviously superior to those of undeveloped/weakly developed laminar fine-grained sedimentary rocks and have a very good positive correlation with them. Compared with the laminar structure of Marine fine-grained sedimentary rocks, the laminar lacustrine fine-grained sedimentary rocks are limited by the sedimentary environment being closer to the provenance area, the frequent change of sedimentary environment hydrodynamics, and the more obvious control by climate and tectonic activities. As a result, the reservoir physical properties and oil and gas enrichment characteristics of different types of laminar rocks are not the same. The summary of relevant differences is still unclear and needs to be revealed.[Method] By focusing on the relevant literature at home and abroad in the past ten years, the types and causes of pores and fractures of lamellar fine-grained sedimentary rocks are reviewed, and the controlling effects of lamellar composition, continuity and sequence combination on reservoir physical properties and hydrocarbon enrichment characteristics are described respectively. [Results] It is believed that the laminar structure has the advantages of frequent turnover of vertical material composition, abnormal development of internal micro-fractures and different evolution of organic matter under the laminar structure, which further improves the ability of oil and gas enrichment on the basis of fine-grained sedimentary rocks. . [Prospects] It is pointed out that there is still a lack of difference and comparison of reservoir physical properties of fine grained sedimentary rocks which are all laminated due to different factors such as pores and fractures in each other's layers, and it will be the development direction in the future to use computer to invert macro reservoir sedimentary model based on micro laminar data to guide unconventional reservoir development
[Objective] Statistics of published literature and analysis of previous research results show that the reservoir physical properties and oil and gas enrichment of laminar fine-grained sedimentary rocks are obviously superior to those of undeveloped/weakly developed laminar fine-grained sedimentary rocks and have a very good positive correlation with them. Compared with the laminar structure of Marine fine-grained sedimentary rocks, the laminar lacustrine fine-grained sedimentary rocks are limited by the sedimentary environment being closer to the provenance area, the frequent change of sedimentary environment hydrodynamics, and the more obvious control by climate and tectonic activities. As a result, the reservoir physical properties and oil and gas enrichment characteristics of different types of laminar rocks are not the same. The summary of relevant differences is still unclear and needs to be revealed.[Method] By focusing on the relevant literature at home and abroad in the past ten years, the types and causes of pores and fractures of lamellar fine-grained sedimentary rocks are reviewed, and the controlling effects of lamellar composition, continuity and sequence combination on reservoir physical properties and hydrocarbon enrichment characteristics are described respectively. [Results] It is believed that the laminar structure has the advantages of frequent turnover of vertical material composition, abnormal development of internal micro-fractures and different evolution of organic matter under the laminar structure, which further improves the ability of oil and gas enrichment on the basis of fine-grained sedimentary rocks. . [Prospects] It is pointed out that there is still a lack of difference and comparison of reservoir physical properties of fine grained sedimentary rocks which are all laminated due to different factors such as pores and fractures in each other's layers, and it will be the development direction in the future to use computer to invert macro reservoir sedimentary model based on micro laminar data to guide unconventional reservoir development
, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.059
Abstract:
[Objective] The study of "Carbonate Factory" emphasizes the specific effects of biological communities on the carbonate production process and scale moderation, which contributes significantly to our understanding of large-scale carbonate sedimentation. Although the concept and application of the "Carbonate Factory" have gained attention in the field of carbonate sedimentology, there is still a lack of systematic understanding of how to interpret the origin, developmental processes, and influencing factors of specific types of carbonate sedimentation in geological history, particularly in deep time. [Methods] This study examines the Gushan Formation of the Cambrian Miaolingian in the Yunmengshan area (Henan Province) as an example of a microbial carbonate factory. A multi-scale grid-based quantitative evaluation method is used to describe the specific form, internal structure, and construction process of the carbonate factory. [Results and Discussions] Our results show that benthic microbial communities were the primary builders of the microbial carbonate factory in the study area. They formed unique structures, including the stromatolite, thrombolite, leiolite, and microbial-induced sedimentary structure (MISS). Various particle types, including ooids, flat pebbles, and microbialite breccias, were preserved within the microbial buildups. The development of the microbial carbonate factories occurred episodically during the Guzhangian Age (Miaolingian) and had relatively small scales (height of <1 m); however, they extended widely in space and exhibited different macroscopic shapes such as subspherical, domical, and tabular. The interior structures of the microbial carbonate factories consisted of individual forming styles as well as vertical combinations of composite forms. [Conclusions] By analyzing various factors influencing the development of the factories, we found that higher nutrient levels may have played a crucial role in the development of microbial carbonate factories in the tide-flat environment. Additionally, the flooding event during the Guzhangian Age led to the eventual closure of the factories. This study provides an ancient example similar to the modern Hamelin Pool microbial carbonate factory in Australia, which has good reference value for understanding the types, characteristics, and evolutionary patterns of carbonate factories in the Cambrian period.
[Objective] The study of "Carbonate Factory" emphasizes the specific effects of biological communities on the carbonate production process and scale moderation, which contributes significantly to our understanding of large-scale carbonate sedimentation. Although the concept and application of the "Carbonate Factory" have gained attention in the field of carbonate sedimentology, there is still a lack of systematic understanding of how to interpret the origin, developmental processes, and influencing factors of specific types of carbonate sedimentation in geological history, particularly in deep time. [Methods] This study examines the Gushan Formation of the Cambrian Miaolingian in the Yunmengshan area (Henan Province) as an example of a microbial carbonate factory. A multi-scale grid-based quantitative evaluation method is used to describe the specific form, internal structure, and construction process of the carbonate factory. [Results and Discussions] Our results show that benthic microbial communities were the primary builders of the microbial carbonate factory in the study area. They formed unique structures, including the stromatolite, thrombolite, leiolite, and microbial-induced sedimentary structure (MISS). Various particle types, including ooids, flat pebbles, and microbialite breccias, were preserved within the microbial buildups. The development of the microbial carbonate factories occurred episodically during the Guzhangian Age (Miaolingian) and had relatively small scales (height of <1 m); however, they extended widely in space and exhibited different macroscopic shapes such as subspherical, domical, and tabular. The interior structures of the microbial carbonate factories consisted of individual forming styles as well as vertical combinations of composite forms. [Conclusions] By analyzing various factors influencing the development of the factories, we found that higher nutrient levels may have played a crucial role in the development of microbial carbonate factories in the tide-flat environment. Additionally, the flooding event during the Guzhangian Age led to the eventual closure of the factories. This study provides an ancient example similar to the modern Hamelin Pool microbial carbonate factory in Australia, which has good reference value for understanding the types, characteristics, and evolutionary patterns of carbonate factories in the Cambrian period.
, Available online
Abstract:
The marine red beds are distributed across various stages in geological history and are often interpreted as products of special environments, which have attracted widespread attention. The Sowa Formation in the Jurassic Qiangtang Basin is a set of sedimentary rocks composed of clastic and carbonate mixed sediments. In the Sowa Formation exposed in Bilocuo, Shuanghu County, Tibet, the red beds are mainly composed of carbonate sediments. This study explores the causes of their red color and their significance in deposition and diagenesis. Field sedimentology and downhole thin section identification of the Sowa Formation's red beds reveal that the rocks are mainly composed of grain-supported limestone, with abundant debris from cephalopods, echinoderms, bivalves, bryozoans, gastropods, and other benthic organisms. Biogenic debris and terrestrial quartz debris are the main components of the ooids, which display characteristics of a high-energy beach environment. Spectroscopic studies and scanning electron microscopy show that the main cause of the red color is submicron- to micron-sized pseudo-hexagonal and tetragonal hematite crystals. The coloration minerals are concentrated in the ooid cortex structure, and the cementing material is virtually devoid of coloration minerals. This suggests that during early diagenesis, especially during the formation of ooids and peloids, iron-loving microorganisms played an important role in capturing iron oxide. Furthermore, the geochemical analysis of carbonate minerals shows that the rock's redness is positively correlated with the flux of terrestrial debris input. Additionally, it exhibits a positive Ce/Ce* anomaly (1.1-1.3) and a pattern of enriched-middle rare earth elements “bulge”, indicating that the iron oxides underwent reductive dissolution. Based on these findings, the study reconstructed the red coloration process of the Sowa Formation's red beds. The input of terrestrial iron-bearing minerals provided the material basis for the red coloration, and then, during early diagenesis, reductive fluids dissolved the iron-bearing minerals, providing free iron ions for iron-loving microorganisms, allowing them to recrystallize and ultimately form hydroxyl iron and cause red coloration through chemical or biological processes.
The marine red beds are distributed across various stages in geological history and are often interpreted as products of special environments, which have attracted widespread attention. The Sowa Formation in the Jurassic Qiangtang Basin is a set of sedimentary rocks composed of clastic and carbonate mixed sediments. In the Sowa Formation exposed in Bilocuo, Shuanghu County, Tibet, the red beds are mainly composed of carbonate sediments. This study explores the causes of their red color and their significance in deposition and diagenesis. Field sedimentology and downhole thin section identification of the Sowa Formation's red beds reveal that the rocks are mainly composed of grain-supported limestone, with abundant debris from cephalopods, echinoderms, bivalves, bryozoans, gastropods, and other benthic organisms. Biogenic debris and terrestrial quartz debris are the main components of the ooids, which display characteristics of a high-energy beach environment. Spectroscopic studies and scanning electron microscopy show that the main cause of the red color is submicron- to micron-sized pseudo-hexagonal and tetragonal hematite crystals. The coloration minerals are concentrated in the ooid cortex structure, and the cementing material is virtually devoid of coloration minerals. This suggests that during early diagenesis, especially during the formation of ooids and peloids, iron-loving microorganisms played an important role in capturing iron oxide. Furthermore, the geochemical analysis of carbonate minerals shows that the rock's redness is positively correlated with the flux of terrestrial debris input. Additionally, it exhibits a positive Ce/Ce* anomaly (1.1-1.3) and a pattern of enriched-middle rare earth elements “bulge”, indicating that the iron oxides underwent reductive dissolution. Based on these findings, the study reconstructed the red coloration process of the Sowa Formation's red beds. The input of terrestrial iron-bearing minerals provided the material basis for the red coloration, and then, during early diagenesis, reductive fluids dissolved the iron-bearing minerals, providing free iron ions for iron-loving microorganisms, allowing them to recrystallize and ultimately form hydroxyl iron and cause red coloration through chemical or biological processes.
, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.079
Abstract:
[Objective] After more than 50 years of exploration, Langgu Sag has entered the stage of oil and gas exploration and development with lithologic and structural-lithologic reservoirs as the main targets. Previous studies have been carried out on the large-scale sedimentary characteristics, hydrocarbon accumulation factors and models of Langgu Sag. However, relatively little is known of the spatial distribution characteristics and the distribution rules of the fine sand bodies. The main controlling factors of hydrocarbon accumulation and their distribution are not uniform, which restricts the evaluation and production of subtle reservoirs. [Methods] This study comprehensively used core data, well logging, seismic data, analytical tests and production data to systematically study the Shahejie Formation in the Jiuzhou-Wanzhuang area. The study aims to identify and classify sedimentary facies and microfacies types, accurately characterize the spatial distribution of sand bodies, and analyze reservoirs formation control factors such as source rocks, traps and fault dredging systems. The hydrocarbon accumulation model is established, leading to the prediction of favorable concealed lithologic or structural-lithologic reservoirs distribution zones. [Results and Discussions] The lithology is mainly fine-grained clastic rock; the sedimentary sequence is not typical, a deformation structure is clearly developed, and floating mud gravel of sandy clastic flow origin can be seen. This reflects the characteristics of the dynamic conditions of traction flow in the distal fan delta. In the study area, there are two provenance supply systems in the south and north, and a braided channel extends from the SE of the Daxing Fault to the interior of the lake in a finger-like way, forming two depositional centers in Jiuzhou and Wanzhuang. In the study area, an underwater distributary channel at the front of the fan delta extends for some distance and migrates frequently. The estuary is unstable, with an underdeveloped or small-scale estuarine bar. Mature source rocks, effective traps and drainage systems are the main controls of hydrocarbon accumulation in the middle section of Sha-3 in the study area. The abundance of organic matter shows that the oil source of the lower submember of Sha-3 in the study area comes from underlying source rocks of the lower submember of Sha-3. Using forward modeling and RGB attribute fusion, sensitive attribute optimization was performed to predict the distribution range of high-quality sandstone reservoirs combined with a series of anticlinal tectonic settings to form good structural traps along with lithologic up-dip pinch-out traps. As oil source faults, the Daxing and Jiuzhou Faults and their secondary branches are the main channels connecting the oil and gas resources of the lower submember of Sha-3 and the reservoirs of the middle submember of Sha-3, and they also control the formation of traps as a whole. [Conclusions] The results show that the study area is primarily characterized by fan-delta systems and lake systems. Within the fan-delta system, various microfacies types were identified (e.g., braided channels, submarine distributary channels, delta front sandbars, and sheet-like sands). The spatial distribution of sand bodies is characterized by thick layers of distributary channel-sandbar complexes with finger-like distribution and continuous thin sheet-like sands. The organic configurations of oil source faults, structures and even lithologic traps are the main causes of hydrocarbon accumulation in the study area, and the reservoir lithology within the traps determines the oil, gas and water distribution. Finally, favorable lithologic or structural-lithologic reservoirs development target areas are predicted in the SE wing of the Jiuzhou plunging nose area, NW wing of the Jiuzhou plunging nose structure and NE wing of the Tongxi ancient structural ridge.
