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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In recent years, several exploration wells in the Ordovician Wulalike Formation in the western edge of Ordos Basin have obtained industrial gas flow, breaking through the restricted zone of migmatites exploration from shallow water to deep water. However, the sedimentary characteristics and exploration potential are still unclear. In order to enhance the geological understanding of deep-water migmatites and guide the next step of exploration work, typical drilling and outcrops samples combined with thin sections, and related experimental data are used to conduct systematic research on the lithofacies sedimentary facies characteristics, distribution patterns migmatites, and exploration potential of source reservoir cap combination. Research has shown that: ① the Ordovician Wulalike Formation in the western margin of the Ordos Basin mainly develops 22 types of lithofacies and 12 types of lithofacies combinations, reflecting the sedimentary characteristics of platform, shelf, slope, and basin facies, respectively; ② The Wulalike Formation as a whole features paleogeographic pattern and stratigraphic distribution characteristics of "low in the west and high in the east, thick in the west and thin in the east". Its bottom is the largest transgressive surface in the Ordovician period, and two complete third-order sequences are developed upwards. During the sedimentary period of SQ1 in the lower part, the water body was generally deep, while the depth of seawater becomes shallow upwards, and the sedimentary facies belt shows a trend of narrowing and retreating westward.③Combining the relationship between Wulalike Formation and the Upper Paleozoic configuration, it is believed that there are multiple sets of source reservoir cap combinations within the Wulalike Formation. Among them, the intertidal reef facies limestone in sequence SQ2 and the slope-basin facies shale in sequence SQ1 have a good spatial matching relationship, corresponding to limestone gas reservoirs and shale gas reservoirs, respectively. These are new Ordovician field of key deepening research in the western margin area, and the future exploration potential cannot be ignored.
In recent years, several exploration wells in the Ordovician Wulalike Formation in the western edge of Ordos Basin have obtained industrial gas flow, breaking through the restricted zone of migmatites exploration from shallow water to deep water. However, the sedimentary characteristics and exploration potential are still unclear. In order to enhance the geological understanding of deep-water migmatites and guide the next step of exploration work, typical drilling and outcrops samples combined with thin sections, and related experimental data are used to conduct systematic research on the lithofacies sedimentary facies characteristics, distribution patterns migmatites, and exploration potential of source reservoir cap combination. Research has shown that: ① the Ordovician Wulalike Formation in the western margin of the Ordos Basin mainly develops 22 types of lithofacies and 12 types of lithofacies combinations, reflecting the sedimentary characteristics of platform, shelf, slope, and basin facies, respectively; ② The Wulalike Formation as a whole features paleogeographic pattern and stratigraphic distribution characteristics of "low in the west and high in the east, thick in the west and thin in the east". Its bottom is the largest transgressive surface in the Ordovician period, and two complete third-order sequences are developed upwards. During the sedimentary period of SQ1 in the lower part, the water body was generally deep, while the depth of seawater becomes shallow upwards, and the sedimentary facies belt shows a trend of narrowing and retreating westward.③Combining the relationship between Wulalike Formation and the Upper Paleozoic configuration, it is believed that there are multiple sets of source reservoir cap combinations within the Wulalike Formation. Among them, the intertidal reef facies limestone in sequence SQ2 and the slope-basin facies shale in sequence SQ1 have a good spatial matching relationship, corresponding to limestone gas reservoirs and shale gas reservoirs, respectively. These are new Ordovician field of key deepening research in the western margin area, and the future exploration potential cannot be ignored.
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[Objective] The second member of the Lucaogou Formation (Lu2) of the Middle Permian in the Malang depression is the main source of lacustrine carbonate shale oil in the Santanghu Basin, however, the study on the coupling relationship between carbon-oxygen isotope composition and paleoenvironmental characteristics and organic matter enrichment is relatively weak. [Methods] In order to clarify the paleoenvironmental characteristics and the enrichment mechanism of organic matter, total organic carbon content, carbon-oxygen isotope and micronutrient of carbonate samples were analyzed in this study. [Results and Discussions] The results show that:①the carbon isotopes of the carbonate rocks in the second member of Lu Formation are all positive, and the oxygen isotopes are all negative, from bottom to top, the carbon-oxygen isotopes of Lu2 member show the characteristics of high-low-high, and have obvious response relationship with sedimentary cycle, paleoenvironment and paleoproductivity.②The lower part of the middle dessert is a deep water environment with drought, brackish water and strong reduction, and the paleoproductivity is low. The upper part is a deep water environment with semi-arid, brackish water and weak reduction, the paleoproductivity is high in arid, salt water, weak reduction-weak oxidation semi-deep water environment. [Conclusions] Based on the analysis of total organic carbon content and paleoenvironmental conditions, it is considered that the accumulation of organic matter is mainly controlled by paleoproductivity, and the reduction environment with high salinity contributes to the preservation of organic matter, the high-quality source rocks are developed in the upper and upper cycles of the middle sweet spot, while the lower cycles of the middle sweet spot are relatively poor.
[Objective] The second member of the Lucaogou Formation (Lu2) of the Middle Permian in the Malang depression is the main source of lacustrine carbonate shale oil in the Santanghu Basin, however, the study on the coupling relationship between carbon-oxygen isotope composition and paleoenvironmental characteristics and organic matter enrichment is relatively weak. [Methods] In order to clarify the paleoenvironmental characteristics and the enrichment mechanism of organic matter, total organic carbon content, carbon-oxygen isotope and micronutrient of carbonate samples were analyzed in this study. [Results and Discussions] The results show that:①the carbon isotopes of the carbonate rocks in the second member of Lu Formation are all positive, and the oxygen isotopes are all negative, from bottom to top, the carbon-oxygen isotopes of Lu2 member show the characteristics of high-low-high, and have obvious response relationship with sedimentary cycle, paleoenvironment and paleoproductivity.②The lower part of the middle dessert is a deep water environment with drought, brackish water and strong reduction, and the paleoproductivity is low. The upper part is a deep water environment with semi-arid, brackish water and weak reduction, the paleoproductivity is high in arid, salt water, weak reduction-weak oxidation semi-deep water environment. [Conclusions] Based on the analysis of total organic carbon content and paleoenvironmental conditions, it is considered that the accumulation of organic matter is mainly controlled by paleoproductivity, and the reduction environment with high salinity contributes to the preservation of organic matter, the high-quality source rocks are developed in the upper and upper cycles of the middle sweet spot, while the lower cycles of the middle sweet spot are relatively poor.
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[Objective] Xinying Bay, Hainan Province, retains a relatively complete sedimentary record of marine stratigraphy since the Pleistocene. Due to its closure and stability, it serves as a good window to reflect the paleoenvironmental changes since the Pleistocene in the Northern South China Sea. [Methods] Based on the analysis of whole rock major elements and Sr-Nd isotopes, the source of sediment material and the evolution of paleoclimate and paleoclimate in this area since Pleistocene were reconstructed, and the driving mechanism was discussed. [Results and Discussions] The borehole has three relatively obvious sections from bottom to top. The bottom U1 section has a relatively low εNd(0) value and a relatively high 86Sr/87Sr value. The middle U2 section has relatively high ratios of Al/Ti, K/Ti, Fe/Ti, and Mg/Ti. The results of provenance analysis show that the sediments of the borehole come from the intermediate source area, and the U1 section contains more older sedimentary materials, and the Sr-Nd isotope ratio is similar to that of the Red river sediments, while the U2 and U3 sections are similar to the Cretaceous-Permian feldspar granite in Hainan Island. The paleoenvironmental analysis shows that this region has experienced changes from dry cold to warm wet, and then to dry cold since the Pleistocene. [Conclusions] The sedimentary period of section U1 corresponds to the coldest MIS16 period in the Northern Hemisphere, which combined with previous chronological studies, and the dry and cold climate and relatively low sea level enable the clastic sediments of the Indochina continent to be transported to Xinying Bay. Then the East Asian summer monsoon strengthened, and the climate changed from cold and dry to warm and humid. As a result, the source area of U2 section was dominated by granitic rocks in Hainan Island because the sea level raised. The U3 section has undergone regional tectonic uplift, and the sedimentary source area is dominated by granite in the island.
[Objective] Xinying Bay, Hainan Province, retains a relatively complete sedimentary record of marine stratigraphy since the Pleistocene. Due to its closure and stability, it serves as a good window to reflect the paleoenvironmental changes since the Pleistocene in the Northern South China Sea. [Methods] Based on the analysis of whole rock major elements and Sr-Nd isotopes, the source of sediment material and the evolution of paleoclimate and paleoclimate in this area since Pleistocene were reconstructed, and the driving mechanism was discussed. [Results and Discussions] The borehole has three relatively obvious sections from bottom to top. The bottom U1 section has a relatively low εNd(0) value and a relatively high 86Sr/87Sr value. The middle U2 section has relatively high ratios of Al/Ti, K/Ti, Fe/Ti, and Mg/Ti. The results of provenance analysis show that the sediments of the borehole come from the intermediate source area, and the U1 section contains more older sedimentary materials, and the Sr-Nd isotope ratio is similar to that of the Red river sediments, while the U2 and U3 sections are similar to the Cretaceous-Permian feldspar granite in Hainan Island. The paleoenvironmental analysis shows that this region has experienced changes from dry cold to warm wet, and then to dry cold since the Pleistocene. [Conclusions] The sedimentary period of section U1 corresponds to the coldest MIS16 period in the Northern Hemisphere, which combined with previous chronological studies, and the dry and cold climate and relatively low sea level enable the clastic sediments of the Indochina continent to be transported to Xinying Bay. Then the East Asian summer monsoon strengthened, and the climate changed from cold and dry to warm and humid. As a result, the source area of U2 section was dominated by granitic rocks in Hainan Island because the sea level raised. The U3 section has undergone regional tectonic uplift, and the sedimentary source area is dominated by granite in the island.
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Abstract: [Objective] The Late Triassic is a crucial period for the Mesozoic Qiangtang Basin evolution. However, the previous researches concentrated on the sedimentology of the Upper Triassic strata are rare in Qiangtang Basin, which is not conducive to elaborately analyzing the characterization of Late Triassic sedimentary evolution and predicting the distribution of source and reservoir rocks. [Methods] Based on the measured section, we synthesized the thin section, grain size of detrital particle and typical primary sedimentary structure to identify the sedimentary facies of the Jiapila, Bolila and Bagong Formations in the Jiangai Darina section and then establish the Late Triassic sedimentary evolution model in the central Qiangtang Basin. In addition, the whole-rock and clay minerals, physical properties, and total organic carbon (TOC) contents of sandstone and mudstone samples were analyzed to evaluate the characteristics of source and reservoir rocks. [Results] (1) In the Jiangai Darina section, the sedimentary facies of the Upper Triassic strata have experienced the evolution of the fan-delta facies→barrier-free coastal facies→carbonate ramp facies→neritic shelf facies→delta facies upward, and can be identified ten subfacies and eight microfacies totally. (2) The Upper Triassic strata in the study area constitute an upward deepening transgressive succession and then shallower regressive succession. Among them, the transgressive succession is mainly composed of the Jiapila and Bolila Formations, while the regressive succession is mianly composed of the Bagong Formation. (3) The sandstone samples from the Jiapila and Bagong Formations are ultra-low porosity and ultra-low permeability reservoir with secondary pores primarily. The mudstone samples of the Bagong Formation from the Jiangai Darina section are poor source rocks and non source rocks, while become better to north (Woruoshan section). We inferred that the depression between Jiangai Darina and Woruoshan may develop well source rocks and have a good exploration prospect based on the latest tectono-lithofacies paleogeographic data, but it still need to be confirmed. [Conclusion] These results would provide a valuable reference for the researches of Late Triassic sedimentary-tectonic evolution and oil and gas resource evaluation in Qiangtang Basin.
Abstract: [Objective] The Late Triassic is a crucial period for the Mesozoic Qiangtang Basin evolution. However, the previous researches concentrated on the sedimentology of the Upper Triassic strata are rare in Qiangtang Basin, which is not conducive to elaborately analyzing the characterization of Late Triassic sedimentary evolution and predicting the distribution of source and reservoir rocks. [Methods] Based on the measured section, we synthesized the thin section, grain size of detrital particle and typical primary sedimentary structure to identify the sedimentary facies of the Jiapila, Bolila and Bagong Formations in the Jiangai Darina section and then establish the Late Triassic sedimentary evolution model in the central Qiangtang Basin. In addition, the whole-rock and clay minerals, physical properties, and total organic carbon (TOC) contents of sandstone and mudstone samples were analyzed to evaluate the characteristics of source and reservoir rocks. [Results] (1) In the Jiangai Darina section, the sedimentary facies of the Upper Triassic strata have experienced the evolution of the fan-delta facies→barrier-free coastal facies→carbonate ramp facies→neritic shelf facies→delta facies upward, and can be identified ten subfacies and eight microfacies totally. (2) The Upper Triassic strata in the study area constitute an upward deepening transgressive succession and then shallower regressive succession. Among them, the transgressive succession is mainly composed of the Jiapila and Bolila Formations, while the regressive succession is mianly composed of the Bagong Formation. (3) The sandstone samples from the Jiapila and Bagong Formations are ultra-low porosity and ultra-low permeability reservoir with secondary pores primarily. The mudstone samples of the Bagong Formation from the Jiangai Darina section are poor source rocks and non source rocks, while become better to north (Woruoshan section). We inferred that the depression between Jiangai Darina and Woruoshan may develop well source rocks and have a good exploration prospect based on the latest tectono-lithofacies paleogeographic data, but it still need to be confirmed. [Conclusion] These results would provide a valuable reference for the researches of Late Triassic sedimentary-tectonic evolution and oil and gas resource evaluation in Qiangtang Basin.
Abstract:
[Objective] Manganese (Mn), as a typical redox-sensitive metal element, shows a strong correlation between its enrichment in sediments and the redox conditions of the bottom water in basin. The western Hunan region hosts extensive Neoproterozoic marine sedimentary manganese deposits. A detailed study of the sedimentary redox conditions of these manganese deposits aids in elucidating their metallogenic mechanisms, constraining the marine manganese cycling during the mineralization period, and providing theoretical support for regional mineralization potential assessments. [Methods] This study involved mineralogical, geochemical, and inorganic carbon isotope analyses of 16 manganese ore samples of varying grades from the Datangpo Formation of the the Nanhua System from the Minle area in western Hunan. [Results] Mineralogical and carbon isotope analyses reveal that high-grade (MnO>20%) and medium-grade (1020 μm) subhedral platy rhodochrosite, with relative enrichment in heavier carbon isotope (δ13C=-7.4‰~-5.3‰, n=6). Pyrite morphology and element geochemical proxies (Mo, V, Ni concentrations and Ni/Co, V/Cr ratios) indicate that high-grade manganese ore layers were deposited in an oxic condition, medium-grade manganese ore layers in a suboxic condition, and low-grade manganese ore layers in an anoxic condition. Additionally, high-grade manganese ores exhibit geochemical characteristics indicative of hydrothermal deposition, such as high Eu* values and high Fe/Ti ratios. [Conclusions] These findings suggest that rhodochrosite in medium- to high-grade manganese ores formed through the reaction of manganese oxides with organic matter during diagenesis, while the rhodochrosite in low-grade manganese ores likely precipitated from Mn2+ and CO32- under high alkalinity and anoxic conditions in the Minle area of western Hunan. The submarine gas-hydrothermal activity in the deep-water basin of northeastern Guizhou likely supplied Mn2? for manganese deposit in western Hunan, while the oxidation of bottom water in the basin was the key controlling factor for manganese enrichment and mineralization in the region.
[Objective] Manganese (Mn), as a typical redox-sensitive metal element, shows a strong correlation between its enrichment in sediments and the redox conditions of the bottom water in basin. The western Hunan region hosts extensive Neoproterozoic marine sedimentary manganese deposits. A detailed study of the sedimentary redox conditions of these manganese deposits aids in elucidating their metallogenic mechanisms, constraining the marine manganese cycling during the mineralization period, and providing theoretical support for regional mineralization potential assessments. [Methods] This study involved mineralogical, geochemical, and inorganic carbon isotope analyses of 16 manganese ore samples of varying grades from the Datangpo Formation of the the Nanhua System from the Minle area in western Hunan. [Results] Mineralogical and carbon isotope analyses reveal that high-grade (MnO>20%) and medium-grade (10
Abstract:
【Objective】The trace element records of modern and ancient dunes in the southern part of the Mu Us Desert provide environmental information on their weathering, transportation and deposition processes. The aim of this study is to gain a deeper understanding of the sediment sources and climate environment in this area.【Methods】 Samples of modern and ancient dunes in the southern Mu Us Desert were collected, and the content characteristics and correlations of 14 trace elements including phosphorus (P), lead (Pb), and rubidium (Rb) were analyzed to explore the differences in trace element contents and spatial distribution characteristics among different types of dunes.【Results】 (1) The trace elements in modern and ancient dunes are mainly barium (Ba), strontium (Sr), and phosphorus (P), while the contents of arsenic (As), niobium (Nb), and copper (Cu) are relatively low.Their distribution patterns show certain regional characteristics. (2) The trace element contents in fixed dunes are significantly higher than those in mobile dunes, mainly due to the nature of the dunes and vegetation coverage; while the trace element contents in ancient dunes are higher than those in modern dunes, mainly influenced by sedimentary history, climate change, and special geomorphic positions. (3) The ratios of Sr/Cu, Rb/Sr, and Sr/Ba in modern and ancient dunes are comparable, indicating that they were formed in similar sedimentary environments.【Conclusion】 There are certain similarities and differences in the trace element contents of modern and ancient dunes and different types of dunes. The changes in trace element contents in ancient dunes can provide clues to the sources of modern dunes to a certain extent. The ratios of trace elements in modern and ancient dunes have certain implications for climate and environmental conditions.
【Objective】The trace element records of modern and ancient dunes in the southern part of the Mu Us Desert provide environmental information on their weathering, transportation and deposition processes. The aim of this study is to gain a deeper understanding of the sediment sources and climate environment in this area.【Methods】 Samples of modern and ancient dunes in the southern Mu Us Desert were collected, and the content characteristics and correlations of 14 trace elements including phosphorus (P), lead (Pb), and rubidium (Rb) were analyzed to explore the differences in trace element contents and spatial distribution characteristics among different types of dunes.【Results】 (1) The trace elements in modern and ancient dunes are mainly barium (Ba), strontium (Sr), and phosphorus (P), while the contents of arsenic (As), niobium (Nb), and copper (Cu) are relatively low.Their distribution patterns show certain regional characteristics. (2) The trace element contents in fixed dunes are significantly higher than those in mobile dunes, mainly due to the nature of the dunes and vegetation coverage; while the trace element contents in ancient dunes are higher than those in modern dunes, mainly influenced by sedimentary history, climate change, and special geomorphic positions. (3) The ratios of Sr/Cu, Rb/Sr, and Sr/Ba in modern and ancient dunes are comparable, indicating that they were formed in similar sedimentary environments.【Conclusion】 There are certain similarities and differences in the trace element contents of modern and ancient dunes and different types of dunes. The changes in trace element contents in ancient dunes can provide clues to the sources of modern dunes to a certain extent. The ratios of trace elements in modern and ancient dunes have certain implications for climate and environmental conditions.
Abstract:
[Objective] The beach facies dolomite reservoir of the Middle Permian Qixia Formation in the central Sichuan Basin exhibits significant potential for oil and gas exploration, but the systematic study on diagenetic sequence and pore evolution is relatively weak. [Methods] The petrological characteristics and pore genesis of the Qixia Formation were investigated through core observation, thin section analysis, cathodoluminescence examination, and image recognition techniques. This study aims to delineate diagenetic variations and pore evolution among different lithologies. [Results] In the Gaoshiti area, four types of rocks are identified within the Qixia Formation: micrite limestones, micrite grain limestones, sparry grain limestone, and residual grain dolostone. Four types of Reservoir space are observed: intergranular dissolved pores, intragranular dissolved pores, fractures and vugs. Each rock type has experienced distinct diagenesis: type of dissolution and its intensity vary across different lithologies. The two kinds of granular limestone are mainly dissolved by meteoric water, and the residual granular dolomite is more strongly dissolved by meteoric water, and on this basis, dolomitization and burial period dissolution occur. Recrystallization is more pronounced in residual grain dolomite whereas compaction and pressure dissolution is more evident in micrite grain limestone. The key diagenesis and stages influencing pore development vary among different types of rock: the pores of the two types of granular limestone are mainly formed by quasi-syngenetic dissolution, and then partially destroyed by compaction and cementation during the burial stage. The dissolution and dolomitization in the para-syngenetic stage are the key to the formation and preservation of the pores of the residual granular dolomites, while the dissolution and tectonic fracture in the burial stage are beneficial supplement, and the cementation in the shallow burial stage destroys the pores. [Conclusion] The difference of diagenesis caused the difference of pore evolution and formed four lithologies with decreasing pore development degree: Residual grain dolostone (plane porosity: 2.10 %), sparry grain limestone (plane porosity: 1.24 %), micrite grain limestone (plane porosity: 0.41 %), and micrite limestone (pyknotic).
[Objective] The beach facies dolomite reservoir of the Middle Permian Qixia Formation in the central Sichuan Basin exhibits significant potential for oil and gas exploration, but the systematic study on diagenetic sequence and pore evolution is relatively weak. [Methods] The petrological characteristics and pore genesis of the Qixia Formation were investigated through core observation, thin section analysis, cathodoluminescence examination, and image recognition techniques. This study aims to delineate diagenetic variations and pore evolution among different lithologies. [Results] In the Gaoshiti area, four types of rocks are identified within the Qixia Formation: micrite limestones, micrite grain limestones, sparry grain limestone, and residual grain dolostone. Four types of Reservoir space are observed: intergranular dissolved pores, intragranular dissolved pores, fractures and vugs. Each rock type has experienced distinct diagenesis: type of dissolution and its intensity vary across different lithologies. The two kinds of granular limestone are mainly dissolved by meteoric water, and the residual granular dolomite is more strongly dissolved by meteoric water, and on this basis, dolomitization and burial period dissolution occur. Recrystallization is more pronounced in residual grain dolomite whereas compaction and pressure dissolution is more evident in micrite grain limestone. The key diagenesis and stages influencing pore development vary among different types of rock: the pores of the two types of granular limestone are mainly formed by quasi-syngenetic dissolution, and then partially destroyed by compaction and cementation during the burial stage. The dissolution and dolomitization in the para-syngenetic stage are the key to the formation and preservation of the pores of the residual granular dolomites, while the dissolution and tectonic fracture in the burial stage are beneficial supplement, and the cementation in the shallow burial stage destroys the pores. [Conclusion] The difference of diagenesis caused the difference of pore evolution and formed four lithologies with decreasing pore development degree: Residual grain dolostone (plane porosity: 2.10 %), sparry grain limestone (plane porosity: 1.24 %), micrite grain limestone (plane porosity: 0.41 %), and micrite limestone (pyknotic).
Abstract:
The study of fine-grained sediment transport mechanisms is an important part of the "source-to-sink" system theory of fine-grained sediments, which is significant for restoring sedimentary environments, understanding the distribution of fine-grained sediments, and predicting unconventional oil and gas resources. Due to the fine granularity of fine-grained sediments, which makes them difficult to observe, and the rich variety of transport mechanisms, each corresponding to different sedimentary structures, there is currently a lack of summary on the characteristics of fine-grained sediment transport mechanisms. This paper synthesizes current research findings and systematically organizes the transport mechanisms and characteristics of fine-grained sediments, dividing them into three major categories: physical transport, chemical transport, and biological transport. Physical transport includes river flow, wind, bottom flow, plume flow and six types of gravity flow transport, triggered by wind, tides, earthquakes, floods, storms, and volcanic eruptions; dissolved substances such as clay minerals, dissolved organic carbon, carbonate minerals, and iron minerals, which are transported in colloidal solutions or true solutions, are influenced by environmental factors such as pH value, Eh value, temperature, pressure, ion concentration, or charge, and can be transported chemically; vertical upward transport, transport near the sediment-water interface, and comprehensive transport by multiple types of organisms are the three forms of biological transport of fine-grained sediments. The purpose of this paper is to clarify the transportation methods of fine-grained sediments, enhance the understanding of the transportation mechanisms of fine-grained sediments, and thus promote the development of fine-grained sedimentology theory. It provides a solid theoretical foundation and scientific basis for clarifying the distribution characteristics of fine-grained sedimentary strata and predicting the distribution of unconventional oil and gas resources.
The study of fine-grained sediment transport mechanisms is an important part of the "source-to-sink" system theory of fine-grained sediments, which is significant for restoring sedimentary environments, understanding the distribution of fine-grained sediments, and predicting unconventional oil and gas resources. Due to the fine granularity of fine-grained sediments, which makes them difficult to observe, and the rich variety of transport mechanisms, each corresponding to different sedimentary structures, there is currently a lack of summary on the characteristics of fine-grained sediment transport mechanisms. This paper synthesizes current research findings and systematically organizes the transport mechanisms and characteristics of fine-grained sediments, dividing them into three major categories: physical transport, chemical transport, and biological transport. Physical transport includes river flow, wind, bottom flow, plume flow and six types of gravity flow transport, triggered by wind, tides, earthquakes, floods, storms, and volcanic eruptions; dissolved substances such as clay minerals, dissolved organic carbon, carbonate minerals, and iron minerals, which are transported in colloidal solutions or true solutions, are influenced by environmental factors such as pH value, Eh value, temperature, pressure, ion concentration, or charge, and can be transported chemically; vertical upward transport, transport near the sediment-water interface, and comprehensive transport by multiple types of organisms are the three forms of biological transport of fine-grained sediments. The purpose of this paper is to clarify the transportation methods of fine-grained sediments, enhance the understanding of the transportation mechanisms of fine-grained sediments, and thus promote the development of fine-grained sedimentology theory. It provides a solid theoretical foundation and scientific basis for clarifying the distribution characteristics of fine-grained sedimentary strata and predicting the distribution of unconventional oil and gas resources.
Abstract:
Tidal forces have an important influence on the form and scale of Marine shelf deltas and the development and evolution of branch channels. The quantitative control mechanism of different amplitude tidal ranges on the dam body and branch channels of continental shelf deltas is a hot scientific issue. In this paper, a single factor control method is used to analyze the evolution of the key geologic bodies in the continental shelf delta under different tidal ranges by using Delft 3D hydrodynamic simulation software to set up four control groups: no, small, medium and spring difference. The experimental results show that the downcut depth and width of the branch channel decrease with the increase of the flow distance when there is no tidal effect. When tidal action is added, the number of distributary channels decreases with the increase of tidal range, but the downcut degree and width of distributary channels increase. The width-to-depth ratio of the branch channel ranges from 2 to 10 when there is no tidal action, and decreases to 0 when there is low tidal range. Under the influence of middle tidal range and spring tidal range, the width-to-depth ratio of the branch channel corresponds to 0 to 3 and 2 to 4 respectively. The results show that tidal action is beneficial to increase the broad-to-thickness ratio of sand body, and the delta morphology changes more stable with the increase of tidal range. The number of branch channels in the delta under the influence of tides decreases significantly, which is mainly due to the periodic influx and retreat of tides in the lateral direction, which promotes the formation of lateral channels and tidal channels. Under the influence of middle-spring difference, the lateral migration distance of the branch channel is shorter, the branch channel is more stable, and the dam body is more isolated from each other, which provides an important reference for reservoir configuration analysis of similar underground sediments.
Tidal forces have an important influence on the form and scale of Marine shelf deltas and the development and evolution of branch channels. The quantitative control mechanism of different amplitude tidal ranges on the dam body and branch channels of continental shelf deltas is a hot scientific issue. In this paper, a single factor control method is used to analyze the evolution of the key geologic bodies in the continental shelf delta under different tidal ranges by using Delft 3D hydrodynamic simulation software to set up four control groups: no, small, medium and spring difference. The experimental results show that the downcut depth and width of the branch channel decrease with the increase of the flow distance when there is no tidal effect. When tidal action is added, the number of distributary channels decreases with the increase of tidal range, but the downcut degree and width of distributary channels increase. The width-to-depth ratio of the branch channel ranges from 2 to 10 when there is no tidal action, and decreases to 0 when there is low tidal range. Under the influence of middle tidal range and spring tidal range, the width-to-depth ratio of the branch channel corresponds to 0 to 3 and 2 to 4 respectively. The results show that tidal action is beneficial to increase the broad-to-thickness ratio of sand body, and the delta morphology changes more stable with the increase of tidal range. The number of branch channels in the delta under the influence of tides decreases significantly, which is mainly due to the periodic influx and retreat of tides in the lateral direction, which promotes the formation of lateral channels and tidal channels. Under the influence of middle-spring difference, the lateral migration distance of the branch channel is shorter, the branch channel is more stable, and the dam body is more isolated from each other, which provides an important reference for reservoir configuration analysis of similar underground sediments.
Abstract:
[Significance] Since the beginning of the Industrial Revolution, human activities have resulted in the sustained release of greenhouse gases, including carbon dioxide (CO2) into the atmosphere. This has been primarily driven by the combustion of fossil fuels, which has resulted in profound climatic disturbances, environmental transformations, and widespread biological crises. Similarly, the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) represents a period of massive carbon release into the atmosphere, during which carbon emissions occurred at a rate strikingly comparable to current anthropogenic carbon emissions. It is of paramount importance to gain a comprehensive understanding of the processes and mechanisms that regulated carbon release during the PETM. Such knowledge can provide valuable insights into the impact of these emissions on Earth's habitability. Furthermore, these findings have significant implications for our attempts to gain an understanding of present-day and future climate change. It is consequently of the highest scientific importance to study this ancient climatic event, as it offers a natural experiment for evaluating the potential consequences of contemporary carbon emissions on global climate dynamics and ecological stability. [Progress] The trigger of the PETM has been the subject of considerable debate among scholars in the past few decades. Despite extensive research, the exact mechanism that instigated the massive carbon release during the PETM remains unresolved. Nevertheless, the findings of recent studies have indicated a temporal correlation between magmatism in the North Atlantic Large Igneous Province (NAIP) and the PETM. This evidence suggests that volcanic activity in NAIP was likely to be have been the trigger of the climatic perturbation. While this hypothesis adds to our insights into the triggering mechanisms of PETM events, our understanding of the exact cause-and-effect relationship between volcanic activity and climate fluctuations during this transition remains incomplete. A significant challenge in fully establishing this relationship is the difficulty of accurately tracing volcanic activity in the sedimentary record during this period. This is due to the complex nature of volcanic products and their subsequent alteration over millions of years, which makes it challenging to identify and distinguish between different volcanic events. [Conclusions and Prospects] During the past decade, mercury (Hg) concentrations and their isotopic compositions in sediments has emerged as a promising tool for tracing volcanic activity throughout geological history. However, the current research focusing on the Hg record of the PETM is largely limited to near-shore areas proximal to the NAIP eruption sites. Few studies have explored the Hg concentrations in sediments from open-ocean regions situated at a considerable distance from the eruption centers, leaving a significant gap in our understanding of the broader extent of NAIP's influence. The spatial limitations of this study restrict our ability to fully assess the global impact of volcanic emissions on Earth's climate and ecosystems during the PETM. This paper provides a comprehensive review of the current state of research on the use of mercury deposition as a tracer of ancient volcanic activity during the PETM. It identifies existing research limitations and suggests key directions for future studies. It also reviews the possible relationship between the volcanic activity of the NAIP and the climatic events of the PETM, emphasizing the need for further interdisciplinary research to resolve outstanding issues and refine our understanding of this critical period in Earth's history.
[Significance] Since the beginning of the Industrial Revolution, human activities have resulted in the sustained release of greenhouse gases, including carbon dioxide (CO2) into the atmosphere. This has been primarily driven by the combustion of fossil fuels, which has resulted in profound climatic disturbances, environmental transformations, and widespread biological crises. Similarly, the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) represents a period of massive carbon release into the atmosphere, during which carbon emissions occurred at a rate strikingly comparable to current anthropogenic carbon emissions. It is of paramount importance to gain a comprehensive understanding of the processes and mechanisms that regulated carbon release during the PETM. Such knowledge can provide valuable insights into the impact of these emissions on Earth's habitability. Furthermore, these findings have significant implications for our attempts to gain an understanding of present-day and future climate change. It is consequently of the highest scientific importance to study this ancient climatic event, as it offers a natural experiment for evaluating the potential consequences of contemporary carbon emissions on global climate dynamics and ecological stability. [Progress] The trigger of the PETM has been the subject of considerable debate among scholars in the past few decades. Despite extensive research, the exact mechanism that instigated the massive carbon release during the PETM remains unresolved. Nevertheless, the findings of recent studies have indicated a temporal correlation between magmatism in the North Atlantic Large Igneous Province (NAIP) and the PETM. This evidence suggests that volcanic activity in NAIP was likely to be have been the trigger of the climatic perturbation. While this hypothesis adds to our insights into the triggering mechanisms of PETM events, our understanding of the exact cause-and-effect relationship between volcanic activity and climate fluctuations during this transition remains incomplete. A significant challenge in fully establishing this relationship is the difficulty of accurately tracing volcanic activity in the sedimentary record during this period. This is due to the complex nature of volcanic products and their subsequent alteration over millions of years, which makes it challenging to identify and distinguish between different volcanic events. [Conclusions and Prospects] During the past decade, mercury (Hg) concentrations and their isotopic compositions in sediments has emerged as a promising tool for tracing volcanic activity throughout geological history. However, the current research focusing on the Hg record of the PETM is largely limited to near-shore areas proximal to the NAIP eruption sites. Few studies have explored the Hg concentrations in sediments from open-ocean regions situated at a considerable distance from the eruption centers, leaving a significant gap in our understanding of the broader extent of NAIP's influence. The spatial limitations of this study restrict our ability to fully assess the global impact of volcanic emissions on Earth's climate and ecosystems during the PETM. This paper provides a comprehensive review of the current state of research on the use of mercury deposition as a tracer of ancient volcanic activity during the PETM. It identifies existing research limitations and suggests key directions for future studies. It also reviews the possible relationship between the volcanic activity of the NAIP and the climatic events of the PETM, emphasizing the need for further interdisciplinary research to resolve outstanding issues and refine our understanding of this critical period in Earth's history.
Abstract:
During the Chang 7 period of the Yanchang Formation, Late Triassic in Ordos Basin, a set of continuously traceable shale was deposited, and the shale is currently the main stratigraphic strata for unconventional oil exploration and development. The shale oil reservoir at Chang 73 sub-member has features of fast lateral changing fast and vertical stacking, which make problems in practice such as unclear reservoir distribution, high exploration difficulty, and low drilling rate, etc. In order to clarify the distribution pattern of laminated-type shale oil reservoirs, we propose a shale oil reservoir distribution pattern controlled by seismic reflection characteristics of progradations and sedimentary paleogeomorphology by using seismic, geological, and logging data deeply. Firstly, through the latest 3D seismic data, the stratigraphic dip flipping method is used to recover sedimentary paleogeomorphology. Then, we mark the seismic reflection of lacustrine mudstones and make seismic stratigraphic comparison and division, and propose a four stage progradational clinoforms and distribution patterns of shale oil reservoir based on the sedimentary paleogeomorphology. Finally, the deep-water gravity flow sedimentary process of the Chang 73 sub-member laminated shale oil reservoir is inferred from above conclusions, and the inspiration of this research for unconventional oil and gas exploration and development in the Ordos Basin is discussed.
During the Chang 7 period of the Yanchang Formation, Late Triassic in Ordos Basin, a set of continuously traceable shale was deposited, and the shale is currently the main stratigraphic strata for unconventional oil exploration and development. The shale oil reservoir at Chang 73 sub-member has features of fast lateral changing fast and vertical stacking, which make problems in practice such as unclear reservoir distribution, high exploration difficulty, and low drilling rate, etc. In order to clarify the distribution pattern of laminated-type shale oil reservoirs, we propose a shale oil reservoir distribution pattern controlled by seismic reflection characteristics of progradations and sedimentary paleogeomorphology by using seismic, geological, and logging data deeply. Firstly, through the latest 3D seismic data, the stratigraphic dip flipping method is used to recover sedimentary paleogeomorphology. Then, we mark the seismic reflection of lacustrine mudstones and make seismic stratigraphic comparison and division, and propose a four stage progradational clinoforms and distribution patterns of shale oil reservoir based on the sedimentary paleogeomorphology. Finally, the deep-water gravity flow sedimentary process of the Chang 73 sub-member laminated shale oil reservoir is inferred from above conclusions, and the inspiration of this research for unconventional oil and gas exploration and development in the Ordos Basin is discussed.
Abstract:
[Objective]Distributive fluvial system (DFS) are widely developed in modern and ancient sedimentary strata and are important hydrocarbon reservoirs. Multiple DFS interacting with each other and evolving axial rivers may be developed in narrow, shallow, narrow lacustrine basin with low accommodation. [Methods]Reproduced the deposition process through flume simulation experiments, and used a high-precision 3D scanner with a self-developed program to visual analysis the deposition area in three dimensions, to clarify the stage-by-stage evolution characteristics of the DFS. [Results and Discussions]1) with the expansion of the DFS scale, the water flow on the surface of the DFS gradually aggregates, and the initial flow pattern is sheet flow, then evolves into unrestricted flow, and finally restricted flow; 2) as the basin can accommodate less space, the axial water flow in the basin gradually aggregates into axial river, and the axial river has a destructive effect on the two sides of the DFS and constantly breaks, and finally forms a Large-scale fluvial deposition; 3) When multiple DFS are developed in a narrow shallow lacustrine basin, the sedimentary sands are mainly concentrated at the DFS near the source and downstream of the axial river, and the longer the basin development time, the larger the scale of fluvial deposition. [Conclusions]This paper describes the developmental processes and sand body spreading patterns of multiple DFS and axial rivers developed in a narrow, shallow lacustrine basin with low accommodation and sufficient supply of material sources at the basin scale, which provides theoretical support for oil and gas exploration and the study of distributive fluvial system.
[Objective]Distributive fluvial system (DFS) are widely developed in modern and ancient sedimentary strata and are important hydrocarbon reservoirs. Multiple DFS interacting with each other and evolving axial rivers may be developed in narrow, shallow, narrow lacustrine basin with low accommodation. [Methods]Reproduced the deposition process through flume simulation experiments, and used a high-precision 3D scanner with a self-developed program to visual analysis the deposition area in three dimensions, to clarify the stage-by-stage evolution characteristics of the DFS. [Results and Discussions]1) with the expansion of the DFS scale, the water flow on the surface of the DFS gradually aggregates, and the initial flow pattern is sheet flow, then evolves into unrestricted flow, and finally restricted flow; 2) as the basin can accommodate less space, the axial water flow in the basin gradually aggregates into axial river, and the axial river has a destructive effect on the two sides of the DFS and constantly breaks, and finally forms a Large-scale fluvial deposition; 3) When multiple DFS are developed in a narrow shallow lacustrine basin, the sedimentary sands are mainly concentrated at the DFS near the source and downstream of the axial river, and the longer the basin development time, the larger the scale of fluvial deposition. [Conclusions]This paper describes the developmental processes and sand body spreading patterns of multiple DFS and axial rivers developed in a narrow, shallow lacustrine basin with low accommodation and sufficient supply of material sources at the basin scale, which provides theoretical support for oil and gas exploration and the study of distributive fluvial system.
Abstract:
Abstract: [ Objective ] The Upper Paleozoic Yanghugou Formation to Taiyuan Formation in the northwestern margin of the Ordos Basin has a good prospect for oil and gas exploration. The strata are completely developed and continuous, with large thickness changes and various types of sedimentary facies. Defining the distribution characteristics of sand bodies and clarifying the law of sedimentary evolution directly affect the selection of preferred exploration zones for oil and gas. [ Method ] This paper takes the Yanghugou Formation to Taiyuan Formation in the northwestern margin of Ordos Basin as the target horizon. On the basis of previous studies, through typical field profile measurement, drilling core observation, paleocurrent direction analysis, logging data and test data analysis, the sedimentary environment and sedimentary facies type characteristics, sedimentary evolution and sedimentary model of the study area are studied.[ Result and conclusion ] The research shows that there are 19 lithofacies types and two sedimentary systems in the study area, including 4 sedimentary facies types, and 13 sedimentary microfacies are further divided. The Yanghugou Formation-Taiyuan Formation in the study area is mainly supplied by the two provenance systems of the Alxa ancient land in the northwest of the basin and the Yinshan ancient land in the northeast. The Dickinson triangle plot reveals that the tectonic background of the provenance area is dominated by the recycled orogenic belt. The characteristics of heavy mineral assemblages are clear. The northwestern margin of the basin has obvious affinity with the Alashan Group ( Ar3-Pt1 ), the Archean Jining Group ( Ar3 ), and the Wulashan Group ( Ar1-2 ). The ZTR index shows that the unstable minerals gradually decrease from north to south ; the analysis of paleocurrent direction also reflects the material sources from northwest to southeast and from northeast to southwest.On the basis of the above provenance analysis, paleo-sedimentary environment evolution and sedimentary facies type characteristics, it is clear that the main body of Yanghugou Formation-Taiyuan Formation in the study area is the coexistence stage of sea and land. During the sedimentary period of Yanghugou Formation, under the background of the revival of Helan aulacogen and the backlog of north-south tectonics, the sea water enters rapidly. The whole study area is controlled by the delta-clastic coastal sedimentary system. The northern source supply is sufficient, resulting in the development of tidal-controlled delta deposits in the north. Affected by tides and waves, tidal flat-barrier island-Desalination of lagoons-shelf sedimentary microfacies are developed in the south. During the deposition period of the Taiyuan Formation, the crust continued to sink and seawater invaded. During this period, the basin became the most widely distributed period of the sea area. The sedimentary environment was basically similar to that of the Yanghugou Formation. The overall performance was the coexistence of tidal-controlled delta, tidal flat, Desalination of lagoons-barrier island sedimentary environment, and the erosion range in the northern region was relatively reduced, the source supply continued to increase, and the tidal-controlled delta range extended wider to the south.
Abstract: [ Objective ] The Upper Paleozoic Yanghugou Formation to Taiyuan Formation in the northwestern margin of the Ordos Basin has a good prospect for oil and gas exploration. The strata are completely developed and continuous, with large thickness changes and various types of sedimentary facies. Defining the distribution characteristics of sand bodies and clarifying the law of sedimentary evolution directly affect the selection of preferred exploration zones for oil and gas. [ Method ] This paper takes the Yanghugou Formation to Taiyuan Formation in the northwestern margin of Ordos Basin as the target horizon. On the basis of previous studies, through typical field profile measurement, drilling core observation, paleocurrent direction analysis, logging data and test data analysis, the sedimentary environment and sedimentary facies type characteristics, sedimentary evolution and sedimentary model of the study area are studied.[ Result and conclusion ] The research shows that there are 19 lithofacies types and two sedimentary systems in the study area, including 4 sedimentary facies types, and 13 sedimentary microfacies are further divided. The Yanghugou Formation-Taiyuan Formation in the study area is mainly supplied by the two provenance systems of the Alxa ancient land in the northwest of the basin and the Yinshan ancient land in the northeast. The Dickinson triangle plot reveals that the tectonic background of the provenance area is dominated by the recycled orogenic belt. The characteristics of heavy mineral assemblages are clear. The northwestern margin of the basin has obvious affinity with the Alashan Group ( Ar3-Pt1 ), the Archean Jining Group ( Ar3 ), and the Wulashan Group ( Ar1-2 ). The ZTR index shows that the unstable minerals gradually decrease from north to south ; the analysis of paleocurrent direction also reflects the material sources from northwest to southeast and from northeast to southwest.On the basis of the above provenance analysis, paleo-sedimentary environment evolution and sedimentary facies type characteristics, it is clear that the main body of Yanghugou Formation-Taiyuan Formation in the study area is the coexistence stage of sea and land. During the sedimentary period of Yanghugou Formation, under the background of the revival of Helan aulacogen and the backlog of north-south tectonics, the sea water enters rapidly. The whole study area is controlled by the delta-clastic coastal sedimentary system. The northern source supply is sufficient, resulting in the development of tidal-controlled delta deposits in the north. Affected by tides and waves, tidal flat-barrier island-Desalination of lagoons-shelf sedimentary microfacies are developed in the south. During the deposition period of the Taiyuan Formation, the crust continued to sink and seawater invaded. During this period, the basin became the most widely distributed period of the sea area. The sedimentary environment was basically similar to that of the Yanghugou Formation. The overall performance was the coexistence of tidal-controlled delta, tidal flat, Desalination of lagoons-barrier island sedimentary environment, and the erosion range in the northern region was relatively reduced, the source supply continued to increase, and the tidal-controlled delta range extended wider to the south.
Abstract:
Abstract:[Significance] The study of the provenance of fine-grained sedimentary rocks is a crucial first step in the "source-to-sink" system theory of fine-grained sedimentary rocks. It is of great importance for restoring the ancient environment, understanding the formation mechanism of fine-grained sedimentary rocks, and predicting the distribution of unconventional oil and gas resources. Fine-grained sedimentary rocks are characterized by small particle size, complex composition, and difficulty in observation and research, with different material components corresponding to a variety of sources and origins. A review of the existing research results at home and abroad shows that there is currently a lack of systematic organization and summary of research outcomes regarding the provenance and origins of fine-grained sedimentary materials.[Progress] This paper synthesizes current research findings and categorizes the sources of fine-grained sedimentary rocks into three major types: terrigenous, endogenic, and volcanic-hydrothermal. It provides an in-depth summary and conclusion on the common sources and origins of fine-grained sediments, pointing out: (1) Clay minerals are of terrigenous origin, authigenic transformation from other minerals, transformation between clay minerals, hydrolysis of submarine volcanic materials, and biogenic mediation by extracellular polymeric substances; (2) Quartz mainly originates from the weathering of terrigenous materials, intra-basin biological activity, devitrification of volcanic ash materials, and authigenic formation; (3) Feldspar originates from the weathering of terrigenous detritus, input from volcanic-hydrothermal activity, and recent studies have also indicated that feldspar can be formed through microbial chemical processes; (4) Carbonate minerals are primarily endogenic, formed through chemical, bio-chemical, biological, and transport-deposition processes within the basin, and the input of terrigenous and volcanic-hydrothermal materials not only directly provides carbonate minerals for fine-grained sedimentary rocks but also promotes the formation of carbonate minerals within the basin; (5) Pyrite is mainly formed by the two ore-forming elements, iron and sulfur, through dissimilatory iron reduction and iron shuttling mechanisms, microbial reduction, and thermogenic reduction of sulfate within the basin; (6) Organic matter can be divided into terrigenous vitrinite, inertinite, and some liptinite, as well as endogenic liptinite, zooclastic organic debris, and secondary organic matter. Future research on the provenance and origins of fine-grained sedimentary rocks will develop in a multidisciplinary and high-precision direction, and there is still an urgent need for a systematic approach suitable for the study of the provenance of fine-grained sedimentary rocks.[Conclusion] This paper aims to clarify the provenance and origins of fine-grained sedimentary rocks, enhance the understanding of the sources and formation mechanisms of fine-grained sediments, and thus promote the development of fine-grained sedimentology theory. It provides a solid theoretical foundation and scientific basis for identifying the distribution characteristics of fine-grained sedimentary strata and predicting the distribution of unconventional oil and gas resources.
Abstract:[Significance] The study of the provenance of fine-grained sedimentary rocks is a crucial first step in the "source-to-sink" system theory of fine-grained sedimentary rocks. It is of great importance for restoring the ancient environment, understanding the formation mechanism of fine-grained sedimentary rocks, and predicting the distribution of unconventional oil and gas resources. Fine-grained sedimentary rocks are characterized by small particle size, complex composition, and difficulty in observation and research, with different material components corresponding to a variety of sources and origins. A review of the existing research results at home and abroad shows that there is currently a lack of systematic organization and summary of research outcomes regarding the provenance and origins of fine-grained sedimentary materials.[Progress] This paper synthesizes current research findings and categorizes the sources of fine-grained sedimentary rocks into three major types: terrigenous, endogenic, and volcanic-hydrothermal. It provides an in-depth summary and conclusion on the common sources and origins of fine-grained sediments, pointing out: (1) Clay minerals are of terrigenous origin, authigenic transformation from other minerals, transformation between clay minerals, hydrolysis of submarine volcanic materials, and biogenic mediation by extracellular polymeric substances; (2) Quartz mainly originates from the weathering of terrigenous materials, intra-basin biological activity, devitrification of volcanic ash materials, and authigenic formation; (3) Feldspar originates from the weathering of terrigenous detritus, input from volcanic-hydrothermal activity, and recent studies have also indicated that feldspar can be formed through microbial chemical processes; (4) Carbonate minerals are primarily endogenic, formed through chemical, bio-chemical, biological, and transport-deposition processes within the basin, and the input of terrigenous and volcanic-hydrothermal materials not only directly provides carbonate minerals for fine-grained sedimentary rocks but also promotes the formation of carbonate minerals within the basin; (5) Pyrite is mainly formed by the two ore-forming elements, iron and sulfur, through dissimilatory iron reduction and iron shuttling mechanisms, microbial reduction, and thermogenic reduction of sulfate within the basin; (6) Organic matter can be divided into terrigenous vitrinite, inertinite, and some liptinite, as well as endogenic liptinite, zooclastic organic debris, and secondary organic matter. Future research on the provenance and origins of fine-grained sedimentary rocks will develop in a multidisciplinary and high-precision direction, and there is still an urgent need for a systematic approach suitable for the study of the provenance of fine-grained sedimentary rocks.[Conclusion] This paper aims to clarify the provenance and origins of fine-grained sedimentary rocks, enhance the understanding of the sources and formation mechanisms of fine-grained sediments, and thus promote the development of fine-grained sedimentology theory. It provides a solid theoretical foundation and scientific basis for identifying the distribution characteristics of fine-grained sedimentary strata and predicting the distribution of unconventional oil and gas resources.
Abstract:
[Significance] Peat bogs play an important role in the global carbon cycle as a depositional carrier of paleo-wildfire events and paleoclimate information. By systematically sorting out wildfires types in peat bogs and clarifying the academic terminology related to wildfire products such as charcoal, the carbon source and sink effects of wildfires in peat bogs will be discussed in this study, which will be useful for the study of the carbon cycle in deep time. [Progress] Wildfire product charcoal, approximately equivalent to the inertinite in coal, is a relatively stable carbon store of plant incomplete combustion residues, which can provide a record of wildfire activities in the geological history of millennia to billions of years. Changes in charcoal material composition (e.g., polysaccharides and lignin) and microstructure (e.g., cell wall homogenization) can reflect the temperature range of paleo-wildfires. Wildfire types can be recovered and atmospheric oxygen content can be constrained using inertinite reflectance and inertinite content. The impacts of wildfires on the global carbon cycle include both short-term carbon source and long-term carbon sink effects. Wildfires lead to direct large carbon emissions and carbon release from deep peat burning. However, wildfire-driven persistent changes in soil microorganisms, aggregates, and organic matter can directly offset some of the carbon losses, and charcoal provides a stable carbon store. [Conclusions and Prospects] Based on the carbon cycle model of peatland under normal burial conditions, the influence factors of wildfire, soil aggregates, fungi and bacteria were introduced to propose a post-fire peatland carbon cycle model. Using the inertinite wildfire genesis and greenhouse gas emission models, and taking the carbon emission and carbon storage of wildfires in early Cretaceous peat (coal-forming) bogs in Northeast China as an example, the results show that the long-term (million-year time scale) carbon sinks of forest vegetation growth and peatland are fully capable of neutralizing the short-term (year time scale) carbon source effect brought by wildfires. In the future, when evaluating the deep-time carbon cycle response to wildfires, it is necessary to take into account the length of the time period and wildfires intensity, and improve the understanding of climate change and environmental evolution caused by wildfire in order to promote the in-depth integration of deep-time and present-day climate change and carbon cycle research.
[Significance] Peat bogs play an important role in the global carbon cycle as a depositional carrier of paleo-wildfire events and paleoclimate information. By systematically sorting out wildfires types in peat bogs and clarifying the academic terminology related to wildfire products such as charcoal, the carbon source and sink effects of wildfires in peat bogs will be discussed in this study, which will be useful for the study of the carbon cycle in deep time. [Progress] Wildfire product charcoal, approximately equivalent to the inertinite in coal, is a relatively stable carbon store of plant incomplete combustion residues, which can provide a record of wildfire activities in the geological history of millennia to billions of years. Changes in charcoal material composition (e.g., polysaccharides and lignin) and microstructure (e.g., cell wall homogenization) can reflect the temperature range of paleo-wildfires. Wildfire types can be recovered and atmospheric oxygen content can be constrained using inertinite reflectance and inertinite content. The impacts of wildfires on the global carbon cycle include both short-term carbon source and long-term carbon sink effects. Wildfires lead to direct large carbon emissions and carbon release from deep peat burning. However, wildfire-driven persistent changes in soil microorganisms, aggregates, and organic matter can directly offset some of the carbon losses, and charcoal provides a stable carbon store. [Conclusions and Prospects] Based on the carbon cycle model of peatland under normal burial conditions, the influence factors of wildfire, soil aggregates, fungi and bacteria were introduced to propose a post-fire peatland carbon cycle model. Using the inertinite wildfire genesis and greenhouse gas emission models, and taking the carbon emission and carbon storage of wildfires in early Cretaceous peat (coal-forming) bogs in Northeast China as an example, the results show that the long-term (million-year time scale) carbon sinks of forest vegetation growth and peatland are fully capable of neutralizing the short-term (year time scale) carbon source effect brought by wildfires. In the future, when evaluating the deep-time carbon cycle response to wildfires, it is necessary to take into account the length of the time period and wildfires intensity, and improve the understanding of climate change and environmental evolution caused by wildfire in order to promote the in-depth integration of deep-time and present-day climate change and carbon cycle research.