[Objective] After more than 50 years of exploration, Langgu Sag has entered the stage of oil and gas exploration and development with lithologic and structural-lithologic reservoirs as the main targets. Previous studies have been carried out on the large-scale sedimentary characteristics, hydrocarbon accumulation factors and models of Langgu Sag. However, relatively little is known of the spatial distribution characteristics and the distribution rules of the fine sand bodies. The main controlling factors of hydrocarbon accumulation and their distribution are not uniform, which restricts the evaluation and production of subtle reservoirs. [Methods] This study comprehensively used core data, well logging, seismic data, analytical tests and production data to systematically study the Shahejie Formation in the Jiuzhou-Wanzhuang area. The study aims to identify and classify sedimentary facies and microfacies types, accurately characterize the spatial distribution of sand bodies, and analyze reservoirs formation control factors such as source rocks, traps and fault dredging systems. The hydrocarbon accumulation model is established, leading to the prediction of favorable concealed lithologic or structural-lithologic reservoirs distribution zones. [Results and Discussions] The lithology is mainly fine-grained clastic rock; the sedimentary sequence is not typical, a deformation structure is clearly developed, and floating mud gravel of sandy clastic flow origin can be seen. This reflects the characteristics of the dynamic conditions of traction flow in the distal fan delta. In the study area, there are two provenance supply systems in the south and north, and a braided channel extends from the SE of the Daxing Fault to the interior of the lake in a finger-like way, forming two depositional centers in Jiuzhou and Wanzhuang. In the study area, an underwater distributary channel at the front of the fan delta extends for some distance and migrates frequently. The estuary is unstable, with an underdeveloped or small-scale estuarine bar. Mature source rocks, effective traps and drainage systems are the main controls of hydrocarbon accumulation in the middle section of Sha-3 in the study area. The abundance of organic matter shows that the oil source of the lower submember of Sha-3 in the study area comes from underlying source rocks of the lower submember of Sha-3. Using forward modeling and RGB attribute fusion, sensitive attribute optimization was performed to predict the distribution range of high-quality sandstone reservoirs combined with a series of anticlinal tectonic settings to form good structural traps along with lithologic up-dip pinch-out traps. As oil source faults, the Daxing and Jiuzhou Faults and their secondary branches are the main channels connecting the oil and gas resources of the lower submember of Sha-3 and the reservoirs of the middle submember of Sha-3, and they also control the formation of traps as a whole. [Conclusions] The results show that the study area is primarily characterized by fan-delta systems and lake systems. Within the fan-delta system, various microfacies types were identified (e.g., braided channels, submarine distributary channels, delta front sandbars, and sheet-like sands). The spatial distribution of sand bodies is characterized by thick layers of distributary channel-sandbar complexes with finger-like distribution and continuous thin sheet-like sands. The organic configurations of oil source faults, structures and even lithologic traps are the main causes of hydrocarbon accumulation in the study area, and the reservoir lithology within the traps determines the oil, gas and water distribution. Finally, favorable lithologic or structural-lithologic reservoirs development target areas are predicted in the SE wing of the Jiuzhou plunging nose area, NW wing of the Jiuzhou plunging nose structure and NE wing of the Tongxi ancient structural ridge.
, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.069
Abstract:
As one of the high-resolution geological records with seasonal to inter-annual time scales, the lacustrine varves play an essential role in paleoclimatic and paleoenvironmental research. In this review, we summarized the formation and preservation of the lacustrine varve, their identification and classification, varve chronology, as well as their implications for paleoclimatic and paleoenvironmental changes. Our findings reveal that 1) the formation and preservation of the lacustrine varve are influenced by seasonal paleoclimatic and paleoenvironmental changes, and are mainly distributed in high-latitude areas of the Northern Hemisphere; 2) the geophysical, geochemical, and geobiological features, or cross-validation of other radiometric dating methods are necessary to verify the annual nature of the varve; 3) the lacustrine varve can be used to establish accurate or floating geochronologies; and 4) lacustrine varve has been also used to reconstruct paleoclimatic and paleoenvironmental changes, but research on the lacustrine varve is unevenly distributed, with a temporal focus mainly on the Quaternary and a spatial focus mainly on Europe and the Americas. Based on current progresses and problems of the lacustrine varve research, we proposed the following prospects: 1) strengthen modern sediment monitoring and optimize the identification criteria; 2) systematically construct and improve the research system of the lacustrine varve with multiple research approaches; and 3) dig deep into the deep-time lacustrine varve, and focus on frontier scientific issues such as annual and inter-annual paleoclimate change.
As one of the high-resolution geological records with seasonal to inter-annual time scales, the lacustrine varves play an essential role in paleoclimatic and paleoenvironmental research. In this review, we summarized the formation and preservation of the lacustrine varve, their identification and classification, varve chronology, as well as their implications for paleoclimatic and paleoenvironmental changes. Our findings reveal that 1) the formation and preservation of the lacustrine varve are influenced by seasonal paleoclimatic and paleoenvironmental changes, and are mainly distributed in high-latitude areas of the Northern Hemisphere; 2) the geophysical, geochemical, and geobiological features, or cross-validation of other radiometric dating methods are necessary to verify the annual nature of the varve; 3) the lacustrine varve can be used to establish accurate or floating geochronologies; and 4) lacustrine varve has been also used to reconstruct paleoclimatic and paleoenvironmental changes, but research on the lacustrine varve is unevenly distributed, with a temporal focus mainly on the Quaternary and a spatial focus mainly on Europe and the Americas. Based on current progresses and problems of the lacustrine varve research, we proposed the following prospects: 1) strengthen modern sediment monitoring and optimize the identification criteria; 2) systematically construct and improve the research system of the lacustrine varve with multiple research approaches; and 3) dig deep into the deep-time lacustrine varve, and focus on frontier scientific issues such as annual and inter-annual paleoclimate change.
, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.071
Abstract:
Intraformational carbonate breccias and conglomerates composed of flat intraclasts (often called “flat-pebble conglomerates”) are the universal phenomena in mixed carbonate and siliciclastic deposits of the Cambrian-Ordovician successions, suggesting unique paleoecologic, paleoceanographic, and paleoclimatic conditions during the Cambrian-Ordovician greenhouse periods. Flat-pebble conglomerates are often interpreted as storm deposits, yet depositional processes of them, especially of those with mound-shaped geometry and edgewise clastic fabric, still remain controversial. This paper revisits mound-shaped, edgewise flat-pebble conglomerates in the Furongian Chaomidian Formation (Shandong Province, China) using traditional sedimentological measures in order to illustrate the potential complexity of their depositional processes. Detailed field observations on the bed that contains flat-pebble conglomerate mounds were carried out in six outcrops of the Jiulongshan section. The conglomerate mounds are present in between two oolite layers, sitting on a typical, smooth and sharp hardground surface that truncates the underlying oolites. The conglomerate mounds are characterized by remarkable convex-up geometry with a relatively flat base, although irregular geometry also occurs in outcrops. The conglomerate consists dominantly of oligomictic pebble- to cobble-size clasts of finely laminated peloidal grainstone with subangular to subrounded corners, a few rounded homogeneous lime mudstone clasts with red rims, and a few bioclastic grainstone clasts and oolite clasts with glauconite grains. The matrix is composed mostly of white, crudely laminated and clotted microbialites (mainly micro-sparite) and orange dolomites. The matrix also contains many ooids (including broken and multigeneration ooids), fossil fragments (trilobites, echinoderms, brachiopods, and algae), peloids, and abundant glauconite grains. Fragments and debris of micritic Girvanella often occur in matrix. Calcified Girvanella is also identified present along the clast edges. The crudely laminated microbialites locally occur on the top of clasts and show small-scale (a few to 10s of cm wide and a few cm thick) domal macrostructures. The conglomerates are clast-supported and clasts are generally disorganized without preferred orientation. In some cases, however, some intact thin-bedded peloidal grainstones with thin (a few mm thick) shales or horizontal clasts occur in the basal part, whereas more inclined and vertical clasts in the upper part. Both clasts and matrix grains are truncated along the upper boundaries of the breccia lenses. Particularly when the flat-pebble conglomerate mounds are as thick as the oolite bed, they show a flat and smooth surface, overlain by calcareous shale facies. Flat-pebble clasts were derived from rip-up of thickly laminated to thinly bedded peloidal grainstones by strong currents and/or waves. The flat pebbles were transported from nearby and deposited as discrete dunes of various scales under the reworking of storm-induced combined flows. The abundant fossil fragments, broken ooids, and debris of calcified microbes in matrix of the conglomerates are collectively indicative of high-energy, strong-agitating conditions. During deposition of flat pebbles, microbes grew both on top of and in between pebbles, which acted as binding medium that prevented re-orientation of the edgewise clasts and further trapping flat pebbles, eventually forming flat-pebble mounds of various sizes. The flat-pebble mounds underwent substantial reworking by waves after deposition while ooids were being deposited. The study illustrates complex and dynamic depositional conditions for the mound-shaped flat-pebble conglomerates, suggesting multiple episodes of storm events. Detailed sedimentological studies on flat-pebble conglomerate will provide insights into frequency, intensity, and sedimentary processes of deep-time storm events.
Intraformational carbonate breccias and conglomerates composed of flat intraclasts (often called “flat-pebble conglomerates”) are the universal phenomena in mixed carbonate and siliciclastic deposits of the Cambrian-Ordovician successions, suggesting unique paleoecologic, paleoceanographic, and paleoclimatic conditions during the Cambrian-Ordovician greenhouse periods. Flat-pebble conglomerates are often interpreted as storm deposits, yet depositional processes of them, especially of those with mound-shaped geometry and edgewise clastic fabric, still remain controversial. This paper revisits mound-shaped, edgewise flat-pebble conglomerates in the Furongian Chaomidian Formation (Shandong Province, China) using traditional sedimentological measures in order to illustrate the potential complexity of their depositional processes. Detailed field observations on the bed that contains flat-pebble conglomerate mounds were carried out in six outcrops of the Jiulongshan section. The conglomerate mounds are present in between two oolite layers, sitting on a typical, smooth and sharp hardground surface that truncates the underlying oolites. The conglomerate mounds are characterized by remarkable convex-up geometry with a relatively flat base, although irregular geometry also occurs in outcrops. The conglomerate consists dominantly of oligomictic pebble- to cobble-size clasts of finely laminated peloidal grainstone with subangular to subrounded corners, a few rounded homogeneous lime mudstone clasts with red rims, and a few bioclastic grainstone clasts and oolite clasts with glauconite grains. The matrix is composed mostly of white, crudely laminated and clotted microbialites (mainly micro-sparite) and orange dolomites. The matrix also contains many ooids (including broken and multigeneration ooids), fossil fragments (trilobites, echinoderms, brachiopods, and algae), peloids, and abundant glauconite grains. Fragments and debris of micritic Girvanella often occur in matrix. Calcified Girvanella is also identified present along the clast edges. The crudely laminated microbialites locally occur on the top of clasts and show small-scale (a few to 10s of cm wide and a few cm thick) domal macrostructures. The conglomerates are clast-supported and clasts are generally disorganized without preferred orientation. In some cases, however, some intact thin-bedded peloidal grainstones with thin (a few mm thick) shales or horizontal clasts occur in the basal part, whereas more inclined and vertical clasts in the upper part. Both clasts and matrix grains are truncated along the upper boundaries of the breccia lenses. Particularly when the flat-pebble conglomerate mounds are as thick as the oolite bed, they show a flat and smooth surface, overlain by calcareous shale facies. Flat-pebble clasts were derived from rip-up of thickly laminated to thinly bedded peloidal grainstones by strong currents and/or waves. The flat pebbles were transported from nearby and deposited as discrete dunes of various scales under the reworking of storm-induced combined flows. The abundant fossil fragments, broken ooids, and debris of calcified microbes in matrix of the conglomerates are collectively indicative of high-energy, strong-agitating conditions. During deposition of flat pebbles, microbes grew both on top of and in between pebbles, which acted as binding medium that prevented re-orientation of the edgewise clasts and further trapping flat pebbles, eventually forming flat-pebble mounds of various sizes. The flat-pebble mounds underwent substantial reworking by waves after deposition while ooids were being deposited. The study illustrates complex and dynamic depositional conditions for the mound-shaped flat-pebble conglomerates, suggesting multiple episodes of storm events. Detailed sedimentological studies on flat-pebble conglomerate will provide insights into frequency, intensity, and sedimentary processes of deep-time storm events.
, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.075
Abstract:
[Objective] According to the spreading, subducting, and shearing between lithospheric plates, the continental margin could be classified into three types: the passive margin, active margin, and the transform margin. Although transform margins have a short period of investigation, they fostered giant hydrocarbon discoveries in recent years. For example, in Ivory Basin., Guyana Basin, and Ruvuma Basin, a lot of hydrocarbons were discovered. ExxonMobil even listed the depositional characteristics of submarine fans on transform margins as the key field of oil and gas prospecting. Due to the study about transform margins is relatively weak, compared with the classical submarine fans, there are less works on those fans on the transform margins. [Methods] Using the late drift stage of Potiguar margin as an example, the current study utilizes the PaleoScan-based 3D intelligent interpreting approach and RGB color blending of spectral decomposition to reveal depositional characteristics and models of deep-water fans on transform margins. [Results] Submarine fans on Potiguar transform margin is composed of deep-water channels and terminal fans. In cross sections, deep-water channels continuously stacked, resulting in unpunctuated channel-growth patterns. In map view, the documented channel-lobes complexes are volumetrically small with a lack of overbank elements, and converged and stacked into a rim-shaped planform distribution pattern. [Conclusions] The unpunctuated channel-growth patterns in cross sections are interpreted to be depositional responses to narrow shelfs; the shelfs on Potiguar margin have widths of 30-60 km, with an average value of 43 km. Those narrow shelfs encouraged the continuous delivery of terrestrial sediments into deep-water sites during any periods of the base-level fluctuations. The depositional characteristics of channel-lobe complexes in map view are ascribed to the narrow and steep slopes of Potiguar transform margin. Those slopes have widths of 10-30 km and gradients of 4°-8°, whose average values are 23 km and 5.4°, respectively. Such basin margin topography frosted vigorous sediment-gravity flows with high velocity and strong incise ability, which disfavoured overbank spilling and in turn, resulted in small-scale channel-lobe complexes in map view. Furthermore, due to the existence of seamounts and/or marginal ridges, gravity flows were blocked from moving further downstream, thus resulting in a rim-shaped planform distribution pattern of channel-lobe complexes.
[Objective] According to the spreading, subducting, and shearing between lithospheric plates, the continental margin could be classified into three types: the passive margin, active margin, and the transform margin. Although transform margins have a short period of investigation, they fostered giant hydrocarbon discoveries in recent years. For example, in Ivory Basin., Guyana Basin, and Ruvuma Basin, a lot of hydrocarbons were discovered. ExxonMobil even listed the depositional characteristics of submarine fans on transform margins as the key field of oil and gas prospecting. Due to the study about transform margins is relatively weak, compared with the classical submarine fans, there are less works on those fans on the transform margins. [Methods] Using the late drift stage of Potiguar margin as an example, the current study utilizes the PaleoScan-based 3D intelligent interpreting approach and RGB color blending of spectral decomposition to reveal depositional characteristics and models of deep-water fans on transform margins. [Results] Submarine fans on Potiguar transform margin is composed of deep-water channels and terminal fans. In cross sections, deep-water channels continuously stacked, resulting in unpunctuated channel-growth patterns. In map view, the documented channel-lobes complexes are volumetrically small with a lack of overbank elements, and converged and stacked into a rim-shaped planform distribution pattern. [Conclusions] The unpunctuated channel-growth patterns in cross sections are interpreted to be depositional responses to narrow shelfs; the shelfs on Potiguar margin have widths of 30-60 km, with an average value of 43 km. Those narrow shelfs encouraged the continuous delivery of terrestrial sediments into deep-water sites during any periods of the base-level fluctuations. The depositional characteristics of channel-lobe complexes in map view are ascribed to the narrow and steep slopes of Potiguar transform margin. Those slopes have widths of 10-30 km and gradients of 4°-8°, whose average values are 23 km and 5.4°, respectively. Such basin margin topography frosted vigorous sediment-gravity flows with high velocity and strong incise ability, which disfavoured overbank spilling and in turn, resulted in small-scale channel-lobe complexes in map view. Furthermore, due to the existence of seamounts and/or marginal ridges, gravity flows were blocked from moving further downstream, thus resulting in a rim-shaped planform distribution pattern of channel-lobe complexes.
, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.068
Abstract:
Abstract: The pressure differences between source and reservoir rocks is not only the driving force for unconventional oil and gas accumulation, but also an indispensable key content in the study of the genesis of shale oil sweet spots. In addition, laminar structures are widely developed in continental shale, and the degree of development results in differences in the accumulation dynamics of reservoir rocks, which affect the accumulation of shale oil and gas. However, there are relatively few studies on the accumulation dynamics of shale oil. The sweet spot section of the Permian Lucaogou Formation in the Jimusar Sag was taken as the research object, and the intrinsic relationship between the development degree of laminar structure and shale oil and gas accumulation was revealed from the perspective of accumulation dynamics. Through evaluation of source rocks, classification of petrographic types and characterization of pores, etc. The characteristics of source rocks, different types of reservoir rocks, and source-reservoir assemblages in the study area were obtained. Using the equivalent depth method and fluid inclusion simulation, the pressure difference between source rocks and reservoir rocks during the accumulation period was recovered, and the accumulation dynamics of different types of reservoir rocks were obtained. The results show that the study area is dominated by source-reservoir interbedded combinations, and the hydrocarbon generation of high-quality source rocks creates a strong source-reservoir pressure difference between source and reservoir, which promotes the continuous migration of oil and gas to adjacent reservoir spaces; Interbedded silty and argillaceous laminae are widely developed in the reservoir rocks, which constitute a large area of frequent contact between source and reservoir. The degree of development results in differences in the accumulation dynamics of different types of reservoir rocks, and the laminar reservoir has developed laminar structure and the migration distance of oil and gas is shortened, so that it has stronger accumulation power and oil-bearing property. The development of laminar reservoir rocks in the lower sweet spot is a favorable area for studying oil and gas migration and accumulation in the shale sweet spot.
Abstract: The pressure differences between source and reservoir rocks is not only the driving force for unconventional oil and gas accumulation, but also an indispensable key content in the study of the genesis of shale oil sweet spots. In addition, laminar structures are widely developed in continental shale, and the degree of development results in differences in the accumulation dynamics of reservoir rocks, which affect the accumulation of shale oil and gas. However, there are relatively few studies on the accumulation dynamics of shale oil. The sweet spot section of the Permian Lucaogou Formation in the Jimusar Sag was taken as the research object, and the intrinsic relationship between the development degree of laminar structure and shale oil and gas accumulation was revealed from the perspective of accumulation dynamics. Through evaluation of source rocks, classification of petrographic types and characterization of pores, etc. The characteristics of source rocks, different types of reservoir rocks, and source-reservoir assemblages in the study area were obtained. Using the equivalent depth method and fluid inclusion simulation, the pressure difference between source rocks and reservoir rocks during the accumulation period was recovered, and the accumulation dynamics of different types of reservoir rocks were obtained. The results show that the study area is dominated by source-reservoir interbedded combinations, and the hydrocarbon generation of high-quality source rocks creates a strong source-reservoir pressure difference between source and reservoir, which promotes the continuous migration of oil and gas to adjacent reservoir spaces; Interbedded silty and argillaceous laminae are widely developed in the reservoir rocks, which constitute a large area of frequent contact between source and reservoir. The degree of development results in differences in the accumulation dynamics of different types of reservoir rocks, and the laminar reservoir has developed laminar structure and the migration distance of oil and gas is shortened, so that it has stronger accumulation power and oil-bearing property. The development of laminar reservoir rocks in the lower sweet spot is a favorable area for studying oil and gas migration and accumulation in the shale sweet spot.
, Available online ,
doi: 10.14027/j.issn.1000-0550.2023.070
Abstract:
Bioturbation changes the petrophysical properties of host rocks by changing the primary sedimentary fabric, decreasing or increasing the porosity and permeability of the primary formation, which in turn affects the reservoir properties and fluid flow characteristics. This paper reviews the reservoir space types, pore structure characteristics, reservoir media nature, fluid transport characteristics, reservoir types and their property characteristics of bioturbated hydrocarbon and water reservoirs. The reservoir space types of bioturbated reservoirs include: primary intergranular pores, intra-grain dissolved pores, inter-grain dissolved pores and intergranular pores. According to the relationship between the permeability of burrows and the host sediments, the bioturbated reservoir can be divided into dual-porosity biogenic reservoir media and dual-permeability biogenic reservoir media, and the two types of reservoir media have significant difference in burrow types, migration dynamics, fluid transport characteristics, and depositional environment; according to the burrow characteristics of bioturbated reservoir, fluid transport characteristics in reservoir media and reservoir petrophysical characteristics, bioturbated reservoirs can be divided into five types: (1) Surface-constrained bioturbated reservoirs, (2) Non-surface-constrained bioturbated reservoirs, (3) Weakly defined bioturbated reservoirs, (4) Cryptic bioturbated reservoirs, and (5) Diagenetic bioturbated reservoirs. The main controlling factors affecting the petroproperties of bioturbated reservoirs are analyzed in detail, including the permeability ratio of burrow-fills and hosting matrix, bioturbation intensity and connectivity, burrow-surface area, and burrow architecture. At present, the geophysical identification, reservoir description and reservoir modeling of bioturbated reservoirs are still at the pilot investigation stage, but it is foreseeable that strengthening the study of bioturbated hydrocarbon and water reservoirs is of great significance and important implications for enriching the theory of reservoir geology, increasing oil and gas storage, enhancing production and recovery.
Bioturbation changes the petrophysical properties of host rocks by changing the primary sedimentary fabric, decreasing or increasing the porosity and permeability of the primary formation, which in turn affects the reservoir properties and fluid flow characteristics. This paper reviews the reservoir space types, pore structure characteristics, reservoir media nature, fluid transport characteristics, reservoir types and their property characteristics of bioturbated hydrocarbon and water reservoirs. The reservoir space types of bioturbated reservoirs include: primary intergranular pores, intra-grain dissolved pores, inter-grain dissolved pores and intergranular pores. According to the relationship between the permeability of burrows and the host sediments, the bioturbated reservoir can be divided into dual-porosity biogenic reservoir media and dual-permeability biogenic reservoir media, and the two types of reservoir media have significant difference in burrow types, migration dynamics, fluid transport characteristics, and depositional environment; according to the burrow characteristics of bioturbated reservoir, fluid transport characteristics in reservoir media and reservoir petrophysical characteristics, bioturbated reservoirs can be divided into five types: (1) Surface-constrained bioturbated reservoirs, (2) Non-surface-constrained bioturbated reservoirs, (3) Weakly defined bioturbated reservoirs, (4) Cryptic bioturbated reservoirs, and (5) Diagenetic bioturbated reservoirs. The main controlling factors affecting the petroproperties of bioturbated reservoirs are analyzed in detail, including the permeability ratio of burrow-fills and hosting matrix, bioturbation intensity and connectivity, burrow-surface area, and burrow architecture. At present, the geophysical identification, reservoir description and reservoir modeling of bioturbated reservoirs are still at the pilot investigation stage, but it is foreseeable that strengthening the study of bioturbated hydrocarbon and water reservoirs is of great significance and important implications for enriching the theory of reservoir geology, increasing oil and gas storage, enhancing production and recovery.
Articles in press have been peer-reviewed and accepted, which are not yet assigned to volumes /issues, but are citable by Digital Object Identifier (DOI).
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2023, 41(4): 959-967.
doi: 10.14027/j.issn.1000-0550.2022.010
Abstract:
Oolitic limestone is a significant indicator of the paleoenvironment, and also provides an important hydrocarbon reservoir. However, ever since ooids were first recognized more than a century ago their origin, whether organic or inorganic, has been controversial. This study systematically summarizes the physicochemical and microbiological genesis of typical ooids and their structural types. A new formation mechanism for ooids is proposed, based on previous research reports. The research review and case analysis suggests that microorganisms mediate the formation of new oolitic circles. The distribution of carbonate minerals in the oolitic circles is influenced by the energy of the sedimentary water body, and constructive microbial communities （e.g., photosynthetic microorganisms and sulfate reduction bacteria） promote the precipitation of the oolitic circles. The circular structure is mainly radial, randomly distributed and tangential. Other observed oolitic structures have all been modified by the action of destructive drilling organisms and different degrees of diagenesis. The most primitive structure of an ooid is radial growth formed by the mineralization of amorphous calcium carbonate （ACC） in a low-energy, static water environment. The random distribution and tangential structure are the result of hydrodynamic shearing. The obvious dark concentric thin layers observed in ooids are the product of biomineralization of the microbial community that appears intermittently during the growth of the ooid after constructive or destructive colonization. These three structures develop either individually or in combination depending on the hydrodynamics of their environment. The core supply rate, the calcium carbonate saturation and energy of the sedimentary water body, and the action of the constructive microbial community, all influence the size of the oolitic particle size.
Oolitic limestone is a significant indicator of the paleoenvironment, and also provides an important hydrocarbon reservoir. However, ever since ooids were first recognized more than a century ago their origin, whether organic or inorganic, has been controversial. This study systematically summarizes the physicochemical and microbiological genesis of typical ooids and their structural types. A new formation mechanism for ooids is proposed, based on previous research reports. The research review and case analysis suggests that microorganisms mediate the formation of new oolitic circles. The distribution of carbonate minerals in the oolitic circles is influenced by the energy of the sedimentary water body, and constructive microbial communities （e.g., photosynthetic microorganisms and sulfate reduction bacteria） promote the precipitation of the oolitic circles. The circular structure is mainly radial, randomly distributed and tangential. Other observed oolitic structures have all been modified by the action of destructive drilling organisms and different degrees of diagenesis. The most primitive structure of an ooid is radial growth formed by the mineralization of amorphous calcium carbonate （ACC） in a low-energy, static water environment. The random distribution and tangential structure are the result of hydrodynamic shearing. The obvious dark concentric thin layers observed in ooids are the product of biomineralization of the microbial community that appears intermittently during the growth of the ooid after constructive or destructive colonization. These three structures develop either individually or in combination depending on the hydrodynamics of their environment. The core supply rate, the calcium carbonate saturation and energy of the sedimentary water body, and the action of the constructive microbial community, all influence the size of the oolitic particle size.
2023, 41(4): 968-991.
doi: 10.14027/j.issn.1000-0550.2022.127
Abstract:
As the important part of a karst system, caves preserve numerous geological and archaeological deposits, including autochthonous, allochthonous, chemical, biological, and anthropogenic deposits, which are disturbed by the post-depositional processes in the cave deposit process. Micromorphology is the study of undisturbed, oriented samples, with the aid of microscopic and ultramicroscopic techniques, to identify the composition, texture, and structure that cannot be observed by the naked eye and deduce their chronological, spatial, and genetic relationships. Here, we reviewed the current research on micromorphological analysis of different cave deposits. The micromorphological analysis has been applied widely, including the restoration of the cave paleoclimate and paleoenvironment, the reconstruction of the cave deposit and burial process, the construction of stratigraphic chronology framework, and the interpretation of ancient human activities and genetic information. However, micromorphological analysis has not fully applied on the cave deposits in China. We are curious as to the broad application prospect of this effective research method.