Abstract:
Abstract (Objective) In marine strata of the Toarcian Oceanic Anoxic Event (T-OAE), the widespread siderites are believed to result from the low sulfate concentration and increased terrestrial iron supply. Similar large amount of siderites were also reported in paleolakes in the same period. However, the mechanism of lacustrine siderite and its connection with the T-OAE remain unexplored, which is crucial to better comprehend the lacustrine biogeochemical cycling in early Toarcian. (Method) Mineralogical and carbon isotope geochemical analyses were performed on the siderite samples from the lacustrine Anya section of the Ordos paleolake. By integrating major and trace element data, we investigated the sources of iron and carbon, as well as the sedimentary environment. This allowed us to explore the formation mechanism of siderites under the T-OAE climatic change. (Result) The coexistence of pyrites and siderites was observed under scanning electron microscopy. The values of inorganic carbon isotopes(δ13Ccarb) vary from ?11.25 to +16.32 ‰, and the range of organic carbon isotope(δ13Corg) values is from ?32.03 to +14.33 ‰. The rare earth elements (REEs) exhibited an enrichment of light REEs and the depletion of heavy REEs, with Eu anomalies ranging from 0.69 to 0.85. (Conclusion) The iron source of the Anya siderites is derived from terrestrial inputs. Carbon involved in siderite formation included HCO3- produced via the methanogenesis, as well as carbon released from organic matter decomposition and the methane aerobic oxidation, either bacterially in the suboxic zone, or archaeally below oxic-anoxic interface right after methane production. The pore fluids during siderite formation was suboxic to anoxic environment. During the T-OAE, intensified continental weathering and increased surface runoff input fluxed abundant iron ions into lake basins. The widespread anoxia, abundant organic matter content, and low sulfate concentrations in the lakes created favorable conditions for siderites, leading to the extensive siderite depositions. Future work is needed to further verify whether such T-OAE-related siderites is a regional influence or a worldwide phenomenon.
Abstract (Objective) In marine strata of the Toarcian Oceanic Anoxic Event (T-OAE), the widespread siderites are believed to result from the low sulfate concentration and increased terrestrial iron supply. Similar large amount of siderites were also reported in paleolakes in the same period. However, the mechanism of lacustrine siderite and its connection with the T-OAE remain unexplored, which is crucial to better comprehend the lacustrine biogeochemical cycling in early Toarcian. (Method) Mineralogical and carbon isotope geochemical analyses were performed on the siderite samples from the lacustrine Anya section of the Ordos paleolake. By integrating major and trace element data, we investigated the sources of iron and carbon, as well as the sedimentary environment. This allowed us to explore the formation mechanism of siderites under the T-OAE climatic change. (Result) The coexistence of pyrites and siderites was observed under scanning electron microscopy. The values of inorganic carbon isotopes(δ13Ccarb) vary from ?11.25 to +16.32 ‰, and the range of organic carbon isotope(δ13Corg) values is from ?32.03 to +14.33 ‰. The rare earth elements (REEs) exhibited an enrichment of light REEs and the depletion of heavy REEs, with Eu anomalies ranging from 0.69 to 0.85. (Conclusion) The iron source of the Anya siderites is derived from terrestrial inputs. Carbon involved in siderite formation included HCO3- produced via the methanogenesis, as well as carbon released from organic matter decomposition and the methane aerobic oxidation, either bacterially in the suboxic zone, or archaeally below oxic-anoxic interface right after methane production. The pore fluids during siderite formation was suboxic to anoxic environment. During the T-OAE, intensified continental weathering and increased surface runoff input fluxed abundant iron ions into lake basins. The widespread anoxia, abundant organic matter content, and low sulfate concentrations in the lakes created favorable conditions for siderites, leading to the extensive siderite depositions. Future work is needed to further verify whether such T-OAE-related siderites is a regional influence or a worldwide phenomenon.
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[Objective] To understand the distribution patterns of Cretaceous sand bodies in the eastern depression of the Doseo Basin, this study employs physical sedimentation simulation techniques. An experimental setup with a movable baseboard was designed to investigate the evolution mechanisms of the channel-lobe system in the study area and to develop an effective regional sedimentary model, providing theoretical support for future favorable zone predictions. [Methods] Building on previous research on lobe development and evolution and channel classification [17], this study introduces a new classification method for lobes. Lobes are categorized into four types: agglomerative, superimposed, erosional, and amalgamated. Additionally, to accurately describe the development features and evolution of each lobe type, the study further analyzes the internal structures of lobes and identifies various constituent units. [Results and Discussions] (1) A consistent overlapping relationship exists between channels and lobes, where the migration, evolution, or disappearance of channels leads to the formation of new lobes. (2) Within the channel-lobe system, three main evolution mechanisms are driven by hydrodynamic strength: erosion of existing lobes, formation of lobes dominated by sandy deposition, and formation of mud layers dominated by fine-grained deposition. (3) The characteristics of channels determine the type of lobe development, while lobe morphology is influenced by factors such as sedimentary slope, tectonic activity, base level, and sediment source conditions. (4) The connectivity of sand bodies is affected by the constituent units of lobes, their contact relationships, lobe properties, and the types of lobe complexes. Later channel evolution can improve sand body connectivity to some extent. (5) The eastern depression of the Doseo Basin exhibits two sedimentary models: deep-water and shallow-water delta systems. In the deep-water delta model, the channel evolution area is larger, and connectivity improvements are more pronounced. In contrast, the shallow-water delta model features larger lobe deposition areas and wider planar distribution of lobes. [Conclusion] The new lobe classification method and the channel-lobe system evolution mechanism are applicable to the study of sand body connectivity and sedimentary models in the study area, and they are expected to be widely used in future delta sedimentary simulation research.
[Objective] To understand the distribution patterns of Cretaceous sand bodies in the eastern depression of the Doseo Basin, this study employs physical sedimentation simulation techniques. An experimental setup with a movable baseboard was designed to investigate the evolution mechanisms of the channel-lobe system in the study area and to develop an effective regional sedimentary model, providing theoretical support for future favorable zone predictions. [Methods] Building on previous research on lobe development and evolution and channel classification [17], this study introduces a new classification method for lobes. Lobes are categorized into four types: agglomerative, superimposed, erosional, and amalgamated. Additionally, to accurately describe the development features and evolution of each lobe type, the study further analyzes the internal structures of lobes and identifies various constituent units. [Results and Discussions] (1) A consistent overlapping relationship exists between channels and lobes, where the migration, evolution, or disappearance of channels leads to the formation of new lobes. (2) Within the channel-lobe system, three main evolution mechanisms are driven by hydrodynamic strength: erosion of existing lobes, formation of lobes dominated by sandy deposition, and formation of mud layers dominated by fine-grained deposition. (3) The characteristics of channels determine the type of lobe development, while lobe morphology is influenced by factors such as sedimentary slope, tectonic activity, base level, and sediment source conditions. (4) The connectivity of sand bodies is affected by the constituent units of lobes, their contact relationships, lobe properties, and the types of lobe complexes. Later channel evolution can improve sand body connectivity to some extent. (5) The eastern depression of the Doseo Basin exhibits two sedimentary models: deep-water and shallow-water delta systems. In the deep-water delta model, the channel evolution area is larger, and connectivity improvements are more pronounced. In contrast, the shallow-water delta model features larger lobe deposition areas and wider planar distribution of lobes. [Conclusion] The new lobe classification method and the channel-lobe system evolution mechanism are applicable to the study of sand body connectivity and sedimentary models in the study area, and they are expected to be widely used in future delta sedimentary simulation research.
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Abstract: [Objective] In order to define the high-quality reservoir development model of Xu3 Member in the source rock stratum, which is the tight sandstone gas exploration in the Xu3 Member of Xujiahe Formation in Western Sichuan Depression to provide theoretical guidance.[Methods] The data of core, thin section, scanning electron microscope, fluid inclusion, situ stable carbon and oxygen isotopes, porosity and permeability are integrated, and based on the basic characteristics of Xu3 Member tight sandstone reservoirs in Western Sichuan Depression and the types of diagenesis, the heterogeneity of the reservoirs and the development model of high-quality reservoirs are further analyzed systematically. [Results and Discussions] It was found that mainly lithic quartz sandstone and litharenite sandstone were developed in Xu3 Member, and the reservoir space was mainly composed of intragranular dissolution pore and fracture, with porosity <7% and permeability <1mD. So the sandstone reservoirs could be divided into types of intragranular dissolution pore and fracture- intragranular dissolution pore. The diagenesis of the Xu3 Member sandstones included compaction, cementation and dissolution, and experienced early humic acid, middle organic acid and late hydrothermal fluids during the evolution process. In addition, two types of vertical sedimentary cycle of sandstone with sandstone and sandstone with mudstone had been identified in the Xu3 Member. [Conclusions] The results indicated that the tight sandstone was altered by the early humic acid and middle organic acid continuously via the intergranular pore throat and fracture and in favour of reservoir formation. However, the late hydrothermal fluid just acted in the late large scale fracture and had insignificant effect on the reservoir quality. In addition, the high-quality reservoir of the sandstone with sandstone vertical sedimentary cycle mainly develops in the lower part of the cycle which characterized by relatively coarse-grain, but the high-quality reservoir of the sandstone with mudstone vertical sedimentary cycle mainly develops in the lower part of the cycle with relatively coarse-grain, and the upper part of the cycle which adjacent to the mudstone.
Abstract: [Objective] In order to define the high-quality reservoir development model of Xu3 Member in the source rock stratum, which is the tight sandstone gas exploration in the Xu3 Member of Xujiahe Formation in Western Sichuan Depression to provide theoretical guidance.[Methods] The data of core, thin section, scanning electron microscope, fluid inclusion, situ stable carbon and oxygen isotopes, porosity and permeability are integrated, and based on the basic characteristics of Xu3 Member tight sandstone reservoirs in Western Sichuan Depression and the types of diagenesis, the heterogeneity of the reservoirs and the development model of high-quality reservoirs are further analyzed systematically. [Results and Discussions] It was found that mainly lithic quartz sandstone and litharenite sandstone were developed in Xu3 Member, and the reservoir space was mainly composed of intragranular dissolution pore and fracture, with porosity <7% and permeability <1mD. So the sandstone reservoirs could be divided into types of intragranular dissolution pore and fracture- intragranular dissolution pore. The diagenesis of the Xu3 Member sandstones included compaction, cementation and dissolution, and experienced early humic acid, middle organic acid and late hydrothermal fluids during the evolution process. In addition, two types of vertical sedimentary cycle of sandstone with sandstone and sandstone with mudstone had been identified in the Xu3 Member. [Conclusions] The results indicated that the tight sandstone was altered by the early humic acid and middle organic acid continuously via the intergranular pore throat and fracture and in favour of reservoir formation. However, the late hydrothermal fluid just acted in the late large scale fracture and had insignificant effect on the reservoir quality. In addition, the high-quality reservoir of the sandstone with sandstone vertical sedimentary cycle mainly develops in the lower part of the cycle which characterized by relatively coarse-grain, but the high-quality reservoir of the sandstone with mudstone vertical sedimentary cycle mainly develops in the lower part of the cycle with relatively coarse-grain, and the upper part of the cycle which adjacent to the mudstone.
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[Objective] The Danxia strata, a representative of Cretaceous continental red beds, offers key insights into red bed sedimentation and Cretaceous geological events through its climate signals. [Methods] This study examines fine-grained clastic rocks from the second and fourth members of the Changba Formation and the Jinshiyan Member of the Danxia Formation in the Upper Cretaceous Danxia Basin. Sedimentology and elemental geochemistry etc. were used to explore the sedimentary environment and paleoclimate significance during key Late Cretaceous stages (Cenomanian, Turonian, Campanian). [Results and Discussions] The results indicate that the fine-grained clastic rocks of these formations were deposited during a warm and humid climate phase, with suboxic to oxic water conditions. The water bodies were predominantly brackish, while localized high-salinity brackish and low oxygen environments (e.g., the fourth member of the Changba Formation) were associated with lake shrinkage and climatic aridification. Water depth variations exhibited trends of initial contraction followed by expansion, gradual contraction, and initial expansion followed by contraction, which align with the changes in sedimentary facies and environment. [Conclusions] The Upper Cretaceous terrestrial sedimentary records of the Danxia Basin illustrate the climatic evolution of intermontane basins, shaped by global climate patterns of the Late Cretaceous, as well as by significant influences from local topographic and geomorphic features.
[Objective] The Danxia strata, a representative of Cretaceous continental red beds, offers key insights into red bed sedimentation and Cretaceous geological events through its climate signals. [Methods] This study examines fine-grained clastic rocks from the second and fourth members of the Changba Formation and the Jinshiyan Member of the Danxia Formation in the Upper Cretaceous Danxia Basin. Sedimentology and elemental geochemistry etc. were used to explore the sedimentary environment and paleoclimate significance during key Late Cretaceous stages (Cenomanian, Turonian, Campanian). [Results and Discussions] The results indicate that the fine-grained clastic rocks of these formations were deposited during a warm and humid climate phase, with suboxic to oxic water conditions. The water bodies were predominantly brackish, while localized high-salinity brackish and low oxygen environments (e.g., the fourth member of the Changba Formation) were associated with lake shrinkage and climatic aridification. Water depth variations exhibited trends of initial contraction followed by expansion, gradual contraction, and initial expansion followed by contraction, which align with the changes in sedimentary facies and environment. [Conclusions] The Upper Cretaceous terrestrial sedimentary records of the Danxia Basin illustrate the climatic evolution of intermontane basins, shaped by global climate patterns of the Late Cretaceous, as well as by significant influences from local topographic and geomorphic features.
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[Objective] The Taiyuan Formation of Permian system in Ordos Basin has the characteristics of large thickness, wide distribution and rich types of oil and gas resources, showing great exploration potential. At present, the study of this formation is mainly concentrated in the eastern part of the basin, while the exploration and study of Taiyuan Formation in the western part of the basin need to be further discussed due to the complex and variable tectonic pattern and sedimentary evolution.[Methods] The detrital material source, tectonic setting and paleogeographic evolution of Taiyuan Formation in western Ordos Basin are systematically studied by means of outcrop observation, drilling sample collection, detrital zircon U-Pb dating and paleo-flow analysis. [Results] The sediments in the northeastern part of the study area (Group A) are mainly from the Yinshan orogenic belt under the collision-compressional tectonic background, with strong provenances. The delta plain, delta front, tidal sand ridge and tidal sand bar are successively developed in the middle of the basin. The sediments in the northwest (Group B) are derived from the Alxa block under the collisional compression and convergent orogenic tectonic background, and the delta plain, delta front and lagoon-tidal flat develop successively towards the middle of the basin. The sediments in the southern (Group D) area came from the North Qilian and North Qinling tectonic belts under the extension-subduction-collision tectonic environment of the Paleo-Tethyan Ocean. The central paleo-uplift of the Taiyuan Period was slow, the provenance-supply was weak, and the mainly developed barrier island-barrier tidal flat deposits. [Conclusions] The northern part of the study area is characterized by high uplift and strong provenance supply in the context of collision and convergence orogenic structures, and large tide-delta complex system, while the southern part is characterized by weak provenance supply in the context of tensile extension structures, and is dominated by tidal flat and lagoon. This study not only deepens the understanding of the sedimentary system and provenance supply mechanism in the western Ordos Basin, but also provides a new perspective and reference for the reconstruction of the tectono-sedimentary evolution process and paleogeographic pattern in the western Ordos Basin.
[Objective] The Taiyuan Formation of Permian system in Ordos Basin has the characteristics of large thickness, wide distribution and rich types of oil and gas resources, showing great exploration potential. At present, the study of this formation is mainly concentrated in the eastern part of the basin, while the exploration and study of Taiyuan Formation in the western part of the basin need to be further discussed due to the complex and variable tectonic pattern and sedimentary evolution.[Methods] The detrital material source, tectonic setting and paleogeographic evolution of Taiyuan Formation in western Ordos Basin are systematically studied by means of outcrop observation, drilling sample collection, detrital zircon U-Pb dating and paleo-flow analysis. [Results] The sediments in the northeastern part of the study area (Group A) are mainly from the Yinshan orogenic belt under the collision-compressional tectonic background, with strong provenances. The delta plain, delta front, tidal sand ridge and tidal sand bar are successively developed in the middle of the basin. The sediments in the northwest (Group B) are derived from the Alxa block under the collisional compression and convergent orogenic tectonic background, and the delta plain, delta front and lagoon-tidal flat develop successively towards the middle of the basin. The sediments in the southern (Group D) area came from the North Qilian and North Qinling tectonic belts under the extension-subduction-collision tectonic environment of the Paleo-Tethyan Ocean. The central paleo-uplift of the Taiyuan Period was slow, the provenance-supply was weak, and the mainly developed barrier island-barrier tidal flat deposits. [Conclusions] The northern part of the study area is characterized by high uplift and strong provenance supply in the context of collision and convergence orogenic structures, and large tide-delta complex system, while the southern part is characterized by weak provenance supply in the context of tensile extension structures, and is dominated by tidal flat and lagoon. This study not only deepens the understanding of the sedimentary system and provenance supply mechanism in the western Ordos Basin, but also provides a new perspective and reference for the reconstruction of the tectono-sedimentary evolution process and paleogeographic pattern in the western Ordos Basin.
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[Objective] A large number of trace fossils Thalassinoides developed in the Cambrian, Henan Province. By studying the morphology and distribution characteristics of different ichnospecies and analyzing their sedimentary environment controlling factors. [Methods] Based on lithology and ichnography, the morphology, size, disturbance depth and disturbance intensity of Thalassinoides in this area were combined with sedimentary environment parameters. [Results and Discussions] The dense network Thalassinoides suevicus features Y-shaped branches with enlarged intersections, develops in the intertidal zone where water is turbulent and oxygen is abundant.Sparse Thalassionides horizontalis Type 1, which is Y-shaped long branches with large diameters, is formed in the shallow water area in front of the oolitic beach with abundant oxygen and nutrients due to water turbulence. Thalassionides horizontalis Type 2, T-shaped short branches with smaller diamerters, occurs in deeper waters on the seaward side in front of the oolitic beach. The three-dimensional, boxed burrows of Thalassionides bacae, featuring vertical tubes, branches, and thick lining walls, developed in interbeach-confined seas and deep subtidal zones where oxygen and nutrients were deficient. [Conclusions] The variation in different ichnospecies and morphologies of Thalassinoides is controlled by factors such as water depth, water kinetic energy, nutrients and oxygen content of the sedimentary environment. The trace maker adopted different strategies to cope with the changing sedimentary environment.
[Objective] A large number of trace fossils Thalassinoides developed in the Cambrian, Henan Province. By studying the morphology and distribution characteristics of different ichnospecies and analyzing their sedimentary environment controlling factors. [Methods] Based on lithology and ichnography, the morphology, size, disturbance depth and disturbance intensity of Thalassinoides in this area were combined with sedimentary environment parameters. [Results and Discussions] The dense network Thalassinoides suevicus features Y-shaped branches with enlarged intersections, develops in the intertidal zone where water is turbulent and oxygen is abundant.Sparse Thalassionides horizontalis Type 1, which is Y-shaped long branches with large diameters, is formed in the shallow water area in front of the oolitic beach with abundant oxygen and nutrients due to water turbulence. Thalassionides horizontalis Type 2, T-shaped short branches with smaller diamerters, occurs in deeper waters on the seaward side in front of the oolitic beach. The three-dimensional, boxed burrows of Thalassionides bacae, featuring vertical tubes, branches, and thick lining walls, developed in interbeach-confined seas and deep subtidal zones where oxygen and nutrients were deficient. [Conclusions] The variation in different ichnospecies and morphologies of Thalassinoides is controlled by factors such as water depth, water kinetic energy, nutrients and oxygen content of the sedimentary environment. The trace maker adopted different strategies to cope with the changing sedimentary environment.
Abstract:
[Objective] The formation of sedimentary systems within straits is intricately linked to the unique topographical constraints that influence both facies characteristics and sediment distribution patterns. While current research on shallow-water strait sedimentation focuses primarily on narrower straits (less than 50 km wide) dominated by tidal processes, wider straits present more complex dynamics. This study investigates how the Bohai Strait, a shallow strait with a width of 106 km, utilizes its unique topography to influence the distribution of modern sedimentary systems. [Methods] An extensive dataset of surface sediment grain sizes, combined with four shallow seismic profiles, was used to characterize the sedimentary environment. Additionally, a Regional Ocean Modeling System (ROMS) simulation was employed for winter (December 2020 – February 2021) to better understand the hydrodynamic processes influencing sediment dynamics within and surrounding the Bohai Strait. [Results] Our results reveal significant differences in sediment dynamics between the northern and southern parts of the strait. The northern region exhibits a high-energy environment dominated by erosion, while the southern region displays a lower-energy environment conducive to deposition. Surface sediment types vary spatially, with coarser grains predominating in the north and narrow regions, while finer grains are observed on both sides (east-west) and in the south. A large-scale, sandy flood-tidal delta appears around the Laotieshan Channel in the north. The asymmetric tidal currents flowing in and out of the channel are likely responsible for this feature, with no evidence of an ebb-tidal delta formation. In contrast, the southern part of the strait exhibits two distinct sedimentary systems:(1)Shandong Mud Wedge: This system lies along the Shandong Peninsula's coast, shaped by the substantial sediment supply from the Yellow River and the influence of coastal currents. (2)Scour Troughs and Sandy Tidal Deltas: These smaller features are attributed to the protective effect of islands present in the southern strait, combined with the abundant supply of fine-grained sediments. [Conclusions] This study highlights the critical role of the strait's complex topography of the confinement in shaping regional sediment transport dynamics and the resulting distribution of sedimentary systems.
[Objective] The formation of sedimentary systems within straits is intricately linked to the unique topographical constraints that influence both facies characteristics and sediment distribution patterns. While current research on shallow-water strait sedimentation focuses primarily on narrower straits (less than 50 km wide) dominated by tidal processes, wider straits present more complex dynamics. This study investigates how the Bohai Strait, a shallow strait with a width of 106 km, utilizes its unique topography to influence the distribution of modern sedimentary systems. [Methods] An extensive dataset of surface sediment grain sizes, combined with four shallow seismic profiles, was used to characterize the sedimentary environment. Additionally, a Regional Ocean Modeling System (ROMS) simulation was employed for winter (December 2020 – February 2021) to better understand the hydrodynamic processes influencing sediment dynamics within and surrounding the Bohai Strait. [Results] Our results reveal significant differences in sediment dynamics between the northern and southern parts of the strait. The northern region exhibits a high-energy environment dominated by erosion, while the southern region displays a lower-energy environment conducive to deposition. Surface sediment types vary spatially, with coarser grains predominating in the north and narrow regions, while finer grains are observed on both sides (east-west) and in the south. A large-scale, sandy flood-tidal delta appears around the Laotieshan Channel in the north. The asymmetric tidal currents flowing in and out of the channel are likely responsible for this feature, with no evidence of an ebb-tidal delta formation. In contrast, the southern part of the strait exhibits two distinct sedimentary systems:(1)Shandong Mud Wedge: This system lies along the Shandong Peninsula's coast, shaped by the substantial sediment supply from the Yellow River and the influence of coastal currents. (2)Scour Troughs and Sandy Tidal Deltas: These smaller features are attributed to the protective effect of islands present in the southern strait, combined with the abundant supply of fine-grained sediments. [Conclusions] This study highlights the critical role of the strait's complex topography of the confinement in shaping regional sediment transport dynamics and the resulting distribution of sedimentary systems.
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Abstract: [Objective] The Ordovician Kukersite oil shales that composed almost exclusively of Gloeocapsomorpha prisca (G. prisca) alginite are an important set Paleozoic source rocks from Paleozoic around the planet, but they have only been sporadically detected and reported in the Tarim Basin in China. Therefore, rapid identification of G. prisca in source rocks is an important geochemical work. Kerogen can be used to trace the source rock quickly for its enrichment of the parent material of hydrocarbon generation. [Method] Thus the kerogen from Estonian oil shale was analyzed using sequential stepwise pyrolysis with 50 °C intervals from 310 °C to 610 °C to investigate its chemical constitutions. [Results and discussion] The results illustrated that the pyrolyzed hydrocarbons formed upon sequential stepwise pyrolysis are dominated by 5-n-alkyl-1,3-benzenediols probably reflect a major contribution of selectively preserved, highly resistant biomacromolecules from the outer cell walls of G. prisca. It is also characterized by high content of short-chain alkanes, but abnormal high carbon number (>nC29) n-alkane/enes appear at 560 ℃. Besides, the consistent formation of alkyl benzenes, alkyl thiophenes and alkyl ketones also appeared at the middle to high temperature points (460 ~ 560 ℃). All pyrolyzates have the characteristics of lower carbon number, alkyl side chains with a distinct distribution of weak odd-over-even carbon numbers. The extremely abundant and continuous generation of 5-n-alkyl-1,3-benzenediols and its homologues in the pyrolysis products can help to quickly identify whether the source rocks contained G. Prisca or not. In addition, the composition characteristics, product changes and product correlation of the pyrolyzates at different temperatures are helpful for the investigation of kerogen structure. The results of sequential stepwise pyrolysis suggested that the macromolecules of kerogen were formed mainly by polymerization of 5-n-alkyl-1,3-benzenediols in G. prisca. The units in polymer macromolecules including phenol rings, thiophene rings, and normal alkyl chains, are intermolecular connected by C-C and C-O bonds. [Conclusions] The distribution changes of different series of compounds obtained at different temperatures by sequential stepwise pyrolysis can be applied to other organic-rich oil shales, which may reveal the details of algal evolution and determine the various sources of organic matter of kerogen.
Abstract: [Objective] The Ordovician Kukersite oil shales that composed almost exclusively of Gloeocapsomorpha prisca (G. prisca) alginite are an important set Paleozoic source rocks from Paleozoic around the planet, but they have only been sporadically detected and reported in the Tarim Basin in China. Therefore, rapid identification of G. prisca in source rocks is an important geochemical work. Kerogen can be used to trace the source rock quickly for its enrichment of the parent material of hydrocarbon generation. [Method] Thus the kerogen from Estonian oil shale was analyzed using sequential stepwise pyrolysis with 50 °C intervals from 310 °C to 610 °C to investigate its chemical constitutions. [Results and discussion] The results illustrated that the pyrolyzed hydrocarbons formed upon sequential stepwise pyrolysis are dominated by 5-n-alkyl-1,3-benzenediols probably reflect a major contribution of selectively preserved, highly resistant biomacromolecules from the outer cell walls of G. prisca. It is also characterized by high content of short-chain alkanes, but abnormal high carbon number (>nC29) n-alkane/enes appear at 560 ℃. Besides, the consistent formation of alkyl benzenes, alkyl thiophenes and alkyl ketones also appeared at the middle to high temperature points (460 ~ 560 ℃). All pyrolyzates have the characteristics of lower carbon number, alkyl side chains with a distinct distribution of weak odd-over-even carbon numbers. The extremely abundant and continuous generation of 5-n-alkyl-1,3-benzenediols and its homologues in the pyrolysis products can help to quickly identify whether the source rocks contained G. Prisca or not. In addition, the composition characteristics, product changes and product correlation of the pyrolyzates at different temperatures are helpful for the investigation of kerogen structure. The results of sequential stepwise pyrolysis suggested that the macromolecules of kerogen were formed mainly by polymerization of 5-n-alkyl-1,3-benzenediols in G. prisca. The units in polymer macromolecules including phenol rings, thiophene rings, and normal alkyl chains, are intermolecular connected by C-C and C-O bonds. [Conclusions] The distribution changes of different series of compounds obtained at different temperatures by sequential stepwise pyrolysis can be applied to other organic-rich oil shales, which may reveal the details of algal evolution and determine the various sources of organic matter of kerogen.
Abstract:
[Significance] The study of detrital-carbonate mixed components can indicate paleoclimate, paleoenvironment, provenance supply, and sea/lake level change, and is closely related to mineral and oil & gas resources, so it is paid more and more attention. [Progress] Mixed sediments can be mainly divided into compositional mixing (narrow sense) and structural mixing (broad sense), and mixed sediments as mixed sedimentary products, the previous classification mainly includes four, three, and two components. However, it has been controversial whether clay components should participate in the classification of mixed deposits. This paper provides a new idea of classification, which can provide another choice for the study of similar mixed sediments [Conclusions] Based on the division of clastic and carbonate components, the hydrodynamic conditions of the sedimentary period can be judged by quantitative statistics of fine sediment content. Compared with the traditional classification scheme, the four components of carbonate grains, detrital grains, (dolo)micrite, and clay are retained, while the visual presentation effect and convenient operation feasibility are taken into account. In addition, mixed sedimentation was redefined into four types: punctuated mixing, facies mixing, in situ mixing, and precipitation mixing. Four kinds of processes that cannot reflect the original sedimentary environment, such as source mixing, diagenetic mixing, karst mixing, and fracture mixing, are classified as false mixing. [Prospects] As two branches of sedimentology, carbonate rock and clastic rock have been studied as independent subject systems. The study of mixed sediments is also expected to help understand carbonate-clastic components' mineral sources, interaction modes, and deposition processes and improve the discipline system of clastic and carbonate rocks.
[Significance] The study of detrital-carbonate mixed components can indicate paleoclimate, paleoenvironment, provenance supply, and sea/lake level change, and is closely related to mineral and oil & gas resources, so it is paid more and more attention. [Progress] Mixed sediments can be mainly divided into compositional mixing (narrow sense) and structural mixing (broad sense), and mixed sediments as mixed sedimentary products, the previous classification mainly includes four, three, and two components. However, it has been controversial whether clay components should participate in the classification of mixed deposits. This paper provides a new idea of classification, which can provide another choice for the study of similar mixed sediments [Conclusions] Based on the division of clastic and carbonate components, the hydrodynamic conditions of the sedimentary period can be judged by quantitative statistics of fine sediment content. Compared with the traditional classification scheme, the four components of carbonate grains, detrital grains, (dolo)micrite, and clay are retained, while the visual presentation effect and convenient operation feasibility are taken into account. In addition, mixed sedimentation was redefined into four types: punctuated mixing, facies mixing, in situ mixing, and precipitation mixing. Four kinds of processes that cannot reflect the original sedimentary environment, such as source mixing, diagenetic mixing, karst mixing, and fracture mixing, are classified as false mixing. [Prospects] As two branches of sedimentology, carbonate rock and clastic rock have been studied as independent subject systems. The study of mixed sediments is also expected to help understand carbonate-clastic components' mineral sources, interaction modes, and deposition processes and improve the discipline system of clastic and carbonate rocks.
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Abstract: [Objective] The Luojiawopeng Formation is a set of purplish red sand and gravel accumulation strata in the Lower Pleistocene Series in the southeastern margin of Songnen Plain. The clay mineral analysis of this formation is conducive to understanding the paleoclimate characteristics in this region and defining its stratigraphic age. [Methods] Whole rock geochemistry, XRD, SEM and HRTEM analysis of clay minerals in Luojiawopeng Formation were carried out to reveal the composition and transformation characteristics of clay minerals in this formation. Comparation were taken on the aspect of clay mineral composition, between the red clay in the Chinese Loess Plateau and Luojiawopeng Formation. [Results] The clay mineral composition of Luojiawopeng Formation is dominated by kaolinite (content of 57%~73%), followed by illite (ranging from 25% ~ 41%) and the content of biotite /vermiculite mixed layer minerals is the least (average 1%). Kaolinite shows pseudo hexagonal morphology, and high degree of euhedral and crystallinity indicate its authigenic origin, together with high illite crystallinity (average 0.55) and illite chemical index (average 0.50), together with high clay/quartz ratio all indicate intense weathering characteristic. The transformation process of clay minerals is illite → kaolinite and biotite → biotite /vermiculite mixed layer minerals → kaolinite, which is consistent with the significant kaolinization trend of constant element 4Si-M+-R2+ ternary diagram, combined with the high CIA value and hematite/goethite ratio of the formation, all indicates that this formation formed in a humid and hot climate environment with increasingly strong weathering. [Conclusions] It is speculated that the Luojiawopeng formation was formed in the humid and hot climate background, rahter than the moraine accumulation as previously reported, and the stratigraphic chronology of the formation may be in the humid and hot period when the East Asian summer monsoon prevailed before the early Pleistocene.
Abstract: [Objective] The Luojiawopeng Formation is a set of purplish red sand and gravel accumulation strata in the Lower Pleistocene Series in the southeastern margin of Songnen Plain. The clay mineral analysis of this formation is conducive to understanding the paleoclimate characteristics in this region and defining its stratigraphic age. [Methods] Whole rock geochemistry, XRD, SEM and HRTEM analysis of clay minerals in Luojiawopeng Formation were carried out to reveal the composition and transformation characteristics of clay minerals in this formation. Comparation were taken on the aspect of clay mineral composition, between the red clay in the Chinese Loess Plateau and Luojiawopeng Formation. [Results] The clay mineral composition of Luojiawopeng Formation is dominated by kaolinite (content of 57%~73%), followed by illite (ranging from 25% ~ 41%) and the content of biotite /vermiculite mixed layer minerals is the least (average 1%). Kaolinite shows pseudo hexagonal morphology, and high degree of euhedral and crystallinity indicate its authigenic origin, together with high illite crystallinity (average 0.55) and illite chemical index (average 0.50), together with high clay/quartz ratio all indicate intense weathering characteristic. The transformation process of clay minerals is illite → kaolinite and biotite → biotite /vermiculite mixed layer minerals → kaolinite, which is consistent with the significant kaolinization trend of constant element 4Si-M+-R2+ ternary diagram, combined with the high CIA value and hematite/goethite ratio of the formation, all indicates that this formation formed in a humid and hot climate environment with increasingly strong weathering. [Conclusions] It is speculated that the Luojiawopeng formation was formed in the humid and hot climate background, rahter than the moraine accumulation as previously reported, and the stratigraphic chronology of the formation may be in the humid and hot period when the East Asian summer monsoon prevailed before the early Pleistocene.
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[Objective] The shale gas of the Cambrian Qiongzhusi Formation in the Sichuan Basin has good prospects for exploration and development. It is of great significance to reveal the characteristics of its sedimentary environment for the evaluation of shale gas resources in the Qiongzhusi Formation. [Methods] Taking the shale series of Qiongzhusi Formation in Chengjiaba section of northern Sichuan as the research object, based on detailed field geological survey, the whole rock X-ray diffraction and geochemical analysis were carried out, and the characteristic elements and ratio parameters were optimized to reveal the sedimentary paleoenvironment and conditions of organic-rich shale in Qiongzhusi Formation in northern Sichuan. [Results] (1) The first and second members of Qiongzhusi Formation are mainly gray-black or black mudstone and silty mudstone, with siliceous rock facies and siliceous shale facies, with horizontal bedding, which is a deep-water shelf facies. (2) The shale TOC content of Qiongzhusi Formation is relatively high, ranging from 0.22 % to 4.34 %, with an average of 2.68 %. (3) The geochemical characteristics of the elements show that the climate was warm and humid during the deposition of the black shale of the Qiongzhusi Formation, the paleoproductivity and deposition rate were high, and the water body was anoxic and highly retained. [Conclusions] It is considered that the formation of organic-rich shale in Qiongzhusi Formation is controlled by redox conditions, paleoproductivity, paleoclimate and deposition rate.
[Objective] The shale gas of the Cambrian Qiongzhusi Formation in the Sichuan Basin has good prospects for exploration and development. It is of great significance to reveal the characteristics of its sedimentary environment for the evaluation of shale gas resources in the Qiongzhusi Formation. [Methods] Taking the shale series of Qiongzhusi Formation in Chengjiaba section of northern Sichuan as the research object, based on detailed field geological survey, the whole rock X-ray diffraction and geochemical analysis were carried out, and the characteristic elements and ratio parameters were optimized to reveal the sedimentary paleoenvironment and conditions of organic-rich shale in Qiongzhusi Formation in northern Sichuan. [Results] (1) The first and second members of Qiongzhusi Formation are mainly gray-black or black mudstone and silty mudstone, with siliceous rock facies and siliceous shale facies, with horizontal bedding, which is a deep-water shelf facies. (2) The shale TOC content of Qiongzhusi Formation is relatively high, ranging from 0.22 % to 4.34 %, with an average of 2.68 %. (3) The geochemical characteristics of the elements show that the climate was warm and humid during the deposition of the black shale of the Qiongzhusi Formation, the paleoproductivity and deposition rate were high, and the water body was anoxic and highly retained. [Conclusions] It is considered that the formation of organic-rich shale in Qiongzhusi Formation is controlled by redox conditions, paleoproductivity, paleoclimate and deposition rate.
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The dolomite problem remains one of the most contentious and prominent issues in the field of sedimentology. Previous studies have demonstrated that the direct precipitation of ordered dolomite under low-temperature, inorganic conditions is challenging both in laboratory settings and modern natural sedimentary environments. The formation of dolomite is a kinetically controlled process and several crucial factors have been identified, including the hydration of Mg2+, the presence of sulfate inhibitor, nucleation sites, and the ordering of cations. The role of sulfate in the formation of dolomite has garnered considerable attention, yet it remains a subject of substantial debate. The hypothesis that sulfate inhibits the formation of dolomite has long been widely accepted by geologists, serving as an explanatory framework for elucidating the evolution of dolomite abundance and seawater properties throughout geological history. However, with the advancement of research, particularly in ongoing investigations into the formation mechanism of microbial dolomite, a contentious debate has arisen regarding the role of sulfate, as some scholars argued that the presence of sulfate does not inhibit low-temperature dolomite precipitation. The controversy regarding the controversial role of sulfate arises from: (1) The large variation in SO42- concentration in modern natural sedimentary environments where dolomite is precipitated; (2) The distinct roles of SO42- vary under inorganic and organic，high-temperature and low-temperature conditions; (3) The limitations of applying conceptual patterns derived from laboratory contexts with singular factors to complex sedimentary environments. The ‘Sulfate enigma’ remains an unresolved issue in understanding the dolomite genesis. Here, we present a systematic review of the diverse perspectives regarding the role of sulfate in dolomite formation over the past 60 years. Firstly, we elaborate on the two prevailing perspectives regarding how SO42- inhabits dolomite formation. Subsequently, we assess the efficacy of SO42- as an inhibitor under various conditions, and reinterpret its role within the microbial dolomite model. Finally, we summarize the role of sulfate in the laboratory synthesis of dolomite analogs while addressing existing challenges and limitations. This study aims to enhance the understanding of the ‘dolomite problem’ and provide theoretical support for further elucidating the relationship between dolomite abundance in geological history and the evolution of paleoceanic properties.
The dolomite problem remains one of the most contentious and prominent issues in the field of sedimentology. Previous studies have demonstrated that the direct precipitation of ordered dolomite under low-temperature, inorganic conditions is challenging both in laboratory settings and modern natural sedimentary environments. The formation of dolomite is a kinetically controlled process and several crucial factors have been identified, including the hydration of Mg2+, the presence of sulfate inhibitor, nucleation sites, and the ordering of cations. The role of sulfate in the formation of dolomite has garnered considerable attention, yet it remains a subject of substantial debate. The hypothesis that sulfate inhibits the formation of dolomite has long been widely accepted by geologists, serving as an explanatory framework for elucidating the evolution of dolomite abundance and seawater properties throughout geological history. However, with the advancement of research, particularly in ongoing investigations into the formation mechanism of microbial dolomite, a contentious debate has arisen regarding the role of sulfate, as some scholars argued that the presence of sulfate does not inhibit low-temperature dolomite precipitation. The controversy regarding the controversial role of sulfate arises from: (1) The large variation in SO42- concentration in modern natural sedimentary environments where dolomite is precipitated; (2) The distinct roles of SO42- vary under inorganic and organic，high-temperature and low-temperature conditions; (3) The limitations of applying conceptual patterns derived from laboratory contexts with singular factors to complex sedimentary environments. The ‘Sulfate enigma’ remains an unresolved issue in understanding the dolomite genesis. Here, we present a systematic review of the diverse perspectives regarding the role of sulfate in dolomite formation over the past 60 years. Firstly, we elaborate on the two prevailing perspectives regarding how SO42- inhabits dolomite formation. Subsequently, we assess the efficacy of SO42- as an inhibitor under various conditions, and reinterpret its role within the microbial dolomite model. Finally, we summarize the role of sulfate in the laboratory synthesis of dolomite analogs while addressing existing challenges and limitations. This study aims to enhance the understanding of the ‘dolomite problem’ and provide theoretical support for further elucidating the relationship between dolomite abundance in geological history and the evolution of paleoceanic properties.
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A systematic study was conducted on the sedimentary system and evolution of the Paleogene Oligocene in the YA area of the Songnan low uplift in the Qiongdongnan Basin, using comprehensive methods such as drilling core, thin section identification, paleontology, particle size analysis, logging, and seismic interpretation. The lithofacies and paleogeography of the Paleogene in the YA area were restored.Research has shown that the lithology of the middle and lower part of the Oligocene (Yacheng Formation) is mainly composed of medium to coarse sandstone and gravel bearing sandstone. The sandstone has poor sorting ability, and the mineral composition gradually tends to stabilize from bottom to top. The maturity gradually increases, and the probability accumulation curve of particle size mainly shows suspended and jumping characteristics. The fossil abundance is extremely low, and the sedimentary facies types are mainly fan delta, shore shallow lake, and lakeshore plain.The lithology of the upper part of the Oligocene (Lingshui Formation) is mainly composed of fine sandstone and mudstone, with a significant increase in fossil abundance. The sedimentary facies are mainly barrier coasts and shallow water continental shelves. The research area underwent a transition from marine terrestrial transitional sedimentation to shallow marine sedimentation during the Oligocene. The fault activity in the Early Oligocene (Yacheng Formation) area formed a structural pattern of Songnan low protrusions and alternating concave and convex edges. The water body was shallow, with shallow lake facies developed in the center of the depression, fan deltas developed in steep slopes, and braided river delta facies developed in gentle slopes. The seismic facies were mainly characterized by pre accumulation and chaotic reflection structures; The fault activity in the Late Oligocene (Lingshui Formation) area caused the deepening of sedimentary water bodies. The area mainly developed shallow sea shelf facies and deep sea shelf facies, and the seismic facies were mainly characterized by parallel sub parallel reflection structures. The sedimentary pattern of the Yacheng Formation is as follows: braided river deltas are developed in the gentle slope zone and shallow water areas of the depression, fan deltas are developed in the steep terrain and deep water areas, fan delta deposits are developed in the steep slope zone of the depression, and coastal shallow lake (sea) deposits are developed in the subsidence center. The sedimentary pattern of the Lingshui Formation is characterized by the development of coarse-grained thick layer sediments at the fault, and fine-grained thin layer wedge-shaped sediments at the center of the depression.
A systematic study was conducted on the sedimentary system and evolution of the Paleogene Oligocene in the YA area of the Songnan low uplift in the Qiongdongnan Basin, using comprehensive methods such as drilling core, thin section identification, paleontology, particle size analysis, logging, and seismic interpretation. The lithofacies and paleogeography of the Paleogene in the YA area were restored.Research has shown that the lithology of the middle and lower part of the Oligocene (Yacheng Formation) is mainly composed of medium to coarse sandstone and gravel bearing sandstone. The sandstone has poor sorting ability, and the mineral composition gradually tends to stabilize from bottom to top. The maturity gradually increases, and the probability accumulation curve of particle size mainly shows suspended and jumping characteristics. The fossil abundance is extremely low, and the sedimentary facies types are mainly fan delta, shore shallow lake, and lakeshore plain.The lithology of the upper part of the Oligocene (Lingshui Formation) is mainly composed of fine sandstone and mudstone, with a significant increase in fossil abundance. The sedimentary facies are mainly barrier coasts and shallow water continental shelves. The research area underwent a transition from marine terrestrial transitional sedimentation to shallow marine sedimentation during the Oligocene. The fault activity in the Early Oligocene (Yacheng Formation) area formed a structural pattern of Songnan low protrusions and alternating concave and convex edges. The water body was shallow, with shallow lake facies developed in the center of the depression, fan deltas developed in steep slopes, and braided river delta facies developed in gentle slopes. The seismic facies were mainly characterized by pre accumulation and chaotic reflection structures; The fault activity in the Late Oligocene (Lingshui Formation) area caused the deepening of sedimentary water bodies. The area mainly developed shallow sea shelf facies and deep sea shelf facies, and the seismic facies were mainly characterized by parallel sub parallel reflection structures. The sedimentary pattern of the Yacheng Formation is as follows: braided river deltas are developed in the gentle slope zone and shallow water areas of the depression, fan deltas are developed in the steep terrain and deep water areas, fan delta deposits are developed in the steep slope zone of the depression, and coastal shallow lake (sea) deposits are developed in the subsidence center. The sedimentary pattern of the Lingshui Formation is characterized by the development of coarse-grained thick layer sediments at the fault, and fine-grained thin layer wedge-shaped sediments at the center of the depression.
Abstract:
[Objective] There is a close relationship between the cathodoluminescence (CL) characteristics of carbonate minerals and their trace and rare earth element (REE) contents. This study aims to investigate the relationship between these factors. [Methods] Cathodoluminescence and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were used to test carbonate rock samples from the Lower and Middle Ordovician on the southern margin of the Ordos Basin. Statistical methods and classification algorithms were applied to analyze the test data, and common REE indicators were used to evaluate the properties of diagenetic fluids. [Results] The study reveals that matrix dolomite exhibits weak to moderate red luminescence under cathodoluminescence, with both zoned and uniform luminescence. Dolomite cements, with high Mn and Fe contents, are often zoned or non-luminescent. ANOVA and Tukey's HSD post-hoc tests indicate that Mn, Fe, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb contents, and the Fe/Mn ratio significantly influence the cathodoluminescence of carbonate minerals. Non-luminescent and strongly luminescent groups are relatively easy to distinguish: non-luminescent minerals generally have Fe contents greater than 10,000 ppm or Mn contents less than 40 ppm. Additionally, the non-luminescent group with Fe contents over 10,000 ppm displays REE distribution patterns enriched in MREE, while the strongly luminescent group shows LREE depletion and low Fe/Mn ratios. Using comprehensive dimensionality-reduced parameters of trace and rare earth elements, in conjunction with Mn content, effectively distinguishes the extremely weakly luminescent, weakly luminescent, and moderately luminescent groups. The nature of diagenetic fluids during diagenesis impacts carbonate sediment composition, mineral content, and trace and rare earth element variations, directly influencing carbonate mineral cathodoluminescence. [Conclusion] By combining in situ trace element testing with various data processing methods, this study provides a more quantitative understanding of the impact of trace and rare earth element contents on cathodoluminescence intensity. These findings offer valuable insights for both domestic and international scholars studying the factors affecting cathodoluminescence.
[Objective] There is a close relationship between the cathodoluminescence (CL) characteristics of carbonate minerals and their trace and rare earth element (REE) contents. This study aims to investigate the relationship between these factors. [Methods] Cathodoluminescence and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were used to test carbonate rock samples from the Lower and Middle Ordovician on the southern margin of the Ordos Basin. Statistical methods and classification algorithms were applied to analyze the test data, and common REE indicators were used to evaluate the properties of diagenetic fluids. [Results] The study reveals that matrix dolomite exhibits weak to moderate red luminescence under cathodoluminescence, with both zoned and uniform luminescence. Dolomite cements, with high Mn and Fe contents, are often zoned or non-luminescent. ANOVA and Tukey's HSD post-hoc tests indicate that Mn, Fe, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb contents, and the Fe/Mn ratio significantly influence the cathodoluminescence of carbonate minerals. Non-luminescent and strongly luminescent groups are relatively easy to distinguish: non-luminescent minerals generally have Fe contents greater than 10,000 ppm or Mn contents less than 40 ppm. Additionally, the non-luminescent group with Fe contents over 10,000 ppm displays REE distribution patterns enriched in MREE, while the strongly luminescent group shows LREE depletion and low Fe/Mn ratios. Using comprehensive dimensionality-reduced parameters of trace and rare earth elements, in conjunction with Mn content, effectively distinguishes the extremely weakly luminescent, weakly luminescent, and moderately luminescent groups. The nature of diagenetic fluids during diagenesis impacts carbonate sediment composition, mineral content, and trace and rare earth element variations, directly influencing carbonate mineral cathodoluminescence. [Conclusion] By combining in situ trace element testing with various data processing methods, this study provides a more quantitative understanding of the impact of trace and rare earth element contents on cathodoluminescence intensity. These findings offer valuable insights for both domestic and international scholars studying the factors affecting cathodoluminescence.
Abstract:
The Ordovician Majiagou Formation in the southern Sulige gas field is mainly a karst reservoir with proved reserves of over 100 billion square meters of gas. In the process of development and production, the formation water is serious, the gas-water relationship is complicated, the gas-water distribution law and the main control factors are unclear, which restricts the natural gas production capacity release in this area to a large extent. Based on the analysis of formation water chemical characteristics, the formation environment of formation water is analyzed by using chemical parameters such as sodium chloride coefficient, desulfurization coefficient, sodium calcium coefficient, magnesium calcium coefficient and metamorphism coefficient, and then the gas-water distribution law is studied through the identification of single well water level, the correlation of well profile and the characterization of plane distribution characteristics. Finally, the main controlling factors of gas and water distribution are discussed in terms of source rock, reservoir heterogeneity and structure. The results show that the formation water in the southern part of the Sulige gas field has a relatively concentrated salinity distribution with an mean of 83598.7mg/L, a light acidic pH, and a CaCl2 water type. The formation water as a whole is characterized by low sodium chloride coefficient, low desulphurization coefficient, low magnesium calcium coefficient, low sodium calcium coefficient and high metamorphism coefficient, indicating that the formation is well sealed. It is beneficial to gas reservoir preservation, and the plane characteristics of each parameter are similar and controlled by karst reservoir. According to the genetic difference, spatial distribution and reservoir characteristics, the formation water is divided into water in the lower part of type I structure, isolated lensing water in type II structure and water retention in type III low permeability zone. The water in the lower part of type I structure mainly develops in the karst area and is controlled by the karst residual hill unit, and the water in type II lensing water is scattered in the plane, and the water in type III low permeability is difficult to identify due to the plane distribution of karst depressions and trenches. The distribution of formation water is controlled by three factors: source rock, karst reservoir heterogeneity and local structure of the same karst unit. The lack of hydrocarbon supply capacity of source rock is fundamental to the development of formation water bodies. The distribution pattern of gas and water is determined by the heterogeneity of karst reservoir, and the differentiation of gas and water is caused by local structure. The same karst unit has a unified gas-water contact.
The Ordovician Majiagou Formation in the southern Sulige gas field is mainly a karst reservoir with proved reserves of over 100 billion square meters of gas. In the process of development and production, the formation water is serious, the gas-water relationship is complicated, the gas-water distribution law and the main control factors are unclear, which restricts the natural gas production capacity release in this area to a large extent. Based on the analysis of formation water chemical characteristics, the formation environment of formation water is analyzed by using chemical parameters such as sodium chloride coefficient, desulfurization coefficient, sodium calcium coefficient, magnesium calcium coefficient and metamorphism coefficient, and then the gas-water distribution law is studied through the identification of single well water level, the correlation of well profile and the characterization of plane distribution characteristics. Finally, the main controlling factors of gas and water distribution are discussed in terms of source rock, reservoir heterogeneity and structure. The results show that the formation water in the southern part of the Sulige gas field has a relatively concentrated salinity distribution with an mean of 83598.7mg/L, a light acidic pH, and a CaCl2 water type. The formation water as a whole is characterized by low sodium chloride coefficient, low desulphurization coefficient, low magnesium calcium coefficient, low sodium calcium coefficient and high metamorphism coefficient, indicating that the formation is well sealed. It is beneficial to gas reservoir preservation, and the plane characteristics of each parameter are similar and controlled by karst reservoir. According to the genetic difference, spatial distribution and reservoir characteristics, the formation water is divided into water in the lower part of type I structure, isolated lensing water in type II structure and water retention in type III low permeability zone. The water in the lower part of type I structure mainly develops in the karst area and is controlled by the karst residual hill unit, and the water in type II lensing water is scattered in the plane, and the water in type III low permeability is difficult to identify due to the plane distribution of karst depressions and trenches. The distribution of formation water is controlled by three factors: source rock, karst reservoir heterogeneity and local structure of the same karst unit. The lack of hydrocarbon supply capacity of source rock is fundamental to the development of formation water bodies. The distribution pattern of gas and water is determined by the heterogeneity of karst reservoir, and the differentiation of gas and water is caused by local structure. The same karst unit has a unified gas-water contact.
Abstract:
[Objective] An suite of Neoproterozoic diabase dykes is extensively exposed in the Jinkouhe area, western Sichuan Province, offering crucial insights into the tectonic evolution of the western Yangtze Craton. These diabases bear key implication for understanding the early tectono-magmatic history of the Yangtze Craton and its relationship with the assembly and fragmentation of the Rodinia supercontinent. [Methods] SHRIMP zircon U-Pb geochronology and whole-rock geochemistry analyses were conducted on the Jinkouhe diabases. [Results] SHRIMP zircon U-Pb dating of the diabase samples yields an age of 823 ± 10 Ma (MSWD = 1.30, n = 10). The diabases are classified as tholeiitic basalt series, displaying Nb-Ta depletion and negative Eu anomalies. Their geochemical signatures are indicative of both island arc and intraplate basaltic affinities. [Conclusion] The Jinkouhe diabases are interpreted to may have been originated from partial melting of a spinel-garnet lherzolite mantle source, which was metasomatized by subduction-related melts. Together with regional geological data, it is proposed that these diabases were most likely formed within a post-collisional extensional setting, reflecting tectonic processes associated with the final amalgamation of the Yangtze Craton in the context of the Rodinia supercontinent assembly.