As the important part of a karst system, caves preserve numerous geological and archaeological deposits, including autochthonous, allochthonous, chemical, biological, and anthropogenic deposits, which are disturbed by the post-depositional processes in the cave deposit process. Micromorphology is the study of undisturbed, oriented samples, with the aid of microscopic and ultramicroscopic techniques, to identify the composition, texture, and structure that cannot be observed by the naked eye and deduce their chronological, spatial, and genetic relationships. Here, we reviewed the current research on micromorphological analysis of different cave deposits. The micromorphological analysis has been applied widely, including the restoration of the cave paleoclimate and paleoenvironment, the reconstruction of the cave deposit and burial process, the construction of stratigraphic chronology framework, and the interpretation of ancient human activities and genetic information. However, micromorphological analysis has not fully applied on the cave deposits in China. We are curious as to the broad application prospect of this effective research method.
2023, 41(4): 992-1001.
doi: 10.14027/j.issn.1000-0550.2022.020
Abstract:
Multi-proxy Analysis from a stalagmite that grew during Ice Age Termination III （referred to as T III） is conducted to comprehensively understand the climate change characteristics and monsoon mechanisms during this period. Based on isotopes, stalagmite laminae growth diameter, and lithologic characteristic analysis of the stalagmite （No： YXB） from Yongxing Cave, Hubei province, the Asian monsoon climate change sequence during the T III was reconstructed. The lamina growth diameter is related to δ18O and has the same variation characteristics, i.e., when stalagmites δ18O is negative, the laminae growth diameter decreases, and when δ18O is positive, the laminae growth diameter increases. When the change of laminae growth diameter is same as stalagmite δ18O, there is an obvious weak monsoon event （known as “YD-like event”） during T III. The lithologic characteristics of stalagmites also have an obvious response to this event. In this period, stalagmites develop white opaque lamina, which is obviously different from the gray transparent lamina developed in other periods. This shows that the karst system signals, such as laminae growth diameter and lithology, also respond to δ18O indications of climate change. Stalagmite δ13C is same as δ18O, but the response to YD-like events is not obvious. It shows that in the Asian monsoon region, the vegetation represented by δ13C responds to the deglaciation process, but is not sensitive to the weakening response of monsoon during the transition from glacial period to interglacial period. Using power spectrum analysis of the above indices, periodic components, such as 522 a, 223⁃261 a, 130⁃145 a, 73⁃82 a, 64 a, and 30 a, are obtained, which may be the result of the coupling of solar activity and ocean-atmosphere interaction.
Multi-proxy Analysis from a stalagmite that grew during Ice Age Termination III （referred to as T III） is conducted to comprehensively understand the climate change characteristics and monsoon mechanisms during this period. Based on isotopes, stalagmite laminae growth diameter, and lithologic characteristic analysis of the stalagmite （No： YXB） from Yongxing Cave, Hubei province, the Asian monsoon climate change sequence during the T III was reconstructed. The lamina growth diameter is related to δ18O and has the same variation characteristics, i.e., when stalagmites δ18O is negative, the laminae growth diameter decreases, and when δ18O is positive, the laminae growth diameter increases. When the change of laminae growth diameter is same as stalagmite δ18O, there is an obvious weak monsoon event （known as “YD-like event”） during T III. The lithologic characteristics of stalagmites also have an obvious response to this event. In this period, stalagmites develop white opaque lamina, which is obviously different from the gray transparent lamina developed in other periods. This shows that the karst system signals, such as laminae growth diameter and lithology, also respond to δ18O indications of climate change. Stalagmite δ13C is same as δ18O, but the response to YD-like events is not obvious. It shows that in the Asian monsoon region, the vegetation represented by δ13C responds to the deglaciation process, but is not sensitive to the weakening response of monsoon during the transition from glacial period to interglacial period. Using power spectrum analysis of the above indices, periodic components, such as 522 a, 223⁃261 a, 130⁃145 a, 73⁃82 a, 64 a, and 30 a, are obtained, which may be the result of the coupling of solar activity and ocean-atmosphere interaction.
2023, 41(4): 1002-1010.
doi: 10.14027/j.issn.1000-0550.2022.014
Abstract:
A gravity core sample with 533 cm long obtained in the southern Marina Trench was analyzed by grain-size smear tests, XRF scanning, paleomagnetism and magnetic anisotropy. The paleomagnetic analysis revealed the Brunhes-Matuyama reversal event （B-M boundary） at 507 cm, near the bottom of the core, indicating that the sample contains the record of at least 0.78 million years of the depositional environment. The chronological framework was established by analyzing the relative paleomagnetic intensity （RPI） and long-term variation in paleomagnetic inclination. The grain-size analysis and XRF scans indicate that the sediment type in the core underwent a fundamental change from bottom to top： at the bottom it is dominated by pelagic clay with evidence of terrigenous input； at the top it is dominated by siliceous ooze consisting mainly of diatoms. Analysis indicated that this change was mainly because of the appearance of the Antarctic Bottom Water （AABW） during the Mid-Brunhes Event （MBE）. The paleomagnetism establishes the age model, and the magnetic anisotropy and sediment composition indicate that the MBE began to influence this area with the appearance of the AABW around 553 ka. The sediment type began to change from terrigenous input to biogenesis, at about 417 ka, by which time the main composition of the sediment was already biogenetic. The AABW enhanced the change until the sediment was almost completely composed of pure siliceous ooze from 336 ka until the present day, indicating the termination of the MBE in this area.
A gravity core sample with 533 cm long obtained in the southern Marina Trench was analyzed by grain-size smear tests, XRF scanning, paleomagnetism and magnetic anisotropy. The paleomagnetic analysis revealed the Brunhes-Matuyama reversal event （B-M boundary） at 507 cm, near the bottom of the core, indicating that the sample contains the record of at least 0.78 million years of the depositional environment. The chronological framework was established by analyzing the relative paleomagnetic intensity （RPI） and long-term variation in paleomagnetic inclination. The grain-size analysis and XRF scans indicate that the sediment type in the core underwent a fundamental change from bottom to top： at the bottom it is dominated by pelagic clay with evidence of terrigenous input； at the top it is dominated by siliceous ooze consisting mainly of diatoms. Analysis indicated that this change was mainly because of the appearance of the Antarctic Bottom Water （AABW） during the Mid-Brunhes Event （MBE）. The paleomagnetism establishes the age model, and the magnetic anisotropy and sediment composition indicate that the MBE began to influence this area with the appearance of the AABW around 553 ka. The sediment type began to change from terrigenous input to biogenesis, at about 417 ka, by which time the main composition of the sediment was already biogenetic. The AABW enhanced the change until the sediment was almost completely composed of pure siliceous ooze from 336 ka until the present day, indicating the termination of the MBE in this area.
2023, 41(4): 1011-1024.
doi: 10.14027/j.issn.1000-0550.2021.164
Abstract:
The Cenozoic Claron Formation spanning the Paleocene to Eocene, which is widely exposed in the western United States, is suitable for studying climatic and environmental change in this period. The Claron Formation has generally been interpreted as a fluvial-lacustrine deposit, but eolian deposit features are evident from field observations. Therefore, identifying eolian components in the strata and discussing their significance is of vital importance for interpreting the sedimentary environment of the Claron Formation. The area of the Claron Formation covered by this study was the Bryce Canyon National Park. The eolian deposits in the strata were firstly identified by field observation of the sedimentary characteristics and the surface textures of quartz grains. Then the eolian components of the rock were determined by non-parametric grain-size end-member analysis to unmix the grain-size components. It was found that most of layers are red in color, and the deep-to-light variation of the red color of the strata and the off-white color vary overall with the bedding/horizon. The sediments were found to be homogeneous, mainly composed of silt and clay and rich in carbonate, with well developed vertical joints. Aggradational deposit properties were clearly observed in the red layers, evidence that the sedimentation and weathering processes were simultaneous. These field sedimentary characteristics indicate that the red layers are mainly eolian deposits. The quartz grains in the red samples were found to have surfaces characterized by large and small mechanical saucer-shaped pits, deep troughs, round pits, upturned plates and precipitation of SiO2, all of which are indicative of an eolian environment. This provides further evidence of eolian deposition in the red layers. Six end members with different sedimentary significance were obtained from the non-parametric grain-size end-member analysis model： soil-forming components； components of hydrostatic sedimentation formed in soak/ephemeral lake； components transported by high altitude air streams over long distances； components of dust settling after storms； alluvial-diluvial components； and near-source or far-source components transported by storms. End members 3, 4 and 6 （first mode grain size 5.33, 11.93 and 42.34 μm, respectively） were identified as eolian components, with an average content of approximately 50% in the strata. This indicates that eolian deposition accounted for more than half of the sediments in the strata. Moreover, the eolian components were found to occupy a large proportion in each layer, indicating that they were a stable strata component. Obvious variation of the content of each end member in the strata indicates inconsistent sedimentary environments at different times. The strata consist of alternate layers of eolian sediments, alluvial-diluvial deposition and soak/ephemeral lake deposition. The climate was humid during the periods of alluvial-diluvial and soak/ephemeral lake sedimentation, and arid during eolian deposition and soil formation.
The Cenozoic Claron Formation spanning the Paleocene to Eocene, which is widely exposed in the western United States, is suitable for studying climatic and environmental change in this period. The Claron Formation has generally been interpreted as a fluvial-lacustrine deposit, but eolian deposit features are evident from field observations. Therefore, identifying eolian components in the strata and discussing their significance is of vital importance for interpreting the sedimentary environment of the Claron Formation. The area of the Claron Formation covered by this study was the Bryce Canyon National Park. The eolian deposits in the strata were firstly identified by field observation of the sedimentary characteristics and the surface textures of quartz grains. Then the eolian components of the rock were determined by non-parametric grain-size end-member analysis to unmix the grain-size components. It was found that most of layers are red in color, and the deep-to-light variation of the red color of the strata and the off-white color vary overall with the bedding/horizon. The sediments were found to be homogeneous, mainly composed of silt and clay and rich in carbonate, with well developed vertical joints. Aggradational deposit properties were clearly observed in the red layers, evidence that the sedimentation and weathering processes were simultaneous. These field sedimentary characteristics indicate that the red layers are mainly eolian deposits. The quartz grains in the red samples were found to have surfaces characterized by large and small mechanical saucer-shaped pits, deep troughs, round pits, upturned plates and precipitation of SiO2, all of which are indicative of an eolian environment. This provides further evidence of eolian deposition in the red layers. Six end members with different sedimentary significance were obtained from the non-parametric grain-size end-member analysis model： soil-forming components； components of hydrostatic sedimentation formed in soak/ephemeral lake； components transported by high altitude air streams over long distances； components of dust settling after storms； alluvial-diluvial components； and near-source or far-source components transported by storms. End members 3, 4 and 6 （first mode grain size 5.33, 11.93 and 42.34 μm, respectively） were identified as eolian components, with an average content of approximately 50% in the strata. This indicates that eolian deposition accounted for more than half of the sediments in the strata. Moreover, the eolian components were found to occupy a large proportion in each layer, indicating that they were a stable strata component. Obvious variation of the content of each end member in the strata indicates inconsistent sedimentary environments at different times. The strata consist of alternate layers of eolian sediments, alluvial-diluvial deposition and soak/ephemeral lake deposition. The climate was humid during the periods of alluvial-diluvial and soak/ephemeral lake sedimentation, and arid during eolian deposition and soil formation.
2023, 41(4): 1025-1039.
doi: 10.14027/j.issn.1000-0550.2021.149
Abstract:
The fresh color of sediment/rock is the intuitive response of its internal composition and fabric and records the rich climate, environment, structure, and diagenetic transformation. The Shangshaximiao Formation of the Middle Jurassic in the Sichuan Basin is a set of clastic strata from river lake facies. The profile is well exposed, fresh, and continuously changeable. It is an excellent object for studying the origin of sediment/rock color and its indicative significance of climate and environment. Through test and analysis of mineral composition, element content, and iron speciation of mudstone samples with gray-green, gray, and red colors in the Shangshaximiao Formation, we found that the change of hematite content directly causes the color difference in the mudstone in Shaximiao Formation. For red mudstone, the average values of chemical index of alteration （CIA）, chemical Index of Weathering （CIW）, weather eluviation index （Ba）, regression index, clayization index, and residual coefficient are 70.27, 82.05, 1.14, 0.26, 0.27, and 2.38, respectively, indicating the strongest chemical weathering intensity. The corresponding geochemical indexes of gray samples are 62.65, 71.06, 2.22, 0.75, 0.23 and 1.19, respectively. The grey-green samples were 58.50, 65.11, 1.92, 0.78, 0.26 and 1.34 respectively, and the chemical weathering was the weakest. The red sample contains the highest hematite iron content. The gray-green sample mainly represents paramagnetic ferrous in clay minerals. The geochemical contents of the three iron elements in the gray sample have a slight difference, mainly trivalent iron. The change of iron chemical species content in samples with different colors shows that the Fe element forming hematite in red bed samples may come from the weathering of source rock and clay minerals subjected to secondary weathering. At present, the causes of the different colors can only be confirmed to be related to the weathering of source rocks to varying degrees, which cannot be attributed to the hot and arid climate conditions. It is necessary to distinguish the climate type in combination with other indicators.