[Objective] An suite of Neoproterozoic diabase dykes is extensively exposed in the Jinkouhe area, western Sichuan Province, offering crucial insights into the tectonic evolution of the western Yangtze Craton. These diabases bear key implication for understanding the early tectono-magmatic history of the Yangtze Craton and its relationship with the assembly and fragmentation of the Rodinia supercontinent. [Methods] SHRIMP zircon U-Pb geochronology and whole-rock geochemistry analyses were conducted on the Jinkouhe diabases. [Results] SHRIMP zircon U-Pb dating of the diabase samples yields an age of 823 ± 10 Ma (MSWD = 1.30, n = 10). The diabases are classified as tholeiitic basalt series, displaying Nb-Ta depletion and negative Eu anomalies. Their geochemical signatures are indicative of both island arc and intraplate basaltic affinities. [Conclusion] The Jinkouhe diabases are interpreted to may have been originated from partial melting of a spinel-garnet lherzolite mantle source, which was metasomatized by subduction-related melts. Together with regional geological data, it is proposed that these diabases were most likely formed within a post-collisional extensional setting, reflecting tectonic processes associated with the final amalgamation of the Yangtze Craton in the context of the Rodinia supercontinent assembly.
Abstract:
[Objective] In recent years, the exploration of new type of natural gas reservoirs in marine clastic rocks of Shiqiantan Formation in Shiqiantan Depression of Jundong Region has gained significant breakthroughs, but the depositional characteristics and patterns of Shiqiantan Formation are not clear, and the configuration of source and storage is not realized, which restricts the next step of exploration and deployment.[Methods] The sedimentary paleomorphology of Shiqiantan Formation was recovered on the basis of isochronous stratigraphic division and comparison, and different sedimentary phases were identified by combining seismic phases, continuous well sections and microscopic depositional features such as cores and thin sections, the evolutionary process of sedimentary system was constructed, and the sedimentary evolutionary model was established. [Results and Conclusions] The Shiqiantan Formationdevelops a complete three-stage stratigraphic sequence, which can be divided into the early transgression systems tract (ETST), the late transgression systems tract (LTST) and the highstand systems tract (HST) in combination with the paleogeomorphic slope folding. During the sedimentary period of the Shiqiantan Formation, the overall depression is a narrow and elongated sea trough running in a northwest southeast direction, with various types of ancient landforms such as rifted sea troughs, multi-level gentle slopes, fault controlled steep slopes, and eroded gullies. Identify sedimentary facies types such as nearshore underwater fans, fan deltas, slope fans, and basin floor fans through typical logging data, rock cores, and seismic facies characteristics. The ancient landforms have a significant controlling effect on the distribution of sedimentary facies. Fan deltas and nearshore underwater fans are mainly distributed near the southern fault controlled steep slope zone, while slope fans are mainly developed on the northern multi-level slope break gentle slope zone, and basin floor fans are mainly developed in the trough. The entire sedimentary process formed an evolutionary model of multi-stage "stacked tile style retrogradations" of submarine fan slope fan sedimentation under the background of rapid marine invasion and large-scale braided river delta sedimentation in HST. High quality mature source rocks are developed in the transgressive domain, and the basin floor fans and slope fans on the "source" and "source side" of the northern gentle slope zone can form a "finger shaped interaction" favorable source and reservoir configuration with high-quality marine source rocks, with superior storage conditions, making it a favorable target for the next step of hidden oil and gas exploration.
[Objective] In recent years, the exploration of new type of natural gas reservoirs in marine clastic rocks of Shiqiantan Formation in Shiqiantan Depression of Jundong Region has gained significant breakthroughs, but the depositional characteristics and patterns of Shiqiantan Formation are not clear, and the configuration of source and storage is not realized, which restricts the next step of exploration and deployment.[Methods] The sedimentary paleomorphology of Shiqiantan Formation was recovered on the basis of isochronous stratigraphic division and comparison, and different sedimentary phases were identified by combining seismic phases, continuous well sections and microscopic depositional features such as cores and thin sections, the evolutionary process of sedimentary system was constructed, and the sedimentary evolutionary model was established. [Results and Conclusions] The Shiqiantan Formationdevelops a complete three-stage stratigraphic sequence, which can be divided into the early transgression systems tract (ETST), the late transgression systems tract (LTST) and the highstand systems tract (HST) in combination with the paleogeomorphic slope folding. During the sedimentary period of the Shiqiantan Formation, the overall depression is a narrow and elongated sea trough running in a northwest southeast direction, with various types of ancient landforms such as rifted sea troughs, multi-level gentle slopes, fault controlled steep slopes, and eroded gullies. Identify sedimentary facies types such as nearshore underwater fans, fan deltas, slope fans, and basin floor fans through typical logging data, rock cores, and seismic facies characteristics. The ancient landforms have a significant controlling effect on the distribution of sedimentary facies. Fan deltas and nearshore underwater fans are mainly distributed near the southern fault controlled steep slope zone, while slope fans are mainly developed on the northern multi-level slope break gentle slope zone, and basin floor fans are mainly developed in the trough. The entire sedimentary process formed an evolutionary model of multi-stage "stacked tile style retrogradations" of submarine fan slope fan sedimentation under the background of rapid marine invasion and large-scale braided river delta sedimentation in HST. High quality mature source rocks are developed in the transgressive domain, and the basin floor fans and slope fans on the "source" and "source side" of the northern gentle slope zone can form a "finger shaped interaction" favorable source and reservoir configuration with high-quality marine source rocks, with superior storage conditions, making it a favorable target for the next step of hidden oil and gas exploration.
Abstract:
[Objective] The catastrophic failure of large submarine landslides can result in the deformation and destruction of thousands of square kilometers of seafloor, transporting hundreds to thousands of cubic kilometers of submarine sediments. This process dramatically reconstructs the seafloor topography of the continental shelf-slope region and has a profound impact on subsequent submarine sedimentation processes. [Methods] The topographic features of different large submarine landslides were qualitatively described using multibeam bathymetric and seismic reflection data, and the key geometric parameters of the submarine landslide top surface, such as area and volume, were quantitatively characterized. Based on the scale, morphological features, and formation mechanisms of the associated reliefs on the submarine landslide top surface, these landslides were separated into three categories: head evacuation zone, locally negative accommodation associated with internal fault systems, and locally negative accommodation associated with internal deformation blocks. The mechanisms of the three types of negative accommodation on the subsequent turbidity current system are then discussed separately. [Results] Firstly, the head evacuation zone is typically associated with hundreds to thousands of square kilometers of negative accommodation, which acts as a "funnel" during sediment transport along the continental margin, effectively capturing and concentrating subsequent turbidity currents while enhancing the transport efficiency of gravel and coarse sand and playing a crucial role in the accumulation of marine organic matter. Secondly, the striped negative accommodation associated with internal fault systems and the irregular negative accommodation associated with internal deformation blocks can regulate the sedimentation dynamics of subsequent turbidity currents, such as constraining flow direction, enhancing erosion intensity, and forcing channels to avulse. Finally, the negative accommodations associated with the submarine landslide top surface may produce synergistic effects, influencing the sediment filling and evolution of sedimentary basins and the distribution of sedimentary centers over millions of years. [Conclusion] The investigation of the morphological characteristics of submarine landslide top surfaces and their controlling effects on the subsequent turbidity currents sedimentary dynamic process can provide key geological information for clarifying the transport process of marginal sediments, identifying the distribution of sand-rich reservoirs in deep-sea sedimentary basins, and predicting the development range of catastrophic turbidity currents.
[Objective] The catastrophic failure of large submarine landslides can result in the deformation and destruction of thousands of square kilometers of seafloor, transporting hundreds to thousands of cubic kilometers of submarine sediments. This process dramatically reconstructs the seafloor topography of the continental shelf-slope region and has a profound impact on subsequent submarine sedimentation processes. [Methods] The topographic features of different large submarine landslides were qualitatively described using multibeam bathymetric and seismic reflection data, and the key geometric parameters of the submarine landslide top surface, such as area and volume, were quantitatively characterized. Based on the scale, morphological features, and formation mechanisms of the associated reliefs on the submarine landslide top surface, these landslides were separated into three categories: head evacuation zone, locally negative accommodation associated with internal fault systems, and locally negative accommodation associated with internal deformation blocks. The mechanisms of the three types of negative accommodation on the subsequent turbidity current system are then discussed separately. [Results] Firstly, the head evacuation zone is typically associated with hundreds to thousands of square kilometers of negative accommodation, which acts as a "funnel" during sediment transport along the continental margin, effectively capturing and concentrating subsequent turbidity currents while enhancing the transport efficiency of gravel and coarse sand and playing a crucial role in the accumulation of marine organic matter. Secondly, the striped negative accommodation associated with internal fault systems and the irregular negative accommodation associated with internal deformation blocks can regulate the sedimentation dynamics of subsequent turbidity currents, such as constraining flow direction, enhancing erosion intensity, and forcing channels to avulse. Finally, the negative accommodations associated with the submarine landslide top surface may produce synergistic effects, influencing the sediment filling and evolution of sedimentary basins and the distribution of sedimentary centers over millions of years. [Conclusion] The investigation of the morphological characteristics of submarine landslide top surfaces and their controlling effects on the subsequent turbidity currents sedimentary dynamic process can provide key geological information for clarifying the transport process of marginal sediments, identifying the distribution of sand-rich reservoirs in deep-sea sedimentary basins, and predicting the development range of catastrophic turbidity currents.
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The existing body of research on bauxite oil and gas reservoirs is limited in scope, both in terms of its domestic and international dimensions. The discovery of a bauxite reservoir with high-yield industrial gas flow in the Taiyuan Formation in the Longdong area, southwestern Ordos Basin, represents a significant advancement in the exploration of bauxite gas reservoirs. Additionally, the recent identification of bauxite strata in the Benxi Formation in the Linxing area of the northeastern margin of the basin, through the test of actual production, suggests promising exploration potential. [Objective] In order to further explore the potential of natural gas exploration and the development of bauxite series in the Linxing area, it is necessary to conduct a comprehensive analysis of the fundamental geological characteristics of the sedimentary environment, the composition of the rock minerals, the characteristics of the reservoir pores and the structure of the bauxite series. In addition, it is essential to identify the factors that control the development of bauxite in the study area. It would be beneficial to ascertain which areas are most conducive to such activity. [Methods] In this study, a comprehensive analysis was conducted on the sedimentary environment, reservoir characteristics and sedimentary model of the Benxi Formation bauxite rock series in the Linxing area. This analysis was based on a synthesis of logging and seismic data, X-ray diffraction, casting thin sections, scanning electron microscopy, major and trace elements, high-pressure mercury injection, N2, CO2 adsorption and conventional physical properties, and other experimental methods. [Results and Discussions] The bauxite rock series in the study area is characterised by a high concentration of diaspore and clay minerals, exhibiting a distinct three-stage vertical structure. The lower portion is rich in iron, the middle contains a higher aluminium content, and the upper section has a lower iron concentration. The pore types observed in the bauxite reservoir include dissolution pores, intercrystalline pores, organic pores and microfractures. The dissolution pore represents the predominant reservoir type, with pore sizes typically ranging between 2 and 50 nm. The sorting and connectivity of the pores are relatively good. The average porosity is 3.64%, with an average permeability of 7.24 × 10-3 μm2. [Conclusions] A comprehensive analysis indicates that the development thickness of bauxite rock series is contingent upon the sedimentary environment and karst paleogeomorphology. The shallow water sedimentary environment, characterised by high temperatures and humidity, low oxygen levels and alternating marine and terrestrial conditions, provides optimal conditions for the formation and preservation of bauxite rock series. The slope, or buried pit, represents a crucial area for the exploration and development of bauxite rock series. This understanding is anticipated to provide a geological foundation for the exploration and development of natural gas in bauxite rock series with comparable geological backgrounds in this region.
The existing body of research on bauxite oil and gas reservoirs is limited in scope, both in terms of its domestic and international dimensions. The discovery of a bauxite reservoir with high-yield industrial gas flow in the Taiyuan Formation in the Longdong area, southwestern Ordos Basin, represents a significant advancement in the exploration of bauxite gas reservoirs. Additionally, the recent identification of bauxite strata in the Benxi Formation in the Linxing area of the northeastern margin of the basin, through the test of actual production, suggests promising exploration potential. [Objective] In order to further explore the potential of natural gas exploration and the development of bauxite series in the Linxing area, it is necessary to conduct a comprehensive analysis of the fundamental geological characteristics of the sedimentary environment, the composition of the rock minerals, the characteristics of the reservoir pores and the structure of the bauxite series. In addition, it is essential to identify the factors that control the development of bauxite in the study area. It would be beneficial to ascertain which areas are most conducive to such activity. [Methods] In this study, a comprehensive analysis was conducted on the sedimentary environment, reservoir characteristics and sedimentary model of the Benxi Formation bauxite rock series in the Linxing area. This analysis was based on a synthesis of logging and seismic data, X-ray diffraction, casting thin sections, scanning electron microscopy, major and trace elements, high-pressure mercury injection, N2, CO2 adsorption and conventional physical properties, and other experimental methods. [Results and Discussions] The bauxite rock series in the study area is characterised by a high concentration of diaspore and clay minerals, exhibiting a distinct three-stage vertical structure. The lower portion is rich in iron, the middle contains a higher aluminium content, and the upper section has a lower iron concentration. The pore types observed in the bauxite reservoir include dissolution pores, intercrystalline pores, organic pores and microfractures. The dissolution pore represents the predominant reservoir type, with pore sizes typically ranging between 2 and 50 nm. The sorting and connectivity of the pores are relatively good. The average porosity is 3.64%, with an average permeability of 7.24 × 10-3 μm2. [Conclusions] A comprehensive analysis indicates that the development thickness of bauxite rock series is contingent upon the sedimentary environment and karst paleogeomorphology. The shallow water sedimentary environment, characterised by high temperatures and humidity, low oxygen levels and alternating marine and terrestrial conditions, provides optimal conditions for the formation and preservation of bauxite rock series. The slope, or buried pit, represents a crucial area for the exploration and development of bauxite rock series. This understanding is anticipated to provide a geological foundation for the exploration and development of natural gas in bauxite rock series with comparable geological backgrounds in this region.
Abstract:
[Objective] To clarify whether the western edge of the Kaijiang-Liangping Trough and the eastern edge of the Pengxi-Wusheng intra-platform depression intersect in the north during the Late Permian Changxing Early Triassic Feixianguan period in northwest Sichuan, the sedimentary facies distribution of each layer in the region was constructed, and the sedimentary filling evolution process was analyzed. [Methods] Based on the latest drilling, field outcrop, and seismic data, this article systematically analyzes the distribution of lithofacies and paleogeography during the Changxing-Feixianguan period, as well as the evolution process of sedimentary filling, on the basis of stratigraphic and sedimentary facies division and comparison. [Results and Discussions] The intersection area of Changxing Formation and Feixianguan Formation can identify six types of sedimentary facies: shelf basin, slope, platform edge, open platform, restricted platform, and evaporative platform; Based on the sedimentary records of the front slope of the platform, it is clear that the western edge of the Kaijiang-Liangping trough and the eastern edge of the Pengxi-Wusheng intra-platform depression are merged to form a unified platform edge belt in the northwest Sichuan Majiaoba Shangsi area. The platform edge belt and the front slope show a northwest pointing interdistribution, rather than a smooth belt distribution; The intersection area of the two troughs in the Changxing Formation presents a sedimentary pattern of two troughs sandwiched by a platform from southwest to northeast. In the northwest direction of the platform edge zone, there are finger shaped distribution of platform edge biological reefs and shoals, which have the characteristics of developing bioclastic shoals in the first section of the platform edge zone and developing biological reefs and shoals in the second section of the platform edge zone; The sedimentary period of the first and second members of the Feixianguan Formation inherited the overall sedimentary pattern of the Changxing period. However, in the early stage of the Feixianguan Formation, only local platform edge oolitic beaches were formed due to sea flooding. In the late stage of the Feixianguan Formation to the Feixianguan Formation, platform edge oolitic beaches gradually developed and expanded in scope, and overall had the characteristic of eastward migration. The slope in front of the platform was prone to sliding and sedimentation; During the sedimentation period of the Feisan section, the sea trough gradually filled up, and the finger shaped platform edge zone disappeared, leaving only a small amount of lagoons and only developing ooid shoals in the Majiaoba area; The Feisi section deposited its entire area and filled it up, forming an evaporative platform facies. The platform margin zone in this region did not migrate northwestward along the finger shaped platform margin zone, but rather exhibited eastward migration characteristics. [Conclusions] The determination of Changxing-Feixianguan connectivity and the definition of five sedimentary filling evolution stages in Kaijiang-Liangping Trough and Pengxi-Wusheng intra-platform depression supplemented the understanding of sedimentary pattern and sedimentary filling evolution process in the intersection area of Changxing-Feixianguan trough, and formed a unique example of sedimentary filling evolution sequence in the transition area connected by two rows of cross-platform edge belts in the same period. It also provides ideas and references for oil and gas exploration in this area.
[Objective] To clarify whether the western edge of the Kaijiang-Liangping Trough and the eastern edge of the Pengxi-Wusheng intra-platform depression intersect in the north during the Late Permian Changxing Early Triassic Feixianguan period in northwest Sichuan, the sedimentary facies distribution of each layer in the region was constructed, and the sedimentary filling evolution process was analyzed. [Methods] Based on the latest drilling, field outcrop, and seismic data, this article systematically analyzes the distribution of lithofacies and paleogeography during the Changxing-Feixianguan period, as well as the evolution process of sedimentary filling, on the basis of stratigraphic and sedimentary facies division and comparison. [Results and Discussions] The intersection area of Changxing Formation and Feixianguan Formation can identify six types of sedimentary facies: shelf basin, slope, platform edge, open platform, restricted platform, and evaporative platform; Based on the sedimentary records of the front slope of the platform, it is clear that the western edge of the Kaijiang-Liangping trough and the eastern edge of the Pengxi-Wusheng intra-platform depression are merged to form a unified platform edge belt in the northwest Sichuan Majiaoba Shangsi area. The platform edge belt and the front slope show a northwest pointing interdistribution, rather than a smooth belt distribution; The intersection area of the two troughs in the Changxing Formation presents a sedimentary pattern of two troughs sandwiched by a platform from southwest to northeast. In the northwest direction of the platform edge zone, there are finger shaped distribution of platform edge biological reefs and shoals, which have the characteristics of developing bioclastic shoals in the first section of the platform edge zone and developing biological reefs and shoals in the second section of the platform edge zone; The sedimentary period of the first and second members of the Feixianguan Formation inherited the overall sedimentary pattern of the Changxing period. However, in the early stage of the Feixianguan Formation, only local platform edge oolitic beaches were formed due to sea flooding. In the late stage of the Feixianguan Formation to the Feixianguan Formation, platform edge oolitic beaches gradually developed and expanded in scope, and overall had the characteristic of eastward migration. The slope in front of the platform was prone to sliding and sedimentation; During the sedimentation period of the Feisan section, the sea trough gradually filled up, and the finger shaped platform edge zone disappeared, leaving only a small amount of lagoons and only developing ooid shoals in the Majiaoba area; The Feisi section deposited its entire area and filled it up, forming an evaporative platform facies. The platform margin zone in this region did not migrate northwestward along the finger shaped platform margin zone, but rather exhibited eastward migration characteristics. [Conclusions] The determination of Changxing-Feixianguan connectivity and the definition of five sedimentary filling evolution stages in Kaijiang-Liangping Trough and Pengxi-Wusheng intra-platform depression supplemented the understanding of sedimentary pattern and sedimentary filling evolution process in the intersection area of Changxing-Feixianguan trough, and formed a unique example of sedimentary filling evolution sequence in the transition area connected by two rows of cross-platform edge belts in the same period. It also provides ideas and references for oil and gas exploration in this area.
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Abstract: [Objective] The provenance composition and evolution of the Lower Jurassic Badaowan Formation and Sangonghe Formation in the Dongdaohaizi Sag of the Junggar Basin are of great significance for the early Jurassic tectonic activity of the Karamaili orogenic belt in the provenance area. [Methods] Based on the composition of sandstone clasts, rare earth elements and detrital zircon U-Pb ages, the provenance characteristics and evolution process of the Badaowan Formation and Sangonghe Formation were analyzed. [Results] The results show that the Lower Jurassic sandstone in the study area is dominated by with an average content of 37.7% of rock fragments in thin sections, mainly tuff fragments and basalt fragments, and a small amount of metamorphic rock fragments.The Badaowan Formation shows no obvious differentiation between light (LREE) and heavy rare earth (HREE), while the Sangonghe Formation has the characteristics of slight LREE enrichment and HREE loss, and the age of detrital zircons in the Badaowan Formation mainly falls in the Permian and Devonian periods, while the age data of the Sangonghe Formation is mainly from the Carboniferous period, and there are obvious differences in age composition.[Conclusion] The analysis by synthesis of provenance characteristics, the parent rocks in the Lower Jurassic source area of the Dongdaohaizi Sag are dominated by medium-acid magmatic rocks and mafic magmatic rocks, and the tectonic background is mainly the transitional recycled zone of the recirculating orogenic belt, which is consistent with the mixed source formed by ocean-land subduction in the eastern Karamaili orogenic belt and the Karamaili orogenic belt after the closure of the ocean basin. The provenance of the Badaowan Formation to the Sangonghe Formation in the Dongdaohaizi Sag has undergone a conversion from the main source of oceanic crustal subduction to the closed source of the Carboniferous ocean-land, which has a good response to the increasing uplift process of the Early Jurassic of the Karamaili Orogenic Belt, indicating the continuous uplift and differential denudation process of the Early Jurassic of the Karamaili Orogenic Belt.
Abstract: [Objective] The provenance composition and evolution of the Lower Jurassic Badaowan Formation and Sangonghe Formation in the Dongdaohaizi Sag of the Junggar Basin are of great significance for the early Jurassic tectonic activity of the Karamaili orogenic belt in the provenance area. [Methods] Based on the composition of sandstone clasts, rare earth elements and detrital zircon U-Pb ages, the provenance characteristics and evolution process of the Badaowan Formation and Sangonghe Formation were analyzed. [Results] The results show that the Lower Jurassic sandstone in the study area is dominated by with an average content of 37.7% of rock fragments in thin sections, mainly tuff fragments and basalt fragments, and a small amount of metamorphic rock fragments.The Badaowan Formation shows no obvious differentiation between light (LREE) and heavy rare earth (HREE), while the Sangonghe Formation has the characteristics of slight LREE enrichment and HREE loss, and the age of detrital zircons in the Badaowan Formation mainly falls in the Permian and Devonian periods, while the age data of the Sangonghe Formation is mainly from the Carboniferous period, and there are obvious differences in age composition.[Conclusion] The analysis by synthesis of provenance characteristics, the parent rocks in the Lower Jurassic source area of the Dongdaohaizi Sag are dominated by medium-acid magmatic rocks and mafic magmatic rocks, and the tectonic background is mainly the transitional recycled zone of the recirculating orogenic belt, which is consistent with the mixed source formed by ocean-land subduction in the eastern Karamaili orogenic belt and the Karamaili orogenic belt after the closure of the ocean basin. The provenance of the Badaowan Formation to the Sangonghe Formation in the Dongdaohaizi Sag has undergone a conversion from the main source of oceanic crustal subduction to the closed source of the Carboniferous ocean-land, which has a good response to the increasing uplift process of the Early Jurassic of the Karamaili Orogenic Belt, indicating the continuous uplift and differential denudation process of the Early Jurassic of the Karamaili Orogenic Belt.
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[Objective] Organisms are extremely responsive to the environments in which they live, and the traces they create are the result of interactions between organisms and environments, and to a certain extent reflect the characteristics of the depositional environment. Biological sedimentary structures are a powerful tool in understanding the ecology and depositional processes of modern coastal sedimentary environments. [Methods]The composition and distribution characteristics of modern biogenic traces in the tidal flat environments of the Pearl River Delta were studied by field observations and 3D reconstruction. [Results]The following key understanding was obtained after the study: the distribution of organisms in the supratidal, intertidal and subtidal varies greatly, and the biological traces are mainly distributed in the intertidal zone. In the supratidal zone, there are mainly Ligia oceanica and Uca arcuata, and the main traces created are Uca arcuata level feeding traces, excretion traces, trackways, and intra-layer I-shape dwelling burrows. Biological traces in the intertidal mud flat environment mainly include feeding, excretion, and trackways and I-shaped dwelling burrows at the level of Uca arcuata; crawling traces and Y-, U-, and I-shaped dwelling burrows at the level of Periophthalmus cantonensis; trackways and I- and Y-shaped dwelling burrows at the level of Orisarma dehaani. Biological traces in the mixed intertidal flat environment mainly include excretion traces and intra-layer I-, U-, and Y-shaped dwelling burrows of Perinereis aibuhitensis, Y-, U-, and I-shaped dwelling burrows of Ligia oceanica, and crawling traces of Vittina coromandeliana and Neritina pulligera. Biological traces in the sandy intertidal environment include feeding and excretion traces at the level of Ocypode cordimand and intra-layer I-shaped dwelling traces. The subtidal environment was not accessible for observation and no biological traces were found. [Conclusions] The research work on modern intertidal biological traces in the Pearl River Delta has not only supplemented the modern sedimentological data on tidal flat environments in the Pearl River Delta, but also provided modern empirical evidence for paleohermitology and paleoenvironmental reconstruction.
[Objective] Organisms are extremely responsive to the environments in which they live, and the traces they create are the result of interactions between organisms and environments, and to a certain extent reflect the characteristics of the depositional environment. Biological sedimentary structures are a powerful tool in understanding the ecology and depositional processes of modern coastal sedimentary environments. [Methods]The composition and distribution characteristics of modern biogenic traces in the tidal flat environments of the Pearl River Delta were studied by field observations and 3D reconstruction. [Results]The following key understanding was obtained after the study: the distribution of organisms in the supratidal, intertidal and subtidal varies greatly, and the biological traces are mainly distributed in the intertidal zone. In the supratidal zone, there are mainly Ligia oceanica and Uca arcuata, and the main traces created are Uca arcuata level feeding traces, excretion traces, trackways, and intra-layer I-shape dwelling burrows. Biological traces in the intertidal mud flat environment mainly include feeding, excretion, and trackways and I-shaped dwelling burrows at the level of Uca arcuata; crawling traces and Y-, U-, and I-shaped dwelling burrows at the level of Periophthalmus cantonensis; trackways and I- and Y-shaped dwelling burrows at the level of Orisarma dehaani. Biological traces in the mixed intertidal flat environment mainly include excretion traces and intra-layer I-, U-, and Y-shaped dwelling burrows of Perinereis aibuhitensis, Y-, U-, and I-shaped dwelling burrows of Ligia oceanica, and crawling traces of Vittina coromandeliana and Neritina pulligera. Biological traces in the sandy intertidal environment include feeding and excretion traces at the level of Ocypode cordimand and intra-layer I-shaped dwelling traces. The subtidal environment was not accessible for observation and no biological traces were found. [Conclusions] The research work on modern intertidal biological traces in the Pearl River Delta has not only supplemented the modern sedimentological data on tidal flat environments in the Pearl River Delta, but also provided modern empirical evidence for paleohermitology and paleoenvironmental reconstruction.
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Abstract: [Objective] The abundant ichnofossils were developed in the Pinghu Formation and Baoshi Formation of the Eocene in Pingbei area, Xihu Sag. It is of practical significance for the division of sedimentary system in Xihu Sag to study the characteristics and distribution of its ichnofabrics and its indication of sedimentary environment. [Methods] Through core observations, the study identified ichnofossils and ichnofabrics in the Pingbei Area. The IDIPA technique was employed to objectively quantify ichnofossil abundance and accurately determine both the bioturbation index and the ichnofabric index. By integrating these findings with ichnological indices, this study summarizes the characteristics of the planar distribution and vertical evolution of ichnofabric in the study area. [Results and Discussions] (1) The research identified 6 ichnogenera of ichnofossils and divided them into 4 types of ichnofabrics, including Planolites ichnofabric, Thalassinoides ichnofabric, Teichichnus ichnofabric and Beaconites ichnofabric. (2) The study area features a high landform in the northwest and a low landform in the southeast. Seawater invades from south to north, and the sedimentary environment transitions from the subtidal zone to the intertidal zone, and finally to the supratidal zone, where the highest terrain is located in the northwest. The evolution pattern of the corresponding ichnofabrics follows the sequence Thalassinoides → Teichichnus → Planolites → Beaconites, consistent with the results of regional sedimentary zoning and paleoclimate analysis. (3) From the Pinghu to Baoshi Formation in the study area, it was found that the increase in the size, diversity, and abundance of ichnofossils. The tiering transitioned from simple and shallow to complex and deep. The variety of organisms and the degree of bioturbation increased, and the biological habits evolved continuously, indicating that the sedimentary environment changed from from anoxic to oxic. [Conclusions] Based on the characteristics of ichnofossils, ichnofabrics, and sedimentary structures, the response relationship between the ichnofabrics and the sedimentary environment was established in the Pinghu Formation and Baoshi Formation in Pingbei area. The research results provide new evidence for the changes in sedimentary environment from the perspective of ichnology in the Eocene of Xihu Sag.
Abstract: [Objective] The abundant ichnofossils were developed in the Pinghu Formation and Baoshi Formation of the Eocene in Pingbei area, Xihu Sag. It is of practical significance for the division of sedimentary system in Xihu Sag to study the characteristics and distribution of its ichnofabrics and its indication of sedimentary environment. [Methods] Through core observations, the study identified ichnofossils and ichnofabrics in the Pingbei Area. The IDIPA technique was employed to objectively quantify ichnofossil abundance and accurately determine both the bioturbation index and the ichnofabric index. By integrating these findings with ichnological indices, this study summarizes the characteristics of the planar distribution and vertical evolution of ichnofabric in the study area. [Results and Discussions] (1) The research identified 6 ichnogenera of ichnofossils and divided them into 4 types of ichnofabrics, including Planolites ichnofabric, Thalassinoides ichnofabric, Teichichnus ichnofabric and Beaconites ichnofabric. (2) The study area features a high landform in the northwest and a low landform in the southeast. Seawater invades from south to north, and the sedimentary environment transitions from the subtidal zone to the intertidal zone, and finally to the supratidal zone, where the highest terrain is located in the northwest. The evolution pattern of the corresponding ichnofabrics follows the sequence Thalassinoides → Teichichnus → Planolites → Beaconites, consistent with the results of regional sedimentary zoning and paleoclimate analysis. (3) From the Pinghu to Baoshi Formation in the study area, it was found that the increase in the size, diversity, and abundance of ichnofossils. The tiering transitioned from simple and shallow to complex and deep. The variety of organisms and the degree of bioturbation increased, and the biological habits evolved continuously, indicating that the sedimentary environment changed from from anoxic to oxic. [Conclusions] Based on the characteristics of ichnofossils, ichnofabrics, and sedimentary structures, the response relationship between the ichnofabrics and the sedimentary environment was established in the Pinghu Formation and Baoshi Formation in Pingbei area. The research results provide new evidence for the changes in sedimentary environment from the perspective of ichnology in the Eocene of Xihu Sag.
Abstract:
[Objective] The western part of the Ordos Basin was located in the Qilian Sea area in the Middle-Late Ordovician Wulalike period, where a thick layer of black marine shale was developed. In recent years, many exploration wells in the Ordos Basin have produced industrial oil and gas flow from the Wulalike Formation, which demonstrates a good potential for exploration and development of marine shale oil and gas. The study of the Ordovician paleogeography in the western part of the basin is conducive to clarifying the distribution of hydrocarbon source rocks and reservoirs, as well as the next exploration direction of marine shale gas. [Methods] Through a large amount of field outcrops, drilling cores, rock thin sections, and elemental geochemistry data, this paper comprehensively studies the petrological characteristics, sedimentary facies types, and sedimentary evolution of the Wulalike Formation. [Results] The results show that: (1) Wulalike formation includes various types of rocks such as siliceous shale, calcareous shale, clay shale, mixed shale, and granular limestone, among which laminated siliceous shale was identified as the most favorable lithofacies for shale gas exploration; (2) Based on the analysis of sedimentary facies, five sedimentary facies types were identified from west to east: basin facies, broad sea shelf facies, slope facies, and carbonate platform facies; (3) During the Wulalike period, the western part of the Ordos Basin experienced multiple transgressive-regressive processes, with the water gradually becoming shallower and the sedimentary environment transitioning from deep water to shallow water. [Conclusion] In conclusion, a carbonate platform margin sedimentary model of the Wulalike period in the western Ordos Basin was established, and it was proposed that the broad sea shelf, slope, and granular shoal are favorable exploration facies for natural gas in the next step.
[Objective] The western part of the Ordos Basin was located in the Qilian Sea area in the Middle-Late Ordovician Wulalike period, where a thick layer of black marine shale was developed. In recent years, many exploration wells in the Ordos Basin have produced industrial oil and gas flow from the Wulalike Formation, which demonstrates a good potential for exploration and development of marine shale oil and gas. The study of the Ordovician paleogeography in the western part of the basin is conducive to clarifying the distribution of hydrocarbon source rocks and reservoirs, as well as the next exploration direction of marine shale gas. [Methods] Through a large amount of field outcrops, drilling cores, rock thin sections, and elemental geochemistry data, this paper comprehensively studies the petrological characteristics, sedimentary facies types, and sedimentary evolution of the Wulalike Formation. [Results] The results show that: (1) Wulalike formation includes various types of rocks such as siliceous shale, calcareous shale, clay shale, mixed shale, and granular limestone, among which laminated siliceous shale was identified as the most favorable lithofacies for shale gas exploration; (2) Based on the analysis of sedimentary facies, five sedimentary facies types were identified from west to east: basin facies, broad sea shelf facies, slope facies, and carbonate platform facies; (3) During the Wulalike period, the western part of the Ordos Basin experienced multiple transgressive-regressive processes, with the water gradually becoming shallower and the sedimentary environment transitioning from deep water to shallow water. [Conclusion] In conclusion, a carbonate platform margin sedimentary model of the Wulalike period in the western Ordos Basin was established, and it was proposed that the broad sea shelf, slope, and granular shoal are favorable exploration facies for natural gas in the next step.
Abstract:
The Santanghu Basin is an important oil and gas exploration area in northern Xinjiang, and a good understanding of sedimentary facies, sandbody distribution and associated provenance system within the basin play an important role in guiding the oil and gas exploration and development of the study area. This study uses core and well logging data to systematically study the distribution characteristics and depositional evolutions for the lower to middle Jurassic Tiaohu-Malang depressions in the Santanghu Basin. Additionally, heavy minerals and detrital U-Pb dating were combined to analyze the provenance for key intervals. During the lower to middle Jurassic, the Tiaohu-Malang depressions was mainly in a braided-river deltaic depositional environment. The Badaowan Formation was characterized by widespread distribution of braided-river delta fronts due to the large lacustrine basin. The sedimentary system was more developed in the northern part of Tiaohu Depression and extends far to the south, while the southern system has a limited distribution. The sedimentary system in the northern and southern parts of the Malang Depression extends a short distance into the depression. The Sangonghe Formation was dominated by isolated distributary channel deposits on the braided delta front with decreased lacustrine basin. As the lacustrine basin of the Tiaohu Depression migrated southward during the early Xishanyao time, a large area of lower delta plain developed in the north, and delta front developed in the central and southern parts. In the Malang Depression, the braided river delta fronts in the north are contiguously distributed, while the sand bodies in the south are relatively isolated. The analysis of heavy minerals and zircon U-Pb ages suggest that main sediments in the northeastern Tiaohu Depression were originated from the western Erdelunjin Mountains through a long transport distance during the lower Jurassic period. In the northern Malang Depression, the source-sink system had two possible sediment transport paths in the middle Jurassic time. Sediments were transported from the eastern part of the Erdelunjin Mountains and deposited near the Shayisubei and the Chahaquan area, and they were subsequently transported and deposited to the northern part of the Malang Depression as the area were uplifted. Another possible explanation is that sediments flowed from the eastern Erdelunjin Mountains into the northern part of the Malang Depression along the low paleotopographic areas with some sediments contributed from the Shayisubei Mountains.
The Santanghu Basin is an important oil and gas exploration area in northern Xinjiang, and a good understanding of sedimentary facies, sandbody distribution and associated provenance system within the basin play an important role in guiding the oil and gas exploration and development of the study area. This study uses core and well logging data to systematically study the distribution characteristics and depositional evolutions for the lower to middle Jurassic Tiaohu-Malang depressions in the Santanghu Basin. Additionally, heavy minerals and detrital U-Pb dating were combined to analyze the provenance for key intervals. During the lower to middle Jurassic, the Tiaohu-Malang depressions was mainly in a braided-river deltaic depositional environment. The Badaowan Formation was characterized by widespread distribution of braided-river delta fronts due to the large lacustrine basin. The sedimentary system was more developed in the northern part of Tiaohu Depression and extends far to the south, while the southern system has a limited distribution. The sedimentary system in the northern and southern parts of the Malang Depression extends a short distance into the depression. The Sangonghe Formation was dominated by isolated distributary channel deposits on the braided delta front with decreased lacustrine basin. As the lacustrine basin of the Tiaohu Depression migrated southward during the early Xishanyao time, a large area of lower delta plain developed in the north, and delta front developed in the central and southern parts. In the Malang Depression, the braided river delta fronts in the north are contiguously distributed, while the sand bodies in the south are relatively isolated. The analysis of heavy minerals and zircon U-Pb ages suggest that main sediments in the northeastern Tiaohu Depression were originated from the western Erdelunjin Mountains through a long transport distance during the lower Jurassic period. In the northern Malang Depression, the source-sink system had two possible sediment transport paths in the middle Jurassic time. Sediments were transported from the eastern part of the Erdelunjin Mountains and deposited near the Shayisubei and the Chahaquan area, and they were subsequently transported and deposited to the northern part of the Malang Depression as the area were uplifted. Another possible explanation is that sediments flowed from the eastern Erdelunjin Mountains into the northern part of the Malang Depression along the low paleotopographic areas with some sediments contributed from the Shayisubei Mountains.
Abstract:
Abstract: [Objective] Research on the weathering process of the aggradation red earth in subtropical China has long been crucial for understanding the evolution of the Quaternary environment. However, a comprehensive knowledge of the weathering environment of the aggradation red earth is hampered by the infrequent reporting of research on the weathering characteristics of the aggradation red earth at the spatial scale. [Methods] Based on a systematic analysis of the weathering characteristics of the aggradational red earth sections in southern China, this study focused on the Jinqu Basin, where non-zonal factors have a significant impact. The research primarily explored the chemical weathering characteristics and formation mechanisms of red earth within the basin, to deepen our understanding of the weathering features of aggradational red earth. [Results] The study shows that: 1) On a large scale, the weathering intensity of aggradational red earth in southern China is strongly correlated with hydrothermal conditions, with weathering intensifying as latitude decreases. However, the chemical weathering of red earth in certain locations or specific sections does not entirely conform to the latitudinal zonality in the mid-subtropical region between 25?N and 31?N, where aggradational red earth is widely spread. 2) The geochemical composition of aggradational red earth in the Jinqu Basin exhibits good consistency, with minimal differences in element enrichment or depletion among samples. However, there is regional variability in the degree of chemical weathering in the developmental stages of vermicular and typical red clays following the stagnation of vermicularization in the Jinqu Basin, compared with the chemical weathering characteristics of other aggradational red earth sections at the same latitude. 3) Influenced by a combination of factors such as provenance, topography, and local climate, the weathering characteristics of the aggradational red earth in the Jinqu Basin exhibit certain non-latitudinal zonal features. [Conclusion] The weathering characteristics of the aggradational red earth in southern China primarily follow a latitudinal zonal pattern under the large-scale monsoon evolution pattern. However, owing to the influence of non-zonal factors including topography, water, and differences in the geographic features of potential provenance, the chemical weathering of aggradational red earth also exhibits certain non-zonal characteristics within the mid-subtropical region between 25?N and 31?N. The relatively small and enclosed basin terrain of the Jinqu Basin, along with local microclimate conditions and contribution of bedrock weathering products to the red earth provenance, plays a significant role in interpreting the chemical weathering information of the red earth. Therefore, it is crucial to consider regional impacts while discussing the chemical weathering characteristics in different areas.
Abstract: [Objective] Research on the weathering process of the aggradation red earth in subtropical China has long been crucial for understanding the evolution of the Quaternary environment. However, a comprehensive knowledge of the weathering environment of the aggradation red earth is hampered by the infrequent reporting of research on the weathering characteristics of the aggradation red earth at the spatial scale. [Methods] Based on a systematic analysis of the weathering characteristics of the aggradational red earth sections in southern China, this study focused on the Jinqu Basin, where non-zonal factors have a significant impact. The research primarily explored the chemical weathering characteristics and formation mechanisms of red earth within the basin, to deepen our understanding of the weathering features of aggradational red earth. [Results] The study shows that: 1) On a large scale, the weathering intensity of aggradational red earth in southern China is strongly correlated with hydrothermal conditions, with weathering intensifying as latitude decreases. However, the chemical weathering of red earth in certain locations or specific sections does not entirely conform to the latitudinal zonality in the mid-subtropical region between 25?N and 31?N, where aggradational red earth is widely spread. 2) The geochemical composition of aggradational red earth in the Jinqu Basin exhibits good consistency, with minimal differences in element enrichment or depletion among samples. However, there is regional variability in the degree of chemical weathering in the developmental stages of vermicular and typical red clays following the stagnation of vermicularization in the Jinqu Basin, compared with the chemical weathering characteristics of other aggradational red earth sections at the same latitude. 3) Influenced by a combination of factors such as provenance, topography, and local climate, the weathering characteristics of the aggradational red earth in the Jinqu Basin exhibit certain non-latitudinal zonal features. [Conclusion] The weathering characteristics of the aggradational red earth in southern China primarily follow a latitudinal zonal pattern under the large-scale monsoon evolution pattern. However, owing to the influence of non-zonal factors including topography, water, and differences in the geographic features of potential provenance, the chemical weathering of aggradational red earth also exhibits certain non-zonal characteristics within the mid-subtropical region between 25?N and 31?N. The relatively small and enclosed basin terrain of the Jinqu Basin, along with local microclimate conditions and contribution of bedrock weathering products to the red earth provenance, plays a significant role in interpreting the chemical weathering information of the red earth. Therefore, it is crucial to consider regional impacts while discussing the chemical weathering characteristics in different areas.
Abstract:
[Objectives] Recent research suggests that the basin water depth as a downstream condition can govern delta morphodynamics. This is because basin water depth affects the subaerial and subaqueous allocation of sediment in the delta. Compared to deep-water deltas, shallow-water deltas have more sediment distribution in the subaerial part. As a result, the aggradation rate of distributary channels in shallow water deltas is higher, making the channel more active in terms of migration and avulsion. Recently, the Grade Index (Gindex) model is proposed to quantitively illustrate this process. [Methods] This paper elaborates the origin, theoretical modeling, experimental validation, and application of the grade index model and discusses its limitations. The grade here refers the graded state of rivers, which means sediment supplied into the river is conveyed without net deposition or net erosion but completely bypassed through the river. The grade index is defined as the ratio of the volume of sediment allocated subaerially to the total volume of sediment input in per unit time. According to its definition, the Gindex is a dimensionless number between 0 and 1. [Results] Theoretical analyses reveal that the Gindex negatively relates to the basin water depth, though also relates to the delta’s geometrical parameters including the radius of the delta plain and the slopes of the topset and foreset. If the basin water is deeper, the Gindex is closer to 0, which means less sediment is deposited subaerially per unit time. As a result, the channel is more stable and closer to the state of grade. Conversely, the Gindex gets closer to 1 with decreasing basin water depth. As a result, the delta plain becomes more aggradational, by which the channel becomes more unstable. The Gindex is able to reflect important geomorphodynamic parameters of the delta such as the rate of progradation, the rate of aggradation, the rate of channel migration, and the timescale of channel avulsion. Each of these parameters can be calculated as the product or quotient between Gindex and their counterparts obtained with negligibly small basin water depth, while the former is determined by the delta’s geometrical parameters and basin water depth and the latter is determined by the delta’s geometrical parameters and total sediment supply rate. This means that for a particular deltaic system with specific geometrical parameters, sediment supply rate and basin water depth, it has theoretical values for the grade index and geomorphodynamic parameters, both of which can be calculated. This speculation has been verified by tank experiments. The Gindex model is derived based on global mass balance of the deltaic system. Local and/or tentative depositional, erosional and dispersal processes such like related to the backwater effect and coastal processes including waves, tides and longshore currents, as well as effects outside of the depositional system (i.e. vegetation, anthropogenic process), are not considered. [Conclusion] So, the grade index model exclusively separates the "contribution" of basin water depth from others in terms of delta morphodynamics. On the one hand, it can reveal the principle of the differentiation of deep-water and shallow-water delta landforms, and on the other hand, it can help to explain the influence of factors other than basin water depth on the evolution of delta landforms. The grade index model has the potential for general application in modern alluvial-deltaic systems, while its application to ancient systems is yet to be explored.
[Objectives] Recent research suggests that the basin water depth as a downstream condition can govern delta morphodynamics. This is because basin water depth affects the subaerial and subaqueous allocation of sediment in the delta. Compared to deep-water deltas, shallow-water deltas have more sediment distribution in the subaerial part. As a result, the aggradation rate of distributary channels in shallow water deltas is higher, making the channel more active in terms of migration and avulsion. Recently, the Grade Index (Gindex) model is proposed to quantitively illustrate this process. [Methods] This paper elaborates the origin, theoretical modeling, experimental validation, and application of the grade index model and discusses its limitations. The grade here refers the graded state of rivers, which means sediment supplied into the river is conveyed without net deposition or net erosion but completely bypassed through the river. The grade index is defined as the ratio of the volume of sediment allocated subaerially to the total volume of sediment input in per unit time. According to its definition, the Gindex is a dimensionless number between 0 and 1. [Results] Theoretical analyses reveal that the Gindex negatively relates to the basin water depth, though also relates to the delta’s geometrical parameters including the radius of the delta plain and the slopes of the topset and foreset. If the basin water is deeper, the Gindex is closer to 0, which means less sediment is deposited subaerially per unit time. As a result, the channel is more stable and closer to the state of grade. Conversely, the Gindex gets closer to 1 with decreasing basin water depth. As a result, the delta plain becomes more aggradational, by which the channel becomes more unstable. The Gindex is able to reflect important geomorphodynamic parameters of the delta such as the rate of progradation, the rate of aggradation, the rate of channel migration, and the timescale of channel avulsion. Each of these parameters can be calculated as the product or quotient between Gindex and their counterparts obtained with negligibly small basin water depth, while the former is determined by the delta’s geometrical parameters and basin water depth and the latter is determined by the delta’s geometrical parameters and total sediment supply rate. This means that for a particular deltaic system with specific geometrical parameters, sediment supply rate and basin water depth, it has theoretical values for the grade index and geomorphodynamic parameters, both of which can be calculated. This speculation has been verified by tank experiments. The Gindex model is derived based on global mass balance of the deltaic system. Local and/or tentative depositional, erosional and dispersal processes such like related to the backwater effect and coastal processes including waves, tides and longshore currents, as well as effects outside of the depositional system (i.e. vegetation, anthropogenic process), are not considered. [Conclusion] So, the grade index model exclusively separates the "contribution" of basin water depth from others in terms of delta morphodynamics. On the one hand, it can reveal the principle of the differentiation of deep-water and shallow-water delta landforms, and on the other hand, it can help to explain the influence of factors other than basin water depth on the evolution of delta landforms. The grade index model has the potential for general application in modern alluvial-deltaic systems, while its application to ancient systems is yet to be explored.
Abstract:
Abstract: [Objective] The first member of Shawan Formation of Neogene in the east side of Chepaizi Uplift of the Junggar Basin has serious carbonate cementation and strong oil-bearing heterogeneity. The formation reasons of carbonate cements in the study area are analyzed deeply, and their effects on reservoir physical properties and oil content are discussed. [Methods] On the basis of core observation, the types, distribution characteristics, formation stages and genesis of shallow buried carbonate cements were studied by using the methods of observation and identification from thin sections, cathode luminescence (CL) analysis and X-Ray Diffraction (XRD) analysis. [Results and Discussions] The results show that there are at least three stages of carbonate cements in the first member of Shawan Formation. The carbonate cements in the first stage are mainly dominated by shell-like calcite and granular siderite. Under polarizing microscope, it can be observed that the edges of some mineral particles are replaced, and the continuity of cement is poor due to the influence of acidic fluids in the later stage. The results of cathode luminescence show that the calcite is bright yellow. The formation of carbonate cements is mainly influenced by paleo-climate and sedimentary water. The local area of the study area was influenced by the development of algae. The second and the third stage of carbonate cements are dominated by poikilitic calcite, of which the second-stage calcite is widely distributed. The results of cathode luminescence show that the calcite cement of the second stage is almost non-luminous and has the characteristics of high magnesium, while the calcite cement of the third stage is orange yellow. Under polarizing microscope, there are obvious corrosion marks at the boundary between the second and third stage of calcite cements. Both of the second and the third stage of carbonate cements are affected by hydrocarbon generation and expulsion from the middle and lower Jurassic source rocks in Changji Depression. Organic acid fluid dissolved the early carbonate cements and acid-soluble particles, providing the main material source for the development of subsequent carbonate cements. It is found that carbonate cement causes the poor physical properties of Shawan Formation reservoir in the early stage. The porosity and permeability of the reservoir are limited improved by the injection of acid fluid in the later stage. When the carbonate cement develops continuously in the plane, it forms thin inter-layers sealed by capillary pressure. Thin inter-layers formed by carbonate tight cementation control hydrocarbon migration and trap types in the reservoir to a certain extent. The tight cementation of carbonate effectively blocks the migration path of oil and gas, and oil and gas can only migrate and accumulate along a few structural fractures, which leads to obvious oil heterogeneity in the same set of sandstone in the study area. In addition, when the carbonate cements developed in the reservoir have large distribution area and high content, appear on the top of the sand body and most of them are basement cementation, a better cap layer will be formed, which will affect the accumulation of oil and gas to a certain extent. [Conclusions] The types, distribution characteristics, formation causes and geological significance of multistage carbonate cements are defined in the paper, which provides support for continuous exploration and development and searching for new exploration targets.
Abstract: [Objective] The first member of Shawan Formation of Neogene in the east side of Chepaizi Uplift of the Junggar Basin has serious carbonate cementation and strong oil-bearing heterogeneity. The formation reasons of carbonate cements in the study area are analyzed deeply, and their effects on reservoir physical properties and oil content are discussed. [Methods] On the basis of core observation, the types, distribution characteristics, formation stages and genesis of shallow buried carbonate cements were studied by using the methods of observation and identification from thin sections, cathode luminescence (CL) analysis and X-Ray Diffraction (XRD) analysis. [Results and Discussions] The results show that there are at least three stages of carbonate cements in the first member of Shawan Formation. The carbonate cements in the first stage are mainly dominated by shell-like calcite and granular siderite. Under polarizing microscope, it can be observed that the edges of some mineral particles are replaced, and the continuity of cement is poor due to the influence of acidic fluids in the later stage. The results of cathode luminescence show that the calcite is bright yellow. The formation of carbonate cements is mainly influenced by paleo-climate and sedimentary water. The local area of the study area was influenced by the development of algae. The second and the third stage of carbonate cements are dominated by poikilitic calcite, of which the second-stage calcite is widely distributed. The results of cathode luminescence show that the calcite cement of the second stage is almost non-luminous and has the characteristics of high magnesium, while the calcite cement of the third stage is orange yellow. Under polarizing microscope, there are obvious corrosion marks at the boundary between the second and third stage of calcite cements. Both of the second and the third stage of carbonate cements are affected by hydrocarbon generation and expulsion from the middle and lower Jurassic source rocks in Changji Depression. Organic acid fluid dissolved the early carbonate cements and acid-soluble particles, providing the main material source for the development of subsequent carbonate cements. It is found that carbonate cement causes the poor physical properties of Shawan Formation reservoir in the early stage. The porosity and permeability of the reservoir are limited improved by the injection of acid fluid in the later stage. When the carbonate cement develops continuously in the plane, it forms thin inter-layers sealed by capillary pressure. Thin inter-layers formed by carbonate tight cementation control hydrocarbon migration and trap types in the reservoir to a certain extent. The tight cementation of carbonate effectively blocks the migration path of oil and gas, and oil and gas can only migrate and accumulate along a few structural fractures, which leads to obvious oil heterogeneity in the same set of sandstone in the study area. In addition, when the carbonate cements developed in the reservoir have large distribution area and high content, appear on the top of the sand body and most of them are basement cementation, a better cap layer will be formed, which will affect the accumulation of oil and gas to a certain extent. [Conclusions] The types, distribution characteristics, formation causes and geological significance of multistage carbonate cements are defined in the paper, which provides support for continuous exploration and development and searching for new exploration targets.
Abstract:
Abstract: [Objective] Climate change caused by astronomical orbital parameters is closely related to biological turnover and sedimentary evolution of the ocean and lakes, which in turn affects the organic matter enrichment in the strata. The late Paleozoic coal-bearing rock system in North China is dominated by coal, mudstone, siltstone, sandstone and tuff observed in a number of depositional cycles in the vertical direction. It is also an important system for current oil and gas exploration and development. The aim of this study is to systematically reveal the influence of the astronomical orbital cycle on organic matter enrichment in this coal-bearing system. [Methods] Natural gamma logging sequences were obtained for four wells (sampling distance 0.05 m) and continuous mineral elements for one well (sampling distance 1 m) in western North China. Astronomical cyclotron time series data and elemental geochemical analysis of typical samples were used to clarify the pattern of organic matter enrichment in stratigraphic cyclotrons at different scales. [Results and Discussions] (1) Six 1.2 Myr ultra-long obliquity cycles and eighteen 405 kyr long eccentricity cycles are recognizable in the Carboniferous–Permian Benxi, Taiyuan and Shanxi Formations. (2) Using Mg/Ca, SiO2/Al2O3, Fe/Mn and V/(V+Ni) ratios as paleoclimate and paleoredox proxies, six long-period variations and 18 medium-period variations were identified, all corresponding with ultra-long obliquities and long eccentricities. (3) Comparative analyses of paleoenvironmental restoration and organic carbon content during the depositional period of the Benxi–Shanxi Formations show that paleoclimate evolution and organic matter enrichment are basically synchronized and controlled by the astronomical orbital cycle, and that during periods of increasing ultra-long obliquity or long eccentricity the climate is warm and humid and the reducing nature of bodies of water is enhanced, which promotes organic matter enrichment. [Conclusions] The above results reveal Carboniferous–Permian climate change in North China influenced by the astronomical orbital cycle and the development of a constrained organic matter-rich stratigraphy, and find that the paleoclimate change during the same period was obviously constrained by the long eccentricity. The findings can be used as a reference for the study of global climate evolution and organic matter enrichment mechanism in the Permian.
Abstract: [Objective] Climate change caused by astronomical orbital parameters is closely related to biological turnover and sedimentary evolution of the ocean and lakes, which in turn affects the organic matter enrichment in the strata. The late Paleozoic coal-bearing rock system in North China is dominated by coal, mudstone, siltstone, sandstone and tuff observed in a number of depositional cycles in the vertical direction. It is also an important system for current oil and gas exploration and development. The aim of this study is to systematically reveal the influence of the astronomical orbital cycle on organic matter enrichment in this coal-bearing system. [Methods] Natural gamma logging sequences were obtained for four wells (sampling distance 0.05 m) and continuous mineral elements for one well (sampling distance 1 m) in western North China. Astronomical cyclotron time series data and elemental geochemical analysis of typical samples were used to clarify the pattern of organic matter enrichment in stratigraphic cyclotrons at different scales. [Results and Discussions] (1) Six 1.2 Myr ultra-long obliquity cycles and eighteen 405 kyr long eccentricity cycles are recognizable in the Carboniferous–Permian Benxi, Taiyuan and Shanxi Formations. (2) Using Mg/Ca, SiO2/Al2O3, Fe/Mn and V/(V+Ni) ratios as paleoclimate and paleoredox proxies, six long-period variations and 18 medium-period variations were identified, all corresponding with ultra-long obliquities and long eccentricities. (3) Comparative analyses of paleoenvironmental restoration and organic carbon content during the depositional period of the Benxi–Shanxi Formations show that paleoclimate evolution and organic matter enrichment are basically synchronized and controlled by the astronomical orbital cycle, and that during periods of increasing ultra-long obliquity or long eccentricity the climate is warm and humid and the reducing nature of bodies of water is enhanced, which promotes organic matter enrichment. [Conclusions] The above results reveal Carboniferous–Permian climate change in North China influenced by the astronomical orbital cycle and the development of a constrained organic matter-rich stratigraphy, and find that the paleoclimate change during the same period was obviously constrained by the long eccentricity. The findings can be used as a reference for the study of global climate evolution and organic matter enrichment mechanism in the Permian.
Abstract:
[Objective]The Lower Triassic Feixianguan Formation in Sichuan basin develops thick oolitic beach reservoirs, which is the key layer of current oil and gas exploration. As the reserve strategic replacement field of Sichuan Basin, the sedimentary system, reservoir characteristics and favorable zone distribution of Feixianguan Formation in Tieshanpo and Qilibei areas are not clear, which restricts the deployment of oil and gas exploration in this area. [Methods]Based on the comprehensive analysis of core, rock slice, logging and seismic data, the sedimentary facies types, evolution rules and favorable reservoir zones of the Lower Triassic Feixianguan Formation in Tieshanpo and Qilibei areas were studied. [Results]The Feixianguan Formation in the study area develops a rimmed platform model, which can be subdivided into five sedimentary facies:restricted platform, open platform, platform edge, slope and basin. The platform margin is the favorable facies belt for the development of oolitic beach. The development of oolitic shoals in the area has obvious aggradation-lateral accretion characteristics, which are mostly superimposed in 2 to 3 periods vertically, and are distributed in ssq2 to ssq4 periods, with the largest scale in ssq2 period. Horizontally, the beach body is unstable and has a tendency to migrate into the basin; The reservoir rock types are mainly (residual) oolitic limestone, (residual) oolitic dolomite and powder crystal-fine crystal dolomite. [Conclusions]The platform margin oolitic beach is a favorable microfacies for reservoir development in Feixianguan Formation, and the porosity and permeability conditions are good. The area of wells Po5-Poxi1-Po2-Po1 in the Tieshanpo area is a favorable reservoir development zone, and the area of wells Qilibei1-Qibei102 in Qilibei area is a potential favorable reservoir development zone.The spatial and temporal distribution and migration law of beach bodies in different areas of the fourth-order sequence framework and the prediction results of favorable reservoir zones can provide a basis for deepening the exploration and development of oolitic beach reservoirs in this area.
[Objective]The Lower Triassic Feixianguan Formation in Sichuan basin develops thick oolitic beach reservoirs, which is the key layer of current oil and gas exploration. As the reserve strategic replacement field of Sichuan Basin, the sedimentary system, reservoir characteristics and favorable zone distribution of Feixianguan Formation in Tieshanpo and Qilibei areas are not clear, which restricts the deployment of oil and gas exploration in this area. [Methods]Based on the comprehensive analysis of core, rock slice, logging and seismic data, the sedimentary facies types, evolution rules and favorable reservoir zones of the Lower Triassic Feixianguan Formation in Tieshanpo and Qilibei areas were studied. [Results]The Feixianguan Formation in the study area develops a rimmed platform model, which can be subdivided into five sedimentary facies:restricted platform, open platform, platform edge, slope and basin. The platform margin is the favorable facies belt for the development of oolitic beach. The development of oolitic shoals in the area has obvious aggradation-lateral accretion characteristics, which are mostly superimposed in 2 to 3 periods vertically, and are distributed in ssq2 to ssq4 periods, with the largest scale in ssq2 period. Horizontally, the beach body is unstable and has a tendency to migrate into the basin; The reservoir rock types are mainly (residual) oolitic limestone, (residual) oolitic dolomite and powder crystal-fine crystal dolomite. [Conclusions]The platform margin oolitic beach is a favorable microfacies for reservoir development in Feixianguan Formation, and the porosity and permeability conditions are good. The area of wells Po5-Poxi1-Po2-Po1 in the Tieshanpo area is a favorable reservoir development zone, and the area of wells Qilibei1-Qibei102 in Qilibei area is a potential favorable reservoir development zone.The spatial and temporal distribution and migration law of beach bodies in different areas of the fourth-order sequence framework and the prediction results of favorable reservoir zones can provide a basis for deepening the exploration and development of oolitic beach reservoirs in this area.
Abstract:
Fluvial deposit is widely developed in natural strata, and meandering river deposit is an important part of fluvial deposit. Due to the frequent channel migration during the development of meandering river and the development of a large number of lateral deposits, the superposition relationship of sand bodies inside the point dam is complicated, so the analysis of the evolution process of meandering river has been the focus of sedimentological research. The analysis of controlling factors of meansional river morphology is of great significance to the study of paleoclimate evolution, continental weathering intensity and the exploration and development of oil and gas reservoirs. Previous scholars summarized the initial conditions for the generation of a zigzagging river by observing modern river sediments, and studied the effects of different clay mineral content, vegetation cover and initial saturation of river bed on the development of a zigzagging river. However, the development period of river sediments in nature is too long, and the dynamic sedimentation process of river cannot be well observed through field investigation and dissected outcrop, and the recording process is susceptible to interference by environmental factors. And lack of quantitative data support. In this paper, the effects of channel migration and dam body development on meander river development under single factor conditions were studied through flume sedimentation simulation experiments. In this study, three sets of experiments under different particle size, flow and clay mineral content were set up, and high-precision 3D laser scanner was used to convert the data into an elevation model for quantitative study of profile structure and bed sediment changes. The experimental results show that: (1) the particle size of the source sand directly affects the curvature of the meander river. Under the condition of constant clay content and constant flow, the smaller the particle size of the sand, the greater the curvature of the meander river formed. There are obvious differences in the structure of bank collapse sand bodies under different particle size conditions; (2) When the discharge affects the sediment transport balance and the flow impact force on the riverbank during the development of meandering river, when the sediment input rate and transport rate are in dynamic equilibrium, the riverbank maintains outward expansion and erosion, and the channel develops into meandering river form; (3) The addition of clay minerals to river banks can improve the permeability resistance of river banks. Under the condition that the source sand grain size and flow rate remain unchanged, the higher the clay mineral content, the lower the width to depth ratio of river channels.
Fluvial deposit is widely developed in natural strata, and meandering river deposit is an important part of fluvial deposit. Due to the frequent channel migration during the development of meandering river and the development of a large number of lateral deposits, the superposition relationship of sand bodies inside the point dam is complicated, so the analysis of the evolution process of meandering river has been the focus of sedimentological research. The analysis of controlling factors of meansional river morphology is of great significance to the study of paleoclimate evolution, continental weathering intensity and the exploration and development of oil and gas reservoirs. Previous scholars summarized the initial conditions for the generation of a zigzagging river by observing modern river sediments, and studied the effects of different clay mineral content, vegetation cover and initial saturation of river bed on the development of a zigzagging river. However, the development period of river sediments in nature is too long, and the dynamic sedimentation process of river cannot be well observed through field investigation and dissected outcrop, and the recording process is susceptible to interference by environmental factors. And lack of quantitative data support. In this paper, the effects of channel migration and dam body development on meander river development under single factor conditions were studied through flume sedimentation simulation experiments. In this study, three sets of experiments under different particle size, flow and clay mineral content were set up, and high-precision 3D laser scanner was used to convert the data into an elevation model for quantitative study of profile structure and bed sediment changes. The experimental results show that: (1) the particle size of the source sand directly affects the curvature of the meander river. Under the condition of constant clay content and constant flow, the smaller the particle size of the sand, the greater the curvature of the meander river formed. There are obvious differences in the structure of bank collapse sand bodies under different particle size conditions; (2) When the discharge affects the sediment transport balance and the flow impact force on the riverbank during the development of meandering river, when the sediment input rate and transport rate are in dynamic equilibrium, the riverbank maintains outward expansion and erosion, and the channel develops into meandering river form; (3) The addition of clay minerals to river banks can improve the permeability resistance of river banks. Under the condition that the source sand grain size and flow rate remain unchanged, the higher the clay mineral content, the lower the width to depth ratio of river channels.
Abstract:
[Objective]The research on sandy braided river delta has lots of achievements, but the sedimentary characteristics and evolution laws of sandy braided river delta keep different views, especially the understanding of mouth bars and distributary sand bars needs to be further study.[Methods]Based on the underground reservoir data, the paper uses the Delft3D software to show the growth and evolution process of the sandy braided river delta into the lake, summarizing it’ s sedimentary characteristics and evolution laws.[Results]The evolution of sandy braided river delta has three stages.In the early stage,the delta grows fastest, and the average diameter growth rate was greater than 6m/step. Sediments are carried into the lake and quickly unloaded, forming a large flower-shaped mouth bar under the water. In the middle stage, the delta plain keeps growing, the delta front keeps large,accounting for more than 50% of the delta. Contiguous sand bodies are built. In the late stage, the delta grows slowly, the average diameter growth rate is maintained at 1m/step.The front area is small, less than 20 % of the overall area.The delta plain has many distributary channels and ditches.There are many ways to transform the distributary sand bars.The delta front sand bars have different degrees of superposition relationship and rhythm combination characteristics, and the distributary sand bars are built on the residual mouth bar.[Conclusions]The sedimentary model of sandy braided river delta was established, which can provides reference for the genetic identification of distributary sand bars and mouth bars for the better study of underground reservoir architecture.
[Objective]The research on sandy braided river delta has lots of achievements, but the sedimentary characteristics and evolution laws of sandy braided river delta keep different views, especially the understanding of mouth bars and distributary sand bars needs to be further study.[Methods]Based on the underground reservoir data, the paper uses the Delft3D software to show the growth and evolution process of the sandy braided river delta into the lake, summarizing it’ s sedimentary characteristics and evolution laws.[Results]The evolution of sandy braided river delta has three stages.In the early stage,the delta grows fastest, and the average diameter growth rate was greater than 6m/step. Sediments are carried into the lake and quickly unloaded, forming a large flower-shaped mouth bar under the water. In the middle stage, the delta plain keeps growing, the delta front keeps large,accounting for more than 50% of the delta. Contiguous sand bodies are built. In the late stage, the delta grows slowly, the average diameter growth rate is maintained at 1m/step.The front area is small, less than 20 % of the overall area.The delta plain has many distributary channels and ditches.There are many ways to transform the distributary sand bars.The delta front sand bars have different degrees of superposition relationship and rhythm combination characteristics, and the distributary sand bars are built on the residual mouth bar.[Conclusions]The sedimentary model of sandy braided river delta was established, which can provides reference for the genetic identification of distributary sand bars and mouth bars for the better study of underground reservoir architecture.
Abstract:
Abstract：[Objective] In this paper, the effect of seasonal lake level changes on the sedimentary characteristics, growth process, and sedimentary architecture of the bar fingers in shallow delta fronts is clarified. [Methods] Based on the modern mud and sand and hydrological data of the bar fingers in the Ganjiang Delta, the sedimentary numerical simulation software Delft3D, which is commonly used in China and abroad, is used to carry out numerical simulation of the sedimentation of the bar fingers under seasonal lake level changes and constant lake level conditions, and to compare the differences in sedimentary architectures. [Results] The study shows that under the condition of seasonal lake level changes, the bar fingers exhibit the following sedimentary architecture and growth evolution characteristics: (1) There are few bar fingers, small curvature, with an average value of about 1.42, long length, with an average value of about 9.2 km, thick in the middle, thin at the edge, with a thickness difference of 15.4 m, there is no obvious confluence between the bar fingers, presenting a plane combination style dominated by bird-foot shape; (2) The bar fingers develop deep distributary channels, the natural levees are wide and thick, and the thickness of the single-stage accretionary body in the mouth bar is large; (3) Under seasonal lake level changes, the bar fingers grow stably. During the period of lake level drop, the bar fingers undergo progradation, the distributary channels are mainly eroded-extended, and mouth bar deposits are formed at the front edge of the distributary channels. The distributary channels are also affected by the mouth bars and will undergo diversion and breach, forming multiple terminal distributary channels, while the natural levees are almost undeveloped; during the period of lake level rise, the bar fingers undergo retrogradation, the erosion of the distributary channels is weak, the distributary channels are abandoned and optimized, and the natural levees on both sides of the distributary channels accumulate and continue to thicken. Under the condition of constant lake level, the bar fingers show the following sedimentary architecture and growth evolution characteristics: (1) There are many bar fingers, with large curvature (average value is about 1.53), short length (average value is about 7.2 km), large overall thickness (maximum and minimum thickness differ by only 4.8 m), no obvious topographic difference, multiple bar fingers are constantly bifurcated and merged locally, forming a complex the bar fingers network, and the plane combination style of the bar fingers is mainly interlaced; (2) Deep distributary channels are also developed in the bar fingers, and the single-stage accretion body of the estuary bar is thick, but the most important difference is that there is no natural levee deposition; (3) The growth process of the bar fingers is relatively simple, mainly multiple the bar fingers grow simultaneously, intertwine with each other, and finally form an interlaced plane combination style. [Conclusion] Therefore, seasonal lake level change is an important formation condition for the bar fingers at the front of shallow deltas, which promotes the development of natural levees, improves the stability of distributary channels and the bar fingers, and plays an important role in controlling the sedimentary architecture and growth process of the bar fingers.
Abstract：[Objective] In this paper, the effect of seasonal lake level changes on the sedimentary characteristics, growth process, and sedimentary architecture of the bar fingers in shallow delta fronts is clarified. [Methods] Based on the modern mud and sand and hydrological data of the bar fingers in the Ganjiang Delta, the sedimentary numerical simulation software Delft3D, which is commonly used in China and abroad, is used to carry out numerical simulation of the sedimentation of the bar fingers under seasonal lake level changes and constant lake level conditions, and to compare the differences in sedimentary architectures. [Results] The study shows that under the condition of seasonal lake level changes, the bar fingers exhibit the following sedimentary architecture and growth evolution characteristics: (1) There are few bar fingers, small curvature, with an average value of about 1.42, long length, with an average value of about 9.2 km, thick in the middle, thin at the edge, with a thickness difference of 15.4 m, there is no obvious confluence between the bar fingers, presenting a plane combination style dominated by bird-foot shape; (2) The bar fingers develop deep distributary channels, the natural levees are wide and thick, and the thickness of the single-stage accretionary body in the mouth bar is large; (3) Under seasonal lake level changes, the bar fingers grow stably. During the period of lake level drop, the bar fingers undergo progradation, the distributary channels are mainly eroded-extended, and mouth bar deposits are formed at the front edge of the distributary channels. The distributary channels are also affected by the mouth bars and will undergo diversion and breach, forming multiple terminal distributary channels, while the natural levees are almost undeveloped; during the period of lake level rise, the bar fingers undergo retrogradation, the erosion of the distributary channels is weak, the distributary channels are abandoned and optimized, and the natural levees on both sides of the distributary channels accumulate and continue to thicken. Under the condition of constant lake level, the bar fingers show the following sedimentary architecture and growth evolution characteristics: (1) There are many bar fingers, with large curvature (average value is about 1.53), short length (average value is about 7.2 km), large overall thickness (maximum and minimum thickness differ by only 4.8 m), no obvious topographic difference, multiple bar fingers are constantly bifurcated and merged locally, forming a complex the bar fingers network, and the plane combination style of the bar fingers is mainly interlaced; (2) Deep distributary channels are also developed in the bar fingers, and the single-stage accretion body of the estuary bar is thick, but the most important difference is that there is no natural levee deposition; (3) The growth process of the bar fingers is relatively simple, mainly multiple the bar fingers grow simultaneously, intertwine with each other, and finally form an interlaced plane combination style. [Conclusion] Therefore, seasonal lake level change is an important formation condition for the bar fingers at the front of shallow deltas, which promotes the development of natural levees, improves the stability of distributary channels and the bar fingers, and plays an important role in controlling the sedimentary architecture and growth process of the bar fingers.
Abstract:
The integration of deposition physical simulation and numerical simulation is an inevitable trend in the development of deposition simulation technology. Taking the shoal water delta as an example, the author explores the feasibility of integrating deposition physical simulation and numerical simulation. Three variables, namely sediment ratio, lake level change, and inlet discharge, were selected to simulate shoal water deltas using deposition physical and numerical simulation methods. Quantitative analysis was conducted using indicators such as the length-width ratio, area, and shoreline roughness. The analysis results indicate that there are differences in details between the physical simulation and numerical simulation of deposition in shoal water deltas, but they are consistent in macroscopic changes. And the similarity between the two simulation results is relatively high. This study is of great significance for the integrated exploration of deposition physical simulation and deposition numerical simulation.
The integration of deposition physical simulation and numerical simulation is an inevitable trend in the development of deposition simulation technology. Taking the shoal water delta as an example, the author explores the feasibility of integrating deposition physical simulation and numerical simulation. Three variables, namely sediment ratio, lake level change, and inlet discharge, were selected to simulate shoal water deltas using deposition physical and numerical simulation methods. Quantitative analysis was conducted using indicators such as the length-width ratio, area, and shoreline roughness. The analysis results indicate that there are differences in details between the physical simulation and numerical simulation of deposition in shoal water deltas, but they are consistent in macroscopic changes. And the similarity between the two simulation results is relatively high. This study is of great significance for the integrated exploration of deposition physical simulation and deposition numerical simulation.
Abstract:
[Objective] Microscopic reservoir characteristics of laminated shales in the third member of the Middle Ordovician Wulalike Formation, western margin of the Ordos Basin have been studied to further understand the effectiveness of laminated shale reservoirs.[Methods] This study employs an integrated approach of X-ray diffraction (XRD), scanning electron microscopy (SEM) and mineral mapping, organic geochemical analysis, CO2 and N2 adsorption and mercury injection capillary pressure tests to comparatively analyze differences in mineralogy, organic geochemistry and pore structures between different textures within laminated shales obtained by mechanical separation.[Result] The laminated shales consist of limestone and tuff laminae and silica-rich beds. Limestone and tuff laminae with density of 60~180/m have lower contents of organic carbon than silica-rich beds. Laminated shales contain both pore and fractures. In silica-rich beds, clay minerals-related interparticle and intraparticle pores are abundant with rare organic pores. Calcite and dolomite intraparticle dissolved pores are dominant pore type in limestone laminae. Tuff laminae contain pyrite intercrystalline pores, clay-related interparticle and intraparticle pores, and dolomite intraparticle dissolved pores. Dissolved pores of carbonate minerals in limestone and tuff laminae are related to dissolution of acid fluids generated by organic matter thermal evolution in silica-rich beds. Near-horizontal fractures develop along boundaries between limestone and tuff laminae and silica-rich beds. Density of the near-horizontal fracture is 63~130 /m, and their width is 0.2~4.9 mm. Limestone and tuff laminae have less abundant micro-pores but more abundant macro-pores than silica-rich beds. The volume of macro-pores in limestone laminae is 2.5~4.3 times, and the contribution of macro-pores to total pore volume is 1.9~2.1 times as much as adjacent silica-rich beds. The volume of macro-pores in tuff laminae is 1.5-2.3 times as much as adjacent silica-rich beds. [Conclusion] In laminated shale reservoirs, oil and gas generated in silica-rich beds migrated along pores and fractures, and preferentially enriched in adjacent limestone and tuff laminae. Limestone and tuff laminae contain more abundant macropores and more free gas than silica-rich beds. The Wulalike Formation laminated shale reservoirs have high proportion of free gas, which are related to limestone and tuff laminae.
[Objective] Microscopic reservoir characteristics of laminated shales in the third member of the Middle Ordovician Wulalike Formation, western margin of the Ordos Basin have been studied to further understand the effectiveness of laminated shale reservoirs.[Methods] This study employs an integrated approach of X-ray diffraction (XRD), scanning electron microscopy (SEM) and mineral mapping, organic geochemical analysis, CO2 and N2 adsorption and mercury injection capillary pressure tests to comparatively analyze differences in mineralogy, organic geochemistry and pore structures between different textures within laminated shales obtained by mechanical separation.[Result] The laminated shales consist of limestone and tuff laminae and silica-rich beds. Limestone and tuff laminae with density of 60~180/m have lower contents of organic carbon than silica-rich beds. Laminated shales contain both pore and fractures. In silica-rich beds, clay minerals-related interparticle and intraparticle pores are abundant with rare organic pores. Calcite and dolomite intraparticle dissolved pores are dominant pore type in limestone laminae. Tuff laminae contain pyrite intercrystalline pores, clay-related interparticle and intraparticle pores, and dolomite intraparticle dissolved pores. Dissolved pores of carbonate minerals in limestone and tuff laminae are related to dissolution of acid fluids generated by organic matter thermal evolution in silica-rich beds. Near-horizontal fractures develop along boundaries between limestone and tuff laminae and silica-rich beds. Density of the near-horizontal fracture is 63~130 /m, and their width is 0.2~4.9 mm. Limestone and tuff laminae have less abundant micro-pores but more abundant macro-pores than silica-rich beds. The volume of macro-pores in limestone laminae is 2.5~4.3 times, and the contribution of macro-pores to total pore volume is 1.9~2.1 times as much as adjacent silica-rich beds. The volume of macro-pores in tuff laminae is 1.5-2.3 times as much as adjacent silica-rich beds. [Conclusion] In laminated shale reservoirs, oil and gas generated in silica-rich beds migrated along pores and fractures, and preferentially enriched in adjacent limestone and tuff laminae. Limestone and tuff laminae contain more abundant macropores and more free gas than silica-rich beds. The Wulalike Formation laminated shale reservoirs have high proportion of free gas, which are related to limestone and tuff laminae.
Abstract:
Based on organic geochemistry, XRD, FE-SEM, combined with the regional structure and sedimentary evolution characteristics, through the comprehensive analysis of the distribution and development characteristics, reservoir characteristics and preservation conditions of shale in the Wulalike Formation (or Pingliang Formation), the formation geological conditions and exploration potential of shale gas in the Ordovician Wulalike Formation (or Pingliang Formation) in the western margin of the Ordos Basin have been systematically studied. The stratigraphic thickness of the Wulalike Formation(or Pingliang Formation) in the western margin of the Ordos Basin varies greatly, with the thickness of about 10 ~ 80m in the north and central parts and more than 1000m in the south part. The TOC is between 0.10% and 1.40%, and the organic matter type is mainly type I (sapropelic type). The shale in the north and middle part was deeply buried , with a high degree of thermal evolution, and is in the gas generation stage, while the southern part is affected by the thrust of the western margin, which generates both oil and gas. Various types of pores are developed in the Wulalike shale, including intergranular pores, intragranular pores, microfractures and a small amount of organic matter pores. Compared with the Longmaxi shales, although the overall porosity of the Wulalike shale is low, the content of brittle mineral is high, microfractures are relatively developed, and its permeability is better than that of the Longmaxi shales. In the western margin of the basin, the fault in Wulalike Formation is generally undeveloped, and the underlying Kelimoli Formation is mainly limestone and the overlying Lashizhong Formation is mainly shale and micrite limestone, which have good sealing capability and favorable for the enrichment of shale gas. From the stratigraphic distribution, gas generation potential, fracturing ability, preservation conditions and other parameters of the Wulalike Formation, it is believed that the south of Tiekesumao in the north part of the western margin and the west of Gufengzhuang in the middle part have good marine shale gas exploration potential.
Based on organic geochemistry, XRD, FE-SEM, combined with the regional structure and sedimentary evolution characteristics, through the comprehensive analysis of the distribution and development characteristics, reservoir characteristics and preservation conditions of shale in the Wulalike Formation (or Pingliang Formation), the formation geological conditions and exploration potential of shale gas in the Ordovician Wulalike Formation (or Pingliang Formation) in the western margin of the Ordos Basin have been systematically studied. The stratigraphic thickness of the Wulalike Formation(or Pingliang Formation) in the western margin of the Ordos Basin varies greatly, with the thickness of about 10 ~ 80m in the north and central parts and more than 1000m in the south part. The TOC is between 0.10% and 1.40%, and the organic matter type is mainly type I (sapropelic type). The shale in the north and middle part was deeply buried , with a high degree of thermal evolution, and is in the gas generation stage, while the southern part is affected by the thrust of the western margin, which generates both oil and gas. Various types of pores are developed in the Wulalike shale, including intergranular pores, intragranular pores, microfractures and a small amount of organic matter pores. Compared with the Longmaxi shales, although the overall porosity of the Wulalike shale is low, the content of brittle mineral is high, microfractures are relatively developed, and its permeability is better than that of the Longmaxi shales. In the western margin of the basin, the fault in Wulalike Formation is generally undeveloped, and the underlying Kelimoli Formation is mainly limestone and the overlying Lashizhong Formation is mainly shale and micrite limestone, which have good sealing capability and favorable for the enrichment of shale gas. From the stratigraphic distribution, gas generation potential, fracturing ability, preservation conditions and other parameters of the Wulalike Formation, it is believed that the south of Tiekesumao in the north part of the western margin and the west of Gufengzhuang in the middle part have good marine shale gas exploration potential.
Abstract:
[Objectives] It is important to clarify the coupling relationship between the differences in pore space characteristics of marine shale and lithology, material composition, pore structure, etc., as well as their geological significance for shale gas enrichment, in order to evaluate the gas bearing properties of the Wulalike Formation shale in the western Ordos Basin. This study aims to determine the pore space characteristics and intrinsic coupling factors of the Wulalike Formation shale gas reservoir, and to discuss the geological significance of shale gas in combination with the vertical development characteristics of lithofacies. [Methods] This study conducted analysis and testing experiments related to reservoir physical properties, pore structure, and adsorption capacity. Based on the previous research results and the classification of typical shale lithofacies, the differences in porosity and their key influencing factors of shale with different lithofacies were clarified. With the gas bearing characteristics of shale as constraints, the longitudinal hydrocarbon enrichment intervals of shale were explored. [Results] The overall porosity of the shale in the Wulalike Formation is relatively small, ranging from 0.37% to 5.01%, with an average of only 2.03%. The porosity of the Wulalike Formation shale shows an increasing trend from bottom to top, TOC, quartz content, and the proportion of biogenic silica decrease accordingly. And the correlation between porosity and permeability is not significant. Unlike the Longmaxi Formation shale, the target shale has high biogenic silica and low TOC content as a whole. Due to the low overall TOC content, fewer organic matter pores, and weak hydrocarbon generation and expulsion ability, and biogenic silica mainly occupies small pores and mesopores spaces. The negative correlation coefficients of small pores, mesopores, macropores, and biogenic silicon content are 0.3922, 0.2118, and 0.0403, respectively. As the ratio of biogenic silica to TOC increases, there is no observed trend in the traditional understanding that porosity increases with the increase of TOC. [Conclusion] Poor hydrocarbon generation ability caused by low TOC content and relatively low degree of thermal evolution limits the accumulation of hydrocarbons in the Wulalike Formation shale, and biogenic silica manifested as cementation reducing pore size rather than supporting pore enlargement. Therefore, compared to detrital siliceous shale and detrital mixed shale, biogenic siliceous shale exhibits lower porosity, poorer pore structure characteristics, and poorer fluid mobility characteristics. However, an increase in organic matter content can improve this phenomenon to some extent in the biogenic siliceous shale. The upper part of the target layer is mainly composed of mixed shale lithofacies, which has high debris content and porosity, but low organic matter content and poor hydrocarbon generation and drainage capacity. After the peak hydrocarbon generation period at the bottom, it is easy to cause formation water backflow. Transitioning towards the bottom into biogenic siliceous shale lithofacies, although the TOC content is relatively high, the biogenic siliceous cementation is unfavorable for reservoir performance. Based on the characteristics of pore space, the alternating development of multiple lithofacies shale sites in the upper part of the development site of biogenic siliceous shale is expected to indicate the enrichment site of shale gas under low TOC background.
[Objectives] It is important to clarify the coupling relationship between the differences in pore space characteristics of marine shale and lithology, material composition, pore structure, etc., as well as their geological significance for shale gas enrichment, in order to evaluate the gas bearing properties of the Wulalike Formation shale in the western Ordos Basin. This study aims to determine the pore space characteristics and intrinsic coupling factors of the Wulalike Formation shale gas reservoir, and to discuss the geological significance of shale gas in combination with the vertical development characteristics of lithofacies. [Methods] This study conducted analysis and testing experiments related to reservoir physical properties, pore structure, and adsorption capacity. Based on the previous research results and the classification of typical shale lithofacies, the differences in porosity and their key influencing factors of shale with different lithofacies were clarified. With the gas bearing characteristics of shale as constraints, the longitudinal hydrocarbon enrichment intervals of shale were explored. [Results] The overall porosity of the shale in the Wulalike Formation is relatively small, ranging from 0.37% to 5.01%, with an average of only 2.03%. The porosity of the Wulalike Formation shale shows an increasing trend from bottom to top, TOC, quartz content, and the proportion of biogenic silica decrease accordingly. And the correlation between porosity and permeability is not significant. Unlike the Longmaxi Formation shale, the target shale has high biogenic silica and low TOC content as a whole. Due to the low overall TOC content, fewer organic matter pores, and weak hydrocarbon generation and expulsion ability, and biogenic silica mainly occupies small pores and mesopores spaces. The negative correlation coefficients of small pores, mesopores, macropores, and biogenic silicon content are 0.3922, 0.2118, and 0.0403, respectively. As the ratio of biogenic silica to TOC increases, there is no observed trend in the traditional understanding that porosity increases with the increase of TOC. [Conclusion] Poor hydrocarbon generation ability caused by low TOC content and relatively low degree of thermal evolution limits the accumulation of hydrocarbons in the Wulalike Formation shale, and biogenic silica manifested as cementation reducing pore size rather than supporting pore enlargement. Therefore, compared to detrital siliceous shale and detrital mixed shale, biogenic siliceous shale exhibits lower porosity, poorer pore structure characteristics, and poorer fluid mobility characteristics. However, an increase in organic matter content can improve this phenomenon to some extent in the biogenic siliceous shale. The upper part of the target layer is mainly composed of mixed shale lithofacies, which has high debris content and porosity, but low organic matter content and poor hydrocarbon generation and drainage capacity. After the peak hydrocarbon generation period at the bottom, it is easy to cause formation water backflow. Transitioning towards the bottom into biogenic siliceous shale lithofacies, although the TOC content is relatively high, the biogenic siliceous cementation is unfavorable for reservoir performance. Based on the characteristics of pore space, the alternating development of multiple lithofacies shale sites in the upper part of the development site of biogenic siliceous shale is expected to indicate the enrichment site of shale gas under low TOC background.
Abstract:
Delta is not only an important part of sedimentology research, but also an important oil-gas enrichment layer in oil and gas exploration. The formation and development of deltas are completed by two or three sedimentary processes in rivers, tides and waves simultaneously. With the deepening of the research, the tide-controlled delta has gradually become the main target of oil and gas exploration and sedimentation research. However, due to the influence of hydrodynamic action, the sand body distribution law of the tide-controlled delta is unclear, the sedimentary facies combination is diverse, and the sedimentary system and characteristics are complex, which leads to great differences in the understanding of the sedimentary characteristics and sedimentary models of the tide-controlled delta. As for the basic research methods of tide-controlled delta, due to the lack of outcrop, the difficulty of sedimentary anatomy and the low resolution of logging interpretation data, there are some deviations in the research of tide-controlled delta. Based on the above problems, an idealized tide-controlled delta model was established by using the sedimentary numerical simulation method (Delft3D). By changing the conditions of river flow and tidal amplitude, the evolution law and main controlling factors of tide-controlled delta were explored. The results show that rivers and tides play different roles in the formation of tide-controlled deltas. Rivers transport sediments from the upper reaches, which accumulate in the estuary, and tides transport and deposit sediments from the upper reaches to the deep sea to form sand bars. With the increase of tidal amplitude, the dam body develops in a "flat" shape toward the sea. The shape of the dam body and the area of the delta are determined by the river flow and tidal amplitude. When the river flow and tidal amplitude increase, the sediment carrying capacity is enhanced, and the sediment can be deposited farther away from the estuary, and the area of the sand bar increases. At the same time, the erosion transformation of the original dam body is carried out, and the sand body is transported to the sea direction, and the average length of the dam body increases. The evolution of tide-controlled deltas can be divided into three periods: sediment accumulation in estuaries; The combination of river and tide transport sediment and form the dam body, and the delta develops rapidly. The delta area continues to grow, but the growth rate slows down.
Delta is not only an important part of sedimentology research, but also an important oil-gas enrichment layer in oil and gas exploration. The formation and development of deltas are completed by two or three sedimentary processes in rivers, tides and waves simultaneously. With the deepening of the research, the tide-controlled delta has gradually become the main target of oil and gas exploration and sedimentation research. However, due to the influence of hydrodynamic action, the sand body distribution law of the tide-controlled delta is unclear, the sedimentary facies combination is diverse, and the sedimentary system and characteristics are complex, which leads to great differences in the understanding of the sedimentary characteristics and sedimentary models of the tide-controlled delta. As for the basic research methods of tide-controlled delta, due to the lack of outcrop, the difficulty of sedimentary anatomy and the low resolution of logging interpretation data, there are some deviations in the research of tide-controlled delta. Based on the above problems, an idealized tide-controlled delta model was established by using the sedimentary numerical simulation method (Delft3D). By changing the conditions of river flow and tidal amplitude, the evolution law and main controlling factors of tide-controlled delta were explored. The results show that rivers and tides play different roles in the formation of tide-controlled deltas. Rivers transport sediments from the upper reaches, which accumulate in the estuary, and tides transport and deposit sediments from the upper reaches to the deep sea to form sand bars. With the increase of tidal amplitude, the dam body develops in a "flat" shape toward the sea. The shape of the dam body and the area of the delta are determined by the river flow and tidal amplitude. When the river flow and tidal amplitude increase, the sediment carrying capacity is enhanced, and the sediment can be deposited farther away from the estuary, and the area of the sand bar increases. At the same time, the erosion transformation of the original dam body is carried out, and the sand body is transported to the sea direction, and the average length of the dam body increases. The evolution of tide-controlled deltas can be divided into three periods: sediment accumulation in estuaries; The combination of river and tide transport sediment and form the dam body, and the delta develops rapidly. The delta area continues to grow, but the growth rate slows down.
Abstract:
Some studies suggest that there is a causal relationship between climate and organic carbon enrichment, but the relevant reports mainly focus on high temperature, high insolation, marine transgression, and cyclical patterns. A comprehensive model establishing the coupling relationship between different climate conditions and the abundance of organic matter in basins from the perspective of the Earth system has not yet been developed. The main source rocks corresponding to large oil and gas fields in China are distributed in various geological periods. Source rocks from the Mesozoic and Cenozoic are mainly developed during periods of high-latitude greenhouse climate, while source rocks from the Paleozoic and Precambrian are mainly developed during periods of deglaciation at mid to low latitudes. The distribution of source rocks during the deglaciation spans four periods: the Neoproterozoic, the Ediacaran-Cambrian transition, the Ordovician-Silurian transition, and the Permian. The unique climate conditions during the deglaciation play a crucial role in the enrichment of organic carbon. The warming and climate fluctuations during the deglaciation, along with changes in ocean currents and volcanic activity, collectively lead to increased productivity of water and oxygen depletion, thereby promoting the accumulation of organic matter and the formation of source rocks. This relationship model between deglaciation climate and source rock reflects the control of the Earth system of oceans, land, and atmosphere on organic carbon enrichment under the influence of climate cycles. It can be used to guide the discovery of major oil and gas fields. However, the contribution of each factor to organic matter enrichment still needs to be quantitatively analyzed through the establishment of ocean-climate models and productivity models.
Some studies suggest that there is a causal relationship between climate and organic carbon enrichment, but the relevant reports mainly focus on high temperature, high insolation, marine transgression, and cyclical patterns. A comprehensive model establishing the coupling relationship between different climate conditions and the abundance of organic matter in basins from the perspective of the Earth system has not yet been developed. The main source rocks corresponding to large oil and gas fields in China are distributed in various geological periods. Source rocks from the Mesozoic and Cenozoic are mainly developed during periods of high-latitude greenhouse climate, while source rocks from the Paleozoic and Precambrian are mainly developed during periods of deglaciation at mid to low latitudes. The distribution of source rocks during the deglaciation spans four periods: the Neoproterozoic, the Ediacaran-Cambrian transition, the Ordovician-Silurian transition, and the Permian. The unique climate conditions during the deglaciation play a crucial role in the enrichment of organic carbon. The warming and climate fluctuations during the deglaciation, along with changes in ocean currents and volcanic activity, collectively lead to increased productivity of water and oxygen depletion, thereby promoting the accumulation of organic matter and the formation of source rocks. This relationship model between deglaciation climate and source rock reflects the control of the Earth system of oceans, land, and atmosphere on organic carbon enrichment under the influence of climate cycles. It can be used to guide the discovery of major oil and gas fields. However, the contribution of each factor to organic matter enrichment still needs to be quantitatively analyzed through the establishment of ocean-climate models and productivity models.
Abstract:
[Objective] In the geological logging of the shale oil core of Chang 7 oil Member of the Yanchang Formation in the Longdong, Ordos Basin, the resolution of single layer thickness of each rock type is basically 10 cm, resulting in a large number of rock type combinations being described as a single rock type for a long time. Exploring a new method for quantitative study of shale oil rock type combination and reservoir Capacity is conducive to the efficient exploration and development of shale oil of the Chang 7 oil member. [Methods] Through the high resolution core observation of the single layer thickness resolution of 1~5 cm, stereo microscope and thin section identification of 405 samples, as well as physical property analysis data, the shale oil rock type of Chang 7 oil member is re-identified, and then the rock type combination and reservoir capacity of Chang 7 oil member are explored quantitatively in this study. [Results] There are 11 main rock types in the shale oil of Chang 7 oil Member of the Yanchang Formation in the Longdong, Ordos Basin. Firstly, four rock type combined forms, including unitype, stratified type, interstratified type and interstratified type, and 65 rock type combinations are quantitatively divided for the first time in Chang 7 oil Member of the Yanchang Formation in the Longdong, Ordos Basin. Secondly, on the basis of quantitative evaluation of reservoir capacity of above 11 rock types, combined with the thickness percentage of each rock type, a new method for quantitatively calculating reservoir capacity of above 65 rock type combinations is proposed for the first time. [Conclusions] In conclusion, this study proves that to guide the efficient exploration and development of shale oil of Chang 7 oil Member, the long-term single rock type study of shale oil should be changed to the study of rock type combination study of shale oil in Chang 7 oil Member of the Yanchang Formation in the Longdong, Ordos Basin. However, this research is still in the exploratory stage and needs to be further improved by combined with a large number of shale oil exploration and development effect of Chang 7 oil Member.
[Objective] In the geological logging of the shale oil core of Chang 7 oil Member of the Yanchang Formation in the Longdong, Ordos Basin, the resolution of single layer thickness of each rock type is basically 10 cm, resulting in a large number of rock type combinations being described as a single rock type for a long time. Exploring a new method for quantitative study of shale oil rock type combination and reservoir Capacity is conducive to the efficient exploration and development of shale oil of the Chang 7 oil member. [Methods] Through the high resolution core observation of the single layer thickness resolution of 1~5 cm, stereo microscope and thin section identification of 405 samples, as well as physical property analysis data, the shale oil rock type of Chang 7 oil member is re-identified, and then the rock type combination and reservoir capacity of Chang 7 oil member are explored quantitatively in this study. [Results] There are 11 main rock types in the shale oil of Chang 7 oil Member of the Yanchang Formation in the Longdong, Ordos Basin. Firstly, four rock type combined forms, including unitype, stratified type, interstratified type and interstratified type, and 65 rock type combinations are quantitatively divided for the first time in Chang 7 oil Member of the Yanchang Formation in the Longdong, Ordos Basin. Secondly, on the basis of quantitative evaluation of reservoir capacity of above 11 rock types, combined with the thickness percentage of each rock type, a new method for quantitatively calculating reservoir capacity of above 65 rock type combinations is proposed for the first time. [Conclusions] In conclusion, this study proves that to guide the efficient exploration and development of shale oil of Chang 7 oil Member, the long-term single rock type study of shale oil should be changed to the study of rock type combination study of shale oil in Chang 7 oil Member of the Yanchang Formation in the Longdong, Ordos Basin. However, this research is still in the exploratory stage and needs to be further improved by combined with a large number of shale oil exploration and development effect of Chang 7 oil Member.
Abstract:
Abstract：[Significance] Sediment gravity flow is an effective recorder of tectonic activities, encompassing climate extreme events and paleoearthquakes. Moreover, it stands as a paramount contributor to the global reserves and production of new oil and gas resources. The event-driven nature of the process and the unique characteristics of the deposition site present significant challenges for conducting field observations on deep-water gravity flow processes, resulting in limited availability of data. Sedimentary simulation has emerged as the primary approach for comprehending the dynamic processes and governing principles of deep-water gravity flow deposition. This paper aims to provide a comprehensive review of the advancements in simulating deep-water gravity flow deposition, encompassing both physical and numerical simulation approaches. [Progress]Through a systematic literature review, it seeks to summarize the current understanding and future research directions pertaining to the process of deep-water gravity flow deposition and its governing principles. Firstly, this section provides a comprehensive summary of the principles, monitoring technology, and progress in laboratory construction for sedimentary physical simulation experiments. Furthermore, it elucidates the influence of material composition and content, flow state, as well as energy differences in fluid on the formation, transportation, and depositional processes of sediment gravity flows .Additionally, the response characteristics of sediment gravity flow alone and under the influence of external fluids such as contour currents are addressed. Furthermore, this study provides a comprehensive review of the historical development of numerical simulation techniques for sediment gravity flow, existing simulation platforms, and their advancements in simulating sedimentary processes influenced by fluid structure, hydrodynamic parameters, and complex topography. [Conclusions and Prospects]The comparative analysis shows that physical simulation is obviously limited by the space-time scale of the laboratory. Meeting the hydrodynamic parameters of the deposition process with real-world accuracy is challenging. The numerical simulation method satisfies the requirement that the simulation scale is consistent with the real model; however, it is constrained by theoretical research in computational fluid dynamics. Moreover, it does not yield ideal results in modeling high concentration particle movement and turbidity current erosion. The future of simulating deep-water gravity flow deposition will heavily rely on interdisciplinary collaboration, integrating key physical simulation results and leveraging the continuity outcomes of numerical simulation to enhance our understanding of the mechanisms behind deep-water gravity flow deposition. This approach presents a novel methodology for exploring oil and gas reserves in deepwater environments.
Abstract：[Significance] Sediment gravity flow is an effective recorder of tectonic activities, encompassing climate extreme events and paleoearthquakes. Moreover, it stands as a paramount contributor to the global reserves and production of new oil and gas resources. The event-driven nature of the process and the unique characteristics of the deposition site present significant challenges for conducting field observations on deep-water gravity flow processes, resulting in limited availability of data. Sedimentary simulation has emerged as the primary approach for comprehending the dynamic processes and governing principles of deep-water gravity flow deposition. This paper aims to provide a comprehensive review of the advancements in simulating deep-water gravity flow deposition, encompassing both physical and numerical simulation approaches. [Progress]Through a systematic literature review, it seeks to summarize the current understanding and future research directions pertaining to the process of deep-water gravity flow deposition and its governing principles. Firstly, this section provides a comprehensive summary of the principles, monitoring technology, and progress in laboratory construction for sedimentary physical simulation experiments. Furthermore, it elucidates the influence of material composition and content, flow state, as well as energy differences in fluid on the formation, transportation, and depositional processes of sediment gravity flows .Additionally, the response characteristics of sediment gravity flow alone and under the influence of external fluids such as contour currents are addressed. Furthermore, this study provides a comprehensive review of the historical development of numerical simulation techniques for sediment gravity flow, existing simulation platforms, and their advancements in simulating sedimentary processes influenced by fluid structure, hydrodynamic parameters, and complex topography. [Conclusions and Prospects]The comparative analysis shows that physical simulation is obviously limited by the space-time scale of the laboratory. Meeting the hydrodynamic parameters of the deposition process with real-world accuracy is challenging. The numerical simulation method satisfies the requirement that the simulation scale is consistent with the real model; however, it is constrained by theoretical research in computational fluid dynamics. Moreover, it does not yield ideal results in modeling high concentration particle movement and turbidity current erosion. The future of simulating deep-water gravity flow deposition will heavily rely on interdisciplinary collaboration, integrating key physical simulation results and leveraging the continuity outcomes of numerical simulation to enhance our understanding of the mechanisms behind deep-water gravity flow deposition. This approach presents a novel methodology for exploring oil and gas reserves in deepwater environments.
Abstract:
As an important carrier for paleoclimate reduction and unconventional oil and gas exploration, the study of fine-grained rock layers has attracted scholars' attention in recent years. However, the current academic research on the formation mechanism and corresponding identification characteristics of laminae in lacustrine fine-grained sedimentary rocks is still unclear. We systematically summarize the formation mechanism, sedimentary characteristics, and control factors of laminae in lacustrine fine-grained sedimentary rocks. Suspended sedimentation, remote dilution of gravity flow, bottom flow, volcanic hydrothermal fluid, and microbial action are all responsible for the formation of laminae in lacustrine fine-grained sedimentary rocks. In genetic identification, although different sedimentary processes may form similar laminae in composition, lamina thickness, particle size, and morphology, there are significant differences in laminae combinations, biological disturbances, and other sedimentary structural features. The formation and distribution of these laminae are controlled by two major factors: paleoclimate and paleogeography. Paleoclimate has a wide and complex control over laminae, and paleogeography controls the distribution pattern of laminae. From the perspective of theoretical development and practical application, there are still some problems in the study of laminae in lacustrine fine-grained sedimentary rocks. In the future, effective methods for extracting and naming laminae information should be developed based on the identification of the formation mechanism of the laminae, integrating the changes in the spatial scale, and focusing on cutting-edge issues such as paleoclimate reduction, carbon burial, life evolution, and Martian sedimentology to meet the major needs of unconventional oil and gas exploration.
As an important carrier for paleoclimate reduction and unconventional oil and gas exploration, the study of fine-grained rock layers has attracted scholars' attention in recent years. However, the current academic research on the formation mechanism and corresponding identification characteristics of laminae in lacustrine fine-grained sedimentary rocks is still unclear. We systematically summarize the formation mechanism, sedimentary characteristics, and control factors of laminae in lacustrine fine-grained sedimentary rocks. Suspended sedimentation, remote dilution of gravity flow, bottom flow, volcanic hydrothermal fluid, and microbial action are all responsible for the formation of laminae in lacustrine fine-grained sedimentary rocks. In genetic identification, although different sedimentary processes may form similar laminae in composition, lamina thickness, particle size, and morphology, there are significant differences in laminae combinations, biological disturbances, and other sedimentary structural features. The formation and distribution of these laminae are controlled by two major factors: paleoclimate and paleogeography. Paleoclimate has a wide and complex control over laminae, and paleogeography controls the distribution pattern of laminae. From the perspective of theoretical development and practical application, there are still some problems in the study of laminae in lacustrine fine-grained sedimentary rocks. In the future, effective methods for extracting and naming laminae information should be developed based on the identification of the formation mechanism of the laminae, integrating the changes in the spatial scale, and focusing on cutting-edge issues such as paleoclimate reduction, carbon burial, life evolution, and Martian sedimentology to meet the major needs of unconventional oil and gas exploration.
Abstract:
[Objective] In the west margin of Ordos Basin, a set of marine graptolite shale is developed in the Wulalike Formation. In recent years, natural gas has been continuously discovered in this set of graptolite shale, and industrial oil flow can be produced, proving that the Wulalike Formation has great exploration potential. This study aims to explore the development characteristics of graptolites in the Wulalike Formation, establish a graptolite biostratigraphic framework, and analyze the sedimentary evolution laws of the Wulalike Formation. [Methods] By analyzing the graptolite characteristics of cored wells and comparing the range of graptolite extension, the temporal attribution of the Wulalike Formation was clarified. Based on the identification results of graptolites, the division of single-well graptolite zones and the establishment of biostratigraphic frameworks were conducted. The distribution characteristics of the graptolite zones were discussed, and the spatial evolution characteristics of black shale were analyzed in combination with the lithological development laws. Additionally, the variation of relative sea level was explored based on the response of graptolite morphological complexity to marine transgression. [Results] The results indicate that: ①The Wulalike Formation belongs to the Darriwilian-Sandbian stages of the Middle to Late Ordovician. Based on graptolite development characteristics, the Wulalike Formation is divided into four graptolite zones, namely the Pterograptus elegans zone, Jiangxigraptus vagus zone, Nemagraptus gracilis zone, and Climacograptus bicornis zone, from bottom to top. ②Through a comparative analysis of the developmental characteristics of the graptolite zones, it is believed that four complete graptolite zones are developed near Well Qitan 9 in the northern Wulalike Formation of the study area, while the Pterograptus elegans and Jiangxigraptus vagus zones are absent in the southern part. ③ The Pterograptus elegans and Nemagraptus gracilis zones in the Wulalike Formation represent two marine transgression periods, which transition upward into the Climacograptus bicornis zone and then into the Lashizhong Formation, during which the relative sea level gradually decreases. [Conclusion] The black shale at the bottom of the Wulalike Formation shows strong diachronism from Pterograptus elegans in Qitan Well 9 to Nemagraptus gracilis in Yintan Well 2. Along the western margin of the Ordos Block, the black shale gradually becomes younger in strata to the south, and the sedimentary center gradually migrates southward. The diachronism of the black shale may manifest as a typical characteristic of "degradational stacking", forming an upward-shallowing stacking pattern, resulting in the black shale of the Wulalike Formation crossing a forced marine regression interface. Additionally, the diachronism of the black shale may also be caused by marine transgression deposition and the progradation process in the highstand systems tract, resulting in the progradation of the black shale towards the south or southwest. Due to the limitations of core sampling, the causes of the diachronism of the black shale in subsequent studies still require further analysis of the formation ages of the limestone at the top and bottom of the Wulalike Formation, along with verification using seismic data. The establishment of a biostratigraphic framework based on graptolite zones provides important guidance for understanding the stratigraphic and sedimentary evolution of the Wulalike Formation on the western margin of the Ordos Basin.
[Objective] In the west margin of Ordos Basin, a set of marine graptolite shale is developed in the Wulalike Formation. In recent years, natural gas has been continuously discovered in this set of graptolite shale, and industrial oil flow can be produced, proving that the Wulalike Formation has great exploration potential. This study aims to explore the development characteristics of graptolites in the Wulalike Formation, establish a graptolite biostratigraphic framework, and analyze the sedimentary evolution laws of the Wulalike Formation. [Methods] By analyzing the graptolite characteristics of cored wells and comparing the range of graptolite extension, the temporal attribution of the Wulalike Formation was clarified. Based on the identification results of graptolites, the division of single-well graptolite zones and the establishment of biostratigraphic frameworks were conducted. The distribution characteristics of the graptolite zones were discussed, and the spatial evolution characteristics of black shale were analyzed in combination with the lithological development laws. Additionally, the variation of relative sea level was explored based on the response of graptolite morphological complexity to marine transgression. [Results] The results indicate that: ①The Wulalike Formation belongs to the Darriwilian-Sandbian stages of the Middle to Late Ordovician. Based on graptolite development characteristics, the Wulalike Formation is divided into four graptolite zones, namely the Pterograptus elegans zone, Jiangxigraptus vagus zone, Nemagraptus gracilis zone, and Climacograptus bicornis zone, from bottom to top. ②Through a comparative analysis of the developmental characteristics of the graptolite zones, it is believed that four complete graptolite zones are developed near Well Qitan 9 in the northern Wulalike Formation of the study area, while the Pterograptus elegans and Jiangxigraptus vagus zones are absent in the southern part. ③ The Pterograptus elegans and Nemagraptus gracilis zones in the Wulalike Formation represent two marine transgression periods, which transition upward into the Climacograptus bicornis zone and then into the Lashizhong Formation, during which the relative sea level gradually decreases. [Conclusion] The black shale at the bottom of the Wulalike Formation shows strong diachronism from Pterograptus elegans in Qitan Well 9 to Nemagraptus gracilis in Yintan Well 2. Along the western margin of the Ordos Block, the black shale gradually becomes younger in strata to the south, and the sedimentary center gradually migrates southward. The diachronism of the black shale may manifest as a typical characteristic of "degradational stacking", forming an upward-shallowing stacking pattern, resulting in the black shale of the Wulalike Formation crossing a forced marine regression interface. Additionally, the diachronism of the black shale may also be caused by marine transgression deposition and the progradation process in the highstand systems tract, resulting in the progradation of the black shale towards the south or southwest. Due to the limitations of core sampling, the causes of the diachronism of the black shale in subsequent studies still require further analysis of the formation ages of the limestone at the top and bottom of the Wulalike Formation, along with verification using seismic data. The establishment of a biostratigraphic framework based on graptolite zones provides important guidance for understanding the stratigraphic and sedimentary evolution of the Wulalike Formation on the western margin of the Ordos Basin.