The fresh color of sediment/rock is the intuitive response of its internal composition and fabric and records the rich climate, environment, structure, and diagenetic transformation. The Shangshaximiao Formation of the Middle Jurassic in the Sichuan Basin is a set of clastic strata from river lake facies. The profile is well exposed, fresh, and continuously changeable. It is an excellent object for studying the origin of sediment/rock color and its indicative significance of climate and environment. Through test and analysis of mineral composition, element content, and iron speciation of mudstone samples with gray-green, gray, and red colors in the Shangshaximiao Formation, we found that the change of hematite content directly causes the color difference in the mudstone in Shaximiao Formation. For red mudstone, the average values of chemical index of alteration （CIA）, chemical Index of Weathering （CIW）, weather eluviation index （Ba）, regression index, clayization index, and residual coefficient are 70.27, 82.05, 1.14, 0.26, 0.27, and 2.38, respectively, indicating the strongest chemical weathering intensity. The corresponding geochemical indexes of gray samples are 62.65, 71.06, 2.22, 0.75, 0.23 and 1.19, respectively. The grey-green samples were 58.50, 65.11, 1.92, 0.78, 0.26 and 1.34 respectively, and the chemical weathering was the weakest. The red sample contains the highest hematite iron content. The gray-green sample mainly represents paramagnetic ferrous in clay minerals. The geochemical contents of the three iron elements in the gray sample have a slight difference, mainly trivalent iron. The change of iron chemical species content in samples with different colors shows that the Fe element forming hematite in red bed samples may come from the weathering of source rock and clay minerals subjected to secondary weathering. At present, the causes of the different colors can only be confirmed to be related to the weathering of source rocks to varying degrees, which cannot be attributed to the hot and arid climate conditions. It is necessary to distinguish the climate type in combination with other indicators.
2023, 41(4): 1040-1053.
doi: 10.14027/j.issn.1000-0550.2022.060
Abstract:
For epeiric-sea shallow water deposition, small-scale fluctuations of sea level cause rapid changes of sedimentary environment and lithofacies. The example of the response of lithofacies characteristics to sea-level fluctuations in this study is the Cambrian Cangshan profile （Shandong province）, which has good outcrop conditions and frequent lithofacies changes. The lithological characteristics were analyzed in detail using field observation, section measurement and thin section identification. The area contains seven lithofacies： oolitic limestone, bioclastic limestone, marl, gray sandstone, microbial limestone, shale and sandstone. It is considered that the Mantou Formation in this area mainly developed intertidal zone-barrier island-lagoon deposition. The Zhangxia Formation developed from restricted- and open-platform deposition； and experienced stronger hydrodynamic conditions than the Mantou Formation, with cyclical changes of water energy, depth, light and clarity affecting the growth of microorganisms and the characteristics of microbial rocks. The frequent changes of lithofacies reflect the vertical sea-level fluctuation and sedimentary environment. The open platform dominated in the late period of rising or high sea level, with a high-energy facies zone conducive to the development of oolitic limestone and bioclastic limestone deposits and a low-energy zone below the tide level of the open platform that was conducive to the development of microbial limestone hills and keloid limestone. In the early or descending period of sea-level rise, platform and tidal flat sediments dominated shallow-water deposits, developing more mud limestone and argillaceous limestone. The frequent changes in hydrodynamic conditions on the tidal-flat environment resulted in the development of many sedimentary facies types, including bioclastic limestone, mud limestone, shale and sandstone.
For epeiric-sea shallow water deposition, small-scale fluctuations of sea level cause rapid changes of sedimentary environment and lithofacies. The example of the response of lithofacies characteristics to sea-level fluctuations in this study is the Cambrian Cangshan profile （Shandong province）, which has good outcrop conditions and frequent lithofacies changes. The lithological characteristics were analyzed in detail using field observation, section measurement and thin section identification. The area contains seven lithofacies： oolitic limestone, bioclastic limestone, marl, gray sandstone, microbial limestone, shale and sandstone. It is considered that the Mantou Formation in this area mainly developed intertidal zone-barrier island-lagoon deposition. The Zhangxia Formation developed from restricted- and open-platform deposition； and experienced stronger hydrodynamic conditions than the Mantou Formation, with cyclical changes of water energy, depth, light and clarity affecting the growth of microorganisms and the characteristics of microbial rocks. The frequent changes of lithofacies reflect the vertical sea-level fluctuation and sedimentary environment. The open platform dominated in the late period of rising or high sea level, with a high-energy facies zone conducive to the development of oolitic limestone and bioclastic limestone deposits and a low-energy zone below the tide level of the open platform that was conducive to the development of microbial limestone hills and keloid limestone. In the early or descending period of sea-level rise, platform and tidal flat sediments dominated shallow-water deposits, developing more mud limestone and argillaceous limestone. The frequent changes in hydrodynamic conditions on the tidal-flat environment resulted in the development of many sedimentary facies types, including bioclastic limestone, mud limestone, shale and sandstone.
2023, 41(4): 1054-1066.
doi: 10.14027/j.issn.1000-0550.2021.168
Abstract:
X-Ray Diffraction （XRD） bulk mineral analysis was conducted for 82 surface sediments from the western Arctic Ocean and Bering Sea, with an attempt to elucidate the distribution patterns of minerals, as well as the provenance and transportation of the surface sediments in the Arctic region. The results show that quartz, plagioclase feldspar, potassium feldspar, mica, and chlorite are dominant minerals in sediments, and dolomite, pyroxene, amphibole occur in sediments regionally. The Laptev Sea receives sediments from the Siberian and granites from the New Siberian Islands, several of which are transported to the Canadian Basin by sea ice under the Transpolar Drift and Beaufort Gyre. Sediments rich in quartz in the offshore of Chukchi Sea result from coastal erosion and transportation by local rivers. The Yukon River transport larger amounts of sediments rich in minerals, such as feldspar, mica, chlorite, etc., from the Alaska continent into the Bering Sea shelf, and a portion of it was further transported to the Chukchi Sea and Canadian Basin by currents. The dolomite occurring in the Canadian Basin is from the Arctic Islands and the watershed of the Mackenzie River.
X-Ray Diffraction （XRD） bulk mineral analysis was conducted for 82 surface sediments from the western Arctic Ocean and Bering Sea, with an attempt to elucidate the distribution patterns of minerals, as well as the provenance and transportation of the surface sediments in the Arctic region. The results show that quartz, plagioclase feldspar, potassium feldspar, mica, and chlorite are dominant minerals in sediments, and dolomite, pyroxene, amphibole occur in sediments regionally. The Laptev Sea receives sediments from the Siberian and granites from the New Siberian Islands, several of which are transported to the Canadian Basin by sea ice under the Transpolar Drift and Beaufort Gyre. Sediments rich in quartz in the offshore of Chukchi Sea result from coastal erosion and transportation by local rivers. The Yukon River transport larger amounts of sediments rich in minerals, such as feldspar, mica, chlorite, etc., from the Alaska continent into the Bering Sea shelf, and a portion of it was further transported to the Chukchi Sea and Canadian Basin by currents. The dolomite occurring in the Canadian Basin is from the Arctic Islands and the watershed of the Mackenzie River.
2023, 41(4): 1067-1079.
doi: 10.14027/j.issn.1000-0550.2022.030
Abstract:
To explore the qualitative and quantitative relationship among modern pollen, vegetation, and climate in the adjacent desert of northwest China, 222 topsoil pollen samples, vegetation sample survey results, and meteorological data were used to perform indicator species, pollen representative, and sequence analyses and paleoclimate quantitative reconstruction. The results show that the topsoil pollen in the adjacent desert area can be divided into three desert subzones, as well as shrub, meadow, alpine meadow, and forest-grass transition zones. The representativeness of pollen from major families and genera in each vegetation zone is low, and that of the same species differs significantly in different regions. The pollen assemblage of desert zone 2 and the shrub zone is not consistent with the vegetation investigation. The pollen assemblage and vegetation survey results of other vegetation belts are in good agreement. Indicator species and sequencing analyses show that except for the poor differentiation of the meadow and alpine meadow zones, there is a good distinction among the different zones, and the three important climate variables in the study area are annual mean precipitation （Pann）, July mean temperature （TJuly）, and January mean temperature （TJan）, among which Pann is the most ideal factor for climate reconstruction. The pollen-climate calibration set is established by using the weighted partial least square （WA-PLS） and modern analogy （MAT） methods. The cross-validation results show that the prediction performance of WA-PLS is better than that of MAT.
To explore the qualitative and quantitative relationship among modern pollen, vegetation, and climate in the adjacent desert of northwest China, 222 topsoil pollen samples, vegetation sample survey results, and meteorological data were used to perform indicator species, pollen representative, and sequence analyses and paleoclimate quantitative reconstruction. The results show that the topsoil pollen in the adjacent desert area can be divided into three desert subzones, as well as shrub, meadow, alpine meadow, and forest-grass transition zones. The representativeness of pollen from major families and genera in each vegetation zone is low, and that of the same species differs significantly in different regions. The pollen assemblage of desert zone 2 and the shrub zone is not consistent with the vegetation investigation. The pollen assemblage and vegetation survey results of other vegetation belts are in good agreement. Indicator species and sequencing analyses show that except for the poor differentiation of the meadow and alpine meadow zones, there is a good distinction among the different zones, and the three important climate variables in the study area are annual mean precipitation （Pann）, July mean temperature （TJuly）, and January mean temperature （TJan）, among which Pann is the most ideal factor for climate reconstruction. The pollen-climate calibration set is established by using the weighted partial least square （WA-PLS） and modern analogy （MAT） methods. The cross-validation results show that the prediction performance of WA-PLS is better than that of MAT.
2023, 41(4): 1080-1096.
doi: 10.14027/j.issn.1000-0550.2021.156
Abstract:
In order to establish the deposition model of microbialites in the Fourth member of Dengying Formation in central Sichuan Basin, and to clarify the main controlling deposition factors, a detailed deposition microfacies analysis was carried out on macrostructures and microfabrics using data from drill cores and thin sections. Eight lithofacies were identified in the study area, among which the microbialites include thrombolites and stromatolites. The stromatolites are further divided into wavy-laminated agglutinated stromatolites, wavy-laminated skeletal stromatolite and flat-laminated fine-grained stromatolites. The stacking patterns indicate four types of lithofacies associations： subtidal-restricted lagoon deposition； subtidal thrombolites； shallow-subtidal to intertidal stromatolites to shoal complex； and intertidal stromatolites. The microfacies distribution in the sequence stratigraphic framework shows that microbial mounds and shoals were located mainly in the upper part of the sequences, which became better-developed from bottom to top in this member of the Dengying Formation. The mound-shoals were more developed at the platform margin, decreasing in scale and continuity at the restricted platform. A microbialite deposition model was established based on the macrostructures, microfabrics and vertical sequence of the microbialites for the Fourth member of Dengying Formation. The thrombolites were mainly deposited in the subtidal environment below the wave base, with low hydrodynamics. Clots were locally formed by microbial trapping and binding small grains. The wavy-laminated agglutinated stromatolites were mainly deposited in the lower part of intertidal zone, in which various types of microbes flourished, and were formed by microbial trapping and binding of ooids and peloids in conditions of strong waves and tides. The wavy-laminated skeletal stromatolites were mainly deposited in the upper part of intertidal zone with moderate hydrodynamics dominated by the tide. The sponge structures were formed by microbially induced precipitation and in situ calcification, trapping and binding small amounts of pellets. The flat-laminated, fine-grained stromatolites were mainly deposited in the upper intertidal zone, and the deposition processes were predominantly microbially induced precipitation.
In order to establish the deposition model of microbialites in the Fourth member of Dengying Formation in central Sichuan Basin, and to clarify the main controlling deposition factors, a detailed deposition microfacies analysis was carried out on macrostructures and microfabrics using data from drill cores and thin sections. Eight lithofacies were identified in the study area, among which the microbialites include thrombolites and stromatolites. The stromatolites are further divided into wavy-laminated agglutinated stromatolites, wavy-laminated skeletal stromatolite and flat-laminated fine-grained stromatolites. The stacking patterns indicate four types of lithofacies associations： subtidal-restricted lagoon deposition； subtidal thrombolites； shallow-subtidal to intertidal stromatolites to shoal complex； and intertidal stromatolites. The microfacies distribution in the sequence stratigraphic framework shows that microbial mounds and shoals were located mainly in the upper part of the sequences, which became better-developed from bottom to top in this member of the Dengying Formation. The mound-shoals were more developed at the platform margin, decreasing in scale and continuity at the restricted platform. A microbialite deposition model was established based on the macrostructures, microfabrics and vertical sequence of the microbialites for the Fourth member of Dengying Formation. The thrombolites were mainly deposited in the subtidal environment below the wave base, with low hydrodynamics. Clots were locally formed by microbial trapping and binding small grains. The wavy-laminated agglutinated stromatolites were mainly deposited in the lower part of intertidal zone, in which various types of microbes flourished, and were formed by microbial trapping and binding of ooids and peloids in conditions of strong waves and tides. The wavy-laminated skeletal stromatolites were mainly deposited in the upper part of intertidal zone with moderate hydrodynamics dominated by the tide. The sponge structures were formed by microbially induced precipitation and in situ calcification, trapping and binding small amounts of pellets. The flat-laminated, fine-grained stromatolites were mainly deposited in the upper intertidal zone, and the deposition processes were predominantly microbially induced precipitation.
2023, 41(4): 1097-1109.
doi: 10.14027/j.issn.1000-0550.2022.004
Abstract:
Studies of the spatial distribution of sedimentary microfacies in continental lacustrine basins have mainly concentrated on high-frequency lake level changes. However, this is unrelated to low-frequency lacustrine evolutional stages and lake regression processes. This study was based on core observation, combining well logs and 3D seismic volumes to restore the types of sedimentary microfacies in the Oligocene interval of rocks in the Suning-Dawangzhuang area. The stages and features of lacustrine evolution were investigated by integrating lithological and seismic sedimentological evidence. The spatial distribution at different stages of lacustrine evolution is also discussed. It was found that, against the background of stable down-warp lake basins, the ancient lake in the Raoyang Sag underwent a complete low-frequency evolutional expansion⁃extinction cycle in the Early Oligocene. This occurred in stages： rapid active expansion followed by slow passive contraction, rapid passive contraction, slow active contraction and slow passive extinction. During active expansion, the early distributary channels and mouth bars were reworked into beach bars. The passive contraction of the lake during normal lake regression created broad delta-front channel-mouth bar composite sand bodies and delta-plain distributary channel networks. The active contraction of the lake resulting from forced lake regression formed a dendritic distributary channel system. The continuous extinction process of the lake caused these various types of composite sand body to migrate towards the lake, unlike in the previous stage, thus vertically superposing the different types of composite sand body.