Abstract:
V/(V+Ni), V/Cr, U/Th, Uauto and Ce are the traditional redox proxies of Marine strata, but there are multiple solutions to the redox identification of lacustrine strata. Molybdenum(Mo) is a new redox proxies, but the fixation mechanisms of Mo under various redox conditions in lake environment are not well understood, which limits the application potential of Mo in the reconstruction of lake paleoenvironment. This article systematically tested surface sediment samples from Qinghai Lake, analyzed the planar enrichment characteristics of Mo, and explored the corresponding relationships between Mo content and continental input, grain size, element content, organic matter content of sediment and water environment. The preliminary results show that Qinghai Lake is an alkaline, suboxic and brackish water lake, and Mo element is slightly enriched in the sediments in deep water area. Continental input and grain size of sediment do not affect Mo enrichment. Mo can not be settled and enriched by adsorption of clay minerals and Fe oxyhydroxides in weakly alkaline-alkaline lake basin. Although Mn oxyhydroxides may adsorb Mo and settle, Mo will be re-released from the sediment into the water body as the sediment transforms into a reducing environment. There is a good correlation between organic matter abundance and Mo content, indicating that, at the deep part of lake, the hypolimnion becomes dysoxic. Organic matter adsorption and preservation are the main controlling factors of Mo enrichment in sediments.
V/(V+Ni), V/Cr, U/Th, Uauto and Ce are the traditional redox proxies of Marine strata, but there are multiple solutions to the redox identification of lacustrine strata. Molybdenum(Mo) is a new redox proxies, but the fixation mechanisms of Mo under various redox conditions in lake environment are not well understood, which limits the application potential of Mo in the reconstruction of lake paleoenvironment. This article systematically tested surface sediment samples from Qinghai Lake, analyzed the planar enrichment characteristics of Mo, and explored the corresponding relationships between Mo content and continental input, grain size, element content, organic matter content of sediment and water environment. The preliminary results show that Qinghai Lake is an alkaline, suboxic and brackish water lake, and Mo element is slightly enriched in the sediments in deep water area. Continental input and grain size of sediment do not affect Mo enrichment. Mo can not be settled and enriched by adsorption of clay minerals and Fe oxyhydroxides in weakly alkaline-alkaline lake basin. Although Mn oxyhydroxides may adsorb Mo and settle, Mo will be re-released from the sediment into the water body as the sediment transforms into a reducing environment. There is a good correlation between organic matter abundance and Mo content, indicating that, at the deep part of lake, the hypolimnion becomes dysoxic. Organic matter adsorption and preservation are the main controlling factors of Mo enrichment in sediments.
Abstract:
The discovery of lithium mineralized bodies in multiple layers of the Permian-Jurassic layers in the northern margin of the Yangtze Block is of great significance to the investigation, development and utilization of sedimentary lithium resources. In order to clarify the provenance and tectonic setting of the parent rock in the source area of the lithium-bearing fine clastic rocks of the Jurassic Baitianba Formation, and to discuss the control of the paleo-environment on lithium enrichment, the typical lithology of the strata has been studied in detail, and the XRD and elemental geochemistry studies have been carried out. Results: The main element oxide discriminant function and LaN/YbN-ΣREE, K2O-Rb and La/Th-Hf diagrams show that the potential provenance region is a mixed provenance region of emerging medium-acid igneous rocks, sedimentary rocks and metamorphic rocks. The main element oxide discrimination function and the diagrams of La-Th, Ti/Zr-La/Sc, La-Th-Sc, Th-Sc-Zr/10 and Th-Co-Zr/10 show that the tectonic background of the sedimentary period was active continental margin, and some parent rocks in the source area were formed in continental island arc environment. Ga, Sr/Ba, Sr/Cu, C value, CIA, U/Th, Ni/Co and other paleoenvironmental indicators indicate that lithium-containing fine clastic rocks were deposited in a weakly reduction-oxidizing freshwater environment in a warm and humid climate. The A-CN-K and Th/ Sc-Zr /Sc diagram show that the parent rock of the source area has undergone moderate to intense weathering when the debris was first deposited. The comprehensive study shows that paleosalinity and paleoreduction-oxidation conditions control the enrichment of lithium to some extent, but the content of clay minerals in lithium-containing fine clastic rocks is the key to determine the enrichment of lithium. The lithium content level in the source area plays a leading role in lithium enrichment (" source "), and the sedimentary environment affects the lithium content in the formation (" storage ") by influencing the content of clay minerals.
The discovery of lithium mineralized bodies in multiple layers of the Permian-Jurassic layers in the northern margin of the Yangtze Block is of great significance to the investigation, development and utilization of sedimentary lithium resources. In order to clarify the provenance and tectonic setting of the parent rock in the source area of the lithium-bearing fine clastic rocks of the Jurassic Baitianba Formation, and to discuss the control of the paleo-environment on lithium enrichment, the typical lithology of the strata has been studied in detail, and the XRD and elemental geochemistry studies have been carried out. Results: The main element oxide discriminant function and LaN/YbN-ΣREE, K2O-Rb and La/Th-Hf diagrams show that the potential provenance region is a mixed provenance region of emerging medium-acid igneous rocks, sedimentary rocks and metamorphic rocks. The main element oxide discrimination function and the diagrams of La-Th, Ti/Zr-La/Sc, La-Th-Sc, Th-Sc-Zr/10 and Th-Co-Zr/10 show that the tectonic background of the sedimentary period was active continental margin, and some parent rocks in the source area were formed in continental island arc environment. Ga, Sr/Ba, Sr/Cu, C value, CIA, U/Th, Ni/Co and other paleoenvironmental indicators indicate that lithium-containing fine clastic rocks were deposited in a weakly reduction-oxidizing freshwater environment in a warm and humid climate. The A-CN-K and Th/ Sc-Zr /Sc diagram show that the parent rock of the source area has undergone moderate to intense weathering when the debris was first deposited. The comprehensive study shows that paleosalinity and paleoreduction-oxidation conditions control the enrichment of lithium to some extent, but the content of clay minerals in lithium-containing fine clastic rocks is the key to determine the enrichment of lithium. The lithium content level in the source area plays a leading role in lithium enrichment (" source "), and the sedimentary environment affects the lithium content in the formation (" storage ") by influencing the content of clay minerals.
Abstract:
[Objective] It is of great significance to study the relationship between climate proxies and climate factors in sandy surface sediments to determine the reliability and applicability of climate proxies. [Methods] In this paper, 32 surface sediments were collected on a large spatial scale in Otindag Sandy Land. Through the correlation analysis of chroma, Hm/Gt, magnetic susceptibility and modern climate factors (average annual precipitation and average annual temperature), the relationship between each index and climate factors and their environmental significance were discussed. [Results]The results show that the variation range of a* and b* is small, and the overall trend from east to west is increasing, in which the minimum value of a* is 3.87, the maximum value is 8.26, and the average value is 6.09. The minimum value of b* is 9.49, the maximum is 17.44, and the average is 14.24. a* and b* were negatively correlated with precipitation (correlation coefficients -0.88 and -0.77, P < 0.01), and positively correlated with temperature (correlation coefficients 0.89 and 0.82, P<0.01), indicating that both a* and b* could be used as effective proxy indicators of climate change. And a* is more sensitive to climate factors. The variation range of L* was small, and there was no obvious change rule from the east to the west. The maximum value was 59.54, the minimum value was 48.8, and the average value was 54.69. The relationship between L* and climate factors is not obvious, and its change is mainly directly affected by vegetation, and its indicative significance for climate is not obvious. The relative percentage content of hematite is between 8% and 19%, with an average of 14%, and the relative percentage content of goethite is between 6% and 9%, with an average of 7%. The value of hematite/goethite (Hm/Gt) ranged from 1.2 to 2.73, with an average value of 1.88, showing an increasing trend from east to west. The correlation between hematite and climate factors is higher than that of goethite. The ratio of Hm/Gt is negatively correlated with average annual precipitation (correlation coefficient is -0.85, P<0.01), and positively correlated with average annual temperature (correlation coefficient is 0.84, P<0.01), which reveals the sensitivity of hematite and Hm/Gt to precipitation and temperature. It can effectively reflect the changes of hydrothermal conditions in sandy land. The variation direction of low frequency magnetic susceptibility (χlf) and high frequency magnetic susceptibility (χhf) was the same, showing an increasing trend from the east to the west, and the variation amplitude was small in the east, but larger in the west, and the frequency magnetic susceptibility showed a decreasing trend from the east to the west. The magnetic susceptibility in this region does not show a good correspondence with climate factors. The source of sand material may be the main factor of its variation, indicating the complexity and particularity of the variation of magnetic susceptibility in sand.[Conclusions]Both a* and b* can be used as effective proxy indicators of climate in the study area, while L* is affected by vegetation, which leads to the ambiguity of its climate information. The correlation between hematite and Hm/Gt values and climatic parameters is good, which is an ideal index to indicate the change of water and heat in the sandy land. The magnetic susceptibility of the surface layer of the sandy land is less affected by the climate, and the more reaction is the complexity of the source information in the region.
[Objective] It is of great significance to study the relationship between climate proxies and climate factors in sandy surface sediments to determine the reliability and applicability of climate proxies. [Methods] In this paper, 32 surface sediments were collected on a large spatial scale in Otindag Sandy Land. Through the correlation analysis of chroma, Hm/Gt, magnetic susceptibility and modern climate factors (average annual precipitation and average annual temperature), the relationship between each index and climate factors and their environmental significance were discussed. [Results]The results show that the variation range of a* and b* is small, and the overall trend from east to west is increasing, in which the minimum value of a* is 3.87, the maximum value is 8.26, and the average value is 6.09. The minimum value of b* is 9.49, the maximum is 17.44, and the average is 14.24. a* and b* were negatively correlated with precipitation (correlation coefficients -0.88 and -0.77, P < 0.01), and positively correlated with temperature (correlation coefficients 0.89 and 0.82, P<0.01), indicating that both a* and b* could be used as effective proxy indicators of climate change. And a* is more sensitive to climate factors. The variation range of L* was small, and there was no obvious change rule from the east to the west. The maximum value was 59.54, the minimum value was 48.8, and the average value was 54.69. The relationship between L* and climate factors is not obvious, and its change is mainly directly affected by vegetation, and its indicative significance for climate is not obvious. The relative percentage content of hematite is between 8% and 19%, with an average of 14%, and the relative percentage content of goethite is between 6% and 9%, with an average of 7%. The value of hematite/goethite (Hm/Gt) ranged from 1.2 to 2.73, with an average value of 1.88, showing an increasing trend from east to west. The correlation between hematite and climate factors is higher than that of goethite. The ratio of Hm/Gt is negatively correlated with average annual precipitation (correlation coefficient is -0.85, P<0.01), and positively correlated with average annual temperature (correlation coefficient is 0.84, P<0.01), which reveals the sensitivity of hematite and Hm/Gt to precipitation and temperature. It can effectively reflect the changes of hydrothermal conditions in sandy land. The variation direction of low frequency magnetic susceptibility (χlf) and high frequency magnetic susceptibility (χhf) was the same, showing an increasing trend from the east to the west, and the variation amplitude was small in the east, but larger in the west, and the frequency magnetic susceptibility showed a decreasing trend from the east to the west. The magnetic susceptibility in this region does not show a good correspondence with climate factors. The source of sand material may be the main factor of its variation, indicating the complexity and particularity of the variation of magnetic susceptibility in sand.[Conclusions]Both a* and b* can be used as effective proxy indicators of climate in the study area, while L* is affected by vegetation, which leads to the ambiguity of its climate information. The correlation between hematite and Hm/Gt values and climatic parameters is good, which is an ideal index to indicate the change of water and heat in the sandy land. The magnetic susceptibility of the surface layer of the sandy land is less affected by the climate, and the more reaction is the complexity of the source information in the region.
Abstract:
[Objective] The end-Permian mass extinction event (EPME) led to a global decline in flora and biota. The thick coal seams, prevalent during the Permian, vanished following this event, resulting in a prolonged coal shortage throughout the Triassic. In the Sichuan Basin, following the EPME, spore plants that contributed to coal formation in the lowlands were lost, with no subsequent records of coal seam development. It was only during the early sedimentary period of the Upper Triassic Xujiahe Formation (T3x1) that coal seams reemerged. In the Sichuan Basin, coal deposits resurfaced specifically in the T3x1. This section is characterized by thin coal seams and poor spatial continuity; In the middle to late stages of the Xujiahe Formation sedimentation,the thickness of coal seam sedimentation and its spatial distribution have strong regularity. At present, research on the Late Triassic paleoclimate in the Sichuan Basin mainly focuses on the middle and late stages of the Xujiahe Formation. However, there's a research gap regarding the paleoclimate during the initial coal-forming phase of the Late Triassic (early stage of the Xujiahe Formation). [Methods] To fill this gap, a focused study was conducted on the Norian T3x1 (specifically the Gongnongzhen and Wangjialiang sections) in the northwestern part of the Sichuan Basin. This study involved rock analysis of major and trace elements, combined with field outcrop descriptions and petrological analysis. The aim was to reconstruct the coal-forming paleoclimate and sedimentary environment, thereby exploring the environmental conditions crucial for the mechanisms of coal formation. [Results and Discussions] Research has shown that the sedimentary facies of the T3x1 in the Gongnongzhen section are mainly delta front subfacies, whereas those in the Wangjialiang section are chiefly delta plain subfacies. Weathering indices (CIAcorr, Rb/Sr) and climate indices (Sr/Cu and C values) of the T3x1 in the Gongnongzhen and Wangjialiang sections displayed an overall fluctuating trend: high-medium-high-medium-high. The humid and hot climates correspond to strong chemical weathering intensity, while the warm semi-arid/semi-humid climates correspond to moderate chemical weathering intensity[Conclusions] The paleoclimate during the initial coal-forming period of the Late Triassic Xujiahe Formation in Northwest Sichuan can be divided into two types: (1) hot and humid climates; (2) warm semi-arid to semi-humid alternated climates. In study area, coal seams are associated with hot and humid climates. Hot and humid conditions promote the reproduction of coal forming plants, providing abundant material sources for the formation of coal seams.The paleoclimate of dry to wet alternation during the T3x1 in Northwest Sichuan is closely related to the activity of the super monsoon. The high concentration of PCO2 combined with the influence of super monsoon activity jointly promoted the formations of humid climate and strong chemical weathering in the study area. Further research indicates that coal deposition requires not only a suitable paleoclimate but also an appropriate preservation environment. For instance, coal seams tend to be well-developed and preserved in the swamps of high-level system tracts.
[Objective] The end-Permian mass extinction event (EPME) led to a global decline in flora and biota. The thick coal seams, prevalent during the Permian, vanished following this event, resulting in a prolonged coal shortage throughout the Triassic. In the Sichuan Basin, following the EPME, spore plants that contributed to coal formation in the lowlands were lost, with no subsequent records of coal seam development. It was only during the early sedimentary period of the Upper Triassic Xujiahe Formation (T3x1) that coal seams reemerged. In the Sichuan Basin, coal deposits resurfaced specifically in the T3x1. This section is characterized by thin coal seams and poor spatial continuity; In the middle to late stages of the Xujiahe Formation sedimentation,the thickness of coal seam sedimentation and its spatial distribution have strong regularity. At present, research on the Late Triassic paleoclimate in the Sichuan Basin mainly focuses on the middle and late stages of the Xujiahe Formation. However, there's a research gap regarding the paleoclimate during the initial coal-forming phase of the Late Triassic (early stage of the Xujiahe Formation). [Methods] To fill this gap, a focused study was conducted on the Norian T3x1 (specifically the Gongnongzhen and Wangjialiang sections) in the northwestern part of the Sichuan Basin. This study involved rock analysis of major and trace elements, combined with field outcrop descriptions and petrological analysis. The aim was to reconstruct the coal-forming paleoclimate and sedimentary environment, thereby exploring the environmental conditions crucial for the mechanisms of coal formation. [Results and Discussions] Research has shown that the sedimentary facies of the T3x1 in the Gongnongzhen section are mainly delta front subfacies, whereas those in the Wangjialiang section are chiefly delta plain subfacies. Weathering indices (CIAcorr, Rb/Sr) and climate indices (Sr/Cu and C values) of the T3x1 in the Gongnongzhen and Wangjialiang sections displayed an overall fluctuating trend: high-medium-high-medium-high. The humid and hot climates correspond to strong chemical weathering intensity, while the warm semi-arid/semi-humid climates correspond to moderate chemical weathering intensity[Conclusions] The paleoclimate during the initial coal-forming period of the Late Triassic Xujiahe Formation in Northwest Sichuan can be divided into two types: (1) hot and humid climates; (2) warm semi-arid to semi-humid alternated climates. In study area, coal seams are associated with hot and humid climates. Hot and humid conditions promote the reproduction of coal forming plants, providing abundant material sources for the formation of coal seams.The paleoclimate of dry to wet alternation during the T3x1 in Northwest Sichuan is closely related to the activity of the super monsoon. The high concentration of PCO2 combined with the influence of super monsoon activity jointly promoted the formations of humid climate and strong chemical weathering in the study area. Further research indicates that coal deposition requires not only a suitable paleoclimate but also an appropriate preservation environment. For instance, coal seams tend to be well-developed and preserved in the swamps of high-level system tracts.
Abstract:
[Objective] With the continuous breakthrough of oil and gas exploration and development technology, shale oil has become an important replacement field for petroleum resources in the future. At present, the exploration and development of shale oil in Chang 7 Member of Ordos Basin has made important progress, but the reservoir performance of laminae shale oil is rarely studied. [Methods] Taking the organic-rich shale of Changchang 7 member of Yanchang Chang in the southeast of Ordos Basin as the research object, the development characteristics, reservoir performance and oiliness of different shale types in the Changchang 7 member shale formation were studied by means of thin section observation, scanning electron microscopy, high-pressure mercury intrusion and nitrogen adsorption, so as to classify the types of shale laminae and clarify the occurrence characteristics of shale oil. [Results and Discussions] Laminae is developed in silty mudstone, argillaceous siltstone, siltstone, black shale and tuff in Chang 7 member of the study area, which can be macroscopically divided into three types: thick laminated shale (1cm
[Objective] With the continuous breakthrough of oil and gas exploration and development technology, shale oil has become an important replacement field for petroleum resources in the future. At present, the exploration and development of shale oil in Chang 7 Member of Ordos Basin has made important progress, but the reservoir performance of laminae shale oil is rarely studied. [Methods] Taking the organic-rich shale of Changchang 7 member of Yanchang Chang in the southeast of Ordos Basin as the research object, the development characteristics, reservoir performance and oiliness of different shale types in the Changchang 7 member shale formation were studied by means of thin section observation, scanning electron microscopy, high-pressure mercury intrusion and nitrogen adsorption, so as to classify the types of shale laminae and clarify the occurrence characteristics of shale oil. [Results and Discussions] Laminae is developed in silty mudstone, argillaceous siltstone, siltstone, black shale and tuff in Chang 7 member of the study area, which can be macroscopically divided into three types: thick laminated shale (1cm
Abstract:
[Objective] Powdery~fine-crystalline dolomite dominated by residual granular structure and non-luminous under cathode rays is developed in the reservoir section of Maosan section-Wu section of the Permian of the Yuanba Tectonics in north-central Sichuan Province, and the mechanism of the genesis of this type of dolomite in the study area is not clear at the present time. [Methods] The dolomite genesis mechanism was studied based on the petrological characteristics of the reservoir combined with TIMA scanning of rocks, whole-rock X-ray diffraction (XRD) analysis, in-situ microzonation of major trace elements, strontium isotopes, and in-situ U-Pb chronology of dolomite. [Results] The study shows that: (1) the rock types of the reservoirs in Maosan Section 3 and Wu Section 1 are tuffs, dolomites and sedimentary tuffs. Tuff reservoirs mainly include mud crystal clastic tuff, bright crystal clastic tuff and cloudy tuff; dolomite reservoirs are semi-autogenous~autogenous powder~fine crystalline dolomite; sedimentary tuff reservoirs are mainly composed of volcanic clasts, charcoal, calcium and magnesium, sand clasts and metal minerals, etc. Volcanic clasts are glass clasts, basaltic and other clasts, and the main constituents of calcium and magnesium are dolomite and calcite. (2) The average values of trace elements of dolomite at the top of Maosan Section 3 and Wu Section 1 show extremely high Fe content (10,678.40×10-6), high Mn content (822.95×10-6), Si content (1,929.81×10-6), Al content (394.11×10-6), and high Na+K content (362.38×10-6), indicating that the fluids in the closed environment were formed by the volcanic fluids, which is the main component of calcium and magnesium, and calcite. Indicating that the rock-forming fluids in the confined environment are characterized by high salinity and high alkaline metal content. The 87Sr/86Sr in the matrix part of the dolomite and mud-crystal clastic tuff is within the range of seawater of the same period in the Maokou Group-Wujiaping Group, and it also has a low value of ∑REE, a loss of LREE, and exhibits the characteristics of negative anomalies of Ce (the average value of δPr is 1.03>1, and the average value of δCe is 0.96<1), and negative anomalies of Eu or no anomalies, which suggests that the dolomitization diagenesis fluid is similar to the seawater of the same period. seawater. (3) The U-Pb age of powdery to fine-crystalline dolomite in the Maosan section and Wu section is 245.36±1.08 Ma, and dolomitization mainly occurred in the shallow burial period.[Conclusion] It is concluded that the source of the dolomitization fluid in the powdery~fine crystalline dolomite of Maosan section and Wu section is the compaction and dewatering of clay minerals in the overlying muddy sedimentary tuff and tuffaceous mudstone sections of Wu section 1 and Wu section 2 during the shallow burial period. During this process, a large number of Mg2+, Fe2+, Al3+, and Si4+ ions were precipitated and transported to the granular tuff at the top of the Wu 1 and Maosan 3 Sections and accounted for by the seawater residual from the Maokou Formation to the Wujiaping Stage as the carrier.
[Objective] Powdery~fine-crystalline dolomite dominated by residual granular structure and non-luminous under cathode rays is developed in the reservoir section of Maosan section-Wu section of the Permian of the Yuanba Tectonics in north-central Sichuan Province, and the mechanism of the genesis of this type of dolomite in the study area is not clear at the present time. [Methods] The dolomite genesis mechanism was studied based on the petrological characteristics of the reservoir combined with TIMA scanning of rocks, whole-rock X-ray diffraction (XRD) analysis, in-situ microzonation of major trace elements, strontium isotopes, and in-situ U-Pb chronology of dolomite. [Results] The study shows that: (1) the rock types of the reservoirs in Maosan Section 3 and Wu Section 1 are tuffs, dolomites and sedimentary tuffs. Tuff reservoirs mainly include mud crystal clastic tuff, bright crystal clastic tuff and cloudy tuff; dolomite reservoirs are semi-autogenous~autogenous powder~fine crystalline dolomite; sedimentary tuff reservoirs are mainly composed of volcanic clasts, charcoal, calcium and magnesium, sand clasts and metal minerals, etc. Volcanic clasts are glass clasts, basaltic and other clasts, and the main constituents of calcium and magnesium are dolomite and calcite. (2) The average values of trace elements of dolomite at the top of Maosan Section 3 and Wu Section 1 show extremely high Fe content (10,678.40×10-6), high Mn content (822.95×10-6), Si content (1,929.81×10-6), Al content (394.11×10-6), and high Na+K content (362.38×10-6), indicating that the fluids in the closed environment were formed by the volcanic fluids, which is the main component of calcium and magnesium, and calcite. Indicating that the rock-forming fluids in the confined environment are characterized by high salinity and high alkaline metal content. The 87Sr/86Sr in the matrix part of the dolomite and mud-crystal clastic tuff is within the range of seawater of the same period in the Maokou Group-Wujiaping Group, and it also has a low value of ∑REE, a loss of LREE, and exhibits the characteristics of negative anomalies of Ce (the average value of δPr is 1.03>1, and the average value of δCe is 0.96<1), and negative anomalies of Eu or no anomalies, which suggests that the dolomitization diagenesis fluid is similar to the seawater of the same period. seawater. (3) The U-Pb age of powdery to fine-crystalline dolomite in the Maosan section and Wu section is 245.36±1.08 Ma, and dolomitization mainly occurred in the shallow burial period.[Conclusion] It is concluded that the source of the dolomitization fluid in the powdery~fine crystalline dolomite of Maosan section and Wu section is the compaction and dewatering of clay minerals in the overlying muddy sedimentary tuff and tuffaceous mudstone sections of Wu section 1 and Wu section 2 during the shallow burial period. During this process, a large number of Mg2+, Fe2+, Al3+, and Si4+ ions were precipitated and transported to the granular tuff at the top of the Wu 1 and Maosan 3 Sections and accounted for by the seawater residual from the Maokou Formation to the Wujiaping Stage as the carrier.
Abstract:
[Objective] The Tianshan Mountains in Xinjiang are located in the inner part of the Asia-Europe continent, in the transition zone between the westerly and monsoon circulations, and are sensitive to climate change. Academics have not yet united on the understanding of the Holocene environmental evolution in the region, and supplementing more high-resolution climatic records in the sensitive areas is the basis for clarifying this issue. [Methods]The study material was taken from the Middle Tien Shan Intermountain Basin, we reconstructed the vegetation and climate change processes in the study area since the Middle and Late Holocene, based on the AMS14C dating results and using sporadic pollen as a paleoclimate proxy. [Results and Discussions] 6369-3601 cal yr B.P. The period of Artemisia and Chenopodium was characterized by high content, positive pollen PCA axis 1 scores, and wet-dry fluctuations in the climate, with dryness as the dominant factor and abrupt climate change. 3601-2512 cal yr B.P. The period of spruce Picea content was characterized by elevated content, positive pollen PCA axis 2 scores, and cold-wet climate. 2512-1016 cal yr B.P. The period of Betula was characterized by increased content, positive pollen PCA axis 1 transitionscores, warm dry climate. [Conclusion] The three pollen zones indicate that the Middle and Late Holocene climate in the Zhongtianshan Intermontane Basin went through 3 phases of wet-dry fluctuations (off-dry)-cold-wet-warm-dry. Since the middle to late Holocene, the study area has received less solar radiation in summer, Weak evaporation from the North Atlantic sea surface and low water vapor carried by the westerly circulation, the climate has been arid. in the early Late Holocene, the westerly circulation shifted to the south, Superimposed negative phase of the North Atlantic Oscillation (NAO) transporting large amounts of water vapor and the climate was cold and humid. Then the climate became warm and dry due to the increase of solar radiation in the late winter. The abrupt climate change characterized by cold and dry conditions during 4766-3601 cal yr B.P. was a response to the "4.2 ka B.P." climatic event, which may have been caused by the weakening of the westerly circulation due to the weakening of solar radiation, the intensification of the cold in the middle and high latitudes, and the lowering of the SST in the North Atlantic Ocean.
[Objective] The Tianshan Mountains in Xinjiang are located in the inner part of the Asia-Europe continent, in the transition zone between the westerly and monsoon circulations, and are sensitive to climate change. Academics have not yet united on the understanding of the Holocene environmental evolution in the region, and supplementing more high-resolution climatic records in the sensitive areas is the basis for clarifying this issue. [Methods]The study material was taken from the Middle Tien Shan Intermountain Basin, we reconstructed the vegetation and climate change processes in the study area since the Middle and Late Holocene, based on the AMS14C dating results and using sporadic pollen as a paleoclimate proxy. [Results and Discussions] 6369-3601 cal yr B.P. The period of Artemisia and Chenopodium was characterized by high content, positive pollen PCA axis 1 scores, and wet-dry fluctuations in the climate, with dryness as the dominant factor and abrupt climate change. 3601-2512 cal yr B.P. The period of spruce Picea content was characterized by elevated content, positive pollen PCA axis 2 scores, and cold-wet climate. 2512-1016 cal yr B.P. The period of Betula was characterized by increased content, positive pollen PCA axis 1 transitionscores, warm dry climate. [Conclusion] The three pollen zones indicate that the Middle and Late Holocene climate in the Zhongtianshan Intermontane Basin went through 3 phases of wet-dry fluctuations (off-dry)-cold-wet-warm-dry. Since the middle to late Holocene, the study area has received less solar radiation in summer, Weak evaporation from the North Atlantic sea surface and low water vapor carried by the westerly circulation, the climate has been arid. in the early Late Holocene, the westerly circulation shifted to the south, Superimposed negative phase of the North Atlantic Oscillation (NAO) transporting large amounts of water vapor and the climate was cold and humid. Then the climate became warm and dry due to the increase of solar radiation in the late winter. The abrupt climate change characterized by cold and dry conditions during 4766-3601 cal yr B.P. was a response to the "4.2 ka B.P." climatic event, which may have been caused by the weakening of the westerly circulation due to the weakening of solar radiation, the intensification of the cold in the middle and high latitudes, and the lowering of the SST in the North Atlantic Ocean.
Abstract:
Marine-terrestrial transitional source rocks are the main source rocks in several offshore basins in China, and their differential distribution characteristics restrict the prediction accuracy of source rocks and the effectiveness of oil and gas exploration. And the transport and sedimentation process of terrestrial organic matter determines the quality and distribution of source rock in marine-terrestrial transitional environment. Using a combination of flume sedimentary simulation and 3D laser scanning technology, the dynamic recording and quantitative characterization of the transport process of terrestrial dispersed organic matter under different water salinity conditions are carried out from the perspective of forward modeling. Machine learning algorithms are used to establish a TOC prediction model. The results show that terrestrial organic matter in the marine-terrestrial transitional environment is mainly enriched in the delta front and prodelta. As the transportation distance increases, the abundance of terrestrial organic matter shows a trend of first increasing and then decreasing. Under the influence of salt flocculation, the transportation distance of terrestrial organic matter in saltwater environment is closer to the source area, and the sediment thickness is larger. A TOC prediction model was established under experimental conditions based on three deep learning algorithms, and ultimately selects the prediction model based on random forest algorithm with outlier removal and experience based sedimentary facies assignment as input features as the optimal model. The TOC prediction model under experimental conditions is combined with geological conditions to complete the TOC prediction of source rocks in the Yacheng Formation of the Yanan depression. The results show that the transportation distance of terrestrial organic matter in the Yanan Depression can reach 50 km, and the highest degree of organic matter enrichment occurs at a distance of about 31 km from the source area.
Marine-terrestrial transitional source rocks are the main source rocks in several offshore basins in China, and their differential distribution characteristics restrict the prediction accuracy of source rocks and the effectiveness of oil and gas exploration. And the transport and sedimentation process of terrestrial organic matter determines the quality and distribution of source rock in marine-terrestrial transitional environment. Using a combination of flume sedimentary simulation and 3D laser scanning technology, the dynamic recording and quantitative characterization of the transport process of terrestrial dispersed organic matter under different water salinity conditions are carried out from the perspective of forward modeling. Machine learning algorithms are used to establish a TOC prediction model. The results show that terrestrial organic matter in the marine-terrestrial transitional environment is mainly enriched in the delta front and prodelta. As the transportation distance increases, the abundance of terrestrial organic matter shows a trend of first increasing and then decreasing. Under the influence of salt flocculation, the transportation distance of terrestrial organic matter in saltwater environment is closer to the source area, and the sediment thickness is larger. A TOC prediction model was established under experimental conditions based on three deep learning algorithms, and ultimately selects the prediction model based on random forest algorithm with outlier removal and experience based sedimentary facies assignment as input features as the optimal model. The TOC prediction model under experimental conditions is combined with geological conditions to complete the TOC prediction of source rocks in the Yacheng Formation of the Yanan depression. The results show that the transportation distance of terrestrial organic matter in the Yanan Depression can reach 50 km, and the highest degree of organic matter enrichment occurs at a distance of about 31 km from the source area.
Abstract:
Macrocyclic alkanes are one kind of saturated fatty hydrocarbons which have single ring structure and large ring carbon numbers, which were identified in oil shales, petroleum, soils and higher plants. Because of the difference of macrocyclic alkanes characteristic carbon number with different sample, the equidistant relative retention time is same as long chain alkyl olefin and alkyl cyclohexane in chromatogram, the molecular ion (CnH2n) is same as olefin which have characteristic ion at m/z 97, 111, 125 in mass spectra and other compounds were similar, so it is easy to cause confusion and misunderstanding in actual identification. On account of this, we reviewed the identifications, the biosynthetic pathways and bio-precursors of macrocyclic alkanes. And confirmed the structure of those compounds by NMR analysis of purified monomer compounds in torbanite from Sydney Basin, Australia. Based on the fragmentation mechanism of cyclohexane doped out the fragmentation pathways of macrocyclic alkanes. Finally, according to the different research results provided by predecessors, the possible biochemical synthesis pathway of macrocyclic alkanes was summarized, which is helpful to better understand the parent material and bio-predecessor of macrocyclic alkanes, and better identify these compounds.
Macrocyclic alkanes are one kind of saturated fatty hydrocarbons which have single ring structure and large ring carbon numbers, which were identified in oil shales, petroleum, soils and higher plants. Because of the difference of macrocyclic alkanes characteristic carbon number with different sample, the equidistant relative retention time is same as long chain alkyl olefin and alkyl cyclohexane in chromatogram, the molecular ion (CnH2n) is same as olefin which have characteristic ion at m/z 97, 111, 125 in mass spectra and other compounds were similar, so it is easy to cause confusion and misunderstanding in actual identification. On account of this, we reviewed the identifications, the biosynthetic pathways and bio-precursors of macrocyclic alkanes. And confirmed the structure of those compounds by NMR analysis of purified monomer compounds in torbanite from Sydney Basin, Australia. Based on the fragmentation mechanism of cyclohexane doped out the fragmentation pathways of macrocyclic alkanes. Finally, according to the different research results provided by predecessors, the possible biochemical synthesis pathway of macrocyclic alkanes was summarized, which is helpful to better understand the parent material and bio-predecessor of macrocyclic alkanes, and better identify these compounds.
Abstract:
[ Objective ] The Chang 7 member of Triassic Yanchang Formation in Ordos Basin mainly develops semi-deep lake-deep lake subfacies, and deep-water gravity flow deposits are generally developed. [ Method ] Taking the Chang 7 Member in Fuxian area of the southeastern basin as the research object, based on the fine description results of centimeter-level cores from 13 coring wells, combined with particle size analysis and logging data, the types and characteristics, formation mechanism, distribution law and evolution model of gravity flow deposits in the Chang 7 Member were studied. Combined with oil test and production test data, the control effect of gravity flow on reservoir distribution was analyzed. [ Result ] The results show that the Chang 7 member in Fuxian area mainly develops three types of gravity flow deposits : sliding-slump, sandy debris flow and turbidity flow. The sliding-slump is characterized by the development of roll bedding, crumpled deformation structure, syndepositional stepped small faults and sliding surface, and is dominated by the mixed deposition of sandstone and mudstone. The sandy debris flow develops thick massive sandstone, mudstone tearing debris and mud-encapsulated gravel structure. The thickness of single sand body is between 0.3-3.5 m, and the cumulative thickness can reach more than 10 m. Turbidity flow develops flame structure and Bouma sequence, and incomplete A,B,D and E sections are common. The sand body is small in scale and limited in development. The thickness of single sand body is generally several centimeters to dozens of centimeters. [ Conclusion ] The Chang 7 member is divided into 6 typical logging facies combinations and 11 lithofacies types. The formation mechanism of gravity flow in this area is underwater slope break zone, volcano and earthquake. Along the source direction, the thickening of the stratum reflects the transition of the sedimentary environment from the delta front to the deep lake-semi-deep lake deposit ; vertically, three types of gravity flow overlap, dominated by sandy debris flow. The sandy debris flow in the gravity flow sand body has the best oil content, and the main body is oil spot-oil immersion.
[ Objective ] The Chang 7 member of Triassic Yanchang Formation in Ordos Basin mainly develops semi-deep lake-deep lake subfacies, and deep-water gravity flow deposits are generally developed. [ Method ] Taking the Chang 7 Member in Fuxian area of the southeastern basin as the research object, based on the fine description results of centimeter-level cores from 13 coring wells, combined with particle size analysis and logging data, the types and characteristics, formation mechanism, distribution law and evolution model of gravity flow deposits in the Chang 7 Member were studied. Combined with oil test and production test data, the control effect of gravity flow on reservoir distribution was analyzed. [ Result ] The results show that the Chang 7 member in Fuxian area mainly develops three types of gravity flow deposits : sliding-slump, sandy debris flow and turbidity flow. The sliding-slump is characterized by the development of roll bedding, crumpled deformation structure, syndepositional stepped small faults and sliding surface, and is dominated by the mixed deposition of sandstone and mudstone. The sandy debris flow develops thick massive sandstone, mudstone tearing debris and mud-encapsulated gravel structure. The thickness of single sand body is between 0.3-3.5 m, and the cumulative thickness can reach more than 10 m. Turbidity flow develops flame structure and Bouma sequence, and incomplete A,B,D and E sections are common. The sand body is small in scale and limited in development. The thickness of single sand body is generally several centimeters to dozens of centimeters. [ Conclusion ] The Chang 7 member is divided into 6 typical logging facies combinations and 11 lithofacies types. The formation mechanism of gravity flow in this area is underwater slope break zone, volcano and earthquake. Along the source direction, the thickening of the stratum reflects the transition of the sedimentary environment from the delta front to the deep lake-semi-deep lake deposit ; vertically, three types of gravity flow overlap, dominated by sandy debris flow. The sandy debris flow in the gravity flow sand body has the best oil content, and the main body is oil spot-oil immersion.
Abstract:
[objective] During the sedimentation process of sandy braided rivers, the braided channels undergo frequent, rapid, and continuous shifts leading to erosion and reworking within the eventually preserved braided river deposits, such that deposited braid bars and braid channels are characterized by fragmented morphology, relatively small scale, and undefined quantitative relationships. Traditional sedimentary models of sandy braided river sedimentation are inadequate to effectively guide the characterization of subsurface reservoirs. [methods] To clarify the sedimentary evolution mechanisms of sandy braided rivers and establish a reliable sedimentary architecture model with quantitative size relationships, this paper conducted a flume experiment under constant boundary conditions to reproduce the formation and evolution of a sandy braided river. Using a laser scanner to obtain topographic data at regular time intervals and accurately reconstruct a three-dimensional sedimentary architecture model of the simulated braided river. Further, the study proceeds with analyses of sedimentary evolution mechanisms, dissection of sedimentary architecture, and the construction of quantitative size and relationship models for architecture elements. [conclusions and discussions] The study reveals that: (1) In the initial stage of sandy braided river sedimentation, sediments undergo bedload transportation downstream, forming initial bars. The deflected flow converges into channels, further developing these into lobe-shaped initial bars, which are then reshaped and organized into a stable network of braid channels and bar patterns through the action of the braid channels; (2) Following the formation of the braided river, the braid channels and bars co-evolve continually, primarily through three mechanisms: lateral accretion of bars driven by braid channels, abandonment and infilling of braid channels overlaying existing bars, and scouring of the confluence by braid channels, which results in downstream bar reorganization; (3) During simulation, bars typically form within 1 to 6 run steps and grow to their maximum size before experiencing continuous erosion over 3 to 8 simulation periods, ultimately leading to preservation in only 36.28% of the area; (4) Upon completion of the simulation, the internal structure of the braided river deposit is dominated by braided channel deposits, accounting for approximately 57.9%, which can be classified into complex stacked channels, incised channels, and isolated channels. Bars often undergo erosion and reworking from channels, presenting as smaller, fragmented forms; (5) Within the preserved deposit, the average width-to-thickness ratio of braided channels is 14.1, with an internal accretion ratio of 13.7, while for bars, the ratio is 19.8, with an internal accretion ratio of 25.4. This research constructed the complex sedimentary architecture formed within sandy braided river deposits after persistent and intensive erosional modification by the braid channel network. It establishes a quantitative model of the size and relationships between internal architectural elements, thereby providing a more geologically realistic and quantitative sedimentary architecture model for characterizing subsurface reservoirs.
[objective] During the sedimentation process of sandy braided rivers, the braided channels undergo frequent, rapid, and continuous shifts leading to erosion and reworking within the eventually preserved braided river deposits, such that deposited braid bars and braid channels are characterized by fragmented morphology, relatively small scale, and undefined quantitative relationships. Traditional sedimentary models of sandy braided river sedimentation are inadequate to effectively guide the characterization of subsurface reservoirs. [methods] To clarify the sedimentary evolution mechanisms of sandy braided rivers and establish a reliable sedimentary architecture model with quantitative size relationships, this paper conducted a flume experiment under constant boundary conditions to reproduce the formation and evolution of a sandy braided river. Using a laser scanner to obtain topographic data at regular time intervals and accurately reconstruct a three-dimensional sedimentary architecture model of the simulated braided river. Further, the study proceeds with analyses of sedimentary evolution mechanisms, dissection of sedimentary architecture, and the construction of quantitative size and relationship models for architecture elements. [conclusions and discussions] The study reveals that: (1) In the initial stage of sandy braided river sedimentation, sediments undergo bedload transportation downstream, forming initial bars. The deflected flow converges into channels, further developing these into lobe-shaped initial bars, which are then reshaped and organized into a stable network of braid channels and bar patterns through the action of the braid channels; (2) Following the formation of the braided river, the braid channels and bars co-evolve continually, primarily through three mechanisms: lateral accretion of bars driven by braid channels, abandonment and infilling of braid channels overlaying existing bars, and scouring of the confluence by braid channels, which results in downstream bar reorganization; (3) During simulation, bars typically form within 1 to 6 run steps and grow to their maximum size before experiencing continuous erosion over 3 to 8 simulation periods, ultimately leading to preservation in only 36.28% of the area; (4) Upon completion of the simulation, the internal structure of the braided river deposit is dominated by braided channel deposits, accounting for approximately 57.9%, which can be classified into complex stacked channels, incised channels, and isolated channels. Bars often undergo erosion and reworking from channels, presenting as smaller, fragmented forms; (5) Within the preserved deposit, the average width-to-thickness ratio of braided channels is 14.1, with an internal accretion ratio of 13.7, while for bars, the ratio is 19.8, with an internal accretion ratio of 25.4. This research constructed the complex sedimentary architecture formed within sandy braided river deposits after persistent and intensive erosional modification by the braid channel network. It establishes a quantitative model of the size and relationships between internal architectural elements, thereby providing a more geologically realistic and quantitative sedimentary architecture model for characterizing subsurface reservoirs.
Abstract:
[Significance] Cold seep activities have a significant impact on marine ecosystems and global climate change, and they are widely developed in the global active and passive continental margins. The fundamental process operating at seeps is the anaerobic oxidation of methane (AOM), mediated by a consortium of anaerobic methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB). This procedure will increase the alkalinity of pore water, forming a favorable precipitation environment for carbonate minerals. Cold seep carbonates are the products of submarine cold seep activities, and their geological and geochemical characteristics are often used to trace seepage fluid information and sedimentary environment changes. [Progress] The Taiwan Island is located in the collision zone between the Luzon Island Arc of the Philippine Sea Plate and the Eurasian continental margin, which possesses complex geological structures such as extensive faults, providing appropriate conditions for the development of cold seeps. The cold seep carbonates in Taiwan area are mainly developed in Miocene to Pleistocene strata, which are ideal carriers for the study of ancient cold seeps. A relatively detailed study has been conducted on its fundamental geological and geochemical characteristics, including mineralogy, petrology, and carbon and oxygen isotopes. This paper provides a comprehensive analysis of the geological occurrence, mineralogical and petrological characteristics, carbon and oxygen isotopes, rare earth elements geochemistry, and macrofossil contents of cold seep carbonates in Taiwan area. In addition, it explores the fluid seepage activities and depositional environment characteristics recorded by the cold seep carbonates in Taiwan area, combining the geological and geochemical features of cold seep carbonates from other regions globally. [Conclusions and Prospects] Cold seep carbonates in Taiwan area predominantly occur in blocky and chimney-like forms, which indicate two types of seepage activity. The blocky forms indicate prolonged periods of low-flux diffuse seepage, while the chimney-like forms represent shorter periods of high-flux convective seepage. The primary carbonate minerals in cold seep carbonates are dolomite and calcite, with a significant presence of framboidal pyrites. The size of the pyrite grains may be related to the redox conditions during sedimentation. The carbon isotope composition of cold seep carbonates indicates that the primary sources of carbon are biogenic and thermogenic methane, with additional influence from seawater or residual CO2 from methanogenesis. Notably, Pliocene cold seep carbonates exhibit the widest range in carbon isotope values, suggesting a greater diversity of carbon sources, potentially due to the complex geological structures in Taiwan area at that time. Furthermore, the δ18O values of cold seep carbonates from the Miocene to the Pleistocene in Taiwan area exhibit a progressively positive trend, suggesting these carbonates might have undergone a transition from gas hydrate formation to dissociation and release. Geochemical characteristics of rare earth elements illustrate that the sedimentary environment is dominated by reduction. The cold seep macrofossils are dominated by bivalve fossils, while they have few biological species in the Miocene and Pliocene, but more in the Pleistocene, which may be affected by water depth. In order to improve the in-depth understanding of the ancient cold seep systems in Taiwan area, future research can focus on in situ micro-scale carbon and oxygen isotope analysis of cold seep carbonates, Mo element and its isotope analysis of carbonate minerals, as well as the spatial differences in the growth of macrofauna of different genera of Lucinidae family, in conjunction with geochemical analysis.
[Significance] Cold seep activities have a significant impact on marine ecosystems and global climate change, and they are widely developed in the global active and passive continental margins. The fundamental process operating at seeps is the anaerobic oxidation of methane (AOM), mediated by a consortium of anaerobic methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB). This procedure will increase the alkalinity of pore water, forming a favorable precipitation environment for carbonate minerals. Cold seep carbonates are the products of submarine cold seep activities, and their geological and geochemical characteristics are often used to trace seepage fluid information and sedimentary environment changes. [Progress] The Taiwan Island is located in the collision zone between the Luzon Island Arc of the Philippine Sea Plate and the Eurasian continental margin, which possesses complex geological structures such as extensive faults, providing appropriate conditions for the development of cold seeps. The cold seep carbonates in Taiwan area are mainly developed in Miocene to Pleistocene strata, which are ideal carriers for the study of ancient cold seeps. A relatively detailed study has been conducted on its fundamental geological and geochemical characteristics, including mineralogy, petrology, and carbon and oxygen isotopes. This paper provides a comprehensive analysis of the geological occurrence, mineralogical and petrological characteristics, carbon and oxygen isotopes, rare earth elements geochemistry, and macrofossil contents of cold seep carbonates in Taiwan area. In addition, it explores the fluid seepage activities and depositional environment characteristics recorded by the cold seep carbonates in Taiwan area, combining the geological and geochemical features of cold seep carbonates from other regions globally. [Conclusions and Prospects] Cold seep carbonates in Taiwan area predominantly occur in blocky and chimney-like forms, which indicate two types of seepage activity. The blocky forms indicate prolonged periods of low-flux diffuse seepage, while the chimney-like forms represent shorter periods of high-flux convective seepage. The primary carbonate minerals in cold seep carbonates are dolomite and calcite, with a significant presence of framboidal pyrites. The size of the pyrite grains may be related to the redox conditions during sedimentation. The carbon isotope composition of cold seep carbonates indicates that the primary sources of carbon are biogenic and thermogenic methane, with additional influence from seawater or residual CO2 from methanogenesis. Notably, Pliocene cold seep carbonates exhibit the widest range in carbon isotope values, suggesting a greater diversity of carbon sources, potentially due to the complex geological structures in Taiwan area at that time. Furthermore, the δ18O values of cold seep carbonates from the Miocene to the Pleistocene in Taiwan area exhibit a progressively positive trend, suggesting these carbonates might have undergone a transition from gas hydrate formation to dissociation and release. Geochemical characteristics of rare earth elements illustrate that the sedimentary environment is dominated by reduction. The cold seep macrofossils are dominated by bivalve fossils, while they have few biological species in the Miocene and Pliocene, but more in the Pleistocene, which may be affected by water depth. In order to improve the in-depth understanding of the ancient cold seep systems in Taiwan area, future research can focus on in situ micro-scale carbon and oxygen isotope analysis of cold seep carbonates, Mo element and its isotope analysis of carbonate minerals, as well as the spatial differences in the growth of macrofauna of different genera of Lucinidae family, in conjunction with geochemical analysis.
Abstract:
Abstract: [Objective] In the middle and late stages of oil and gas field development, studying sand architecture is key to excavating residual oil and enhancing recovery. Precisely interpreting similar outcrops can provide a comparable prototype model for predicting underground reservoir architecture. [Methods] The shallow water delta profiles of the Yan'an Formation in the Kaokaowusu Gully and Gulf Mining Industry in the Ordos Basin were the research objects. UAV oblique photography was used to obtain massive outcrop image data, and then 3D digital outcrops were established. Detailed architecture interpretation of digital outcrops was carried out by combining field investigation and indoor analysis. [Results and Discussions] The developmental characteristics and evolutionary models of shallow water delta front architecture during the rising lake level were defined. When the lake level is low, mainly trunk-type distributary channels are developed, with widths of 23.3~48.4 m, thicknesses of 0.89~1.81 m, and width-to-thickness ratios of 26.74. The sandbody superimposition patterns are mainly overlay type. As the lake level increases, fork-type distributary channels, mouth bars, sand sheets, and subaqueous distributary bays gradually develop. The width of the mouth bar is 53.9 m, the thickness is 2.21 m, the width-to-thickness ratio is 24.39, and the superimposition pattern is mainly joint type. When the lake level is higher, mainly terminal-type distributary channels, mouth bars, and sheet sand architectural units are developed. The width of the terminal-type underwater distributary channel ranges from 4.7 to 40.6 m, the thickness ranges from 0.4 to 1.03 m, and the width-to-thickness ratio is from 11.75 to 24.56, isolated in the muddy deposit. [Conclusions] When the supply of material sources is relatively stable, the increase in lake level leads to an increase in accommodative space. The architectural units evolve from trunk-type distributary channels to terminal-type ones, depositing mouth bars and sand sheets. The size of the sand body decreases, but the width-to-thickness ratio increases. Overall, the sand-to-ground ratio decreases, spatial connectivity decreases, and reservoir heterogeneity is enhanced.
Abstract: [Objective] In the middle and late stages of oil and gas field development, studying sand architecture is key to excavating residual oil and enhancing recovery. Precisely interpreting similar outcrops can provide a comparable prototype model for predicting underground reservoir architecture. [Methods] The shallow water delta profiles of the Yan'an Formation in the Kaokaowusu Gully and Gulf Mining Industry in the Ordos Basin were the research objects. UAV oblique photography was used to obtain massive outcrop image data, and then 3D digital outcrops were established. Detailed architecture interpretation of digital outcrops was carried out by combining field investigation and indoor analysis. [Results and Discussions] The developmental characteristics and evolutionary models of shallow water delta front architecture during the rising lake level were defined. When the lake level is low, mainly trunk-type distributary channels are developed, with widths of 23.3~48.4 m, thicknesses of 0.89~1.81 m, and width-to-thickness ratios of 26.74. The sandbody superimposition patterns are mainly overlay type. As the lake level increases, fork-type distributary channels, mouth bars, sand sheets, and subaqueous distributary bays gradually develop. The width of the mouth bar is 53.9 m, the thickness is 2.21 m, the width-to-thickness ratio is 24.39, and the superimposition pattern is mainly joint type. When the lake level is higher, mainly terminal-type distributary channels, mouth bars, and sheet sand architectural units are developed. The width of the terminal-type underwater distributary channel ranges from 4.7 to 40.6 m, the thickness ranges from 0.4 to 1.03 m, and the width-to-thickness ratio is from 11.75 to 24.56, isolated in the muddy deposit. [Conclusions] When the supply of material sources is relatively stable, the increase in lake level leads to an increase in accommodative space. The architectural units evolve from trunk-type distributary channels to terminal-type ones, depositing mouth bars and sand sheets. The size of the sand body decreases, but the width-to-thickness ratio increases. Overall, the sand-to-ground ratio decreases, spatial connectivity decreases, and reservoir heterogeneity is enhanced.
Abstract:
[Objective] The sedimentary environment of the Pearl River Delta is complex. with abundant Perinereis trace fossils. The characteristics，distribution and assemblage of Perinereis and their relationships with sedimentary environment and sediment properties are significant for the study of trace fossils and palaeoenvironment. [Methods] Based on sedimentary and ichnological methods, grain size analysis, salinity, turbidity, total organic carbon (TOC), X-ray scans, and three-dimensional (3D) reconstruction were applied to the modern biogenic sedimentary structures in different microenvironments of the Pearl River Delta tidal flat, discussed the composition，assemblage and distribution characteristics of Perinereis in tidal flat of Pearl River Delta, and analyzed the relationship between the biological assemblage and the sedimentary environments. [Results] 1) The Perinereis mainly lives in the tidal flat area of the tidal channel and the interdistributary bay in the Pearl River Delta. 2) The remains of the Perinereis mainly have grazing trails and dwelling trails, but the grazing trails on the layer are hard to observe, and the dwelling trails in the layer mainly have simple Y-shaped, I-shaped and U-shaped and complex network structures, and there are bulges at the joints. 3) The Perinereis is suitable for living in the tidal flat or tidal channel of the interdistributary bay with low hydrodynamic conditions, low salinity, low turbidity and rich total organic carbon content. [Conclusions] The spatial distribution of Perinereis’ neoichnology is imbalanced, and multiple environmental conditions jointly control the abundance of Perinereis’ neoichnology. The habitat of Perinereis is similar to the trace fossil Polykladichnus, which can belong to both the Mermia and Glossifunites ichnofacies, the trace fossil assemblage of this relic mainly appears in the channel and tidal flat area, and this study supplements the biological data of modern neoichnology of Perinereis.
[Objective] The sedimentary environment of the Pearl River Delta is complex. with abundant Perinereis trace fossils. The characteristics，distribution and assemblage of Perinereis and their relationships with sedimentary environment and sediment properties are significant for the study of trace fossils and palaeoenvironment. [Methods] Based on sedimentary and ichnological methods, grain size analysis, salinity, turbidity, total organic carbon (TOC), X-ray scans, and three-dimensional (3D) reconstruction were applied to the modern biogenic sedimentary structures in different microenvironments of the Pearl River Delta tidal flat, discussed the composition，assemblage and distribution characteristics of Perinereis in tidal flat of Pearl River Delta, and analyzed the relationship between the biological assemblage and the sedimentary environments. [Results] 1) The Perinereis mainly lives in the tidal flat area of the tidal channel and the interdistributary bay in the Pearl River Delta. 2) The remains of the Perinereis mainly have grazing trails and dwelling trails, but the grazing trails on the layer are hard to observe, and the dwelling trails in the layer mainly have simple Y-shaped, I-shaped and U-shaped and complex network structures, and there are bulges at the joints. 3) The Perinereis is suitable for living in the tidal flat or tidal channel of the interdistributary bay with low hydrodynamic conditions, low salinity, low turbidity and rich total organic carbon content. [Conclusions] The spatial distribution of Perinereis’ neoichnology is imbalanced, and multiple environmental conditions jointly control the abundance of Perinereis’ neoichnology. The habitat of Perinereis is similar to the trace fossil Polykladichnus, which can belong to both the Mermia and Glossifunites ichnofacies, the trace fossil assemblage of this relic mainly appears in the channel and tidal flat area, and this study supplements the biological data of modern neoichnology of Perinereis.
Abstract:
Numerical simulation is an important method to study turbidity current. Numerical simulation of turbidity current flow and sedimentary characteristics is of great practical significance for predicting and inverting turbidity current sedimentary environment, studying deep-water sedimentary system and exploring deep-water oil and gas resources and oil and gas reservoirs. In this paper, the numerical calculation model of turbidity current is constructed based on the layer average depth model of Kostic and Parker. By setting the initial conditions of different particle size concentration, inflow thickness and inflow velocity, the flow process and deposition characteristics of submarine turbidity current driven by suspended particles with four particle sizes at a slope of 3 % are simulated and analyzed. The simulation results show that the characteristics of the turbidity current along the way are as follows : ( 1 ) In terms of the thickness of the turbidity current, the turbidity current began to thicken at the initial stage of the evolution of the turbidity current due to the entrainment of the environmental water, but it gradually thinned with the occurrence of sedimentation during the flow process. ( 2 ) In terms of flow velocity, the evolution of turbidity current is divided into three stages : acceleration stage, uniform stage and deceleration stage. Under the condition of the same initial thickness and the same sediment concentration, the higher the content of fine-grained sediments, the more stable the turbidity current is ( that is, it can maintain a uniform motion flow for a long time ). Under the same sediment composition and concentration conditions, the thicker the turbidity current is, the more stable it is. ( 3 ) In terms of sedimentary characteristics, the sediments near the source of the turbidity current accumulate more, and the sediments are mainly accumulated at the central axis. After the central axis, the thickness of the sediments decreases monotonously. The turbidity current with large thickness and high flow rate has a smaller deposition rate, but its deposition quantity is more. These results show that the method applied in this paper is suitable for the study of field-scale turbidity currents and is expected to be applied in nature in the future.
Numerical simulation is an important method to study turbidity current. Numerical simulation of turbidity current flow and sedimentary characteristics is of great practical significance for predicting and inverting turbidity current sedimentary environment, studying deep-water sedimentary system and exploring deep-water oil and gas resources and oil and gas reservoirs. In this paper, the numerical calculation model of turbidity current is constructed based on the layer average depth model of Kostic and Parker. By setting the initial conditions of different particle size concentration, inflow thickness and inflow velocity, the flow process and deposition characteristics of submarine turbidity current driven by suspended particles with four particle sizes at a slope of 3 % are simulated and analyzed. The simulation results show that the characteristics of the turbidity current along the way are as follows : ( 1 ) In terms of the thickness of the turbidity current, the turbidity current began to thicken at the initial stage of the evolution of the turbidity current due to the entrainment of the environmental water, but it gradually thinned with the occurrence of sedimentation during the flow process. ( 2 ) In terms of flow velocity, the evolution of turbidity current is divided into three stages : acceleration stage, uniform stage and deceleration stage. Under the condition of the same initial thickness and the same sediment concentration, the higher the content of fine-grained sediments, the more stable the turbidity current is ( that is, it can maintain a uniform motion flow for a long time ). Under the same sediment composition and concentration conditions, the thicker the turbidity current is, the more stable it is. ( 3 ) In terms of sedimentary characteristics, the sediments near the source of the turbidity current accumulate more, and the sediments are mainly accumulated at the central axis. After the central axis, the thickness of the sediments decreases monotonously. The turbidity current with large thickness and high flow rate has a smaller deposition rate, but its deposition quantity is more. These results show that the method applied in this paper is suitable for the study of field-scale turbidity currents and is expected to be applied in nature in the future.
Abstract:
Bauxite-type lithium-rich claystone deposits with great ore-forming potential have been found in the bauxite-bearing strata formed in different geological periods in the Yunnan-Guizhou area of southwestern China, but the current understanding of the material sources and lithium enrichment mechanisms of these bauxite-type lithium-rich claystones in these areas is still significantly insufficient. This study carried out a comparative analysis of the mineral composition, major trace and rare earth element composition of the bauxite-type lithium-rich claystone series of the Early Permian Daoshitou Formation in Yunnan and the Early Carboniferous Jiajialu Formation in Guizhou, and combined with the previous research results, systematically discussed the provenance characteristics and the limiting factors that caused the abnormal lithium enrichment of these two sets of bauxite-type lithium-rich claystones that formed in different ages but have extremely similar lithofacies characteristics. The results show that the difference in provenance characteristics between the Jiajialu Formation and the Daoshitou Formation lithium-rich claystones in Guizhou and Yunnan has a significant impact on their respective lithium characteristics. Generally, the formation of the Jiajialu Formation claystone with relatively low lithium content is closely related to the weathering and erosion of the impure dolomite of the underlying Loushanguan Group, and its original source may be the Mesoproterozoic-Middle Proterozoic intermediate-acidic magmatic rocks, and it is significantly affected by the magnesium-iron components. The formation of the Daoshitou Formation claystone with relatively high lithium content in Yunnan is significantly affected by the recycled material of the Ordovician sedimentary rock series, and the source connection with the underlying carbonate rock strata is weak. At the same time, its original source is obviously dominated by intermediate-acidic magmatic rocks. In addition, the lithium-bearing minerals in the lithium-rich claystones in the Yunnan-Guizhou area may be kaolinite or illite minerals, and the drainage of the basin during the sedimentary period and the coexistence effect of ions in the water body have played an important role in the enrichment of lithium in the clay. The relevant understanding of this study has important significance for deepening the ore-forming process and limiting mechanism of clay-type lithium deposits.
Bauxite-type lithium-rich claystone deposits with great ore-forming potential have been found in the bauxite-bearing strata formed in different geological periods in the Yunnan-Guizhou area of southwestern China, but the current understanding of the material sources and lithium enrichment mechanisms of these bauxite-type lithium-rich claystones in these areas is still significantly insufficient. This study carried out a comparative analysis of the mineral composition, major trace and rare earth element composition of the bauxite-type lithium-rich claystone series of the Early Permian Daoshitou Formation in Yunnan and the Early Carboniferous Jiajialu Formation in Guizhou, and combined with the previous research results, systematically discussed the provenance characteristics and the limiting factors that caused the abnormal lithium enrichment of these two sets of bauxite-type lithium-rich claystones that formed in different ages but have extremely similar lithofacies characteristics. The results show that the difference in provenance characteristics between the Jiajialu Formation and the Daoshitou Formation lithium-rich claystones in Guizhou and Yunnan has a significant impact on their respective lithium characteristics. Generally, the formation of the Jiajialu Formation claystone with relatively low lithium content is closely related to the weathering and erosion of the impure dolomite of the underlying Loushanguan Group, and its original source may be the Mesoproterozoic-Middle Proterozoic intermediate-acidic magmatic rocks, and it is significantly affected by the magnesium-iron components. The formation of the Daoshitou Formation claystone with relatively high lithium content in Yunnan is significantly affected by the recycled material of the Ordovician sedimentary rock series, and the source connection with the underlying carbonate rock strata is weak. At the same time, its original source is obviously dominated by intermediate-acidic magmatic rocks. In addition, the lithium-bearing minerals in the lithium-rich claystones in the Yunnan-Guizhou area may be kaolinite or illite minerals, and the drainage of the basin during the sedimentary period and the coexistence effect of ions in the water body have played an important role in the enrichment of lithium in the clay. The relevant understanding of this study has important significance for deepening the ore-forming process and limiting mechanism of clay-type lithium deposits.
Abstract:
It is of great significance to study the variation mechanism of magnetic susceptibility and chroma of sediments in different environments for paleoclimate reconstruction. Based on the sampling and measurement of magnetic susceptibility and colorimetry of the surface soils in the western Qilian Mountains in northwest China, this contribution discussed the variations of magnetic susceptibility and colorimetry in terms of the precipitation, temperature and altitude, and established the functional relationship between magnetic susceptibility and colorimetry and climate factors and altitude. The results show that: (1) there is a nonlinear relationship between magnetic susceptibility and average annual temperature and precipitation, and there is a threshold value (~0℃, ~300mm), below which the magnetic susceptibility is inversely proportional, and vice versa; The magnetic susceptibility is negatively correlated with altitude in particularly at low altitude areas. (2) Chroma (brightness, redness, yellowness) has no obvious relationship with temperature and precipitation, and brightness has a significant negative correlation with altitude, and it is more sensitive in low altitude areas. (3) Compared with colorimetry, magnetic susceptibility can better reflect the climatic and elevation changes in the western Qilian Mountains. For altitude variation, the relationship between brightness and altitude is more significant at low altitude, followed by yellowness and magnetic susceptibility. The relationship between redness and brightness and altitude is more significant in high altitude area.
It is of great significance to study the variation mechanism of magnetic susceptibility and chroma of sediments in different environments for paleoclimate reconstruction. Based on the sampling and measurement of magnetic susceptibility and colorimetry of the surface soils in the western Qilian Mountains in northwest China, this contribution discussed the variations of magnetic susceptibility and colorimetry in terms of the precipitation, temperature and altitude, and established the functional relationship between magnetic susceptibility and colorimetry and climate factors and altitude. The results show that: (1) there is a nonlinear relationship between magnetic susceptibility and average annual temperature and precipitation, and there is a threshold value (~0℃, ~300mm), below which the magnetic susceptibility is inversely proportional, and vice versa; The magnetic susceptibility is negatively correlated with altitude in particularly at low altitude areas. (2) Chroma (brightness, redness, yellowness) has no obvious relationship with temperature and precipitation, and brightness has a significant negative correlation with altitude, and it is more sensitive in low altitude areas. (3) Compared with colorimetry, magnetic susceptibility can better reflect the climatic and elevation changes in the western Qilian Mountains. For altitude variation, the relationship between brightness and altitude is more significant at low altitude, followed by yellowness and magnetic susceptibility. The relationship between redness and brightness and altitude is more significant in high altitude area.
Abstract:
[Significance] The architecture of marine sandy beach-bar reservoirs is complex, and dominant seepage channels and barriers are developed inside the reservoirs. There is a lack of architecture models for underground reservoirs, which cannot effectively guide the recovery of remaining oil. [Method] In this paper, we have proposed the architecture pattern of marine sandy beach-bar reservoirs by outcrops, satellite photos and numerical simulation with the Hudson Donghe sandstone as the research objective. Under the guidance of the mode, the architecture of the Donghe sandstone reservoir is finely characterized. [Result] The results show that: the depositional architecture of a single sand bar inside composite beach-bar is controlled by many factors such as shoreline shape, coastal slope, wave direction, and height, multiple types of sandbars can be formed, such as conical bar, tight moon bar, positive linear bar, nonlinear inclined bar, and sandy beak bar. Based on the identification of single sandbar boundaries and guided by the architecture mode, 13 sandbars of different sizes were identified in the C1 layer of the study area, including five tight moon bar, seven forward linear bars and one oblique bar, there are differences in quantitative scale between different sanbars. The length of tight moon bar is about 1.5-3 km, the length of the oblique bar is about 4.5-5 km, and the length of the positive linear bar is more than 6 km. The sandbars exhibits both progradational and retrogradational stacking patterns, while the bars in C1 small layer exhibits progradational lateral separation and progradational lateral stacking patterns. The migration rate of the coastline affects the stacking relationship between the sandbars. The numerical simulation results and outcrop data indicate that there are differences in the development patterns of the internal accretion bodies. The distribution patterns of the internal interlayers include top accretion, top accretion-side accretion, and interval type. In the C1 small layer, three types of distribution patterns of the internal interlayers were identified. The internal interlayers in the No. 16 sandbar exhibit a two-stage distribution feature of "top accretion-side accretion", while the internal interlayers in the No. 19 sandbar exhibit a "side accretion". The angle distribution range of the top and side accretion interlayers is about 1-3 ° and 3-7 °, and the interlayers between dam No. 14 and 15 sandbars are distributed in an "interval" pattern. The development pattern of the interlayers inside the bars of Hudson Donghe sandstone reservoir is summarized. [Conclusion] Fine characterization of the internal architecture of marine sandy beach-bar reservoirs can effectively guide the recovery of remaining oil.
[Significance] The architecture of marine sandy beach-bar reservoirs is complex, and dominant seepage channels and barriers are developed inside the reservoirs. There is a lack of architecture models for underground reservoirs, which cannot effectively guide the recovery of remaining oil. [Method] In this paper, we have proposed the architecture pattern of marine sandy beach-bar reservoirs by outcrops, satellite photos and numerical simulation with the Hudson Donghe sandstone as the research objective. Under the guidance of the mode, the architecture of the Donghe sandstone reservoir is finely characterized. [Result] The results show that: the depositional architecture of a single sand bar inside composite beach-bar is controlled by many factors such as shoreline shape, coastal slope, wave direction, and height, multiple types of sandbars can be formed, such as conical bar, tight moon bar, positive linear bar, nonlinear inclined bar, and sandy beak bar. Based on the identification of single sandbar boundaries and guided by the architecture mode, 13 sandbars of different sizes were identified in the C1 layer of the study area, including five tight moon bar, seven forward linear bars and one oblique bar, there are differences in quantitative scale between different sanbars. The length of tight moon bar is about 1.5-3 km, the length of the oblique bar is about 4.5-5 km, and the length of the positive linear bar is more than 6 km. The sandbars exhibits both progradational and retrogradational stacking patterns, while the bars in C1 small layer exhibits progradational lateral separation and progradational lateral stacking patterns. The migration rate of the coastline affects the stacking relationship between the sandbars. The numerical simulation results and outcrop data indicate that there are differences in the development patterns of the internal accretion bodies. The distribution patterns of the internal interlayers include top accretion, top accretion-side accretion, and interval type. In the C1 small layer, three types of distribution patterns of the internal interlayers were identified. The internal interlayers in the No. 16 sandbar exhibit a two-stage distribution feature of "top accretion-side accretion", while the internal interlayers in the No. 19 sandbar exhibit a "side accretion". The angle distribution range of the top and side accretion interlayers is about 1-3 ° and 3-7 °, and the interlayers between dam No. 14 and 15 sandbars are distributed in an "interval" pattern. The development pattern of the interlayers inside the bars of Hudson Donghe sandstone reservoir is summarized. [Conclusion] Fine characterization of the internal architecture of marine sandy beach-bar reservoirs can effectively guide the recovery of remaining oil.
Abstract:
Abstract: [Objective] The high-resolution climate reconstruction of Liaodong Peninsula is important for exploring the evolution of regional climate environment and high-quality development. The aim of this study is to reconstruct the sedimentary environment and climate history by studying the sediments of the west coast of Dalian. [Methods] By analyzing AMS14C dating, lithology, and geochemical elements of the Laoyuwo (LYW) section to reveal the evolution of sedimentary environment and paleoclimate of the region. [Results and Discussions] The sediment is mainly composed of sand, silt, and gravel, which recorded sedimentary environment and paleoclimate evolution information from the Last Glacial Maximum (LGM) to the Middle Holocene (18815–6802 cal.BP). The main chemical components in the profile are SiO2, Al2O3, K2O, and Fe2O3, the total content of which is 90.34%. The contents of major elements from large to small are SiO2 > Al2O3 > K2O > Fe2O3 > Na2O > CaO > TiO2 > MgO > P2O5 > MnO. The sedimentary records shows that the region experienced a dry and cold alluvial (18.8 cal.ka BP – late LGM), slightly warm and humid coastal intertidal (18.8–16.0 cal.ka BP), warm and humid coastal subtidal (18.8–16.0 aal.ka bp), warm and humid coastal subtidal（(16.0–11.7 cal.ka BP), warmest and wettest coastal salt marsh (11.7–6.8 cal.ka BP), and dry and cold fluvial environment (6.8–0 cal.ka BP). The highest sea level around 6.8 cal.ka BP and the rapid climatic events during Younger Dryas (DY) and 8.0–9.0 ka are also responses in the sediment. [Conclusions] This study provides basic data and information for the Holocene climate reconstruction of Liaodong Peninsula, particularly for the sedimentary environment evolution history of the west coast of Dalian.
Abstract: [Objective] The high-resolution climate reconstruction of Liaodong Peninsula is important for exploring the evolution of regional climate environment and high-quality development. The aim of this study is to reconstruct the sedimentary environment and climate history by studying the sediments of the west coast of Dalian. [Methods] By analyzing AMS14C dating, lithology, and geochemical elements of the Laoyuwo (LYW) section to reveal the evolution of sedimentary environment and paleoclimate of the region. [Results and Discussions] The sediment is mainly composed of sand, silt, and gravel, which recorded sedimentary environment and paleoclimate evolution information from the Last Glacial Maximum (LGM) to the Middle Holocene (18815–6802 cal.BP). The main chemical components in the profile are SiO2, Al2O3, K2O, and Fe2O3, the total content of which is 90.34%. The contents of major elements from large to small are SiO2 > Al2O3 > K2O > Fe2O3 > Na2O > CaO > TiO2 > MgO > P2O5 > MnO. The sedimentary records shows that the region experienced a dry and cold alluvial (18.8 cal.ka BP – late LGM), slightly warm and humid coastal intertidal (18.8–16.0 cal.ka BP), warm and humid coastal subtidal (18.8–16.0 aal.ka bp), warm and humid coastal subtidal（(16.0–11.7 cal.ka BP), warmest and wettest coastal salt marsh (11.7–6.8 cal.ka BP), and dry and cold fluvial environment (6.8–0 cal.ka BP). The highest sea level around 6.8 cal.ka BP and the rapid climatic events during Younger Dryas (DY) and 8.0–9.0 ka are also responses in the sediment. [Conclusions] This study provides basic data and information for the Holocene climate reconstruction of Liaodong Peninsula, particularly for the sedimentary environment evolution history of the west coast of Dalian.
Abstract:
Gulong shale oil is an important replacement resource in the Songliao Basin, with an estimated resource amount of 15.1 billion tons. From the perspective of sedimentary and petrological characteristics, the most prominent feature of Gulong Qingshankou Formation shale is the extensive development of sand dikes, which is not found in shale oil reservoirs in other basins. Therefore, this is also an important information to explore the formation environment of Gulong Qingshankou Formation shale. The most peculiar thing is that in addition to sand dikes, there are two other special dikes in Gulong Qingshankou shale: pyrite dikes and cementite dikes. Pyrite dikes and cementite dikes are generally small in scale, with widths of 1-2 mm. Visible length several centimeters; Mostly curved like intestine, a few slightly curved. Multi-tilt output, tilt direction has a certain rule, 180° symmetry. The pyrite dikes in the shale oil reservoir of Qingshankou Formation in Gulong are formed by late pyritization of sand dikes. The cementation dikes are formed by gravity subsidence caused by density inversion and the formation kinetics of pyrite and tuff dike are also studied. The study of pyrite dikes and puffite dikes in the Gulong shale oil reservoir has three significances: first, the formation time, sedimentary environment, sedimentary process and sediment state of pyrite dikes and tuff dikes can be known; Second, the diagenetic compaction rate of shale can be known. Third, it can assist reservoir evaluation.
Gulong shale oil is an important replacement resource in the Songliao Basin, with an estimated resource amount of 15.1 billion tons. From the perspective of sedimentary and petrological characteristics, the most prominent feature of Gulong Qingshankou Formation shale is the extensive development of sand dikes, which is not found in shale oil reservoirs in other basins. Therefore, this is also an important information to explore the formation environment of Gulong Qingshankou Formation shale. The most peculiar thing is that in addition to sand dikes, there are two other special dikes in Gulong Qingshankou shale: pyrite dikes and cementite dikes. Pyrite dikes and cementite dikes are generally small in scale, with widths of 1-2 mm. Visible length several centimeters; Mostly curved like intestine, a few slightly curved. Multi-tilt output, tilt direction has a certain rule, 180° symmetry. The pyrite dikes in the shale oil reservoir of Qingshankou Formation in Gulong are formed by late pyritization of sand dikes. The cementation dikes are formed by gravity subsidence caused by density inversion and the formation kinetics of pyrite and tuff dike are also studied. The study of pyrite dikes and puffite dikes in the Gulong shale oil reservoir has three significances: first, the formation time, sedimentary environment, sedimentary process and sediment state of pyrite dikes and tuff dikes can be known; Second, the diagenetic compaction rate of shale can be known. Third, it can assist reservoir evaluation.
Abstract:
Abstract: [Objective] The level of oxygen content in shallow sea and atmosphere during the Mesoproterozoic (about 1.8-1.0 Ga) has been controversial.Due to the slow evolution of eukaryotes during this period, the redox state of the surface ocean and atmosphere has been considered to be a relatively stable hypoxic state. However, in recent years, more and more evidence shows that there are dynamic fluctuations in oxygen content during this period. However, due to the heterogeneity of time and space, people 's understanding of the global redox state during this period is still very limited.[Methods] In this study, the redox state of the shallow sea in the southern margin of the North China Craton was studied by analyzing the Ce anomaly, δ13C and Y/Ho indexes of carbonate rocks in the Longjiayuan ( 1.59-1.54Ga ) Formation.[Results] The results show that there are obvious negative Ce anomalies ( 0.53 ~ 0.94 ) and positive δ13C anomalies before and after 1.54 Ga in this area, accompanied by a significant increase in Y / Ho ( average 64 ), and later returned to normal levels.[Conclusion] It indicated that there might be a transient oxidation event. This oxidation event is consistent with the contemporaneous strata of the Jixian System in the northern margin of the North China Craton, indicating that the fluctuation of shallow sea oxygen content during this period may be widespread in the North China Craton. This study can provide direct evidence for the pulse oxygenation event in the Mesoproterozoic, and help to further determine the redox state of the shallow sea during this period and the effect of oxygen on the evolution of eukaryotes.
Abstract: [Objective] The level of oxygen content in shallow sea and atmosphere during the Mesoproterozoic (about 1.8-1.0 Ga) has been controversial.Due to the slow evolution of eukaryotes during this period, the redox state of the surface ocean and atmosphere has been considered to be a relatively stable hypoxic state. However, in recent years, more and more evidence shows that there are dynamic fluctuations in oxygen content during this period. However, due to the heterogeneity of time and space, people 's understanding of the global redox state during this period is still very limited.[Methods] In this study, the redox state of the shallow sea in the southern margin of the North China Craton was studied by analyzing the Ce anomaly, δ13C and Y/Ho indexes of carbonate rocks in the Longjiayuan ( 1.59-1.54Ga ) Formation.[Results] The results show that there are obvious negative Ce anomalies ( 0.53 ~ 0.94 ) and positive δ13C anomalies before and after 1.54 Ga in this area, accompanied by a significant increase in Y / Ho ( average 64 ), and later returned to normal levels.[Conclusion] It indicated that there might be a transient oxidation event. This oxidation event is consistent with the contemporaneous strata of the Jixian System in the northern margin of the North China Craton, indicating that the fluctuation of shallow sea oxygen content during this period may be widespread in the North China Craton. This study can provide direct evidence for the pulse oxygenation event in the Mesoproterozoic, and help to further determine the redox state of the shallow sea during this period and the effect of oxygen on the evolution of eukaryotes.
Abstract:
[Objective] Shallowing-upward sequences are extensively developed in shallow-water carbonate environments, and the identification of shallowing-upward sequences in deep-water carbonate rocks holds a unique advantage for analyzing the evolution of shallow-water carbonate sedimentary environments. [Method] This study focuses on the Late Cambrian Xixiangchi Formation in Xiuqi Town, Chengkou County, on the northern margin of the Yangtze Platform. Through detailed field sedimentological analysis and laboratory microfacies analysis, shallowing-upward sequences in carbonate rocks were identified. The compositional characteristics and vertical stacking relationships were analyzed, thereby exploring the Late Cambrian sedimentary environment evolution in the upper Yangtze region. [Results and Discussions] In the Xixiangchi Formation, 14 sedimentary microfacies have been identified, including MF0 argillaceous shale, MF1 micrite, MF2 bright crystal gravel limestone, MF3 bright crystal sand limestone, MF4 muddy siltstone, MF5 dolomitic microcrystalline limestone, MF6 gravel dolomite, MF7 bright crystal sand dolomite, MF8 sandy gravel grain dolomite, MF9 sandy sandy lithic grain dolomite, MF10 sandy dolomite, MF11 laminated dolomite, MF12 bamboo leaf-like gravel dolomite, and MF13 grain dolomite with dissolution pores. Based on the microfacies associations, six decimeter-scale upward-shallowing tidal sub-environments (C1-1 to C1-6) have been recognized within the Xixiangchi Formation, representing subtidal deposition. Additionally, six decimeter-scale upward-shallowing tidal-subtidal transition sub-environments (C2-1 to C2-6) and two decimeter-scale upward-shallowing intertidal-subtidal transition sub-environments (C3-1 and C3-2) have been identified. These decimeter-scale upward-shallowing cycles constitute three secondary sea-level cycles. These three secondary cycles, from bottom to top, combine to form one upward-shallowing sedimentary cycle within the Xixiangchi Formation, representing a rapid transgression followed by gradual regression. [Conclusions] Based on the identification of shallowing-upward sedimentary sequences and the analysis of their compositional characteristics and vertical stacking relationships, it is believed that the Late Cambrian Xixiangchi Formation was significantly influenced by high-frequency sea-level changes. It as a whole underwent an early rapid marine transgression, followed by a late slow regression, and experienced multiple episodes of secondary sea-level fluctuations. This resulted in a restricted carbonate platform sedimentary model characterized by mixed intertidal subfacies, chalky lagoon subfacies, and inner-shelf grainy shoal subfacies. This study further confirms a global late Cambrian sea-level regression event.
[Objective] Shallowing-upward sequences are extensively developed in shallow-water carbonate environments, and the identification of shallowing-upward sequences in deep-water carbonate rocks holds a unique advantage for analyzing the evolution of shallow-water carbonate sedimentary environments. [Method] This study focuses on the Late Cambrian Xixiangchi Formation in Xiuqi Town, Chengkou County, on the northern margin of the Yangtze Platform. Through detailed field sedimentological analysis and laboratory microfacies analysis, shallowing-upward sequences in carbonate rocks were identified. The compositional characteristics and vertical stacking relationships were analyzed, thereby exploring the Late Cambrian sedimentary environment evolution in the upper Yangtze region. [Results and Discussions] In the Xixiangchi Formation, 14 sedimentary microfacies have been identified, including MF0 argillaceous shale, MF1 micrite, MF2 bright crystal gravel limestone, MF3 bright crystal sand limestone, MF4 muddy siltstone, MF5 dolomitic microcrystalline limestone, MF6 gravel dolomite, MF7 bright crystal sand dolomite, MF8 sandy gravel grain dolomite, MF9 sandy sandy lithic grain dolomite, MF10 sandy dolomite, MF11 laminated dolomite, MF12 bamboo leaf-like gravel dolomite, and MF13 grain dolomite with dissolution pores. Based on the microfacies associations, six decimeter-scale upward-shallowing tidal sub-environments (C1-1 to C1-6) have been recognized within the Xixiangchi Formation, representing subtidal deposition. Additionally, six decimeter-scale upward-shallowing tidal-subtidal transition sub-environments (C2-1 to C2-6) and two decimeter-scale upward-shallowing intertidal-subtidal transition sub-environments (C3-1 and C3-2) have been identified. These decimeter-scale upward-shallowing cycles constitute three secondary sea-level cycles. These three secondary cycles, from bottom to top, combine to form one upward-shallowing sedimentary cycle within the Xixiangchi Formation, representing a rapid transgression followed by gradual regression. [Conclusions] Based on the identification of shallowing-upward sedimentary sequences and the analysis of their compositional characteristics and vertical stacking relationships, it is believed that the Late Cambrian Xixiangchi Formation was significantly influenced by high-frequency sea-level changes. It as a whole underwent an early rapid marine transgression, followed by a late slow regression, and experienced multiple episodes of secondary sea-level fluctuations. This resulted in a restricted carbonate platform sedimentary model characterized by mixed intertidal subfacies, chalky lagoon subfacies, and inner-shelf grainy shoal subfacies. This study further confirms a global late Cambrian sea-level regression event.
Abstract:
Abstract: J1b1 Formation in the Mahu slope area is a set of sandy (gravel) rock deposits of coal-bearing rock series close to the J/T unconformity. The shale rich conglomerate belt near the bottom of the J/T unconformity has obvious oil and gas thickened, and light oil and gas are mainly concentrated in the thin sandstone belt above the coal seam. There is still no research on the origin of oil and gas thickening zone in relatively deep buried area, the percolation mechanism of atmospheric fresh water to overlying strata on unconformity surface, and the origin of light oil and gas enrichment above coal seam of coal-bearing rock series. Therefore, based on the properties of crude oil and carbon isotope analysis of natural gas, combined with the data of burial history, thermal history, pore evolution history, and laser Raman spectrum analysis of hydrocarbon salt water inclusions, the genetic types of J1b1 natural gas and the origin and distribution of hydrocarbon thickening zone and light oil and gas zone are discussed. The results show that: ①J1b1 coal-bearing rock series can be divided into oil and gas thickening zone and light oil and gas zone according to the characteristics of oil and gas density viscosity. The former is mainly distributed in the upper wall of the fault zone, the fault zone, and the bottom of the slope zone adjacent to the J/T unconformity. The latter is mainly distributed in the thin sandstone zone above the coal seam in the slope zone, and the coal-derived gas content is high. ②The origin of the shale rich conglomerate oil and gas thickening zone at the bottom of the slope zone adjacent to the J/T unconformity is closely related to the atmospheric freshwater compacting-centrifugal flow oxidation degradation. The “YANSHAN normal fault-J /T unconformity -shale rich conglomerate assemblage”and the associated capillary imbibition of wetting water phase led to the formation of atmospheric freshwater compaction-centrifugal flow oil-gas thickening zone closely related to the unconformity in the slope area of relatively deep burial. ③The thin sandstone reservoir above the coal seam has the characteristics of “self-generated and self-stored (deinspiratory charging in J1b1 coal seam)” and “bottom-generated and upper-stored (hydrocarbon supply from P1f source rock)”, and has the advantage of light oil and gas enrichment. The coal seam desorption diffused upward through the positive fracture into the thin sandstone at the top, and the methane carbon isotope value was relatively light, which was different from the retained adsorbed gas in the coal seam (δ13C1=-48.2‰ in the former and δ13C1=-43.6‰ in the latter). The geological stratification effect caused by long distance migration of P1f source rock oil and gas further promotes the accumulation of light oil and gas in thin sandstone above the coal seam. The conclusion is that the upper thin sandstone belt of J1b1 is the first choice for exploration of light oil and gas enrichment belt. The quantitative lithological logging identification map of coal-bearing rock series with the combined restraint of CNL-IMP was established, and the effective reservoir distribution area of the upper thin sandstone of J1b1 with a thickness≥10m was identified in the Yanbei1 3D seismic zone.
Abstract: J1b1 Formation in the Mahu slope area is a set of sandy (gravel) rock deposits of coal-bearing rock series close to the J/T unconformity. The shale rich conglomerate belt near the bottom of the J/T unconformity has obvious oil and gas thickened, and light oil and gas are mainly concentrated in the thin sandstone belt above the coal seam. There is still no research on the origin of oil and gas thickening zone in relatively deep buried area, the percolation mechanism of atmospheric fresh water to overlying strata on unconformity surface, and the origin of light oil and gas enrichment above coal seam of coal-bearing rock series. Therefore, based on the properties of crude oil and carbon isotope analysis of natural gas, combined with the data of burial history, thermal history, pore evolution history, and laser Raman spectrum analysis of hydrocarbon salt water inclusions, the genetic types of J1b1 natural gas and the origin and distribution of hydrocarbon thickening zone and light oil and gas zone are discussed. The results show that: ①J1b1 coal-bearing rock series can be divided into oil and gas thickening zone and light oil and gas zone according to the characteristics of oil and gas density viscosity. The former is mainly distributed in the upper wall of the fault zone, the fault zone, and the bottom of the slope zone adjacent to the J/T unconformity. The latter is mainly distributed in the thin sandstone zone above the coal seam in the slope zone, and the coal-derived gas content is high. ②The origin of the shale rich conglomerate oil and gas thickening zone at the bottom of the slope zone adjacent to the J/T unconformity is closely related to the atmospheric freshwater compacting-centrifugal flow oxidation degradation. The “YANSHAN normal fault-J /T unconformity -shale rich conglomerate assemblage”and the associated capillary imbibition of wetting water phase led to the formation of atmospheric freshwater compaction-centrifugal flow oil-gas thickening zone closely related to the unconformity in the slope area of relatively deep burial. ③The thin sandstone reservoir above the coal seam has the characteristics of “self-generated and self-stored (deinspiratory charging in J1b1 coal seam)” and “bottom-generated and upper-stored (hydrocarbon supply from P1f source rock)”, and has the advantage of light oil and gas enrichment. The coal seam desorption diffused upward through the positive fracture into the thin sandstone at the top, and the methane carbon isotope value was relatively light, which was different from the retained adsorbed gas in the coal seam (δ13C1=-48.2‰ in the former and δ13C1=-43.6‰ in the latter). The geological stratification effect caused by long distance migration of P1f source rock oil and gas further promotes the accumulation of light oil and gas in thin sandstone above the coal seam. The conclusion is that the upper thin sandstone belt of J1b1 is the first choice for exploration of light oil and gas enrichment belt. The quantitative lithological logging identification map of coal-bearing rock series with the combined restraint of CNL-IMP was established, and the effective reservoir distribution area of the upper thin sandstone of J1b1 with a thickness≥10m was identified in the Yanbei1 3D seismic zone.
Abstract:
[Objective] The redox states of the early Ediacaran ocean has always been a research hotspot. The formation process of sedimentary barite nodules is studied to explore the redox variation of the Ediacaran ocean immediately after the Snowball Earth event. [Methods] Analysis on sedimentary environments of barite nodules from calcareous mudstone of the lower Doushantuo Formation in Jinguadun section were developed via sedimentologic and petromineralogical methods. [Result and Discussion] Sedimentary beddings of the surrounding rocks are curved around the barite nodules, indicating that these nodules are probably classified to diagenetic nodules and formed in sedimentary soft muds during the early diagenetic stage. The barite, quartz and pyrite are the three top authigenic sedimentary minerals in the nodules. The mineral distribution is stratified in the barite nodules. Specially, the inner layer contains dense pyrite aggregates dominated by euhedral to subhedral pyrite grains and quartz minerals that grow interwoven together. From the core to the outer edge developed radial aggregates by barite and quartz. This study preliminarily demonstrates that the formation of authigenic sedimentary minerals occurring in different parts of the barite nodules probably precipitate in different redox zones. That is to say, the pyrite and quartz minerals in the inner nodule are formed in the sulfate reduction zone, then the formation location of nodules gradually transits from sulfate reduction zone to sulfate-methane transition zone. The Ba2+ sources in the barite probably originate from the methanogenic zone, where dissolution of labile and biogenic barite associated with organic matter occurs. The upward spreading Ba2+ ions react with downward diffusing seawater sulfate radicals and deposit barium sulfate in the upper front of sulfate-methane transition zone. [Conclusion] The formation process of the barite nodules is staged. Observation on barite nodules indicates that the depth of oceanic sulfate reduction chemocline has descende into the loose sediments beneath the interface of sediment and water body after the Snowball Event at about 600 Ma, due to the increase levels of the continental sulfate input at that time. Methane was partly oxidized in sulfate-methane transition zone, thus reducing the atmospheric emission of marine methane.
[Objective] The redox states of the early Ediacaran ocean has always been a research hotspot. The formation process of sedimentary barite nodules is studied to explore the redox variation of the Ediacaran ocean immediately after the Snowball Earth event. [Methods] Analysis on sedimentary environments of barite nodules from calcareous mudstone of the lower Doushantuo Formation in Jinguadun section were developed via sedimentologic and petromineralogical methods. [Result and Discussion] Sedimentary beddings of the surrounding rocks are curved around the barite nodules, indicating that these nodules are probably classified to diagenetic nodules and formed in sedimentary soft muds during the early diagenetic stage. The barite, quartz and pyrite are the three top authigenic sedimentary minerals in the nodules. The mineral distribution is stratified in the barite nodules. Specially, the inner layer contains dense pyrite aggregates dominated by euhedral to subhedral pyrite grains and quartz minerals that grow interwoven together. From the core to the outer edge developed radial aggregates by barite and quartz. This study preliminarily demonstrates that the formation of authigenic sedimentary minerals occurring in different parts of the barite nodules probably precipitate in different redox zones. That is to say, the pyrite and quartz minerals in the inner nodule are formed in the sulfate reduction zone, then the formation location of nodules gradually transits from sulfate reduction zone to sulfate-methane transition zone. The Ba2+ sources in the barite probably originate from the methanogenic zone, where dissolution of labile and biogenic barite associated with organic matter occurs. The upward spreading Ba2+ ions react with downward diffusing seawater sulfate radicals and deposit barium sulfate in the upper front of sulfate-methane transition zone. [Conclusion] The formation process of the barite nodules is staged. Observation on barite nodules indicates that the depth of oceanic sulfate reduction chemocline has descende into the loose sediments beneath the interface of sediment and water body after the Snowball Event at about 600 Ma, due to the increase levels of the continental sulfate input at that time. Methane was partly oxidized in sulfate-methane transition zone, thus reducing the atmospheric emission of marine methane.
Abstract:
The formation and evolution of the Earth's crust is an important aspect of studying the early evolution of the Earth towards livable planets. The successive discovery of early basement rocks and their zircon age information in the Dabie region has made it an important place to study the early Earth. Compared with the limited exposure of basement rocks, the detrital zircons in river sediments can comprehensively reflect the geological evolution information of the source area, and are an effective means to explore the growth and evolution of continental crust. This article conducts U-Pb Hf isotope analysis of zircons in detrital sediments from three different rivers in the Dabie region. The U-Pb zircon age peaks obtained can be divided into four groups: 2676-2424 Ma, 2035-1812 Ma, 890-748 Ma, and 140-120 Ma. Based on the data in this article and previous research results, the following conclusions can be drawn: (1) The magmatic activity records in the Dabie region can be roughly divided into 10 stages and 5 cycles. The quiet periods are 3.0-2.9Ga, 2.4-2.1Ga, 1.8-0.9Ga, 0.70-0.14Ga, and the explosive periods are 4.0-3.0Ga, 2.9-2.4Ga, 2.1-1.8Ga, 0.9-0.7Ga, 0.14-0.12Ga, respectively. (2) The Dabie region mainly experienced four stages of metamorphic events, which occurred in the late Neoarchean (~2.5Ga), middle Paleoproterozoic (~2.0Ga), Triassic (0.24-0.20Ga), and Cretaceous (0.14-0.12Ga). (3) The Dabie region mainly experienced four stages of crustal growth events: initial crustal growth during the Mesozoic era, and massive crustal growth at 4.4-4.1Ga; The crustal growth at 4.1~3.9Ga is relatively slow, with no significant crustal growth; 3.9~2.8Ga sustained crustal growth; The crustal growth rate is relatively slow at 2.8~1.0Ga. (4) Compared to the magmatic, metamorphic, and crustal growth events in the Dabie and Huangling regions, there is a significant difference between the two before~2.0Ga, suggesting that the two were more likely independent micro landmasses before this time.
The formation and evolution of the Earth's crust is an important aspect of studying the early evolution of the Earth towards livable planets. The successive discovery of early basement rocks and their zircon age information in the Dabie region has made it an important place to study the early Earth. Compared with the limited exposure of basement rocks, the detrital zircons in river sediments can comprehensively reflect the geological evolution information of the source area, and are an effective means to explore the growth and evolution of continental crust. This article conducts U-Pb Hf isotope analysis of zircons in detrital sediments from three different rivers in the Dabie region. The U-Pb zircon age peaks obtained can be divided into four groups: 2676-2424 Ma, 2035-1812 Ma, 890-748 Ma, and 140-120 Ma. Based on the data in this article and previous research results, the following conclusions can be drawn: (1) The magmatic activity records in the Dabie region can be roughly divided into 10 stages and 5 cycles. The quiet periods are 3.0-2.9Ga, 2.4-2.1Ga, 1.8-0.9Ga, 0.70-0.14Ga, and the explosive periods are 4.0-3.0Ga, 2.9-2.4Ga, 2.1-1.8Ga, 0.9-0.7Ga, 0.14-0.12Ga, respectively. (2) The Dabie region mainly experienced four stages of metamorphic events, which occurred in the late Neoarchean (~2.5Ga), middle Paleoproterozoic (~2.0Ga), Triassic (0.24-0.20Ga), and Cretaceous (0.14-0.12Ga). (3) The Dabie region mainly experienced four stages of crustal growth events: initial crustal growth during the Mesozoic era, and massive crustal growth at 4.4-4.1Ga; The crustal growth at 4.1~3.9Ga is relatively slow, with no significant crustal growth; 3.9~2.8Ga sustained crustal growth; The crustal growth rate is relatively slow at 2.8~1.0Ga. (4) Compared to the magmatic, metamorphic, and crustal growth events in the Dabie and Huangling regions, there is a significant difference between the two before~2.0Ga, suggesting that the two were more likely independent micro landmasses before this time.
Abstract:
[Objective]The limestone-marlstone alterations (LMAs) are the important archives of climatic, hydrological, and geological events for geologists. But as a typical endmember of the LMAs, the knowledge about the genesis of the LMAs with eyelid-eyeball structure of the Member I of the Maokou Formation in the Sichuan Basin has not come to agreement widely. This not only seriously affects environmental researching of the LMAs with eyelid-eyeball structure, but also affects the efficiency of its exploration. Dolomitization is developed in the LMAs with eyelid-eyeball structure (mainly in the eyelids) of the Member I of the Maokou Formation of the DB1 well during the penecontemporaneous and early diagenetic phase can be used to constrain the depositional environments of carbonate rocks. [Methods] In this paper, petrological and geochemical analyses have been carried out in detailed, the process and the fluid properties of dolomitization has been discussed to constrain the process of LMAs with eyelid-eyeball structure. [Results and Discussions]Three types of dolomitization are developed in the Member I of the Maokou Formation, which are muddy dolomitic (EDM-I); limy dolomitic (EDM-II) and dolomitic marlstone(EDL). EDM-I has the highest degree of dolomitization, distinct bands of cathodoluminescence, a flat rare earth partitioning pattern, higher δ13C and δ18O values but lower Y/Ho values relative to seawater, it was dolomitized by penecontemporaneous seawater mixed with a small amount of meteoric freshwater during the penecontemporaneous phase. EDM-II has the middle degree of dolomitization, a left leaning rare earth partitioning pattern and values of δ13C, δ18O, 87Sr/86Sr, and Y/Ho similar to seawater, it was dolomitized by seawater with high Mg/Ca, which was induced by frequent sea-level rise and fall changes during the syn-sedimentary and penecontemporaneous phase. EDL has the lowest degree of dolomitization, a left leaning rare earth partitioning pattern, higher δ13C and δ18O values relative to EDM-II, and seawater-like Y/Ho values. EDL was dolomitized by the sealed seawater of the syn-sedimentary phase which has been alterated with the wall rocks in the early diagenetic stage. [Conclusions] The dolomitization of the LMAs with eyelid-eyeball structure by weakly evaporating seawater and seawater mixed with freshwater during the penecontemporaneous and early diagenetic phase requires that the LMAs deposited in a shallower water. The high mud content, high strontium isotope and rare earth element values, low carbon and oxygen isotope values and Y/Ho values of the eyelid-like marlstone relative to the eyeball-like limestone indicate that the depth of water for the eyelid-like marlstone is shallower than that of the eyeball-like limestone during they deposited. Therefore, it is inferred that the LMAs in the Member I of the Maokou Formation were produced under cyclic oscillation in the depositional environment, and their genesis may have been mainly influenced by sedimentary process.
[Objective]The limestone-marlstone alterations (LMAs) are the important archives of climatic, hydrological, and geological events for geologists. But as a typical endmember of the LMAs, the knowledge about the genesis of the LMAs with eyelid-eyeball structure of the Member I of the Maokou Formation in the Sichuan Basin has not come to agreement widely. This not only seriously affects environmental researching of the LMAs with eyelid-eyeball structure, but also affects the efficiency of its exploration. Dolomitization is developed in the LMAs with eyelid-eyeball structure (mainly in the eyelids) of the Member I of the Maokou Formation of the DB1 well during the penecontemporaneous and early diagenetic phase can be used to constrain the depositional environments of carbonate rocks. [Methods] In this paper, petrological and geochemical analyses have been carried out in detailed, the process and the fluid properties of dolomitization has been discussed to constrain the process of LMAs with eyelid-eyeball structure. [Results and Discussions]Three types of dolomitization are developed in the Member I of the Maokou Formation, which are muddy dolomitic (EDM-I); limy dolomitic (EDM-II) and dolomitic marlstone(EDL). EDM-I has the highest degree of dolomitization, distinct bands of cathodoluminescence, a flat rare earth partitioning pattern, higher δ13C and δ18O values but lower Y/Ho values relative to seawater, it was dolomitized by penecontemporaneous seawater mixed with a small amount of meteoric freshwater during the penecontemporaneous phase. EDM-II has the middle degree of dolomitization, a left leaning rare earth partitioning pattern and values of δ13C, δ18O, 87Sr/86Sr, and Y/Ho similar to seawater, it was dolomitized by seawater with high Mg/Ca, which was induced by frequent sea-level rise and fall changes during the syn-sedimentary and penecontemporaneous phase. EDL has the lowest degree of dolomitization, a left leaning rare earth partitioning pattern, higher δ13C and δ18O values relative to EDM-II, and seawater-like Y/Ho values. EDL was dolomitized by the sealed seawater of the syn-sedimentary phase which has been alterated with the wall rocks in the early diagenetic stage. [Conclusions] The dolomitization of the LMAs with eyelid-eyeball structure by weakly evaporating seawater and seawater mixed with freshwater during the penecontemporaneous and early diagenetic phase requires that the LMAs deposited in a shallower water. The high mud content, high strontium isotope and rare earth element values, low carbon and oxygen isotope values and Y/Ho values of the eyelid-like marlstone relative to the eyeball-like limestone indicate that the depth of water for the eyelid-like marlstone is shallower than that of the eyeball-like limestone during they deposited. Therefore, it is inferred that the LMAs in the Member I of the Maokou Formation were produced under cyclic oscillation in the depositional environment, and their genesis may have been mainly influenced by sedimentary process.
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[Objective]Mixed sediments were widely developed in Lower First Member of Shahejie Formation in Lixian Slope, clarify the mixed sedimentary characteristics and its control on reservoir is of great significance to determines the target area for exploration and development in the next step. [Methods]Based on core, thin section, well logging seismic, as well as laboratory analysis data, the mixed sedimentary types, distribution regularity, control factors, sedimentary model and high-quality reservoir’s formation mechanism in Lower First Member of Shahejie Formation in Lixian Slope were analyzed. [Results]There are two types of mixed sedimentary in the Lower First Member of Shahejie Formation in the study area, mixed sedimentary rock, mixed sedimentary strata, the mixed sedimentary rock can be divided into 6 types in three major categories, mixed sandstones, mixed mudstones and mixed carbonate rocks, the mixed sedimentary strata can be divided into 16 types in four?lithofacies assemblages, terrigenous rock-carbonate rock, terrigenous rock- mixosedimentite, carbonate rock-mixosedimentite, mixosedimentite. The Lower First Member of Shahejie Formation in Lixian Slope have typical mixed features, which can be divided into 8 mixed sedimentary microfacies, including underwater distributary channel, mouth bar sheet underwater diversion bay, mud flat,?sandy beach bar, carbonate beach bar, inner beach and the semi-deep lake mud,?the mixed sediments have the characteristics of rapid phase transformation in the lateral direction, multiple types of rock superimpose frequently in the vertical, the mixed sediments have different distribution characteristics?of different intervals. The mixed sediments were controlled by climatic and water environment, tectonic background and palaeogeomorphology, sediment supply?and lake level changes, two kinds of mixed depositional model are developed,lowstand period and high-stand periods. The mixed sediments plays a significant role in reservoir controlling factors, the sandy beach bar and carbonate beach bar where developed in high-energy facies zone are the favorable mixed sedimentary microfacies, the closed saline water environment is the foundation of reservoir formation, controlled the formation and distribution of high-quality reservoirs, sedimentary cycles controlled the development degree and distribution palace of high-quality reservoirs. [conclusion] the palaeogeomorphology highland in the southwestern are favorable areas for mixed beach bars development and exploration practice.
[Objective]Mixed sediments were widely developed in Lower First Member of Shahejie Formation in Lixian Slope, clarify the mixed sedimentary characteristics and its control on reservoir is of great significance to determines the target area for exploration and development in the next step. [Methods]Based on core, thin section, well logging seismic, as well as laboratory analysis data, the mixed sedimentary types, distribution regularity, control factors, sedimentary model and high-quality reservoir’s formation mechanism in Lower First Member of Shahejie Formation in Lixian Slope were analyzed. [Results]There are two types of mixed sedimentary in the Lower First Member of Shahejie Formation in the study area, mixed sedimentary rock, mixed sedimentary strata, the mixed sedimentary rock can be divided into 6 types in three major categories, mixed sandstones, mixed mudstones and mixed carbonate rocks, the mixed sedimentary strata can be divided into 16 types in four?lithofacies assemblages, terrigenous rock-carbonate rock, terrigenous rock- mixosedimentite, carbonate rock-mixosedimentite, mixosedimentite. The Lower First Member of Shahejie Formation in Lixian Slope have typical mixed features, which can be divided into 8 mixed sedimentary microfacies, including underwater distributary channel, mouth bar sheet underwater diversion bay, mud flat,?sandy beach bar, carbonate beach bar, inner beach and the semi-deep lake mud,?the mixed sediments have the characteristics of rapid phase transformation in the lateral direction, multiple types of rock superimpose frequently in the vertical, the mixed sediments have different distribution characteristics?of different intervals. The mixed sediments were controlled by climatic and water environment, tectonic background and palaeogeomorphology, sediment supply?and lake level changes, two kinds of mixed depositional model are developed,lowstand period and high-stand periods. The mixed sediments plays a significant role in reservoir controlling factors, the sandy beach bar and carbonate beach bar where developed in high-energy facies zone are the favorable mixed sedimentary microfacies, the closed saline water environment is the foundation of reservoir formation, controlled the formation and distribution of high-quality reservoirs, sedimentary cycles controlled the development degree and distribution palace of high-quality reservoirs. [conclusion] the palaeogeomorphology highland in the southwestern are favorable areas for mixed beach bars development and exploration practice.
Abstract:
[Objective] The Qigebrak Formation developed abundant microbial carbonates, which are the favorable target for deep to ultra-deep oil and gas exploration. However, the existing stratigraphic division scheme of the Qigebrak Formation remains controversial, hindering the analysis of reservoir depositional evolution and distribution prediction. Further in-depth research and clarification are urgently needed. [Methods] This study focused on the Shiairik section in the northwest Aksu area of the Tarim Basin to define the depositional environment and sea-level change, and conduct a sequence stratigraphic division of the Qigebrak Formation based on the analysis of high-precision depositional facies and the Fischer plot. [Results] Ten main facies are recognized from the Qigebrak Formation and grouped into a carbonate ramp platform. Two subfacies; i.e., inner and middle ramp, are developed under this setting. The inner ramp consists of the tidal flat, lagoon, tidal channel, and grain shoals. Eight subtypes of peritidal cycles, two subtypes of shallow subtidal cycles and two subtypes of middle-ramp cycles are identified. Based on the stacking patterns reflected in the Fischer diagrams, analysis of orders of depositional facies and proportion of subtidal facies, the Qigebrak is divided into four third-order T-R sequences (SQ1–SQ4). Among these sequences, SQ1 only records the regressive system tract in the Qigebrak Formation, whereas SQ4 only preserves the transgressive system tract. [Conclusions] This study suggests that (1) it is reasonable to divide the Qigebrak Formation into four sequences; (2) the top of the Qigebrak Formation could have experienced the million-year-scale exposure and erosion, which would favor the formation of scaled reservoirs.