Studies of the spatial distribution of sedimentary microfacies in continental lacustrine basins have mainly concentrated on high-frequency lake level changes. However, this is unrelated to low-frequency lacustrine evolutional stages and lake regression processes. This study was based on core observation, combining well logs and 3D seismic volumes to restore the types of sedimentary microfacies in the Oligocene interval of rocks in the Suning-Dawangzhuang area. The stages and features of lacustrine evolution were investigated by integrating lithological and seismic sedimentological evidence. The spatial distribution at different stages of lacustrine evolution is also discussed. It was found that, against the background of stable down-warp lake basins, the ancient lake in the Raoyang Sag underwent a complete low-frequency evolutional expansion⁃extinction cycle in the Early Oligocene. This occurred in stages： rapid active expansion followed by slow passive contraction, rapid passive contraction, slow active contraction and slow passive extinction. During active expansion, the early distributary channels and mouth bars were reworked into beach bars. The passive contraction of the lake during normal lake regression created broad delta-front channel-mouth bar composite sand bodies and delta-plain distributary channel networks. The active contraction of the lake resulting from forced lake regression formed a dendritic distributary channel system. The continuous extinction process of the lake caused these various types of composite sand body to migrate towards the lake, unlike in the previous stage, thus vertically superposing the different types of composite sand body.
2023, 41(4): 1110-1123.
doi: 10.14027/j.issn.1000-0550.2021.161
Abstract:
Intracraton rifts have had an important influence on favorable areas for marine carbonate oil and gas exploration in the Sichuan Basin and surrounding areas. A large amount of outcrop evidence reveals the existence of Early Cambrian intracraton rifts in western Hubei⁃eastern Chongqing. In this study, full use was made of field outcrop and available drilling data, combined with related its structural background and geodynamic origin. Based on previous studies, the study describes the identification marks of cratonic rifts in the western Hubei⁃eastern Chongqing area during the Early Cambrian. The evolution process of the sedimentary filling of the rift and its influence on the paleogeographic pattern was as follows. （1） The rift was wide in the south and narrow in the north, and gently sloping in the east and steep in the west. （2） It exhibits obvious differentiation which is positively correlated with fault activity. （3） The rift was mainly filled with compensation sediments that transitioned from the initial shelf sedimentation to finally a carbonate platform. The evolution of the rift occurred in three stages： rift （Shuijingtuo Formation deposition period）, depression （Canglangpu Formation deposition period）, and filling （Shilongdong Formation deposition period）. （4） The rift opened and closed in response to the fragmentation/aggregation activity of the supercontinent between the Middle and Upper Yangtze. The structural background of paleogeographic differentiation, syn-sedimentary fault activity and sea level change determined its geographic pattern. This proposed Early Cambrian intracraton rift in the western Hubei⁃eastern Chongqing area provides a new understanding of the tectonic/sedimentary pattern of the internal craton rift in the Sichuan Basin and is also an important guide for oil and gas exploration in the Middle-Upper Yangtze area.
Intracraton rifts have had an important influence on favorable areas for marine carbonate oil and gas exploration in the Sichuan Basin and surrounding areas. A large amount of outcrop evidence reveals the existence of Early Cambrian intracraton rifts in western Hubei⁃eastern Chongqing. In this study, full use was made of field outcrop and available drilling data, combined with related its structural background and geodynamic origin. Based on previous studies, the study describes the identification marks of cratonic rifts in the western Hubei⁃eastern Chongqing area during the Early Cambrian. The evolution process of the sedimentary filling of the rift and its influence on the paleogeographic pattern was as follows. （1） The rift was wide in the south and narrow in the north, and gently sloping in the east and steep in the west. （2） It exhibits obvious differentiation which is positively correlated with fault activity. （3） The rift was mainly filled with compensation sediments that transitioned from the initial shelf sedimentation to finally a carbonate platform. The evolution of the rift occurred in three stages： rift （Shuijingtuo Formation deposition period）, depression （Canglangpu Formation deposition period）, and filling （Shilongdong Formation deposition period）. （4） The rift opened and closed in response to the fragmentation/aggregation activity of the supercontinent between the Middle and Upper Yangtze. The structural background of paleogeographic differentiation, syn-sedimentary fault activity and sea level change determined its geographic pattern. This proposed Early Cambrian intracraton rift in the western Hubei⁃eastern Chongqing area provides a new understanding of the tectonic/sedimentary pattern of the internal craton rift in the Sichuan Basin and is also an important guide for oil and gas exploration in the Middle-Upper Yangtze area.
2023, 41(4): 1124-1137.
doi: 10.14027/j.issn.1000-0550.2021.169
Abstract:
The Arab region in the Middle East has developed extremely thick carbonate deposits since the Late Cretaceous, creating favorable reservoirs for oil and gas resources. The evolution of its sedimentary environment has long been a focus of the international academic community. In this study, three stratigraphic sections （Kermanshan-KM section, Khoramabad-AD section, Hkhormoj-HM section） are taken as the research objects located in the Lurestan-Fars areas on the northern margin of the Arabian Plate （Zagros, Iran）. Detailed field observation and thin section analysis of the Upper Cretaceous Savark, Ilam and Gurpi Formations are conducted. In total, 13 carbonate microfacies were identified and grouped into 3 sedimentary facies： outer, middle, and inner ramps. During the Santonian, these three sections were in a deep-water outer ramp environment, while in the Campanian, the AD and KM sections changed from outer to inner ramp, indicating a sudden shallowing of paleo-water depth. However, at the same time, the HM section was still in outer ramp. Considering the different distances between three sections from the ophiolite belt, we suggest that the shallowing events recorded in sections KM & AD of the Lurestan area during the Campanian are related to the ophiolite obduction in the north, while the HM section in the Fars area is too far away from the ophiolite belt.
The Arab region in the Middle East has developed extremely thick carbonate deposits since the Late Cretaceous, creating favorable reservoirs for oil and gas resources. The evolution of its sedimentary environment has long been a focus of the international academic community. In this study, three stratigraphic sections （Kermanshan-KM section, Khoramabad-AD section, Hkhormoj-HM section） are taken as the research objects located in the Lurestan-Fars areas on the northern margin of the Arabian Plate （Zagros, Iran）. Detailed field observation and thin section analysis of the Upper Cretaceous Savark, Ilam and Gurpi Formations are conducted. In total, 13 carbonate microfacies were identified and grouped into 3 sedimentary facies： outer, middle, and inner ramps. During the Santonian, these three sections were in a deep-water outer ramp environment, while in the Campanian, the AD and KM sections changed from outer to inner ramp, indicating a sudden shallowing of paleo-water depth. However, at the same time, the HM section was still in outer ramp. Considering the different distances between three sections from the ophiolite belt, we suggest that the shallowing events recorded in sections KM & AD of the Lurestan area during the Campanian are related to the ophiolite obduction in the north, while the HM section in the Fars area is too far away from the ophiolite belt.
2023, 41(4): 1138-1152.
doi: 10.14027/j.issn.1000-0550.2021.148
Abstract:
Sandy conglomerate bodies are the result of rapid near-source accumulation of sediment, with multi-phase superposition of fan bodies, and diverse, non-homogeneous lithological properties. Conventional logging is adversely affected by coarse clastic rock formations and fluid complexity, which often hinder the identification of sedimentary microphases. In this study, core-scale full borehole micro-resistivity scanning imaging （FMI） of the sand and gravel body was used to summarize the properties of each sedimentary microphase. The relationships between microphases and lithology, physical properties and oil content were analyzed. The contrast, correlation, angular second-order moments, and the four texture parameters and FMI images of the core sections were used as learning samples for the k-nearest neighbors classification algorithm （KNN） and convolutional neural network （CNN）. The machine-learning and deep-learning networks were trained to classifiy and identify sedimentary microphases. The results show that this sand and gravel body is divided into four microphase types： fan-root main channel, mid-fan braided channel, inter-fan braided channel and fan-end mud. The KNN classification algorithm and CNN network model were both able to identify the sedimentary microphases, but the CNN deep-learning model showed smaller error and greater robustness than traditional KNN machine learning. The application of FMI image-feature extraction together with CNN deepens the understanding of the internal structure of sedimentary microphases in gravels, and provides a basis for fine characterization of sedimentary microphases and effective reservoir prediction.
Sandy conglomerate bodies are the result of rapid near-source accumulation of sediment, with multi-phase superposition of fan bodies, and diverse, non-homogeneous lithological properties. Conventional logging is adversely affected by coarse clastic rock formations and fluid complexity, which often hinder the identification of sedimentary microphases. In this study, core-scale full borehole micro-resistivity scanning imaging （FMI） of the sand and gravel body was used to summarize the properties of each sedimentary microphase. The relationships between microphases and lithology, physical properties and oil content were analyzed. The contrast, correlation, angular second-order moments, and the four texture parameters and FMI images of the core sections were used as learning samples for the k-nearest neighbors classification algorithm （KNN） and convolutional neural network （CNN）. The machine-learning and deep-learning networks were trained to classifiy and identify sedimentary microphases. The results show that this sand and gravel body is divided into four microphase types： fan-root main channel, mid-fan braided channel, inter-fan braided channel and fan-end mud. The KNN classification algorithm and CNN network model were both able to identify the sedimentary microphases, but the CNN deep-learning model showed smaller error and greater robustness than traditional KNN machine learning. The application of FMI image-feature extraction together with CNN deepens the understanding of the internal structure of sedimentary microphases in gravels, and provides a basis for fine characterization of sedimentary microphases and effective reservoir prediction.
2023, 41(4): 1153-1169.
doi: 10.14027/j.issn.1000-0550.2022.001
Abstract:
The depositional period of the Yanghugou Formation in the western margin of the Ordos Basin was a resurrected aulacogen after the Caledonian movement. The Yanghugou Formation has a wide stratigraphic distribution area, large thickness variations, well-developed source-reservoir-caprock association, and huge exploration potential. Owing to the strong tectonic movements and frequent changes in the sedimentary environment, the sedimentary genesis of the sandy sediments are complicated. Currently, there is a lack of systematic research on the genetic mechanism of the Yanghugou Formation sandy sediments. A single depositional model cannot fully summarize the sedimentary characteristics and distribution laws of various sandy sediments. In this study, six types of lithofacies associations were identified through field profile, core observation, drilling data, provenance analysis, and other research methods. Based on the lithology, grain size, sedimentary structure, and sandy sediment distribution characteristics in various periods, we conduct a systematic discussion on its genetic mechanism and dispersion process. The sandy sediments of the Yanghugou Formation in the western margin of the Ordos Basin are mainly by fluvial deltas, tide-controlled deltas, fan deltas, barrier island coasts, barrier-free coasts, and slump gravity flows. The overall climate of the Yanghugou Formation was humid, and the sea level gradually rose during the deposition of the 3rd the 2nd member of the Yanghugou Formation, and then gradually decreased after the 2nd member of the Yanghugou Formation reached the highest levle. The sedimentary period of the 3rd member of the Yanghugou Formation was the early stage of rifting. Tide-controlled and fan delta sandy sediments were primarily developed in the northern region of the study area. Tidal sand ridges can be seen in the central part. The southern sandy sediments are generally barrier-free coastal sediments. The sedimentary period of the 2nd member of the Yanghugou Formation is the climax of rifting. The increase of landform drop leads to the rapid deepening of the water body, and the sandy sediments were primarily distributed on the edge of the basin. Point slump gravity flow sandy sediments developed in the deep-water of the center of the basin. The tidal sand ridges near the central paleo-uplift in the East is gradually transformed into barrier sand dams, and the high parts of the paleo-uplift were deposited with tidal flats and lagoons. During the sedimentary period of the 1st member of the Yanghugou Formation, the tectonic activity weakened and the Ordos Basin gradually connected to the east and west. The provenance supply was sufficient and the landform becomes slower, and a large area of fluvial delta sandy sediments with progradation characteristics are developed. The genetic mechanism of the Yanghugou Formation sandy sediments is affected by many factors, such as tectonic movement, paleogeomorphic evolution, provenance supply, paleoclimate, sedimentary dynamic environment, and so on. However, the distribution of sandy sediments and the process of sandy sediments dispersion are controlled by tectonic activities and paleogeographic evolution. The research results are of great significance for enriching the oil and gas exploration theory in the Ordos Basin and the genetic mechanism of rifted basin sandy sediments.