[Objective] The Qigebrak Formation developed abundant microbial carbonates, which are the favorable target for deep to ultra-deep oil and gas exploration. However, the existing stratigraphic division scheme of the Qigebrak Formation remains controversial, hindering the analysis of reservoir depositional evolution and distribution prediction. Further in-depth research and clarification are urgently needed. [Methods] This study focused on the Shiairik section in the northwest Aksu area of the Tarim Basin to define the depositional environment and sea-level change, and conduct a sequence stratigraphic division of the Qigebrak Formation based on the analysis of high-precision depositional facies and the Fischer plot. [Results] Ten main facies are recognized from the Qigebrak Formation and grouped into a carbonate ramp platform. Two subfacies; i.e., inner and middle ramp, are developed under this setting. The inner ramp consists of the tidal flat, lagoon, tidal channel, and grain shoals. Eight subtypes of peritidal cycles, two subtypes of shallow subtidal cycles and two subtypes of middle-ramp cycles are identified. Based on the stacking patterns reflected in the Fischer diagrams, analysis of orders of depositional facies and proportion of subtidal facies, the Qigebrak is divided into four third-order T-R sequences (SQ1–SQ4). Among these sequences, SQ1 only records the regressive system tract in the Qigebrak Formation, whereas SQ4 only preserves the transgressive system tract. [Conclusions] This study suggests that (1) it is reasonable to divide the Qigebrak Formation into four sequences; (2) the top of the Qigebrak Formation could have experienced the million-year-scale exposure and erosion, which would favor the formation of scaled reservoirs.
Abstract:
Near-source sedimentary system of member 1 of Shawan formation is the main reservoir in Chepaizi area of Junggar basin. Neverthless, there have been different points on depositional characteristics of it. On the basis of previous studies， using the mud logging data， core data， logging data and seismic data, combining with modern fan delta sediment, the depositional characteristics of near-source sedimentary system within the 4th sequence stratigraphic framework of member 1 of Shanwan formation were investigated, and the sedimentary model of it was built up. The results are as follows: (1) Near-source system was made of two complex fan deltas, one is shoal complex fan deltas, the other is complex fan deltas. The main microfacies were distributary and sand bar of fan delta front. (2) The lithology of the distributary was changed from shoreline to lake by conglomerate - glutenite –medium-coarse lithic sandstone bearing conglomerate - medium-coarse feldspar lithic sandstone bearing conglomerate - feldspar lithic fine sandstone bearing conglomerate. The lithic composition was dominated by igneous lithic, while the gravel composition was dominated by igneous gravel and mud-gravel. (3) Near-source system of sand group 1 of member 1 of Shawan formation mainly distributed below the third slope break zone. It reached in the the middle of the project where the far-source system reached as well, and they interacted with each other. Lacustrine range was the smallest during this stage. Near-source system of sand group 2 of member 1 of Shawan formation mainly distributed above the slope break zone and the lacustrine range was the largest this period. Near-source system of sand group 3 of member 1 of Shawan formation mainly distributed near the slope break zone. The slope of the eastern wing was steeper, the gully scale was smaller, the complex fan delta scale was smaller, the slope of the western wing was slower, the valley scale was larger, the composite fan delta scale was larger. The conclusion is that paleogeomorphology and the relative lacustrine level change controlled the sedimentary characteristics of the near-source systems.
Near-source sedimentary system of member 1 of Shawan formation is the main reservoir in Chepaizi area of Junggar basin. Neverthless, there have been different points on depositional characteristics of it. On the basis of previous studies， using the mud logging data， core data， logging data and seismic data, combining with modern fan delta sediment, the depositional characteristics of near-source sedimentary system within the 4th sequence stratigraphic framework of member 1 of Shanwan formation were investigated, and the sedimentary model of it was built up. The results are as follows: (1) Near-source system was made of two complex fan deltas, one is shoal complex fan deltas, the other is complex fan deltas. The main microfacies were distributary and sand bar of fan delta front. (2) The lithology of the distributary was changed from shoreline to lake by conglomerate - glutenite –medium-coarse lithic sandstone bearing conglomerate - medium-coarse feldspar lithic sandstone bearing conglomerate - feldspar lithic fine sandstone bearing conglomerate. The lithic composition was dominated by igneous lithic, while the gravel composition was dominated by igneous gravel and mud-gravel. (3) Near-source system of sand group 1 of member 1 of Shawan formation mainly distributed below the third slope break zone. It reached in the the middle of the project where the far-source system reached as well, and they interacted with each other. Lacustrine range was the smallest during this stage. Near-source system of sand group 2 of member 1 of Shawan formation mainly distributed above the slope break zone and the lacustrine range was the largest this period. Near-source system of sand group 3 of member 1 of Shawan formation mainly distributed near the slope break zone. The slope of the eastern wing was steeper, the gully scale was smaller, the complex fan delta scale was smaller, the slope of the western wing was slower, the valley scale was larger, the composite fan delta scale was larger. The conclusion is that paleogeomorphology and the relative lacustrine level change controlled the sedimentary characteristics of the near-source systems.
Abstract:
The saturated hydrocarbons of 26 coal measure source rock samples in the Upper Paleozoic of Ordos Basin were analyzed by gas chromatography and chromatography-mass spectrometry. According to the distribution characteristics of tricyclic terpanes (TT), the source rock samples in the study area were divided into three different types of distribution patterns. The C19TT is the main peak of the type I source rock, and the content of C19TT, C20TT and C21TT gradually decreases. At the same time, the Pr/Ph ratio is high and the content of C24 tetracyclic terpane is also rich in this type of sample. This kind of samples are mainly humic coal and carbonaceous mudstone, revealing the characteristics of lacustrine facies sedimentary environment. On the contrary, the tricyclic terpanes of type II source rocks are dominated by C23TT, and the contents of C19TT, C20TT and C21TT are gradually increasing, while the Pr/Ph ratio is low, and the content of C24 tetracyclic terpane is not abundant. In addition to coal-bearing mudstone, there are also humic coal and carbonaceous mudstone in these samples, and their sedimentary environment is quite different from that of type I source rocks. The distribution of tricyclic terpanes in type III source rocks is between type I and type II source rocks. On the one hand, the main peak carbon of tricyclic terpane is C23TT, on the other hand, the relative content of C19TT, C20TT and C21TT decreases in turn and shows the characteristics of stepwise distribution. In addition, the Pr/Ph ratio and the content of C24 tetracyclic terpane are between type I and type II source rocks. The results also reveal that with the increase of the thermal evolution degree of source rocks, the total amount of tricyclic terpanes shows an gradually increasing trend, but the distribution patterns of tricyclic terpanes in different types of source rocks have not changed significantly, in other words, the different distribution patterns of tricyclic terpanes in coal-bearing source rocks in the study area are less affected by the thermal evolution degree of organic matter, but mainly controlled by sedimentary environment and parent material type.
The saturated hydrocarbons of 26 coal measure source rock samples in the Upper Paleozoic of Ordos Basin were analyzed by gas chromatography and chromatography-mass spectrometry. According to the distribution characteristics of tricyclic terpanes (TT), the source rock samples in the study area were divided into three different types of distribution patterns. The C19TT is the main peak of the type I source rock, and the content of C19TT, C20TT and C21TT gradually decreases. At the same time, the Pr/Ph ratio is high and the content of C24 tetracyclic terpane is also rich in this type of sample. This kind of samples are mainly humic coal and carbonaceous mudstone, revealing the characteristics of lacustrine facies sedimentary environment. On the contrary, the tricyclic terpanes of type II source rocks are dominated by C23TT, and the contents of C19TT, C20TT and C21TT are gradually increasing, while the Pr/Ph ratio is low, and the content of C24 tetracyclic terpane is not abundant. In addition to coal-bearing mudstone, there are also humic coal and carbonaceous mudstone in these samples, and their sedimentary environment is quite different from that of type I source rocks. The distribution of tricyclic terpanes in type III source rocks is between type I and type II source rocks. On the one hand, the main peak carbon of tricyclic terpane is C23TT, on the other hand, the relative content of C19TT, C20TT and C21TT decreases in turn and shows the characteristics of stepwise distribution. In addition, the Pr/Ph ratio and the content of C24 tetracyclic terpane are between type I and type II source rocks. The results also reveal that with the increase of the thermal evolution degree of source rocks, the total amount of tricyclic terpanes shows an gradually increasing trend, but the distribution patterns of tricyclic terpanes in different types of source rocks have not changed significantly, in other words, the different distribution patterns of tricyclic terpanes in coal-bearing source rocks in the study area are less affected by the thermal evolution degree of organic matter, but mainly controlled by sedimentary environment and parent material type.
Abstract:
Abstract: The Liushagang formation is one of the petroliferous reservoirs in the Fushan Sag, Beibuwan Basin. However, the controlling factors of reservoir quality are unclear and there are no matched prediction technology for reservoir quality, which restrict the process of oil and gas exploration and development. In our study, the controlling factors of reservoir quality are unraveled from the perspective of “three-element controlling reservoir” including sedimentary microfacies, diagenetic facies and fracture facies. In addition, the methods of logging characterization and identification standards are established. The results show that the sedimentary microfacies, diagenetic facies and fractures play important role in controlling reservoir quality in the Liushagang formation. By analyzing the relationships between different types of sedimentary microfacies, diagenetic facies, and fracture facies and parameters of reservoir quality, it can be concluded that the high reservoir quality reservoirs are formed in the dissolution facies in the underwater distributary channel and mouth bad microfacies under high-energy depositional environment. Additionally, the development of fractures has a significant improvement on reservoir quality. By integrating the three controlling factors (sedimentary microfacies + diagenetic facies + fracture facies) and combined with four important reservoir characteristic parameters, four types of reservoirs are classified. The conclusion of oil and gas interpretation and oil test data prove that the proposed method can effectively evaluate and predict the favorable reservoir layers. This research can provide theoretical guidance for the increase of reservoirs and production in the Liushagang formation in Fushan Sag, and provide insights into the fine characterization of reservoirs and the prediction and evaluation of high-quality reservoirs.
Abstract: The Liushagang formation is one of the petroliferous reservoirs in the Fushan Sag, Beibuwan Basin. However, the controlling factors of reservoir quality are unclear and there are no matched prediction technology for reservoir quality, which restrict the process of oil and gas exploration and development. In our study, the controlling factors of reservoir quality are unraveled from the perspective of “three-element controlling reservoir” including sedimentary microfacies, diagenetic facies and fracture facies. In addition, the methods of logging characterization and identification standards are established. The results show that the sedimentary microfacies, diagenetic facies and fractures play important role in controlling reservoir quality in the Liushagang formation. By analyzing the relationships between different types of sedimentary microfacies, diagenetic facies, and fracture facies and parameters of reservoir quality, it can be concluded that the high reservoir quality reservoirs are formed in the dissolution facies in the underwater distributary channel and mouth bad microfacies under high-energy depositional environment. Additionally, the development of fractures has a significant improvement on reservoir quality. By integrating the three controlling factors (sedimentary microfacies + diagenetic facies + fracture facies) and combined with four important reservoir characteristic parameters, four types of reservoirs are classified. The conclusion of oil and gas interpretation and oil test data prove that the proposed method can effectively evaluate and predict the favorable reservoir layers. This research can provide theoretical guidance for the increase of reservoirs and production in the Liushagang formation in Fushan Sag, and provide insights into the fine characterization of reservoirs and the prediction and evaluation of high-quality reservoirs.
Abstract:
Qiangtang Basin, located in the most important oil & gas accumulation belt worldwide - eastern section of Tethys tectonic domain, has been listed as a strategic preparation area for oil & gas resources. However, there had been great arguments on the potential of oil & gas resources, which restricted the overall understanding of oil & gas exploration in Qiangtang Basin. Restoring the denudation history of basin in key tectonic periods and analyzing the burial history of source rocks is of great significance to deepen the hydrocarbon potential of leading source rocks and oil & gas resources in Qiangtang Basin. Based on the current data and previous research results, the main tectonic activities were analyzed and the denudation history of Qiangtang Basin in key tectonic periods were restored by using the structural-sedimentary extrapolation method. At the same time, the burial history of three sets of leading source beds in the Upper Triassic-Jurassic was analyzed by using the TSM basin simulation system. The results showed that: 1) Since the Late Triassic, Qiangtang basin had experienced four periods of tectonic movements: one period from the late Triassic to early Jurassic (210-180Ma)、the late Early Cretaceous (120-110Ma) and the Paleocene to the early Eocene (60-45Ma) and since the early Miocene; 2) At the first period (210-110Ma), Most areas of the basin was uplifted to the surface. The top of the Late Triassic Formation was denuded to form an ancient weathering crust, and then the volcanic rocks were deposited. The central uplift zone of the basin and the Northern Qiangtang were denuded most strongly; Between 120 and 110Ma, the basin strata were folded strongly, and the denudation was most intense in the central uplift zone and its two sides, and in the eastern part of the basin. The denudation is relatively weak in the middle and west of the North Qiangtang depression, and the south of the South Qiangtang. From 60 to 45 Ma, influenced by the long-range effect of the collision between the Indian continent and the Asian continent, the basin shortening rate is 11.9%, and the average uplift and denuded is about 700m. Since 23Ma, the basin continues to be affected by the north-south extrusion stress, and the whole basin escapes to the southeast direction. The basin's thrust faults continue to be active generally and more uniformly, and a number of normal faults or grabens were developed. The uplift rate of all parts of the basin is similar, and the uplift erosion is about 700m to some extent. 3) Influenced by the sedimentary thickness of the stratum and the differential denudation of multi-stage tectonic uplift, the maximum burial of the Upper Triassic Jurassic source beds in Qiangtang Basin occurred twice after the deposition of the J3-K1 Xueshan Formation and after the deposition of the Neogene Nkangtuo Formation and Suonahu Formation, respectively. The two main hydrocarbon generation periods corresponded to the two maximum burial depths and the subsequent tectonic uplift.
Qiangtang Basin, located in the most important oil & gas accumulation belt worldwide - eastern section of Tethys tectonic domain, has been listed as a strategic preparation area for oil & gas resources. However, there had been great arguments on the potential of oil & gas resources, which restricted the overall understanding of oil & gas exploration in Qiangtang Basin. Restoring the denudation history of basin in key tectonic periods and analyzing the burial history of source rocks is of great significance to deepen the hydrocarbon potential of leading source rocks and oil & gas resources in Qiangtang Basin. Based on the current data and previous research results, the main tectonic activities were analyzed and the denudation history of Qiangtang Basin in key tectonic periods were restored by using the structural-sedimentary extrapolation method. At the same time, the burial history of three sets of leading source beds in the Upper Triassic-Jurassic was analyzed by using the TSM basin simulation system. The results showed that: 1) Since the Late Triassic, Qiangtang basin had experienced four periods of tectonic movements: one period from the late Triassic to early Jurassic (210-180Ma)、the late Early Cretaceous (120-110Ma) and the Paleocene to the early Eocene (60-45Ma) and since the early Miocene; 2) At the first period (210-110Ma), Most areas of the basin was uplifted to the surface. The top of the Late Triassic Formation was denuded to form an ancient weathering crust, and then the volcanic rocks were deposited. The central uplift zone of the basin and the Northern Qiangtang were denuded most strongly; Between 120 and 110Ma, the basin strata were folded strongly, and the denudation was most intense in the central uplift zone and its two sides, and in the eastern part of the basin. The denudation is relatively weak in the middle and west of the North Qiangtang depression, and the south of the South Qiangtang. From 60 to 45 Ma, influenced by the long-range effect of the collision between the Indian continent and the Asian continent, the basin shortening rate is 11.9%, and the average uplift and denuded is about 700m. Since 23Ma, the basin continues to be affected by the north-south extrusion stress, and the whole basin escapes to the southeast direction. The basin's thrust faults continue to be active generally and more uniformly, and a number of normal faults or grabens were developed. The uplift rate of all parts of the basin is similar, and the uplift erosion is about 700m to some extent. 3) Influenced by the sedimentary thickness of the stratum and the differential denudation of multi-stage tectonic uplift, the maximum burial of the Upper Triassic Jurassic source beds in Qiangtang Basin occurred twice after the deposition of the J3-K1 Xueshan Formation and after the deposition of the Neogene Nkangtuo Formation and Suonahu Formation, respectively. The two main hydrocarbon generation periods corresponded to the two maximum burial depths and the subsequent tectonic uplift.
Abstract:
[Objective] In the western Sichuan Basin, the Middle Permian extensively features marine carbonate rocks, with dolomite being a focal point of geological investigation. However, the diverse and irregular distribution of dolomite types in the Middle Permian results in significant variations in dolomite characteristics across different regions. The rich variety of dolomite types described above constitutes an excellent set of natural gas reservoirs in the Sichuan Basin. [Methodology] To unravel the fluid dynamics of dolomites in the study area and reconstruct their diagenetic environments, the study extensively reviewed a substantial body of previous literature and references. samples from 16 well cores and 9 sections underwent a comprehensive analysis. Utilizing techniques such as microscopic thin section observation, cathodoluminescence, carbon-oxygen isotopes, strontium isotopes, and ICP-MS rare earth element analysis, the petrological and geochemical features were thoroughly investigated. [Results] The research findings can be summarized as follows: (1) Dolomite Types: Dolomites in the region can be broadly categorized into homogeneous dolomite and zebra-like dolomite. The primary type of homogeneous dolomite is granular dolomite, while zebra-like dolomite includes homogeneous dolomite with dark bands, predominantly filled with hydrothermal saddle dolomite. (2) Isotopic Analysis: Carbon Isotopes: Samples from the study area exhibit positive anomalies in carbon isotopes. Oxygen Isotopes: Oxygen isotope values show significant differences, with the filling material (saddle dolomite) exhibiting notably lower values than homogeneous dolomite. Oxygen isotope values in samples from southwestern Sichuan are significantly lower than those from northwestern Sichuan. (3) Rare Earth Elements: Rare earth element analysis reveals a negative anomaly in δCe and a positive anomaly in δEu, indicating that the oxidation conditions of the products were influenced by later-stage hydrothermal alteration. (4) Strontium Isotopes: Strontium isotopic values of homogeneous dolomite fall within the range of contemporaneous seawater. However, the filling material in southwestern Sichuan exhibits strontium isotopic values higher than the seawater range and significantly higher than homogeneous dolomite. [Conclusion] (1) Hydrothermal Modification: The diagenetic fluids responsible for the formation of homogeneous dolomite in the western to northern Sichuan region are primarily derived from contemporaneous seawater. Subsequent hydrothermal activities lead to modifications, resulting in the formation of hydrothermal saddle dolomite. Notably, the intensity of hydrothermal activity is more pronounced in the southwestern region and relatively weaker in the northwestern part of western Sichuan. (2) Diagenetic Environments: The diagenetic environments of dolomites in the study area encompass four types: marine diagenetic settings, shallow-to-intermediate burial diagenetic environments, and intermediate-to-deep burial diagenetic environments. The marine environment refers to an open-sea, grain shoal environment, predominantly developing fine to medium-crystalline dolomite. Inclusions exhibit a uniform temperature below 85°C. Shallow-to-intermediate burial environments, with burial depths ranging from approximately 800m to 2000m, primarily foster homogeneous fine-crystalline dolomite and some medium-to-coarse-crystalline dolomite. Inclusions exhibit a uniform temperature above 112°C. Hydrothermal saddle dolomite mainly develops in intermediate-to-deep burial environments with burial depths exceeding 3000m, and inclusions exhibit a uniform temperature above 175°C. This comprehensive research provides nuanced insights into the diverse dolomite types and their diagenetic histories, contributing significantly to the broader understanding of sedimentary processes and geological evolution in the western Sichuan Basin during the Middle Permian period.
[Objective] In the western Sichuan Basin, the Middle Permian extensively features marine carbonate rocks, with dolomite being a focal point of geological investigation. However, the diverse and irregular distribution of dolomite types in the Middle Permian results in significant variations in dolomite characteristics across different regions. The rich variety of dolomite types described above constitutes an excellent set of natural gas reservoirs in the Sichuan Basin. [Methodology] To unravel the fluid dynamics of dolomites in the study area and reconstruct their diagenetic environments, the study extensively reviewed a substantial body of previous literature and references. samples from 16 well cores and 9 sections underwent a comprehensive analysis. Utilizing techniques such as microscopic thin section observation, cathodoluminescence, carbon-oxygen isotopes, strontium isotopes, and ICP-MS rare earth element analysis, the petrological and geochemical features were thoroughly investigated. [Results] The research findings can be summarized as follows: (1) Dolomite Types: Dolomites in the region can be broadly categorized into homogeneous dolomite and zebra-like dolomite. The primary type of homogeneous dolomite is granular dolomite, while zebra-like dolomite includes homogeneous dolomite with dark bands, predominantly filled with hydrothermal saddle dolomite. (2) Isotopic Analysis: Carbon Isotopes: Samples from the study area exhibit positive anomalies in carbon isotopes. Oxygen Isotopes: Oxygen isotope values show significant differences, with the filling material (saddle dolomite) exhibiting notably lower values than homogeneous dolomite. Oxygen isotope values in samples from southwestern Sichuan are significantly lower than those from northwestern Sichuan. (3) Rare Earth Elements: Rare earth element analysis reveals a negative anomaly in δCe and a positive anomaly in δEu, indicating that the oxidation conditions of the products were influenced by later-stage hydrothermal alteration. (4) Strontium Isotopes: Strontium isotopic values of homogeneous dolomite fall within the range of contemporaneous seawater. However, the filling material in southwestern Sichuan exhibits strontium isotopic values higher than the seawater range and significantly higher than homogeneous dolomite. [Conclusion] (1) Hydrothermal Modification: The diagenetic fluids responsible for the formation of homogeneous dolomite in the western to northern Sichuan region are primarily derived from contemporaneous seawater. Subsequent hydrothermal activities lead to modifications, resulting in the formation of hydrothermal saddle dolomite. Notably, the intensity of hydrothermal activity is more pronounced in the southwestern region and relatively weaker in the northwestern part of western Sichuan. (2) Diagenetic Environments: The diagenetic environments of dolomites in the study area encompass four types: marine diagenetic settings, shallow-to-intermediate burial diagenetic environments, and intermediate-to-deep burial diagenetic environments. The marine environment refers to an open-sea, grain shoal environment, predominantly developing fine to medium-crystalline dolomite. Inclusions exhibit a uniform temperature below 85°C. Shallow-to-intermediate burial environments, with burial depths ranging from approximately 800m to 2000m, primarily foster homogeneous fine-crystalline dolomite and some medium-to-coarse-crystalline dolomite. Inclusions exhibit a uniform temperature above 112°C. Hydrothermal saddle dolomite mainly develops in intermediate-to-deep burial environments with burial depths exceeding 3000m, and inclusions exhibit a uniform temperature above 175°C. This comprehensive research provides nuanced insights into the diverse dolomite types and their diagenetic histories, contributing significantly to the broader understanding of sedimentary processes and geological evolution in the western Sichuan Basin during the Middle Permian period.
Abstract:
The dolomite evaporite symbiotic system is widely distributed during the Middle Triassic period in the Sichuan Basin, but its sedimentary characteristics lack systematic characterization. The development and distribution patterns and main controlling factors are still unclear. Based on drilling, core, and seismic data, this article characterizes the sedimentary characteristics of the developed dolomite evaporite symbiotic system in the study area at multiple scales, elucidates the genetic mechanisms of different types of symbiotic systems, and further reveals their spatiotemporal distribution patterns and main controlling factors. The research results indicate that: (1) Four types of symbiotic systems are mainly developed in the Leikoupo Formation in the northwest Sichuan Basin: thick layer of dolomite with thin layer of evaporite, interlayer of dolomite and evaporite, thick layer of evaporite with thin layer of dolomite, and overlapping of thick layer of evaporite with thick layer of dolomite. They are respectively formed in gypsum containing lagoons, cloud containing gypsum containing lagoons, gypsum salt lakes, and gypsum salt basins. Among them, thick layer of dolomite mixed with thin layer of evaporite is widely distributed in the four periods of Leikoupo. Thick layer of evaporite mixed with thin layer of dolomite, and the overlap of thick layer of evaporite and thick layer of dolomite is the most developed in the central part of the Leisan and Leisi sedimentary periods of the basin. (3) The uplift of the Longmenshan Island Chain on the west side resulted in southeast compression of the basin, while the uplift of the Xuefeng Mountain on the east side restricted the southern migration of the Luzhou Kaijiang ancient uplift. The southern subduction of the Qinling Mountains jointly formed a nearly northeast southwest structural pattern in the Sichuan Basin, controlling the overall distribution of gypsum and symbiotic systems in a northeast southwest direction. (4) Affected by the significant uplift of the Luzhou Kaijiang ancient uplift, the later subsidence center of the Leikoupo Formation migrated to the west, and the gypsum sedimentary center and four symbiotic systems correspondingly developed from early dispersion to later concentration and migrated to the west. Under the constraints of different types of symbiotic systems, the paleogeography of the Leikoupo Formation was reconstructed for four periods. The above research provides a new understanding for the study of the symbiotic system of dolomite evaporite in the northwest Sichuan region, and also has a guiding role in the reconstruction of regional paleogeography.
The dolomite evaporite symbiotic system is widely distributed during the Middle Triassic period in the Sichuan Basin, but its sedimentary characteristics lack systematic characterization. The development and distribution patterns and main controlling factors are still unclear. Based on drilling, core, and seismic data, this article characterizes the sedimentary characteristics of the developed dolomite evaporite symbiotic system in the study area at multiple scales, elucidates the genetic mechanisms of different types of symbiotic systems, and further reveals their spatiotemporal distribution patterns and main controlling factors. The research results indicate that: (1) Four types of symbiotic systems are mainly developed in the Leikoupo Formation in the northwest Sichuan Basin: thick layer of dolomite with thin layer of evaporite, interlayer of dolomite and evaporite, thick layer of evaporite with thin layer of dolomite, and overlapping of thick layer of evaporite with thick layer of dolomite. They are respectively formed in gypsum containing lagoons, cloud containing gypsum containing lagoons, gypsum salt lakes, and gypsum salt basins. Among them, thick layer of dolomite mixed with thin layer of evaporite is widely distributed in the four periods of Leikoupo. Thick layer of evaporite mixed with thin layer of dolomite, and the overlap of thick layer of evaporite and thick layer of dolomite is the most developed in the central part of the Leisan and Leisi sedimentary periods of the basin. (3) The uplift of the Longmenshan Island Chain on the west side resulted in southeast compression of the basin, while the uplift of the Xuefeng Mountain on the east side restricted the southern migration of the Luzhou Kaijiang ancient uplift. The southern subduction of the Qinling Mountains jointly formed a nearly northeast southwest structural pattern in the Sichuan Basin, controlling the overall distribution of gypsum and symbiotic systems in a northeast southwest direction. (4) Affected by the significant uplift of the Luzhou Kaijiang ancient uplift, the later subsidence center of the Leikoupo Formation migrated to the west, and the gypsum sedimentary center and four symbiotic systems correspondingly developed from early dispersion to later concentration and migrated to the west. Under the constraints of different types of symbiotic systems, the paleogeography of the Leikoupo Formation was reconstructed for four periods. The above research provides a new understanding for the study of the symbiotic system of dolomite evaporite in the northwest Sichuan region, and also has a guiding role in the reconstruction of regional paleogeography.
Abstract:
Since 2019, CNPC has conducted exploration on the Upper Cretaceous Donga strata in the Trakes Slope of the Termit Basin, Niger. Several wells obtained industrial oil flows, demonstrating good exploration potential. Compared to the Paleogene fluvial-deltaic Sokor1 Formation, the detailed characteristics of the Upper Cretaceous marine sandstones of the Donga Formation have not yet investigated in detail. In the present study, based on seismic, wireline and mud logging data, 53 side wall cores and cutting samples from 4 wells were analyzed thin sections, casting thin sections, X-ray diffraction and scanning electron microscope, gamma-ray spectral logging, etc. This study investigate the reservoir characteristics of the DS1~DS3 members of Donga Formation, and analyze their controlling factors. The results show that rock types of DS1 member are fine-medium grained quartz sandstones with high component maturity, whereas that of DS3 member are fine grained lithic quartz sandstones with cements mainly of calcareous minerals. The quartz grains are sub-round to round with moderate to poor sorting. The matrix are mainly composed of kaolinite and calcites, and sandstones exhibit point and line contacts. The most common diagenetic process were compaction, cementation and dissolution, and compaction and cementation are obvious. The sandstones commonly experienced dissolution, and pore types are mainly intergranular pores with medium to ultra-low porosity and permeability. The high-quality reservoirs of the Donga Formation are mainly distributed in the DS1 member. Physical properties of sandstones become better from the west to east in Trakes Slope. The analysis results show that sandstones development in the Donga Formation is mainly controlled by three factors. Firstly, vertical distribution of sedimentary facies and sandstones were mainly controlled by sea level changes. The DS1 member, deposited in the early stage of marine transgression, mainly consists of distributary channel sandstones, whereas DS3 member, deposited during the highest sea level, is dominated by delta front sheet sandstones and distributary channel sandstones. The high salinity of sea water in this period resulted in high content of carbonate cement, and poor physical properties of reservoir rocks. Secondly, the stable gentle slope in the Late Cretaceous was favorable for the development of sand bodies, and the intense strike-slip fault activities in the Paleogene induced the formation of micro-fractures in reservoir rocks, effectively improving their physical properties. Thirdly, the rigid support of quartz sandstones was favorable for the preservation of primary pores, and the dissolution of unstable minerals such as feldspar and calcareous minerals improved the pore structure of reservoir rocks. The development of regional cap rocks of marine mudstones and shales is conducive for the formation of “self-generation and self-preservation” play in the Donga Formation. Compared with the low slope of the Trakes Slope, sandstones with better physical properties are well developed in the middle and high slope which are closer to the eastern provenance. They are favorable exploration areas for the Donga Formation.
Since 2019, CNPC has conducted exploration on the Upper Cretaceous Donga strata in the Trakes Slope of the Termit Basin, Niger. Several wells obtained industrial oil flows, demonstrating good exploration potential. Compared to the Paleogene fluvial-deltaic Sokor1 Formation, the detailed characteristics of the Upper Cretaceous marine sandstones of the Donga Formation have not yet investigated in detail. In the present study, based on seismic, wireline and mud logging data, 53 side wall cores and cutting samples from 4 wells were analyzed thin sections, casting thin sections, X-ray diffraction and scanning electron microscope, gamma-ray spectral logging, etc. This study investigate the reservoir characteristics of the DS1~DS3 members of Donga Formation, and analyze their controlling factors. The results show that rock types of DS1 member are fine-medium grained quartz sandstones with high component maturity, whereas that of DS3 member are fine grained lithic quartz sandstones with cements mainly of calcareous minerals. The quartz grains are sub-round to round with moderate to poor sorting. The matrix are mainly composed of kaolinite and calcites, and sandstones exhibit point and line contacts. The most common diagenetic process were compaction, cementation and dissolution, and compaction and cementation are obvious. The sandstones commonly experienced dissolution, and pore types are mainly intergranular pores with medium to ultra-low porosity and permeability. The high-quality reservoirs of the Donga Formation are mainly distributed in the DS1 member. Physical properties of sandstones become better from the west to east in Trakes Slope. The analysis results show that sandstones development in the Donga Formation is mainly controlled by three factors. Firstly, vertical distribution of sedimentary facies and sandstones were mainly controlled by sea level changes. The DS1 member, deposited in the early stage of marine transgression, mainly consists of distributary channel sandstones, whereas DS3 member, deposited during the highest sea level, is dominated by delta front sheet sandstones and distributary channel sandstones. The high salinity of sea water in this period resulted in high content of carbonate cement, and poor physical properties of reservoir rocks. Secondly, the stable gentle slope in the Late Cretaceous was favorable for the development of sand bodies, and the intense strike-slip fault activities in the Paleogene induced the formation of micro-fractures in reservoir rocks, effectively improving their physical properties. Thirdly, the rigid support of quartz sandstones was favorable for the preservation of primary pores, and the dissolution of unstable minerals such as feldspar and calcareous minerals improved the pore structure of reservoir rocks. The development of regional cap rocks of marine mudstones and shales is conducive for the formation of “self-generation and self-preservation” play in the Donga Formation. Compared with the low slope of the Trakes Slope, sandstones with better physical properties are well developed in the middle and high slope which are closer to the eastern provenance. They are favorable exploration areas for the Donga Formation.
Abstract:
As a kind of hydrocarbon organic matter remaining in source rocks or As a kind of hydrocarbon organic matter that oil or natural gas remains in source rocks or reservoirs, the formation and evolution of bitumen interstitials are closely related to the evolution history of oil reservoirs, which is an important symbol of oil and gas accumulation and transformation process. Previous studies have carried out many analyses on the types, genesis and thermal evolution of bitumen components in reservoirs, but the restriction mechanism of bitumen on reservoirs is still unclear. This study takes the Cretaceous Brazilian reconstructed reservoir in the Yingmai 467 well area in the west of Tabei as an example. With the help of casting thin sections, fluorescent thin sections, laser Raman experiments, combined with logging parameter identification, the relationship between bitumen and oil and gas reservoir stages is discussed, and the influence of different bitumen types on reservoir quality is identified. The results show that : ①According to the main components and formation stages, the bitumen interstitial materials in the study section are divided into two categories : type I is mainly intergranular filling, and most of them are yellow-brown and brown-black under the fluorescence microscope. The main components are oily and bituminous bitumen, and the bitumen reflectivity is more than 1 %. The type II is distributed on the edge of the pore in the form of bitumen lining. Under the fluorescence microscope, it is mostly orange and blue ( white ) color, with colloidal bitumen as the main component. The bitumen reflectivity is low, ranging from 0.42 % to 0.79 %. ② The bitumen interstitial material in Yingmai 467 well area is mainly type I bitumen. Because the oil and gas in the source rock of Huangshanjie Formation migrated through the unconformity at the bottom of the Shushanhe Formation, the fault was filled into the Brazilian reorganized massive sand layer 2 and the Brazilian reorganized thin sand layer, and then gas washing occurred. Type II bitumen is precipitated by retrograde condensation from the source rock oil and gas of the second phase of the Qiakemake Formation along the Cretaceous bottom and the Yingmai 7 fault zone into the Brazilian reorganization. It is affected by the thickness of the sand body and is mainly distributed in the first layer of massive sand. ③Type I bitumen has a strong effect on reservoir reconstruction and occupies part of pore space ; category II bitumen has little effect on reservoir porosity.
As a kind of hydrocarbon organic matter remaining in source rocks or As a kind of hydrocarbon organic matter that oil or natural gas remains in source rocks or reservoirs, the formation and evolution of bitumen interstitials are closely related to the evolution history of oil reservoirs, which is an important symbol of oil and gas accumulation and transformation process. Previous studies have carried out many analyses on the types, genesis and thermal evolution of bitumen components in reservoirs, but the restriction mechanism of bitumen on reservoirs is still unclear. This study takes the Cretaceous Brazilian reconstructed reservoir in the Yingmai 467 well area in the west of Tabei as an example. With the help of casting thin sections, fluorescent thin sections, laser Raman experiments, combined with logging parameter identification, the relationship between bitumen and oil and gas reservoir stages is discussed, and the influence of different bitumen types on reservoir quality is identified. The results show that : ①According to the main components and formation stages, the bitumen interstitial materials in the study section are divided into two categories : type I is mainly intergranular filling, and most of them are yellow-brown and brown-black under the fluorescence microscope. The main components are oily and bituminous bitumen, and the bitumen reflectivity is more than 1 %. The type II is distributed on the edge of the pore in the form of bitumen lining. Under the fluorescence microscope, it is mostly orange and blue ( white ) color, with colloidal bitumen as the main component. The bitumen reflectivity is low, ranging from 0.42 % to 0.79 %. ② The bitumen interstitial material in Yingmai 467 well area is mainly type I bitumen. Because the oil and gas in the source rock of Huangshanjie Formation migrated through the unconformity at the bottom of the Shushanhe Formation, the fault was filled into the Brazilian reorganized massive sand layer 2 and the Brazilian reorganized thin sand layer, and then gas washing occurred. Type II bitumen is precipitated by retrograde condensation from the source rock oil and gas of the second phase of the Qiakemake Formation along the Cretaceous bottom and the Yingmai 7 fault zone into the Brazilian reorganization. It is affected by the thickness of the sand body and is mainly distributed in the first layer of massive sand. ③Type I bitumen has a strong effect on reservoir reconstruction and occupies part of pore space ; category II bitumen has little effect on reservoir porosity.
Abstract:
【Objective】The carbonate-evaporite syngenetic system is widely distributed in the Cambrian of the Sichuan Basin, however, the developmental characteristics, depositional environments, depositional processes, and evolutionary modes of this syngenetic system are weakly studied, and the research methods need to be clarified urgently. 【Methods】The petrological characteristics of the symbiotic system, the state of the evaporites, the depositional environment of the symbiotic system, the depositional process and the evolutionary pattern of the symbiotic system are investigated based on the data of drilling cores, field sections, rock sheets and carbon and oxygen isotopes, and the isotopic signatures of Fe, Mn and S. 【Results】The results show that 1) the developmental characteristics of the symbiotic system, 2) the depositional environment, and 3) the evolutionary pattern of the symbiotic system are not well understood, but are not well understood. The results show that: 1) the carbonate-evaporite symbiotic system in the study area has developed five kinds of carbonate-evaporite symbiotic system rock assemblage sequences, including: carbonate rock and evaporite interbedded, evaporite sandwiched with carbonate rock, evaporite overlain carbonate rock, carbonate rock overlain with evaporite rock, and carbonate rock sandwiched with evaporite rock. 2) the geochemical features of the symbiotic system, including δ18O, mainly concentrated in -8‰～-9‰, and δ13C, mainly concentrated in -8‰～9‰; δ13C is mainly concentrated in -1‰～3‰; the results of using carbon and oxygen isotope values to calculate palaeosalinity and palaeotemperature show that the vast majority of Z values>120‰ and δ13C values>-2‰, and the palaeoseawater temperatures are in the range of 23.10～40.64℃; Fe is mainly concentrated in the range of 0～2000×10-5; and Mn is mainly concentrated in the range of 10-5～30×10-5, which indicates that in the Gautai Group During the Gaotai Formation, the depositional environment was a warm or hot paleoclimate and saline seawater environment, with a high degree of oxidation of the water body, and the rock-forming action in a relatively open system related to atmospheric water was experienced.3) Deposition of marine carbonate rocks and evaporites in a symbiotic system against the background of an arid and hot climate and a Ca-rich and low-SO4 calcite sea with a high degree of salinity The period of time can be divided into the sea level falling evaporite - dolomite deposition stage and sea level rising dolomite - evaporite - greywacke deposition stage; "tidal ping Sabuha mode" and "underwater condensed deposition mode" are two kinds of carbonate rock - evaporite symbiosis system development mode.【Conclusion】The carbonatite-evaporite symbiotic system carries the information of paleoenvironment, paleoclimate and paleohaline water chemistry during the depositional period, and also records the depositional process and evolutionary pattern of the symbiotic system. This study provides new ideas and understanding of the depositional environments and depositional patterns of the carbonatite-evaporite symbiotic system of the evaporitic environment of the marine phase of the Cambrian Gautai Formation.
【Objective】The carbonate-evaporite syngenetic system is widely distributed in the Cambrian of the Sichuan Basin, however, the developmental characteristics, depositional environments, depositional processes, and evolutionary modes of this syngenetic system are weakly studied, and the research methods need to be clarified urgently. 【Methods】The petrological characteristics of the symbiotic system, the state of the evaporites, the depositional environment of the symbiotic system, the depositional process and the evolutionary pattern of the symbiotic system are investigated based on the data of drilling cores, field sections, rock sheets and carbon and oxygen isotopes, and the isotopic signatures of Fe, Mn and S. 【Results】The results show that 1) the developmental characteristics of the symbiotic system, 2) the depositional environment, and 3) the evolutionary pattern of the symbiotic system are not well understood, but are not well understood. The results show that: 1) the carbonate-evaporite symbiotic system in the study area has developed five kinds of carbonate-evaporite symbiotic system rock assemblage sequences, including: carbonate rock and evaporite interbedded, evaporite sandwiched with carbonate rock, evaporite overlain carbonate rock, carbonate rock overlain with evaporite rock, and carbonate rock sandwiched with evaporite rock. 2) the geochemical features of the symbiotic system, including δ18O, mainly concentrated in -8‰～-9‰, and δ13C, mainly concentrated in -8‰～9‰; δ13C is mainly concentrated in -1‰～3‰; the results of using carbon and oxygen isotope values to calculate palaeosalinity and palaeotemperature show that the vast majority of Z values>120‰ and δ13C values>-2‰, and the palaeoseawater temperatures are in the range of 23.10～40.64℃; Fe is mainly concentrated in the range of 0～2000×10-5; and Mn is mainly concentrated in the range of 10-5～30×10-5, which indicates that in the Gautai Group During the Gaotai Formation, the depositional environment was a warm or hot paleoclimate and saline seawater environment, with a high degree of oxidation of the water body, and the rock-forming action in a relatively open system related to atmospheric water was experienced.3) Deposition of marine carbonate rocks and evaporites in a symbiotic system against the background of an arid and hot climate and a Ca-rich and low-SO4 calcite sea with a high degree of salinity The period of time can be divided into the sea level falling evaporite - dolomite deposition stage and sea level rising dolomite - evaporite - greywacke deposition stage; "tidal ping Sabuha mode" and "underwater condensed deposition mode" are two kinds of carbonate rock - evaporite symbiosis system development mode.【Conclusion】The carbonatite-evaporite symbiotic system carries the information of paleoenvironment, paleoclimate and paleohaline water chemistry during the depositional period, and also records the depositional process and evolutionary pattern of the symbiotic system. This study provides new ideas and understanding of the depositional environments and depositional patterns of the carbonatite-evaporite symbiotic system of the evaporitic environment of the marine phase of the Cambrian Gautai Formation.
Abstract:
Paleo-geomorphology has a strong control on the sedimentary system and reservoir distribution. This paper analyzes the single-well facies in Gaoquan Structural Zone of Sikeshu Sag, identifies the characteristics of the sedimentary and reservoirs of the Qingshuihe Formation, and then combines with the paleo-geomorphology of the pre-Qingshuihe Formation in Gaoquan Structural Zone, establishes model of the sedimentary evolution under the control of paleo-geomorphology, and clarifies the influence of micro-geomorphology on the distribution of high-quality reservoirs. The study shows that three slope breaks are developed in the Gaoquan Structural zone of Sikeshu Sag, with a near-northwestern-south-eastern trend. Each slope-folding zone can be divided into two types of paleo-geomorphology units, namely, grooves and platforms. Three phases of regressive fan deltas were formed on the three slope breaks during the lake transgression, and each phase of fan deltas can form 9-15m thick conglomerate reservoirs. On each slope breaks, the groove and platform control the mud content of the conglomerate reservoirs, and the brown conglomerate with high mud content is easily developed in the groove area, while the gray or gray-green conglomerate with low mud content is easily developed in the platform area. The conglomerate with low mud content is ready to form high-quality reservoir in the platform area.
Paleo-geomorphology has a strong control on the sedimentary system and reservoir distribution. This paper analyzes the single-well facies in Gaoquan Structural Zone of Sikeshu Sag, identifies the characteristics of the sedimentary and reservoirs of the Qingshuihe Formation, and then combines with the paleo-geomorphology of the pre-Qingshuihe Formation in Gaoquan Structural Zone, establishes model of the sedimentary evolution under the control of paleo-geomorphology, and clarifies the influence of micro-geomorphology on the distribution of high-quality reservoirs. The study shows that three slope breaks are developed in the Gaoquan Structural zone of Sikeshu Sag, with a near-northwestern-south-eastern trend. Each slope-folding zone can be divided into two types of paleo-geomorphology units, namely, grooves and platforms. Three phases of regressive fan deltas were formed on the three slope breaks during the lake transgression, and each phase of fan deltas can form 9-15m thick conglomerate reservoirs. On each slope breaks, the groove and platform control the mud content of the conglomerate reservoirs, and the brown conglomerate with high mud content is easily developed in the groove area, while the gray or gray-green conglomerate with low mud content is easily developed in the platform area. The conglomerate with low mud content is ready to form high-quality reservoir in the platform area.
Abstract:
[Significance] The sedimentary simulation experiment in a circular flume is one of the effective means to simulate the sedimentary process and reveal its formation mechanism. It holds significant importance in research areas such as hydraulic engineering, environmental science, sedimentology, and oil and gas exploration. The circular flume can sustain continuous fluid flow under the influence of inertial and shear forces and is approximated as transporting and depositing over an infinite distance. Therefore, it can approximately replicate environmental fluid conditions in terms of transport distance and fluid velocity, overcoming the limitations of traditional flume simulations. [Progress] To meet the research needs of different application scenarios, circular flume have gradually evolved into four types, including conventional circular flume, in-situ circular flume, Mini circular tanks, and racetrack flume. Physical simulations in circular flume have achieved fruitful results in studying sediment characteristics, bedform morphology, and settling mechanisms, among other aspects. However, there is still a relative scarcity of research in sedimentary physical simulation. With the development of technology and equipment, research in sedimentary physical simulation has also made significant progress. Gravity flow sedimentation, the dynamics of fine-grained sediment transport, and tidal and wave sedimentation have become important research areas in physical simulation of circular flume. Nevertheless, there are several limitations in circular flume physical simulation, such as the influence of secondary circulation and the tracking of lateral sediment evolution, which will be optimized in subsequent research through improved experimental designs and enhanced measurement accuracy. [Conclusions and Prospects] In summary, expanding the application scope of circular flume physical simulation based on sedimentology principles will make significant contributions to the innovative development of fundamental sedimentology theory, as well as various aspects such as fine-grained sedimentology and unconventional petroleum sedimentology.
[Significance] The sedimentary simulation experiment in a circular flume is one of the effective means to simulate the sedimentary process and reveal its formation mechanism. It holds significant importance in research areas such as hydraulic engineering, environmental science, sedimentology, and oil and gas exploration. The circular flume can sustain continuous fluid flow under the influence of inertial and shear forces and is approximated as transporting and depositing over an infinite distance. Therefore, it can approximately replicate environmental fluid conditions in terms of transport distance and fluid velocity, overcoming the limitations of traditional flume simulations. [Progress] To meet the research needs of different application scenarios, circular flume have gradually evolved into four types, including conventional circular flume, in-situ circular flume, Mini circular tanks, and racetrack flume. Physical simulations in circular flume have achieved fruitful results in studying sediment characteristics, bedform morphology, and settling mechanisms, among other aspects. However, there is still a relative scarcity of research in sedimentary physical simulation. With the development of technology and equipment, research in sedimentary physical simulation has also made significant progress. Gravity flow sedimentation, the dynamics of fine-grained sediment transport, and tidal and wave sedimentation have become important research areas in physical simulation of circular flume. Nevertheless, there are several limitations in circular flume physical simulation, such as the influence of secondary circulation and the tracking of lateral sediment evolution, which will be optimized in subsequent research through improved experimental designs and enhanced measurement accuracy. [Conclusions and Prospects] In summary, expanding the application scope of circular flume physical simulation based on sedimentology principles will make significant contributions to the innovative development of fundamental sedimentology theory, as well as various aspects such as fine-grained sedimentology and unconventional petroleum sedimentology.
Abstract:
Abstract: [Objective] In order to discuss the high-frequency sequence division and effect of high-frequency sedimentary cycle control reservoir in carbonate strata. [Methods] Used the Th/U ratio curve in natural gamma ray spectrum logging as the indicator curve, combined with Fisher diagram and lithological assemblage sequence, high frequency sequence of Ma51-5 sub-member of Majiagou Formation were divided quantitatively in Tao 7 block of Ordos basin. [Results] The research shows that the Th/U ratio in natural gamma-ray spectroscopy logging can be used as an indirect alternative index of astronomical orbit in carbonate strata. The high-frequency sequence can be effectively divided by quantitative and qualitative analysis methods such as spectrum analysis combined with Fisher diagram and lithologic lithofacies analysis. Ma51-5 sub-member in Block 7 can be divided into one third-order sequence, six fourth-order sequences and twenty fifth-order sequences. It is estimated that the average deposition rate of Ma51-5 sub-member is 5.03 cm/kyr and the deposition time is about 2.43 Ma. The gypsum pseudocrystal dolomite , which developed in the upper part of the intertidal zone and in the top of the high-frequency sedimentary cycle with upward shallowing, is the dominant facies belt for reservoir development. Near the high-frequency sequence boundary of the fourth-order sequence is the favorable interval for reservoir development. The frequent changes of sea level cause early karstification, which is the main driving force for the formation of karst model pores in the Ma51-4 sub-member and the basis of later supergene gas karstification. [Conclusion] Quantitative identification and division of high-frequency sequence is impotant for reservoir prediction in carbonate strata.
Abstract: [Objective] In order to discuss the high-frequency sequence division and effect of high-frequency sedimentary cycle control reservoir in carbonate strata. [Methods] Used the Th/U ratio curve in natural gamma ray spectrum logging as the indicator curve, combined with Fisher diagram and lithological assemblage sequence, high frequency sequence of Ma51-5 sub-member of Majiagou Formation were divided quantitatively in Tao 7 block of Ordos basin. [Results] The research shows that the Th/U ratio in natural gamma-ray spectroscopy logging can be used as an indirect alternative index of astronomical orbit in carbonate strata. The high-frequency sequence can be effectively divided by quantitative and qualitative analysis methods such as spectrum analysis combined with Fisher diagram and lithologic lithofacies analysis. Ma51-5 sub-member in Block 7 can be divided into one third-order sequence, six fourth-order sequences and twenty fifth-order sequences. It is estimated that the average deposition rate of Ma51-5 sub-member is 5.03 cm/kyr and the deposition time is about 2.43 Ma. The gypsum pseudocrystal dolomite , which developed in the upper part of the intertidal zone and in the top of the high-frequency sedimentary cycle with upward shallowing, is the dominant facies belt for reservoir development. Near the high-frequency sequence boundary of the fourth-order sequence is the favorable interval for reservoir development. The frequent changes of sea level cause early karstification, which is the main driving force for the formation of karst model pores in the Ma51-4 sub-member and the basis of later supergene gas karstification. [Conclusion] Quantitative identification and division of high-frequency sequence is impotant for reservoir prediction in carbonate strata.
Abstract:
The Yuzhou area is the most highly studied on Upper Paleozoic coal-bearing strata of the southern part of North China Block, which has abundant sedimentological and stratigraphic paleontological research basis, however, due to the lack of absolute chronology data, the division of chronostratigraphy and regional large-scale stratigraphic correlation are affected. In this paper, a laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was applied to date the U-Pb age of detrital zircon of two mudstone samples near the stratigraphic boundary of Taiyuan-Shanxi Formations and Xiashihezi-Shangshihezi Formations in Yuzhou area, and to determine their maximum depositional ages. The results show that: ①The 40 detrital zircons from the bottom sample of Shanxi Formation (ZK1006-5) constitute a continuous young component spectrum ranging from 283Ma to 343Ma, with the youngest single zircon age (YSG age) is 283±9.4Ma. The 18 detrital zircons from the bottom sample of Shangshihezi Formation (ZK2387-3) constitute a continuous young component spectrum ranging from 257Ma to 299Ma, with the youngest single zircon age (YSG age) is 257±6.8Ma.They can represent the maximum deposition age of the sample strata, indicating that the deposition time is no earlier than 283±9.4Ma and 257±6.8Ma. ②The deposition of Shanxi Formation and Shangshihezi Formation in Yuzhou area began in Kungurian and Wuchiapingian, respectively, which is consistent with regionnal biostratigraphic data. ③The Upper Paleozoic coal-bearing strata of the North China Block have obvious and large span of rock strata penetrating, and the overall performance is characterized by inward penetrating of the plate edge gradually through the new characteristics. Based on the previous studies on volcanic events in the Late Paleozoic basin of North China Block, it is concluded that the eastern margin of the basin was strongly active in which the same sedimentary period, and the induced magmatism, tectonic activity, biological succession and transgression may be related to the formation of the ancient continent of Laurisia land at the same time.
The Yuzhou area is the most highly studied on Upper Paleozoic coal-bearing strata of the southern part of North China Block, which has abundant sedimentological and stratigraphic paleontological research basis, however, due to the lack of absolute chronology data, the division of chronostratigraphy and regional large-scale stratigraphic correlation are affected. In this paper, a laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was applied to date the U-Pb age of detrital zircon of two mudstone samples near the stratigraphic boundary of Taiyuan-Shanxi Formations and Xiashihezi-Shangshihezi Formations in Yuzhou area, and to determine their maximum depositional ages. The results show that: ①The 40 detrital zircons from the bottom sample of Shanxi Formation (ZK1006-5) constitute a continuous young component spectrum ranging from 283Ma to 343Ma, with the youngest single zircon age (YSG age) is 283±9.4Ma. The 18 detrital zircons from the bottom sample of Shangshihezi Formation (ZK2387-3) constitute a continuous young component spectrum ranging from 257Ma to 299Ma, with the youngest single zircon age (YSG age) is 257±6.8Ma.They can represent the maximum deposition age of the sample strata, indicating that the deposition time is no earlier than 283±9.4Ma and 257±6.8Ma. ②The deposition of Shanxi Formation and Shangshihezi Formation in Yuzhou area began in Kungurian and Wuchiapingian, respectively, which is consistent with regionnal biostratigraphic data. ③The Upper Paleozoic coal-bearing strata of the North China Block have obvious and large span of rock strata penetrating, and the overall performance is characterized by inward penetrating of the plate edge gradually through the new characteristics. Based on the previous studies on volcanic events in the Late Paleozoic basin of North China Block, it is concluded that the eastern margin of the basin was strongly active in which the same sedimentary period, and the induced magmatism, tectonic activity, biological succession and transgression may be related to the formation of the ancient continent of Laurisia land at the same time.