The depositional period of the Yanghugou Formation in the western margin of the Ordos Basin was a resurrected aulacogen after the Caledonian movement. The Yanghugou Formation has a wide stratigraphic distribution area, large thickness variations, well-developed source-reservoir-caprock association, and huge exploration potential. Owing to the strong tectonic movements and frequent changes in the sedimentary environment, the sedimentary genesis of the sandy sediments are complicated. Currently, there is a lack of systematic research on the genetic mechanism of the Yanghugou Formation sandy sediments. A single depositional model cannot fully summarize the sedimentary characteristics and distribution laws of various sandy sediments. In this study, six types of lithofacies associations were identified through field profile, core observation, drilling data, provenance analysis, and other research methods. Based on the lithology, grain size, sedimentary structure, and sandy sediment distribution characteristics in various periods, we conduct a systematic discussion on its genetic mechanism and dispersion process. The sandy sediments of the Yanghugou Formation in the western margin of the Ordos Basin are mainly by fluvial deltas, tide-controlled deltas, fan deltas, barrier island coasts, barrier-free coasts, and slump gravity flows. The overall climate of the Yanghugou Formation was humid, and the sea level gradually rose during the deposition of the 3rd the 2nd member of the Yanghugou Formation, and then gradually decreased after the 2nd member of the Yanghugou Formation reached the highest levle. The sedimentary period of the 3rd member of the Yanghugou Formation was the early stage of rifting. Tide-controlled and fan delta sandy sediments were primarily developed in the northern region of the study area. Tidal sand ridges can be seen in the central part. The southern sandy sediments are generally barrier-free coastal sediments. The sedimentary period of the 2nd member of the Yanghugou Formation is the climax of rifting. The increase of landform drop leads to the rapid deepening of the water body, and the sandy sediments were primarily distributed on the edge of the basin. Point slump gravity flow sandy sediments developed in the deep-water of the center of the basin. The tidal sand ridges near the central paleo-uplift in the East is gradually transformed into barrier sand dams, and the high parts of the paleo-uplift were deposited with tidal flats and lagoons. During the sedimentary period of the 1st member of the Yanghugou Formation, the tectonic activity weakened and the Ordos Basin gradually connected to the east and west. The provenance supply was sufficient and the landform becomes slower, and a large area of fluvial delta sandy sediments with progradation characteristics are developed. The genetic mechanism of the Yanghugou Formation sandy sediments is affected by many factors, such as tectonic movement, paleogeomorphic evolution, provenance supply, paleoclimate, sedimentary dynamic environment, and so on. However, the distribution of sandy sediments and the process of sandy sediments dispersion are controlled by tectonic activities and paleogeographic evolution. The research results are of great significance for enriching the oil and gas exploration theory in the Ordos Basin and the genetic mechanism of rifted basin sandy sediments.
2023, 41(4): 1170-1180.
doi: 10.14027/j.issn.1000-0550.2021.163
Abstract:
To improve the understanding of heterogeneous reservoirs, a study of the static and dynamic reservoir flow was conducted in block M of the Gudao oilfield （Neogene Guantao Formation）. Static flow in the reservoirs were subdivided into four types： porosity, permeability, flow zone index and shale content. Water injection in each flow unit was assessed using a seepage resistance model. Dynamic flow was evaluated in terms of instantaneous injection of the flow per unit thickness. The difference between the static and dynamic methods was analyzed. It was found that the distribution of injection-production wells largely influences the high-level flow units. Increasing water injection increases oil flow to a certain extent. The difference between static and dynamic flow in individual layers depends largely on the unevenness of the water injection due to sand body rhythm. The reservoir was divided into five potential tapping levels by combining the distribution of the remaining oil and dynamic flow units： level I is the main potential tapping area of remaining oil； level II represents low oil potential and high water consumption.
To improve the understanding of heterogeneous reservoirs, a study of the static and dynamic reservoir flow was conducted in block M of the Gudao oilfield （Neogene Guantao Formation）. Static flow in the reservoirs were subdivided into four types： porosity, permeability, flow zone index and shale content. Water injection in each flow unit was assessed using a seepage resistance model. Dynamic flow was evaluated in terms of instantaneous injection of the flow per unit thickness. The difference between the static and dynamic methods was analyzed. It was found that the distribution of injection-production wells largely influences the high-level flow units. Increasing water injection increases oil flow to a certain extent. The difference between static and dynamic flow in individual layers depends largely on the unevenness of the water injection due to sand body rhythm. The reservoir was divided into five potential tapping levels by combining the distribution of the remaining oil and dynamic flow units： level I is the main potential tapping area of remaining oil； level II represents low oil potential and high water consumption.
2023, 41(4): 1181-1191.
doi: 10.14027/j.issn.1000-0550.2022.056
Abstract:
The Qiongdongnan Basin is an important petroliferous structure at the northern margin of the South China Sea, with reservoirs generally developed in Miocene marine sandstones. Because the basin is located at the boundary between the Indochina Plate and Pacific Plate, paleo-sea currents were significantly active during deposition of the Miocene reservoirs. However, the influence of the currents on reservoir development has been unclear. In this study, the sedimentational properties of typical core samples, stratum imaging logging and clay mineral compositions were analyzed to investigate the interactions between paleocurrents and sedimentation in the Qiongdongnan Basin. The results indicate four types of paleocurrent in different tectonic regions of the basin： NE⁃SE surface currents induced by the winter monsoon in the continental shelf region； NE⁃SE mesopelagic currents driven by a branch of the Kuroshio current in the slope region； NW⁃SE tides induced by the negative terrain between the Yacheng and Zhongjian uplifts in the western basin floor； and deep currents generated from the North Atlantic in the eastern basin floor. These currents enhanced water exchange between the Qiongdongnan Basin and surrounding open sea areas during the Miocene, affecting the development and distribution of reservoirs and also significantly reducing the mud content of sandstone reservoirs. This improved the physical properties of the reservoirs and influenced the formation of high-quality reservoirs. All of the present high-yield gas fields in deep-water areas of the Qiongdongnan Basin （LS25, LS17 and ST34） have recently proven to be transformed by paleocurrents, and this study has produced new geological evidence for future exploration relating to high-quality reservoirs in the basin.
The Qiongdongnan Basin is an important petroliferous structure at the northern margin of the South China Sea, with reservoirs generally developed in Miocene marine sandstones. Because the basin is located at the boundary between the Indochina Plate and Pacific Plate, paleo-sea currents were significantly active during deposition of the Miocene reservoirs. However, the influence of the currents on reservoir development has been unclear. In this study, the sedimentational properties of typical core samples, stratum imaging logging and clay mineral compositions were analyzed to investigate the interactions between paleocurrents and sedimentation in the Qiongdongnan Basin. The results indicate four types of paleocurrent in different tectonic regions of the basin： NE⁃SE surface currents induced by the winter monsoon in the continental shelf region； NE⁃SE mesopelagic currents driven by a branch of the Kuroshio current in the slope region； NW⁃SE tides induced by the negative terrain between the Yacheng and Zhongjian uplifts in the western basin floor； and deep currents generated from the North Atlantic in the eastern basin floor. These currents enhanced water exchange between the Qiongdongnan Basin and surrounding open sea areas during the Miocene, affecting the development and distribution of reservoirs and also significantly reducing the mud content of sandstone reservoirs. This improved the physical properties of the reservoirs and influenced the formation of high-quality reservoirs. All of the present high-yield gas fields in deep-water areas of the Qiongdongnan Basin （LS25, LS17 and ST34） have recently proven to be transformed by paleocurrents, and this study has produced new geological evidence for future exploration relating to high-quality reservoirs in the basin.
2023, 41(4): 1192-1201.
doi: 10.14027/j.issn.1000-0550.2022.012
Abstract:
The Junggar Basin is rich in oil sand resources. The northwestern margin of the Fengcheng oil sand mining area is the most important oil sand distribution area in the Junggar Basin. In this paper, the gas chromatography- mass spectrometry GC-MS of saturated and aromatic hydrocarbons in the oil sand sample extracts, such as normal alkanes, regular steranes, mono-aromatic steranes, short-chain triaromatic steranes, and rearranged steranes, were undetectable； in addition, the abundance of hopanes, pregnane, and long-chain triaromatic steranes were rare. Severe biodegradation has occurred, and the degradation level can reach level 8 or higher. As far as the overall carbon number distribution of tricyclic terpanes is concerned, with the increase of biodegradation, the anti-degradation ability of tricyclic terpanes will decrease with the increase of carbon number, i.e., tricyclic terpanes （TT） are resistant to biodegradation. The distribution appeared to be the following： high carbon number（C28-C31TT） > medium carbon number（C23-C26TT） > low carbon number （C19-C22 TT）. However, for a single tricyclic terpane compound, C19 and C20, C22 and C23, and C26 and C28 tricyclic terpanes tend to increase their resistance to degradation as the carbon number increases. Therefore, the use of the relative ratio of tricyclic terpane compounds, namely C19-C22 TT /C28-C31 TT、C23-C26 TT /C28-C31 TT、C19-C22 TT /C23-C26 TT、C23 TT /C31 TT, is proposed to describe the degree of severe biodegradation of crude oil and provide a geochemical basis for crude oil to undergo secondary alteration, especially biodegradation.
The Junggar Basin is rich in oil sand resources. The northwestern margin of the Fengcheng oil sand mining area is the most important oil sand distribution area in the Junggar Basin. In this paper, the gas chromatography- mass spectrometry GC-MS of saturated and aromatic hydrocarbons in the oil sand sample extracts, such as normal alkanes, regular steranes, mono-aromatic steranes, short-chain triaromatic steranes, and rearranged steranes, were undetectable； in addition, the abundance of hopanes, pregnane, and long-chain triaromatic steranes were rare. Severe biodegradation has occurred, and the degradation level can reach level 8 or higher. As far as the overall carbon number distribution of tricyclic terpanes is concerned, with the increase of biodegradation, the anti-degradation ability of tricyclic terpanes will decrease with the increase of carbon number, i.e., tricyclic terpanes （TT） are resistant to biodegradation. The distribution appeared to be the following： high carbon number（C28-C31TT） > medium carbon number（C23-C26TT） > low carbon number （C19-C22 TT）. However, for a single tricyclic terpane compound, C19 and C20, C22 and C23, and C26 and C28 tricyclic terpanes tend to increase their resistance to degradation as the carbon number increases. Therefore, the use of the relative ratio of tricyclic terpane compounds, namely C19-C22 TT /C28-C31 TT、C23-C26 TT /C28-C31 TT、C19-C22 TT /C23-C26 TT、C23 TT /C31 TT, is proposed to describe the degree of severe biodegradation of crude oil and provide a geochemical basis for crude oil to undergo secondary alteration, especially biodegradation.
2023, 41(4): 1202-1211.
doi: 10.14027/j.issn.1000-0550.2021.153
Abstract:
Tahe oilfield is the Paleozoic marine carbonate oil and gas field with the largest crude oil reserves in China. The content of tricyclic terpanes in Tahe crude oil is unusually rich and significantly higher than hopanes. The reason for this abnormal distribution is still unclear. In this study, gas chromatography and gas chromatography-mass spectrometry （GC-MS） data for crude oil samples from Tahe oilfield were analyzed. The abnormal distribution and genesis of tricyclic terpanes in Tahe crude oil are discussed, covering deposition environment, biodegradation and thermal maturity. The results show that for the deposition environment, the degree of oxidation-reduction and salinization during deposition of organic matter is not the main reason. However, the relative content of tricyclic terpanes increased with increasing bacterial input in organic matter and thermal maturity. Σtricyclic terpanes/Σ17α（H）-hopanes is positively correlated with thermal maturity, indicating that thermal evolution was the most significant driving force for the abnormal distribution of tricyclic terpanes in Tahe crude oils.
Tahe oilfield is the Paleozoic marine carbonate oil and gas field with the largest crude oil reserves in China. The content of tricyclic terpanes in Tahe crude oil is unusually rich and significantly higher than hopanes. The reason for this abnormal distribution is still unclear. In this study, gas chromatography and gas chromatography-mass spectrometry （GC-MS） data for crude oil samples from Tahe oilfield were analyzed. The abnormal distribution and genesis of tricyclic terpanes in Tahe crude oil are discussed, covering deposition environment, biodegradation and thermal maturity. The results show that for the deposition environment, the degree of oxidation-reduction and salinization during deposition of organic matter is not the main reason. However, the relative content of tricyclic terpanes increased with increasing bacterial input in organic matter and thermal maturity. Σtricyclic terpanes/Σ17α（H）-hopanes is positively correlated with thermal maturity, indicating that thermal evolution was the most significant driving force for the abnormal distribution of tricyclic terpanes in Tahe crude oils.
2023, 41(4): 1212-1226.
doi: 10.14027/j.issn.1000-0550.2022.033
Abstract:
Research on coal-bearing rocks in the different sedimentary responses of multiple coal seams and the effect of adjacent glutenite diagenetic is not currently well developed. Through field observations, sporopollen combination, well-seismic profiles, core phase sequence, and logging responses, such as scanning electron microscope and electron probe energy spectrum data, a stable thick coal seam, and limited thin coal seam were analyzed in the study area for different sedimentary responses. The results showed that through the movement along thrust faults I and II of the basin edge, the oscillation behavior of the boundary faults and basin basement subsidence provides the study area with thick layers of peat accumulation, leading to wide slow-ancient slope cover lake invasion. This hinders the swamp drainage, preventing the oxidation of organic matter and reducing the river gradient. Weakening terrigenous clastic particles interfere with the favorable conditions. A large stable thick coal seam was formed near the first lake flood surface in the lacustrine basin, and the maceral indicates that the coal forming swamp has maintained a good hysteretic water reduction condition. The limited thin coal seams are scattered, have obvious phase-controlled characteristics, and are primarily distributed in the low energy facies zones, such as an interfan/interchannel with weak hydrodynamics. The maceral indicates that the coal forming swamp has a semi-oxidation stage with poor local hysteretic reduction conditions. In the penecongenic-early diagenetic stage, humic acid in coal measures formed dissolution pores in feldspar grains, and the dissolution particles were dominated by calcium-rich plagioclase. The occurrence of kaolinite cement products is found near the inner ring edge of the particles with high purity. Complete and partial kaolinite particles are formed by the dissolution of feldspar particles, kaolinite filling, and collapse polycondensation. The former is of high purity, and the latter is of low purity. In the middle diagenetic stage, organic carboxylic acid of the hydrocarbon source forms dissolution pores in feldspar grains； the dissolution components are primarily potassium feldspar, and the residual components are primarily albite. The occurrence of cemented kaolinite is located on the outer ring edge of the particles or filling intergranular pores with low purity. The influence of humic acid in coal measures on the quality of adjacent conglomerate reservoir is inhibition. Based on the limiting sedimentary facies zone and grain size, the vertical radiation thickness of the stable thick coal seam is 10⁃30 m, the porosity of conglomerate in the radiation zone decreases by 2.3%⁃5.2%, and the permeability decreases by （1.3⁃2.1）×10-3 μm2. The vertical radiation thickness of the limited thin coal seam is 3⁃8 m, the porosity of conglomerate in radiation zone decreases by 1.2%⁃3.5%, and the permeability decreases by （0.8⁃1.9）×10-3 μm2. The high content of rigid particles is a prerequisite for the effective preservation of the original intergranular pores, especially the humic acid solution pores in the penicsyngenetic and early diagenetic coal measures. The removal degree of dissolution products, such as kaolinite and silica, further restricts the effectiveness of the pores.
Research on coal-bearing rocks in the different sedimentary responses of multiple coal seams and the effect of adjacent glutenite diagenetic is not currently well developed. Through field observations, sporopollen combination, well-seismic profiles, core phase sequence, and logging responses, such as scanning electron microscope and electron probe energy spectrum data, a stable thick coal seam, and limited thin coal seam were analyzed in the study area for different sedimentary responses. The results showed that through the movement along thrust faults I and II of the basin edge, the oscillation behavior of the boundary faults and basin basement subsidence provides the study area with thick layers of peat accumulation, leading to wide slow-ancient slope cover lake invasion. This hinders the swamp drainage, preventing the oxidation of organic matter and reducing the river gradient. Weakening terrigenous clastic particles interfere with the favorable conditions. A large stable thick coal seam was formed near the first lake flood surface in the lacustrine basin, and the maceral indicates that the coal forming swamp has maintained a good hysteretic water reduction condition. The limited thin coal seams are scattered, have obvious phase-controlled characteristics, and are primarily distributed in the low energy facies zones, such as an interfan/interchannel with weak hydrodynamics. The maceral indicates that the coal forming swamp has a semi-oxidation stage with poor local hysteretic reduction conditions. In the penecongenic-early diagenetic stage, humic acid in coal measures formed dissolution pores in feldspar grains, and the dissolution particles were dominated by calcium-rich plagioclase. The occurrence of kaolinite cement products is found near the inner ring edge of the particles with high purity. Complete and partial kaolinite particles are formed by the dissolution of feldspar particles, kaolinite filling, and collapse polycondensation. The former is of high purity, and the latter is of low purity. In the middle diagenetic stage, organic carboxylic acid of the hydrocarbon source forms dissolution pores in feldspar grains； the dissolution components are primarily potassium feldspar, and the residual components are primarily albite. The occurrence of cemented kaolinite is located on the outer ring edge of the particles or filling intergranular pores with low purity. The influence of humic acid in coal measures on the quality of adjacent conglomerate reservoir is inhibition. Based on the limiting sedimentary facies zone and grain size, the vertical radiation thickness of the stable thick coal seam is 10⁃30 m, the porosity of conglomerate in the radiation zone decreases by 2.3%⁃5.2%, and the permeability decreases by （1.3⁃2.1）×10-3 μm2. The vertical radiation thickness of the limited thin coal seam is 3⁃8 m, the porosity of conglomerate in radiation zone decreases by 1.2%⁃3.5%, and the permeability decreases by （0.8⁃1.9）×10-3 μm2. The high content of rigid particles is a prerequisite for the effective preservation of the original intergranular pores, especially the humic acid solution pores in the penicsyngenetic and early diagenetic coal measures. The removal degree of dissolution products, such as kaolinite and silica, further restricts the effectiveness of the pores.
2023, 41(4): 1227-1239.
doi: 10.14027/j.issn.1000-0550.2022.041
Abstract:
To clarify the fine-grained sedimentary characteristics and depositional models of the Chang 7 oil member of the Triassic Yanchang Formation in the southern Ordos Basin, we take Yishi Village, Yaoqu, and other typical field sections as research objects. Based on field reconnaissance and survey, we analyze the lithofacies and lithofacies assemblage characteristics, discuss sedimentary facies characteristics, and establish different fine-grained sedimentary lithofacies evolution models. The results show that the outcrops in the middle and lower sections of the Yanchang Formation in the Tongchuan area primarily developed overlying and scouring positive-order silt-fine sandstone, massive bedding silt-fine sandstone, soft sedimentary deformed sand-shale mixed, and massive mudstone facies. There are 6 lithofacies types in the horizontal laminar shale facies and tuff facies. The typical characteristics of the lower 73 sub-oil member of the Yishicun section are sandy clastic flows and slump deposits with massive bedding. The deep-water in-situ deposits from different outcrop sections of the Chang 72 sub-oil member, whose lithology transitions from siltstone-silty mudstone to horizontal laminar mudstone to black shale with extremely developed shales, were examined. The Chang 71 sub-oil member of the Yaoqu section is rich in soft sedimentary deformation structures, such as liquefied sandstone veins, argillaceous bands, and flame-like structures in massive sandstones. The lithofacies assemblage types of the fine-grained sediments in the Chang 7 oil member from the Yanchang Formation in the Tongchuan area include background argillaceous deposits, vertical assemblages of tuff and gravity flow deposits, superposition of sliding landslides and background mudstones, gravity flow deposits of sandstones, and mudstones. The sedimentary period of the Chang 73 sub-oil member in Yishi Village was a relatively thick sliding slumping deposit formed by the re-transportation of the delta front sediment. The depositional period of the Chang 72 sub-oil member was composed of deep-water shale deposits, mixed with volcanic ash carried by wind and a small amount of low-density turbidity current deposits and thin siltstones. In the depositional period of the Chang 71 sub-oil member, the sandy debris flow deposits and low-density turbidity current deposits that were formed by the collapse and transport of deltas increased. As a whole, during the sedimentary period of Chang 7 oil member, the lake level was found to rise first and then decrease periodically. The fluctuation of lake level controls the transport mode and deposition mode of fine-grained sediments and has important guiding significance for the study of the transport mechanism and distribution of fine-grained sediments.
To clarify the fine-grained sedimentary characteristics and depositional models of the Chang 7 oil member of the Triassic Yanchang Formation in the southern Ordos Basin, we take Yishi Village, Yaoqu, and other typical field sections as research objects. Based on field reconnaissance and survey, we analyze the lithofacies and lithofacies assemblage characteristics, discuss sedimentary facies characteristics, and establish different fine-grained sedimentary lithofacies evolution models. The results show that the outcrops in the middle and lower sections of the Yanchang Formation in the Tongchuan area primarily developed overlying and scouring positive-order silt-fine sandstone, massive bedding silt-fine sandstone, soft sedimentary deformed sand-shale mixed, and massive mudstone facies. There are 6 lithofacies types in the horizontal laminar shale facies and tuff facies. The typical characteristics of the lower 73 sub-oil member of the Yishicun section are sandy clastic flows and slump deposits with massive bedding. The deep-water in-situ deposits from different outcrop sections of the Chang 72 sub-oil member, whose lithology transitions from siltstone-silty mudstone to horizontal laminar mudstone to black shale with extremely developed shales, were examined. The Chang 71 sub-oil member of the Yaoqu section is rich in soft sedimentary deformation structures, such as liquefied sandstone veins, argillaceous bands, and flame-like structures in massive sandstones. The lithofacies assemblage types of the fine-grained sediments in the Chang 7 oil member from the Yanchang Formation in the Tongchuan area include background argillaceous deposits, vertical assemblages of tuff and gravity flow deposits, superposition of sliding landslides and background mudstones, gravity flow deposits of sandstones, and mudstones. The sedimentary period of the Chang 73 sub-oil member in Yishi Village was a relatively thick sliding slumping deposit formed by the re-transportation of the delta front sediment. The depositional period of the Chang 72 sub-oil member was composed of deep-water shale deposits, mixed with volcanic ash carried by wind and a small amount of low-density turbidity current deposits and thin siltstones. In the depositional period of the Chang 71 sub-oil member, the sandy debris flow deposits and low-density turbidity current deposits that were formed by the collapse and transport of deltas increased. As a whole, during the sedimentary period of Chang 7 oil member, the lake level was found to rise first and then decrease periodically. The fluctuation of lake level controls the transport mode and deposition mode of fine-grained sediments and has important guiding significance for the study of the transport mechanism and distribution of fine-grained sediments.
2023, 41(4): 1240-1256.
doi: 10.14027/j.issn.1000-0550.2021.159
Abstract:
Based on the geochemical analysis of the Lower Cambrian mudstone in the Kuluketage area, the paleoclimate, provenance, and formation of mudstone in the Early Cambrian are discussed. In the study area, the CIA value and SiO2-（Al2O3+K2O+Na2O） diagram show that the paleoclimate in the Early Cambrian was warmer than in the Ediacaran, and became cold and dry again in the Cambrian. The Ce/Ce* and （La/Ce）N values indicate that the Xishanbulake Formation was deposited in a submarine basin near a mid ocean ridge （MOR）, and the overlying Xidashan and underlying Hangeerqiaoke Formations are deposited in a stable continental margin. The La-Th-Sc diagram shows that the tectonic setting of the formation in section QKMK-Ⅰwas a passive continental margin, while section QKMK-Ⅱ. Th-Sc and Th/Sc-La/Sc diagrams and discriminant functions indicate that the parent rock of section QKMK-Ⅰ is a neutral to intermediate-acid igneous rock, and its provenance may be intermediate-acid rock of the Precambrian in the central uplift zone. The parent rock of section QKMK-Ⅱis a mafic to intermediate-acidic igneous rock, and its mafic components obviously increased. Except for the central uplift zone provenance, it may be affected by the effusion of mafic hydrothermal fluids from the seabed.
Based on the geochemical analysis of the Lower Cambrian mudstone in the Kuluketage area, the paleoclimate, provenance, and formation of mudstone in the Early Cambrian are discussed. In the study area, the CIA value and SiO2-（Al2O3+K2O+Na2O） diagram show that the paleoclimate in the Early Cambrian was warmer than in the Ediacaran, and became cold and dry again in the Cambrian. The Ce/Ce* and （La/Ce）N values indicate that the Xishanbulake Formation was deposited in a submarine basin near a mid ocean ridge （MOR）, and the overlying Xidashan and underlying Hangeerqiaoke Formations are deposited in a stable continental margin. The La-Th-Sc diagram shows that the tectonic setting of the formation in section QKMK-Ⅰwas a passive continental margin, while section QKMK-Ⅱ. Th-Sc and Th/Sc-La/Sc diagrams and discriminant functions indicate that the parent rock of section QKMK-Ⅰ is a neutral to intermediate-acid igneous rock, and its provenance may be intermediate-acid rock of the Precambrian in the central uplift zone. The parent rock of section QKMK-Ⅱis a mafic to intermediate-acidic igneous rock, and its mafic components obviously increased. Except for the central uplift zone provenance, it may be affected by the effusion of mafic hydrothermal fluids from the seabed.
2023, 41(4): 1257-1270.
doi: 10.14027/j.issn.1000-0550.2022.005
Abstract:
The black shale deposited during the early Qiongzhusi Formation in the Dianqianbei Depression is an important hydrocarbon source rock. The evolution of the lithofacies paleogeography in the upper and lower members of the Qiongzhusi Formation was restored in a thorough study of the regional geology, field outcrops, cores, thin sections, scanning electron microscopy and drilling data. The strata are thin in the west, and thicker in the tension trough and in the east. The rock types deposited during the same sedimentary periods also display regional differences. In the lower sedimentary period, the western region consists mainly of sandstone, whereas the central and eastern regions consist mainly of shale, with shallow sea-shelf facies as the main facies type. The upper and lower sections indicate varying water depths and sedimentary facies comprising six microfacies. From west to east, the lowest stratum consists mainly of shallow-water sandy shelf microfacies and deep-water argillaceous shelf microfacies, and the upper stratum mainly comprises shallow-water sandy shelf microfacies, shallow-water argillaceous shelf microfacies and shallow-water sandy argillaceous shelf microfacies. The high-quality source rocks of the Qiongzhusi Formation are black shale and carbonaceous shale, with TOC （Total of Organic）content generally above 2%. The argillaceous deep-water shelf subfacies is the most favorable for the development of high-quality shale. Vertically, the high-quality shale mainly occurs at the base of the lowest section of the Qiongzhusi Formation. In plane, it is mainly found in the section along wells CL1, B1, Z101, JZ1 and FS1, controlled by the tension trough in the middle of the study area. In the east, the low-landform and deep-water deposition Jinsha-Zunyi area favors exploration for high-quality shale.
The black shale deposited during the early Qiongzhusi Formation in the Dianqianbei Depression is an important hydrocarbon source rock. The evolution of the lithofacies paleogeography in the upper and lower members of the Qiongzhusi Formation was restored in a thorough study of the regional geology, field outcrops, cores, thin sections, scanning electron microscopy and drilling data. The strata are thin in the west, and thicker in the tension trough and in the east. The rock types deposited during the same sedimentary periods also display regional differences. In the lower sedimentary period, the western region consists mainly of sandstone, whereas the central and eastern regions consist mainly of shale, with shallow sea-shelf facies as the main facies type. The upper and lower sections indicate varying water depths and sedimentary facies comprising six microfacies. From west to east, the lowest stratum consists mainly of shallow-water sandy shelf microfacies and deep-water argillaceous shelf microfacies, and the upper stratum mainly comprises shallow-water sandy shelf microfacies, shallow-water argillaceous shelf microfacies and shallow-water sandy argillaceous shelf microfacies. The high-quality source rocks of the Qiongzhusi Formation are black shale and carbonaceous shale, with TOC （Total of Organic）content generally above 2%. The argillaceous deep-water shelf subfacies is the most favorable for the development of high-quality shale. Vertically, the high-quality shale mainly occurs at the base of the lowest section of the Qiongzhusi Formation. In plane, it is mainly found in the section along wells CL1, B1, Z101, JZ1 and FS1, controlled by the tension trough in the middle of the study area. In the east, the low-landform and deep-water deposition Jinsha-Zunyi area favors exploration for high-quality shale.