Abstract:
Aiming at the problem of unclear fan formation mechanism and sedimentary filling process under the condition of no well, from the perspective of source and sink system, three-dimensional seismic data were used to comprehensively analyze the denudation capacity and transport path of the source area of Bonan low bulge, and the sedimentary response characteristics and coupling mechanism of the large sublacustrine fan in the southeastern slope of Bozhong depression were clarified. The developmental model was summarized. The results show that: (1) The second of Dongying sequence is in the transition stage of lake basin fault depression, which can be divided into two tertiary sequences, in which the sublacustrine fan mainly developed in the highstand systems tract of the lower second of Dongying sequence; (2) The denudation flux in the eastern part of the Bonan low bulge is greater than deposition flux of the subestrustrine fan. The large subestrustrine fan is mainly influenced by the near province-source, and the braided river delta formed in the high part of the uplift does not pass through, and is discharged under the depositional break of the slope along five transport channels spreading from south to north. The coupling of near source supply, transport channel and sedimentary slope break formed a large contiguous lacustrine fan deposit. (3) The sedimentary filling of sublacustrine fan is controlled by the location of restricted palaeogeomorphology and the size of the space that can be accommodated. Among them, the early restricted paleogeomorphology formed A large space, and the fan sand body of the lake bottom was preferentially unloaded, forming three fan sediments, A, B and C. Due to the spatial limitations on both sides and the strong hydrodynamic conditions, the seismic facies showed the characteristics of chaotic downcut waterways and lateral migration superimposed, and the sand body formed was relatively rich in sand. With the inflow of gravity flow, the space that can be contained gradually decreases, and the gravity flow overflows along the recharge channel to the center of the open lake basin, forming two fan bodies D and E. Due to the dilution of water concentration and the change of paleo-geomorphology, the energy gradually weakens. The seismic phase has the characteristics of laminary-strong amplitude reflection, the channel features are not obvious, and the sand richness is moderate. The late source supply and energy are weak, and compared with the local erosion and reconstruction of the early fan, the earthquake shows weak amplitude reflection, which is dominated by the muddy channel. The large-scale sublustrine fan has the spatial and temporal distribution and evolution law of early restricted filling, mid-stage overflow adjustment and late erosion transformation, which constitute the development characteristics of transverse continuous and vertical multi-stage superposition. The three fan bodies A, B and C below the first stage have good sand-rich, shallow burial, good oil and gas migration and accumulation conditions, and good reservoer-cap combination. The sweet area of C-fan is large, which is an important target for lithologic reservoir exploration in Bohai sea in recent years.
Aiming at the problem of unclear fan formation mechanism and sedimentary filling process under the condition of no well, from the perspective of source and sink system, three-dimensional seismic data were used to comprehensively analyze the denudation capacity and transport path of the source area of Bonan low bulge, and the sedimentary response characteristics and coupling mechanism of the large sublacustrine fan in the southeastern slope of Bozhong depression were clarified. The developmental model was summarized. The results show that: (1) The second of Dongying sequence is in the transition stage of lake basin fault depression, which can be divided into two tertiary sequences, in which the sublacustrine fan mainly developed in the highstand systems tract of the lower second of Dongying sequence; (2) The denudation flux in the eastern part of the Bonan low bulge is greater than deposition flux of the subestrustrine fan. The large subestrustrine fan is mainly influenced by the near province-source, and the braided river delta formed in the high part of the uplift does not pass through, and is discharged under the depositional break of the slope along five transport channels spreading from south to north. The coupling of near source supply, transport channel and sedimentary slope break formed a large contiguous lacustrine fan deposit. (3) The sedimentary filling of sublacustrine fan is controlled by the location of restricted palaeogeomorphology and the size of the space that can be accommodated. Among them, the early restricted paleogeomorphology formed A large space, and the fan sand body of the lake bottom was preferentially unloaded, forming three fan sediments, A, B and C. Due to the spatial limitations on both sides and the strong hydrodynamic conditions, the seismic facies showed the characteristics of chaotic downcut waterways and lateral migration superimposed, and the sand body formed was relatively rich in sand. With the inflow of gravity flow, the space that can be contained gradually decreases, and the gravity flow overflows along the recharge channel to the center of the open lake basin, forming two fan bodies D and E. Due to the dilution of water concentration and the change of paleo-geomorphology, the energy gradually weakens. The seismic phase has the characteristics of laminary-strong amplitude reflection, the channel features are not obvious, and the sand richness is moderate. The late source supply and energy are weak, and compared with the local erosion and reconstruction of the early fan, the earthquake shows weak amplitude reflection, which is dominated by the muddy channel. The large-scale sublustrine fan has the spatial and temporal distribution and evolution law of early restricted filling, mid-stage overflow adjustment and late erosion transformation, which constitute the development characteristics of transverse continuous and vertical multi-stage superposition. The three fan bodies A, B and C below the first stage have good sand-rich, shallow burial, good oil and gas migration and accumulation conditions, and good reservoer-cap combination. The sweet area of C-fan is large, which is an important target for lithologic reservoir exploration in Bohai sea in recent years.
Abstract:
[Objective] The previous regional geological data regarded the Sanjie sand and gravel section in Juren Town, Binxian County, Heilongjiang Province as the Luojiaweng Formation, but the study of its stratigraphic properties and sedimentary environment is weak, which greatly limits the in-depth understanding of regional surface processes recorded in this stratum. [Methods] From the perspectives of sedimentology, mineralogy, elemental geochemistry and U-Pb chronology of detrital zircon, the chemical weathering characteristics, source rock properties, sedimentary environment and tectonic setting of the provenance area of this section are discussed. [Results]The results show that the weathered degree of sand and gravel in the three sections is low, the sorting is poor, the roundness is good, and there is no obvious directional arrangement. The gravel lithology is mainly granitic rock (46.31%) and quartzy rock (28.19%), followed by syenite (0.2%), tuff (0.01%) and schist (0.01%). The heavy minerals were mainly sphenite (65.18%) and epidote (11.87%), but the other heavy minerals were less active. Elemental geochemistry reveals that the sediments in the three sections have a weak to moderate degree of chemical weathering, most of the sediments have undergone a primary cycle, and their parent rock type is felsic. According to the geochemical migration and enrichment of elements and the paleoclimate discrimination diagram, the sediment is revealed to be braided river sediment in arid oxidation environment. The zircon U-Pb ages are distributed in a narrow range (134.2~220.3 Ma, with a peak age of ~168 Ma), indicating the detrite contribution from Zhangguangcai Mountain, and indicating the subduction movement of Mudanjiang Ocean and the transformation of extensional environment after the subduction of the eastern oceanic plate to orogeny. Compared with the standard strata of Luojiawang Formation, there are significant differences in sedimentological characteristics, genetic types and geomorphologic characteristics of the three-section section. It is speculated that the formation time of the three-section section is later than that of the standard strata of Luojiawang Formation, and the time is roughly the same as that of Baitushan Formation. [Conclusion]This provides important indications for the division of the Quaternary strata in Harbin and the coupling relationship between regional structure geomorphology climate water system evolution.
[Objective] The previous regional geological data regarded the Sanjie sand and gravel section in Juren Town, Binxian County, Heilongjiang Province as the Luojiaweng Formation, but the study of its stratigraphic properties and sedimentary environment is weak, which greatly limits the in-depth understanding of regional surface processes recorded in this stratum. [Methods] From the perspectives of sedimentology, mineralogy, elemental geochemistry and U-Pb chronology of detrital zircon, the chemical weathering characteristics, source rock properties, sedimentary environment and tectonic setting of the provenance area of this section are discussed. [Results]The results show that the weathered degree of sand and gravel in the three sections is low, the sorting is poor, the roundness is good, and there is no obvious directional arrangement. The gravel lithology is mainly granitic rock (46.31%) and quartzy rock (28.19%), followed by syenite (0.2%), tuff (0.01%) and schist (0.01%). The heavy minerals were mainly sphenite (65.18%) and epidote (11.87%), but the other heavy minerals were less active. Elemental geochemistry reveals that the sediments in the three sections have a weak to moderate degree of chemical weathering, most of the sediments have undergone a primary cycle, and their parent rock type is felsic. According to the geochemical migration and enrichment of elements and the paleoclimate discrimination diagram, the sediment is revealed to be braided river sediment in arid oxidation environment. The zircon U-Pb ages are distributed in a narrow range (134.2~220.3 Ma, with a peak age of ~168 Ma), indicating the detrite contribution from Zhangguangcai Mountain, and indicating the subduction movement of Mudanjiang Ocean and the transformation of extensional environment after the subduction of the eastern oceanic plate to orogeny. Compared with the standard strata of Luojiawang Formation, there are significant differences in sedimentological characteristics, genetic types and geomorphologic characteristics of the three-section section. It is speculated that the formation time of the three-section section is later than that of the standard strata of Luojiawang Formation, and the time is roughly the same as that of Baitushan Formation. [Conclusion]This provides important indications for the division of the Quaternary strata in Harbin and the coupling relationship between regional structure geomorphology climate water system evolution.
Abstract:
C-6 Oilfield is one of the most principal oilfields of Caofeidian oil province with hundred million cubic metre of reserves. The third oil group of Guantao Formation (N1gⅢ), the main production zone of C-6 Oilfield, is sand-rich braided river deposit. The architecture and connectivity of braided river sandstone are the key geological factors affecting the development effect of the Oilfield. Calibrated with limited log data, intelligent fusion technology of multiple seismic attributes was introduced to finely characterizes the spatial distribution of the level-4 architecture units of the braided river reservoir. According to log interpretation, N1gⅢ of C-6 oilfield mainly develops two types of level-4 architecture units, namely, channel bar and braided channel, and braided bar is the best reservoir with high sandstone thickness and excellent physical properties. Based on seismic attribute extraction and correlation analysis with lithological and physical parameters, reflection intensity, relative impedance, sweet point, original amplitude, envelop were chosen as intelligent fusion seismic attributes with Deep Feed-Forward Neural Network (DFNN) algorithm under the supervision of porosity. The 3D attribute of DFNN fusion, representative of lithology and petrophysical property, largely improves the detecting ability of braided river sandstone unit and its boundary, and can be used to finely characterize the plan and section distribution of braided river level-4 architecture units effectively. A NE-SW braided flow zone was developed in N1gⅢ of C-6 oilfield, which could be internally sub-divided into 15 rhombic level-4 architecture units of the braided bar. Distributary channels, another level-4 architecture units, surrounded braided bar in a narrow strip. The level-4 architecture interface between the two units played as seepage barriers for fluid migration. The braided bars cut and overlapped one another vertically, forming “big bar and small channel” plan reservoir architecture pattern. The fine characterization results deepened the understanding of the reservoir connectivity of the braided river reservoir with sparse well pattern, which provided direct geological bases for the making of optimized adjustment plan of C-6 Oilfield.
C-6 Oilfield is one of the most principal oilfields of Caofeidian oil province with hundred million cubic metre of reserves. The third oil group of Guantao Formation (N1gⅢ), the main production zone of C-6 Oilfield, is sand-rich braided river deposit. The architecture and connectivity of braided river sandstone are the key geological factors affecting the development effect of the Oilfield. Calibrated with limited log data, intelligent fusion technology of multiple seismic attributes was introduced to finely characterizes the spatial distribution of the level-4 architecture units of the braided river reservoir. According to log interpretation, N1gⅢ of C-6 oilfield mainly develops two types of level-4 architecture units, namely, channel bar and braided channel, and braided bar is the best reservoir with high sandstone thickness and excellent physical properties. Based on seismic attribute extraction and correlation analysis with lithological and physical parameters, reflection intensity, relative impedance, sweet point, original amplitude, envelop were chosen as intelligent fusion seismic attributes with Deep Feed-Forward Neural Network (DFNN) algorithm under the supervision of porosity. The 3D attribute of DFNN fusion, representative of lithology and petrophysical property, largely improves the detecting ability of braided river sandstone unit and its boundary, and can be used to finely characterize the plan and section distribution of braided river level-4 architecture units effectively. A NE-SW braided flow zone was developed in N1gⅢ of C-6 oilfield, which could be internally sub-divided into 15 rhombic level-4 architecture units of the braided bar. Distributary channels, another level-4 architecture units, surrounded braided bar in a narrow strip. The level-4 architecture interface between the two units played as seepage barriers for fluid migration. The braided bars cut and overlapped one another vertically, forming “big bar and small channel” plan reservoir architecture pattern. The fine characterization results deepened the understanding of the reservoir connectivity of the braided river reservoir with sparse well pattern, which provided direct geological bases for the making of optimized adjustment plan of C-6 Oilfield.
Abstract:
The Middle Permian to Lower Triassic stratigraphy in the Fars region of the southern Persian Gulf harbors substantial oil and gas resources, making it a focal area for China's overseas exploration efforts. The current research lacks a comprehensive sequence stratigraphy and a macroscopic understanding of the sedimentary evolution of the entire oil-bearing succession. This study focuses on the Middle to Upper Permian Dalan Formation and the Lower Triassic Kangan Formation in the region. Utilizing data from individual wells, cross-sections, core samples, thin sections, well logging, and IHS and C&C databases, along with consideration of regional geological context and existing knowledge, the Middle Permian to Early Triassic in the study area is stratigraphically divided into sequences. The study provides an in-depth analysis of the characteristics and evolution of each sequence's sedimentary systems. The results indicate that the Dalan-Kangan formations in the study area exhibit six sequence boundaries and five maximum flooding surfaces. Based on the types of sequence boundaries and the development of maximum flooding surfaces, the Dalan and Kangan formations in the southern Persian Gulf are subdivided into five third-order sequences. The targeted lithology is predominantly carbonate ramp deposits, further categorized into inner ramp, mid-ramp, and outer ramp subfacies. The inner ramp can be subdivided into six depositional microfacies: Sabkha in the intertidal zone, tidal flat, lagoon, back-barrier, shoal middle, and shoal front. The study area represents an arid and hot shallow-water carbonate deposition environment. During the SQ1-SQ2 deposition period, a predominantly progradational sedimentary model is observed, while the SQ3 deposition period follows a retrogradational and aggradational model. The SQ4 deposition period returns to a progradational model, and the SQ5 deposition period is characterized by a retrogradational model.
The Middle Permian to Lower Triassic stratigraphy in the Fars region of the southern Persian Gulf harbors substantial oil and gas resources, making it a focal area for China's overseas exploration efforts. The current research lacks a comprehensive sequence stratigraphy and a macroscopic understanding of the sedimentary evolution of the entire oil-bearing succession. This study focuses on the Middle to Upper Permian Dalan Formation and the Lower Triassic Kangan Formation in the region. Utilizing data from individual wells, cross-sections, core samples, thin sections, well logging, and IHS and C&C databases, along with consideration of regional geological context and existing knowledge, the Middle Permian to Early Triassic in the study area is stratigraphically divided into sequences. The study provides an in-depth analysis of the characteristics and evolution of each sequence's sedimentary systems. The results indicate that the Dalan-Kangan formations in the study area exhibit six sequence boundaries and five maximum flooding surfaces. Based on the types of sequence boundaries and the development of maximum flooding surfaces, the Dalan and Kangan formations in the southern Persian Gulf are subdivided into five third-order sequences. The targeted lithology is predominantly carbonate ramp deposits, further categorized into inner ramp, mid-ramp, and outer ramp subfacies. The inner ramp can be subdivided into six depositional microfacies: Sabkha in the intertidal zone, tidal flat, lagoon, back-barrier, shoal middle, and shoal front. The study area represents an arid and hot shallow-water carbonate deposition environment. During the SQ1-SQ2 deposition period, a predominantly progradational sedimentary model is observed, while the SQ3 deposition period follows a retrogradational and aggradational model. The SQ4 deposition period returns to a progradational model, and the SQ5 deposition period is characterized by a retrogradational model.
Abstract:
[Objective] By analyzing the influence of the periodic change of earth orbit on the periodic change of climate, this paper discusses the climate change characteristics of the Lower Oil Sand Mountain Formation in Qaidam Basin, and establishes a high-resolution astronomical scale for the Lower Oil Sand Mountain in Qaidam Basin based on Milankovitch theory to identify and divide high-frequency sequences. [Methods] Firstly, Laskar algorithm is used to calculate the variation period of the earth's orbital parameters during the summer solstice at 35 north latitude from 14.5~23.8 Ma, and the Miocene cycle theory and Miocene cycle ratio in this sedimentary period are determined. Then, taking wells Xianzhong 39, Xianzhong 8-9 and Xianzhong 8-12 in Nanbaxian oil and gas field as examples, the natural gamma data are analyzed by frequency spectrum and continuous wavelet transform. Finally, according to the orbital period, the average sedimentation rate of the Lower Youshashan Formation is calculated, and the "floating" astronomical scale of well Xianzhong 39 is established. [Results] Through the analysis of frequency spectrum and continuous wavelet transform, the Neogene Lower Youshashan Formation is mainly controlled by eccentricity periods of 400 ka and 95 ka. The average sedimentation rate of the Lower Youshashan Formation is 0.094 41 m/ka, and the sedimentation duration is 7.2 Ma. Based on the 400 ka long eccentric period curve and 95 ka short eccentric period curve as benchmark curves, 18 fourth-order quasi-sequence groups and 72 fifth-order quasi-sequence groups were identified. [Conclusion] The results show that the climate change recorded in the Lower Youshashan Formation is obviously controlled and driven by cycles. Identification and division based on Milankovitch theory can reduce the influence of subjective factors, improve the accuracy of division results, and more accurately describe the climate change characteristics in sediments. These research results are helpful to deeply understand the evolution law of the earth's climate and provide important reference for oil and gas exploration and resource evaluation.
[Objective] By analyzing the influence of the periodic change of earth orbit on the periodic change of climate, this paper discusses the climate change characteristics of the Lower Oil Sand Mountain Formation in Qaidam Basin, and establishes a high-resolution astronomical scale for the Lower Oil Sand Mountain in Qaidam Basin based on Milankovitch theory to identify and divide high-frequency sequences. [Methods] Firstly, Laskar algorithm is used to calculate the variation period of the earth's orbital parameters during the summer solstice at 35 north latitude from 14.5~23.8 Ma, and the Miocene cycle theory and Miocene cycle ratio in this sedimentary period are determined. Then, taking wells Xianzhong 39, Xianzhong 8-9 and Xianzhong 8-12 in Nanbaxian oil and gas field as examples, the natural gamma data are analyzed by frequency spectrum and continuous wavelet transform. Finally, according to the orbital period, the average sedimentation rate of the Lower Youshashan Formation is calculated, and the "floating" astronomical scale of well Xianzhong 39 is established. [Results] Through the analysis of frequency spectrum and continuous wavelet transform, the Neogene Lower Youshashan Formation is mainly controlled by eccentricity periods of 400 ka and 95 ka. The average sedimentation rate of the Lower Youshashan Formation is 0.094 41 m/ka, and the sedimentation duration is 7.2 Ma. Based on the 400 ka long eccentric period curve and 95 ka short eccentric period curve as benchmark curves, 18 fourth-order quasi-sequence groups and 72 fifth-order quasi-sequence groups were identified. [Conclusion] The results show that the climate change recorded in the Lower Youshashan Formation is obviously controlled and driven by cycles. Identification and division based on Milankovitch theory can reduce the influence of subjective factors, improve the accuracy of division results, and more accurately describe the climate change characteristics in sediments. These research results are helpful to deeply understand the evolution law of the earth's climate and provide important reference for oil and gas exploration and resource evaluation.
Abstract:
The East Mariana Basin of the West Pacific Ocean, which is located in the east of the Mariana Trench, south of the Magellan Seamounts, and north of the Caroline Seamounts, is an ideal area for the study of Asina aeolian dust deposits, but the sediment research of the East Mariana Basin is still weak. In order to reveal the sediment geochemical characteristics and provide background data for further sediment provenance, seabed mineral resources evaluation and climate-environment evolution research, element geochemistry of surface sediments in the East Mariana Basin was studied. Based on 28 pelagic clay surface sediment (0-10 cm) samples collected in the east part of the East Mariana Basin using the box sampler and gravity sampler, contents of major elements, trace elements and rare earth elements of the sediments were analyzed by ICP-OES and ICP-MS methods. Then, elements geochemical characteristics were analyzed, and their influencing factors and indicative significance were discussed. The results show that the contents of major elements in the pelagic clay sediments in the study area are roughly the same as those in the neighboring sea areas of the West Pacific Ocean. The distribution pattern of major elements (oxides) in sediments follows SiO2 > Al2O3 > Fe2O3 > Na2O > MgO > K2O > CaO > MnO > TiO2 > P2O5. The highest content of major elements is SiO2, with an average of 49.14%, followed by Al2O3, with an average of 15.85%. The highest content of trace elements was Ba, with an average of 770×10-6, followed by Cu, with an average of 289×10-6. The average of total rare earth elements ∑REE is 284×10-6, which is light rare earth-rich type, with the highest Ce, Nd and La contents. Principal component analysis of elements shows that the composition of chemical elements can be divided into four categories: The first type is closely related to rare earth elements, including rare earth elements ( except Ce ), P2O5, TiO2, etc., the second type is related to Fe-Mn micronodules, including Fe2O3, MnO, Cr, Co, Ni, Cu, Ba and other metal elements, the third type is related to terrigenous debris, including Al2O3, MgO, SiO2, U, Hf, Th, Ce, etc., the fourth type is related to biological sources, including Cd, CaO, Mo. The elements combination indices (Si/Al, Fe/Al, La/Tb, Th/Sc, etc.) and the elements combination projection diagrams (La-Th-Sc triangle diagram, La/Th-Hf bivariate diagram) further reveal that the sediments sources are dominated by terrigenous materials, especially terrestrial aeolian dust materials. Meanwhile, the Chemical Index of Alteration (CIA) indicates that the parent rocks in the sediment source area are in low-medium chemical weathering conditions. The redox sensitive elements (Cr, Ni, V, U, Th, etc.) combination reveals that the bottom sedimentary environment in the study area is oxidation-weak oxidation environment. This study has some reference significance for understanding the influence of the Asian aeolian dust on the sediment provenance of the East Mariana Basin, revealing the sedimentary environment characteristics of the basin and the distribution of seabed mineral resources.
The East Mariana Basin of the West Pacific Ocean, which is located in the east of the Mariana Trench, south of the Magellan Seamounts, and north of the Caroline Seamounts, is an ideal area for the study of Asina aeolian dust deposits, but the sediment research of the East Mariana Basin is still weak. In order to reveal the sediment geochemical characteristics and provide background data for further sediment provenance, seabed mineral resources evaluation and climate-environment evolution research, element geochemistry of surface sediments in the East Mariana Basin was studied. Based on 28 pelagic clay surface sediment (0-10 cm) samples collected in the east part of the East Mariana Basin using the box sampler and gravity sampler, contents of major elements, trace elements and rare earth elements of the sediments were analyzed by ICP-OES and ICP-MS methods. Then, elements geochemical characteristics were analyzed, and their influencing factors and indicative significance were discussed. The results show that the contents of major elements in the pelagic clay sediments in the study area are roughly the same as those in the neighboring sea areas of the West Pacific Ocean. The distribution pattern of major elements (oxides) in sediments follows SiO2 > Al2O3 > Fe2O3 > Na2O > MgO > K2O > CaO > MnO > TiO2 > P2O5. The highest content of major elements is SiO2, with an average of 49.14%, followed by Al2O3, with an average of 15.85%. The highest content of trace elements was Ba, with an average of 770×10-6, followed by Cu, with an average of 289×10-6. The average of total rare earth elements ∑REE is 284×10-6, which is light rare earth-rich type, with the highest Ce, Nd and La contents. Principal component analysis of elements shows that the composition of chemical elements can be divided into four categories: The first type is closely related to rare earth elements, including rare earth elements ( except Ce ), P2O5, TiO2, etc., the second type is related to Fe-Mn micronodules, including Fe2O3, MnO, Cr, Co, Ni, Cu, Ba and other metal elements, the third type is related to terrigenous debris, including Al2O3, MgO, SiO2, U, Hf, Th, Ce, etc., the fourth type is related to biological sources, including Cd, CaO, Mo. The elements combination indices (Si/Al, Fe/Al, La/Tb, Th/Sc, etc.) and the elements combination projection diagrams (La-Th-Sc triangle diagram, La/Th-Hf bivariate diagram) further reveal that the sediments sources are dominated by terrigenous materials, especially terrestrial aeolian dust materials. Meanwhile, the Chemical Index of Alteration (CIA) indicates that the parent rocks in the sediment source area are in low-medium chemical weathering conditions. The redox sensitive elements (Cr, Ni, V, U, Th, etc.) combination reveals that the bottom sedimentary environment in the study area is oxidation-weak oxidation environment. This study has some reference significance for understanding the influence of the Asian aeolian dust on the sediment provenance of the East Mariana Basin, revealing the sedimentary environment characteristics of the basin and the distribution of seabed mineral resources.
Abstract:
[Objective]Dengying Formation in Penglai area of central Sichuan has achieved a major breakthrough in exploration, but the fourth member of Dengying Formation has experienced multiple stages of oil and gas charging due to its large burial depth, old age and complex diagenetic evolution, the relationship between reservoir pore evolution and oil and gas charging is still unclear. [Methods]Based on drilling coring data, the petrological types, reservoir space characteristics, diagenetic types, diagenetic evolution sequence, pore evolution and hydrocarbon charging of the fourth member of Dengying Formation were studied by means of thin section observation, cathodoluminescence, in situ microelement analysis and fluid inclusion. [Results and Discussions]The reservoir rock types of the fourth member of Dengying Formation in Penglai area are mainly crystalline dolomite, granular dolomite and microbial dolomite. The types of reservoir space can be divided into three types: cave, pore and fracture. The main diagenetic types are syngene-parsyngenetic dissolution, epigenetic dissolution, buried dissolution, cementation and filling, tectonic rupture, silicification and compaction. Diagenesis in different stages jointly controls the evolution of reservoir pores in the four members of Dengying Formation, among which the constructive diagenesis is dissolution and rupture in different periods, and the destructive diagenesis is compaction and pressure-dissolution and cementation and filling.[Conclusion] The filling sequence of cement in the solution holes of the fourth member of the reservoir can be divided into: the first generation blade-like dolomite → the second generation powdery dolomite → the first stage bitumen → the third generation fine crystalline dolomite → the fourth generation medium crystalline dolomite → the fifth generation coarse crystalline dolomite → the sixth generation giant crystalline saddle-shaped dolomite → the second stage bitumen → the seventh generation quartz, fluorite and other minerals. According to the information of fluid inclusions captured by cemented fill of each stage, such as type, phase state and homogenization temperature, the oil-gas charging process of Dthe fourth member of Dengying Formation in Penglai Area was reconstructed: Paleo-oil reservoir charging in the middle and late Silurian period (the first phase of fossil oil reservoir) → late Caledonian paleo-oil reservoir destruction → Middle Triassic paleo-oil reservoir charging (the second phase of fossil oil reservoir) → Late Jurassic paleo-gas cracking in paleo-oil reservoir → the adjustment and formation of paleo-gas reservoir from Late Cretaceous to present, in which the late oil cracking gas → gaseous hydrocarbon charging is the main forming period of the fourth member gas reservoir of Dengying Formation.
[Objective]Dengying Formation in Penglai area of central Sichuan has achieved a major breakthrough in exploration, but the fourth member of Dengying Formation has experienced multiple stages of oil and gas charging due to its large burial depth, old age and complex diagenetic evolution, the relationship between reservoir pore evolution and oil and gas charging is still unclear. [Methods]Based on drilling coring data, the petrological types, reservoir space characteristics, diagenetic types, diagenetic evolution sequence, pore evolution and hydrocarbon charging of the fourth member of Dengying Formation were studied by means of thin section observation, cathodoluminescence, in situ microelement analysis and fluid inclusion. [Results and Discussions]The reservoir rock types of the fourth member of Dengying Formation in Penglai area are mainly crystalline dolomite, granular dolomite and microbial dolomite. The types of reservoir space can be divided into three types: cave, pore and fracture. The main diagenetic types are syngene-parsyngenetic dissolution, epigenetic dissolution, buried dissolution, cementation and filling, tectonic rupture, silicification and compaction. Diagenesis in different stages jointly controls the evolution of reservoir pores in the four members of Dengying Formation, among which the constructive diagenesis is dissolution and rupture in different periods, and the destructive diagenesis is compaction and pressure-dissolution and cementation and filling.[Conclusion] The filling sequence of cement in the solution holes of the fourth member of the reservoir can be divided into: the first generation blade-like dolomite → the second generation powdery dolomite → the first stage bitumen → the third generation fine crystalline dolomite → the fourth generation medium crystalline dolomite → the fifth generation coarse crystalline dolomite → the sixth generation giant crystalline saddle-shaped dolomite → the second stage bitumen → the seventh generation quartz, fluorite and other minerals. According to the information of fluid inclusions captured by cemented fill of each stage, such as type, phase state and homogenization temperature, the oil-gas charging process of Dthe fourth member of Dengying Formation in Penglai Area was reconstructed: Paleo-oil reservoir charging in the middle and late Silurian period (the first phase of fossil oil reservoir) → late Caledonian paleo-oil reservoir destruction → Middle Triassic paleo-oil reservoir charging (the second phase of fossil oil reservoir) → Late Jurassic paleo-gas cracking in paleo-oil reservoir → the adjustment and formation of paleo-gas reservoir from Late Cretaceous to present, in which the late oil cracking gas → gaseous hydrocarbon charging is the main forming period of the fourth member gas reservoir of Dengying Formation.
Abstract:
[Objective]The reticulated laterite in southern China is a good geological carrier for Quaternary environmental changes, but there is currently relatively little microscopic research on bedrock reticulation,Not conducive to a comprehensive understanding of reticulation [Methods]Through micro-area analysis techniques, geostatistical and factor analysis, and other methods to conducted elemental geochemical analysis on the white vein micro-area of the bedrock and variegated?horizon in the Langxi profile. [Results]1) Element content in the white vein micro-area of sandstone: The content of iron group elements such as Fe2O3 (1.14-13.29%) and Mn (87×10-6 -3230×10-6) showed a trend of increasing from the center of the white veins to the periphery. However, the spatial distribution of other major elements and stable elements such as Ti (1294×10-6~ 2454×10-6) and Zr (171 ×10-6~ 197×10-6) showed the opposite trend. The spatial distribution of element content in the bedrock layer is basically consistent with that of the variegated?horizon. 2) Ti/Zr (bedrock layer: 7.23-12.89; reticulated layer: 12.82-21.84) and Ti/Al2O3 (bedrock layer: 0.013-0.018; reticulated layer: 0.044-0.062) were divided into two groups through cluster analysis and scatter plot.They have different provenance 3) The weathering of the bedrock layer (CIA: 86.37%~87.49%; SA: 5.23~5.76) is slightly higher than that of the variegated?horizon (CIA: 85.10%~86.07%; SA: 6.91~8.16;). The leaching intensity of elements such as Al2O3 (17.3%)、 Fe2O3 (73.91%) and MnO (76.68%)in the bedrock white vein micro-area and Al2O3 (15.78%) 、Fe2O3 (70.39%) and MnO (74.84%) in the variegated?horizon white vein micro-area showed a trend of decreasing from the center of the white veins to the periphery. 4) The common feature of factors in the white vein micro-area of the bedrock layer and the reticulated layer is that they are mainly factor 1, which reflects the leaching migration of iron and iron group elements in the white vein, as well as the relative enrichment process of constant elements such asAl2O3、SiO2and K2O and stable elements such as Ti and Zr. [Conclusion] The composition of the white reticulated interior of the bedrock layer and the variegated?horizon are non-spatially homogeneous, and the process of reticulation is a spatial process that extends from the center to the periphery.During reticulation, the leaching of iron and iron group elements dominates, but other elements also have a certain degree of migration, mainly characterized by strong leaching at the center of the reticulation and relatively weak leaching at the periphery. The reticulation process of the two is quite similar.
[Objective]The reticulated laterite in southern China is a good geological carrier for Quaternary environmental changes, but there is currently relatively little microscopic research on bedrock reticulation,Not conducive to a comprehensive understanding of reticulation [Methods]Through micro-area analysis techniques, geostatistical and factor analysis, and other methods to conducted elemental geochemical analysis on the white vein micro-area of the bedrock and variegated?horizon in the Langxi profile. [Results]1) Element content in the white vein micro-area of sandstone: The content of iron group elements such as Fe2O3 (1.14-13.29%) and Mn (87×10-6 -3230×10-6) showed a trend of increasing from the center of the white veins to the periphery. However, the spatial distribution of other major elements and stable elements such as Ti (1294×10-6~ 2454×10-6) and Zr (171 ×10-6~ 197×10-6) showed the opposite trend. The spatial distribution of element content in the bedrock layer is basically consistent with that of the variegated?horizon. 2) Ti/Zr (bedrock layer: 7.23-12.89; reticulated layer: 12.82-21.84) and Ti/Al2O3 (bedrock layer: 0.013-0.018; reticulated layer: 0.044-0.062) were divided into two groups through cluster analysis and scatter plot.They have different provenance 3) The weathering of the bedrock layer (CIA: 86.37%~87.49%; SA: 5.23~5.76) is slightly higher than that of the variegated?horizon (CIA: 85.10%~86.07%; SA: 6.91~8.16;). The leaching intensity of elements such as Al2O3 (17.3%)、 Fe2O3 (73.91%) and MnO (76.68%)in the bedrock white vein micro-area and Al2O3 (15.78%) 、Fe2O3 (70.39%) and MnO (74.84%) in the variegated?horizon white vein micro-area showed a trend of decreasing from the center of the white veins to the periphery. 4) The common feature of factors in the white vein micro-area of the bedrock layer and the reticulated layer is that they are mainly factor 1, which reflects the leaching migration of iron and iron group elements in the white vein, as well as the relative enrichment process of constant elements such asAl2O3、SiO2and K2O and stable elements such as Ti and Zr. [Conclusion] The composition of the white reticulated interior of the bedrock layer and the variegated?horizon are non-spatially homogeneous, and the process of reticulation is a spatial process that extends from the center to the periphery.During reticulation, the leaching of iron and iron group elements dominates, but other elements also have a certain degree of migration, mainly characterized by strong leaching at the center of the reticulation and relatively weak leaching at the periphery. The reticulation process of the two is quite similar.
Abstract:
Carbon and oxygen isotopes are one of the important geochemical indexes of carbonate rocks, which play an important role in revealing the characteristics of sedimentary and diagenetic fluids, and have become one of the basic means to study carbonate rocks. At present, a large number of studies on carbon and oxygen isotopes in limestone-dolomite stage have been carried out at home and abroad, but there are few studies on carbon and oxygen isotopes in sulfate-carbonate stage. In the sulfate-carbonate stage of the sedimentary sequence, there are still carbon and oxygen elements that can be tested, which makes this study possible. There are currently studies on carbon and oxygen isotopes of the plaster salt section of Huaying Mountain and the plaster bearing strata of Reichenhall Formation, Australia, but these studies are few and concentrated on surface samples. It is of great theoretical significance to study carbon and oxygen isotopes of underground paste and salt samples. In the process of drilling geothermal well in Doubei Village, Gaotan Town, Linshui County, Sichuan, to the east of Huaying Mountain in Sichuan Basin, carbon and oxygen isotopes of paste salt interbedding cuttings of Jialingjiang-Lekoupo Formation were studied. It is concluded that :(1) The δ18OPDB (‰) of paste salt interbedding cuttings in the Daobei geothermal well ranges from -2.56 to -15.47, with an average value of -9.13. The δ13CPDB (‰) ranges from -4.68 to -0.12, with an average value of -2.86, and the Z-value is generally lower than 120, which is inconsistent with the characteristics of Marine sediments. The δ18OPDB and δ13CPDB values were significantly lower than that of the Triassic paste salt formation in Huaying Mountain and the Reichenhall paste salt formation in Australia; (2) The carbon and oxygen isotopes of the underground salt-salt strata in this area are mainly affected by the thermochemical sulfate reduction (TSR) in the deep-buried stage before the formation fold and the massive inflow of surface fresh water after the formation fold, fracture and uplift. The high formation temperature and the exchange of organic carbon before fold and the desalting of surface water after fold and fracture are the fundamental reasons for the low δ18O and δ13C of the gypsum salt layer in this area. At the same time, there may be a little freshwater action and influence during the depositional stage; (3) The formation temperature calculated by Craig'sequation (1965) was 28.18~111.71℃, with an average of 68.45℃. The formation temperature calculated by Vasconcelos'sequation (2005) ranges from 4.54℃ to 78.21℃, with an average value of 38.91℃. The former is close to the present temperature of the formation, while the latter is lower, which may be related to the selection of δ18O in the calculation formula.
Carbon and oxygen isotopes are one of the important geochemical indexes of carbonate rocks, which play an important role in revealing the characteristics of sedimentary and diagenetic fluids, and have become one of the basic means to study carbonate rocks. At present, a large number of studies on carbon and oxygen isotopes in limestone-dolomite stage have been carried out at home and abroad, but there are few studies on carbon and oxygen isotopes in sulfate-carbonate stage. In the sulfate-carbonate stage of the sedimentary sequence, there are still carbon and oxygen elements that can be tested, which makes this study possible. There are currently studies on carbon and oxygen isotopes of the plaster salt section of Huaying Mountain and the plaster bearing strata of Reichenhall Formation, Australia, but these studies are few and concentrated on surface samples. It is of great theoretical significance to study carbon and oxygen isotopes of underground paste and salt samples. In the process of drilling geothermal well in Doubei Village, Gaotan Town, Linshui County, Sichuan, to the east of Huaying Mountain in Sichuan Basin, carbon and oxygen isotopes of paste salt interbedding cuttings of Jialingjiang-Lekoupo Formation were studied. It is concluded that :(1) The δ18OPDB (‰) of paste salt interbedding cuttings in the Daobei geothermal well ranges from -2.56 to -15.47, with an average value of -9.13. The δ13CPDB (‰) ranges from -4.68 to -0.12, with an average value of -2.86, and the Z-value is generally lower than 120, which is inconsistent with the characteristics of Marine sediments. The δ18OPDB and δ13CPDB values were significantly lower than that of the Triassic paste salt formation in Huaying Mountain and the Reichenhall paste salt formation in Australia; (2) The carbon and oxygen isotopes of the underground salt-salt strata in this area are mainly affected by the thermochemical sulfate reduction (TSR) in the deep-buried stage before the formation fold and the massive inflow of surface fresh water after the formation fold, fracture and uplift. The high formation temperature and the exchange of organic carbon before fold and the desalting of surface water after fold and fracture are the fundamental reasons for the low δ18O and δ13C of the gypsum salt layer in this area. At the same time, there may be a little freshwater action and influence during the depositional stage; (3) The formation temperature calculated by Craig'sequation (1965) was 28.18~111.71℃, with an average of 68.45℃. The formation temperature calculated by Vasconcelos'sequation (2005) ranges from 4.54℃ to 78.21℃, with an average value of 38.91℃. The former is close to the present temperature of the formation, while the latter is lower, which may be related to the selection of δ18O in the calculation formula.
Abstract:
[Objective] The Paleogene Shahejie Formation around the Bozhong sag, Bohai Bay Basin is characterized by the development of mixed rock reservoirs, which are rich in abundant oil and gas resources. The unique biomass cavity pores in mixed rock reservoirs make the initial porosity of mixed rocks cannot be obtained by the conventional initial porosity recovery formula for mixed rocks, and there is a lack of initial porosity recovery methods for mixed rocks both at home and abroad, and the accurate recovery of the initial porosity is a key element in the study of the evolution of the reservoir. [Methods] In this study, modern snail samples were selected to determine the volume of snail body cavities using experimental and formulaic methods. Subsequently, a physical simulation experiment was conducted to simulate the filling conditions of snail body cavities in a real depositional environment. Finally, based on commonly used formulas for calculating initial porosity in reservoirs, a formula suitable for mixed rock reservoirs was derived. [Results and Discussions] Studies have shown that the species of snails is the biggest factor affecting the percentage of body cavity pore volume of snails. Different species of snails have different sizes of effective storage space, i.e., body cavity pore porosity; the main reason affecting the difference in body cavity pore porosity of the same species of snails is the size of the body cavity pore lumen. Taking the mixed rock sample from well QHD36-3-A at a depth of 3765.03m with a high content of fragmented bioclasts as an example, the initial porosity of this mixed rock at that depth was determined to be 51.68%. [Conclusions] In this paper, a new calculation method to find the initial porosity of mixed rocks is established based on the previous formula and combined with physical simulation experiments, which is of great significance for the study of mixed reservoir evolution.
[Objective] The Paleogene Shahejie Formation around the Bozhong sag, Bohai Bay Basin is characterized by the development of mixed rock reservoirs, which are rich in abundant oil and gas resources. The unique biomass cavity pores in mixed rock reservoirs make the initial porosity of mixed rocks cannot be obtained by the conventional initial porosity recovery formula for mixed rocks, and there is a lack of initial porosity recovery methods for mixed rocks both at home and abroad, and the accurate recovery of the initial porosity is a key element in the study of the evolution of the reservoir. [Methods] In this study, modern snail samples were selected to determine the volume of snail body cavities using experimental and formulaic methods. Subsequently, a physical simulation experiment was conducted to simulate the filling conditions of snail body cavities in a real depositional environment. Finally, based on commonly used formulas for calculating initial porosity in reservoirs, a formula suitable for mixed rock reservoirs was derived. [Results and Discussions] Studies have shown that the species of snails is the biggest factor affecting the percentage of body cavity pore volume of snails. Different species of snails have different sizes of effective storage space, i.e., body cavity pore porosity; the main reason affecting the difference in body cavity pore porosity of the same species of snails is the size of the body cavity pore lumen. Taking the mixed rock sample from well QHD36-3-A at a depth of 3765.03m with a high content of fragmented bioclasts as an example, the initial porosity of this mixed rock at that depth was determined to be 51.68%. [Conclusions] In this paper, a new calculation method to find the initial porosity of mixed rocks is established based on the previous formula and combined with physical simulation experiments, which is of great significance for the study of mixed reservoir evolution.
Abstract:
[Objective]Typical beach bar sedimentary sand bodies are developed in the middle and upper member of Shibei Formation in Tainan area of Qinghai Oilfield, which is an important high-quality reservoir. The formation mechanism and distribution pattern of beach bar sand body have always been controversial, which has limited the further exploration and development of the gas field. Therefore, it is urgent to carry out fine characterization of the interior of the beach bar in Tainan area, identify the sedimentary microfacies types, and establish the corresponding deposit model of the beach bar. [Methods] Under the guidance of sedimentology, considering the hydrodynamic difference during the formation of beach bars, the sand body particle size and permeability are different. Using the median grain size as the link, the corresponding logging template of rock facies is summarized, and the interpretation standard and dynamic response of sedimentary microfacies are determined, so as to classify the sedimentary microfacies more scientifically. Based on the modern sedimentary analogy, sand body anatomy in the dense well pattern area of the study area, and the reasonableness of microfacies classification by horizontal Wells and production data, a beach bar sedimentation model suitable for the inland depression lake basin is proposed considering that the formation of beach bars is controlled by multiple factors. [Results] The beach and bar subfacies in the middle and upper part of Sebei Formation in Tainan area can be further divided into the main body of the bar, the edge of the bar, the main body of the beach and the edge of the beach. The bar sand is distributed above the beach sand, extending vertically to the northwest wind, in the form of lenticular and mencrescent, with a length of about 1,250 m and a width of about 250 m. The linear positive correlation between the length and width of the bar sand is about 5, which is consistent with modern sedimentation. As a whole, the beach sand is distributed in the direction of vertical provenance, and broadly and gently covers the edge of the bar sand. By comparing the deposit of beach bar in Tiangiz Lake, the extension direction, distribution rule and length-width ratio of bar sand are well corresponding. Sufficient source supply provides a good material basis for the formation of beach bars. The coupling of palaeostructure, palaeogeomorphology, palaeomonsoon and palaeowater depth controls the development scale of beach bars, the development form and geographical location of bar sands. [Conclusions] The sedimentary model of "open shallow lake, wind wave transformation, oblique row type" is proposed, which can provide theoretical guidance for the identification of beach bar system in inland depression lake basins.
[Objective]Typical beach bar sedimentary sand bodies are developed in the middle and upper member of Shibei Formation in Tainan area of Qinghai Oilfield, which is an important high-quality reservoir. The formation mechanism and distribution pattern of beach bar sand body have always been controversial, which has limited the further exploration and development of the gas field. Therefore, it is urgent to carry out fine characterization of the interior of the beach bar in Tainan area, identify the sedimentary microfacies types, and establish the corresponding deposit model of the beach bar. [Methods] Under the guidance of sedimentology, considering the hydrodynamic difference during the formation of beach bars, the sand body particle size and permeability are different. Using the median grain size as the link, the corresponding logging template of rock facies is summarized, and the interpretation standard and dynamic response of sedimentary microfacies are determined, so as to classify the sedimentary microfacies more scientifically. Based on the modern sedimentary analogy, sand body anatomy in the dense well pattern area of the study area, and the reasonableness of microfacies classification by horizontal Wells and production data, a beach bar sedimentation model suitable for the inland depression lake basin is proposed considering that the formation of beach bars is controlled by multiple factors. [Results] The beach and bar subfacies in the middle and upper part of Sebei Formation in Tainan area can be further divided into the main body of the bar, the edge of the bar, the main body of the beach and the edge of the beach. The bar sand is distributed above the beach sand, extending vertically to the northwest wind, in the form of lenticular and mencrescent, with a length of about 1,250 m and a width of about 250 m. The linear positive correlation between the length and width of the bar sand is about 5, which is consistent with modern sedimentation. As a whole, the beach sand is distributed in the direction of vertical provenance, and broadly and gently covers the edge of the bar sand. By comparing the deposit of beach bar in Tiangiz Lake, the extension direction, distribution rule and length-width ratio of bar sand are well corresponding. Sufficient source supply provides a good material basis for the formation of beach bars. The coupling of palaeostructure, palaeogeomorphology, palaeomonsoon and palaeowater depth controls the development scale of beach bars, the development form and geographical location of bar sands. [Conclusions] The sedimentary model of "open shallow lake, wind wave transformation, oblique row type" is proposed, which can provide theoretical guidance for the identification of beach bar system in inland depression lake basins.
Abstract:
During the Cretaceous period, extreme greenhouse climate, global oceanic anoxia and oxygen enrichment events occurred in geological history, and the Cretaceous red beds that appeared during this period contain important information related to paleoclimate and paleoenvironment, which is of great significance to the understanding of stratigraphic surface systems. In this paper, a set of red mudstones developed during the Cretaceous in the North Yellow Sea Basin of eastern China is taken as the object of study. X-ray diffraction and diffuse reflectance spectroscopy (XRD) analyses were carried out on the red and grey mudstones of the Middle Jurassic to Lower Cretaceous, in order to semi-quantitatively and quantitatively analyze the composition and content of chromogenic minerals in the rocks. We also combined the ordinary thin section and scanning electron microscope methods to observe the characteristics of chromogenic minerals in the red mudstone, such as the morphology, distribution and crystalline size of iron-containing minerals. XRD results show that the chromogenic minerals in the red mudstone are hematite and goethite, of which hematite is the main content, the highest content can reach 14%, while the grey mudstone does not contain hematite; hematite aggregates can be seen under the microscope in the red mudstone, and alteration phenomena can be seen in the local area; hematite can be seen in the form of granular or plate aggregates under the scanning electron microscope; Using the characteristics of changes in hematite and goethite content, it is concluded that the climate was relatively humid from the Late Jurassic to the Early Cretaceous, and hot and dry from the Middle to Late Early Cretaceous. Combined with the paleoclimate data of the North Yellow Sea Basin and its adjacent areas, the method of using iron oxides to reflect the paleoclimate changes in the study area is found to be feasible, and a comprehensive analysis suggests that the chromogenic minerals in the red mudstone of the Lower Cretaceous have indicative significance for the paleoenvironment and paleoclimate.
During the Cretaceous period, extreme greenhouse climate, global oceanic anoxia and oxygen enrichment events occurred in geological history, and the Cretaceous red beds that appeared during this period contain important information related to paleoclimate and paleoenvironment, which is of great significance to the understanding of stratigraphic surface systems. In this paper, a set of red mudstones developed during the Cretaceous in the North Yellow Sea Basin of eastern China is taken as the object of study. X-ray diffraction and diffuse reflectance spectroscopy (XRD) analyses were carried out on the red and grey mudstones of the Middle Jurassic to Lower Cretaceous, in order to semi-quantitatively and quantitatively analyze the composition and content of chromogenic minerals in the rocks. We also combined the ordinary thin section and scanning electron microscope methods to observe the characteristics of chromogenic minerals in the red mudstone, such as the morphology, distribution and crystalline size of iron-containing minerals. XRD results show that the chromogenic minerals in the red mudstone are hematite and goethite, of which hematite is the main content, the highest content can reach 14%, while the grey mudstone does not contain hematite; hematite aggregates can be seen under the microscope in the red mudstone, and alteration phenomena can be seen in the local area; hematite can be seen in the form of granular or plate aggregates under the scanning electron microscope; Using the characteristics of changes in hematite and goethite content, it is concluded that the climate was relatively humid from the Late Jurassic to the Early Cretaceous, and hot and dry from the Middle to Late Early Cretaceous. Combined with the paleoclimate data of the North Yellow Sea Basin and its adjacent areas, the method of using iron oxides to reflect the paleoclimate changes in the study area is found to be feasible, and a comprehensive analysis suggests that the chromogenic minerals in the red mudstone of the Lower Cretaceous have indicative significance for the paleoenvironment and paleoclimate.
Abstract:
There are many curvilinear ridges that have similar planforms as rivers in the northern and southwestern Qaidam Basin. To investigate their formation mechanism, [Methods] we carry out statistical and morphological analyses on 21 sets of gravel samples from the curvilinear ridges, and compared them with the gravel layer sediments in the middle reaches of the Han River. [Results and Discussions] Analysis shows that the ratio of round and sub-round gravels in the curvilinear ridges area ranges from 71.6% to 74.0%, and the ratio of discoid gravels ranges from 44.9% to 54.0%. The correlation coefficients of the gravel morphological features between the distribution area of curvilinear ridges in the Qaidam Basin and the sampling area of the middle reaches of the Han River range from 0.688 to 0.7258. [Conclusions] Studies indicate the following: the gravels in the curvilinear ridges are fluvial deposits. And if based on the modern hydrologic parameters of the Qaidam Basin, the paleocurrent velocity, paleo-discharge and paleo-annual runoff rate of the river indicated by the curvilinear ridges are 0.217 m/s, 1.39 m3/s, and 0.1440 × 108 m3, respectively. The paleo-discharge range of the curvilinear ridges of the Qaidam Basin reconstructed based on the channel width is 14-16 m3/s. Accordingly, the paleo-runoff depth is estimated to be about 2 m, and the corresponding paleocurrent velocity, paleo-discharge and paleo-annual runoff rate are about 0.357 m/s, 14.28 m3/s, and 1.4801×108 m3, respectively. Keywords: Qaidam Basin; Curvilinear ridge; Gravel morphology; Han River; Paleohydrology
There are many curvilinear ridges that have similar planforms as rivers in the northern and southwestern Qaidam Basin. To investigate their formation mechanism, [Methods] we carry out statistical and morphological analyses on 21 sets of gravel samples from the curvilinear ridges, and compared them with the gravel layer sediments in the middle reaches of the Han River. [Results and Discussions] Analysis shows that the ratio of round and sub-round gravels in the curvilinear ridges area ranges from 71.6% to 74.0%, and the ratio of discoid gravels ranges from 44.9% to 54.0%. The correlation coefficients of the gravel morphological features between the distribution area of curvilinear ridges in the Qaidam Basin and the sampling area of the middle reaches of the Han River range from 0.688 to 0.7258. [Conclusions] Studies indicate the following: the gravels in the curvilinear ridges are fluvial deposits. And if based on the modern hydrologic parameters of the Qaidam Basin, the paleocurrent velocity, paleo-discharge and paleo-annual runoff rate of the river indicated by the curvilinear ridges are 0.217 m/s, 1.39 m3/s, and 0.1440 × 108 m3, respectively. The paleo-discharge range of the curvilinear ridges of the Qaidam Basin reconstructed based on the channel width is 14-16 m3/s. Accordingly, the paleo-runoff depth is estimated to be about 2 m, and the corresponding paleocurrent velocity, paleo-discharge and paleo-annual runoff rate are about 0.357 m/s, 14.28 m3/s, and 1.4801×108 m3, respectively. Keywords: Qaidam Basin; Curvilinear ridge; Gravel morphology; Han River; Paleohydrology
Abstract:
[Objective] Chemical weathering is a key geological process that regulates the long-term climate of the earth and participates in the global carbon cycle, and is particularly important for the evolution of terrestrial climate and reconstruction of paleoclimate. [Methods] In this study, 89 aeolian sand and river sand fine-grained components (<63 μm), revealed the spatial distribution characteristics of chemical weathering in the four major sandy lands in Northeast China (Hunshandake Sandy Land, Horqin Sandy Land, Songnen Sandy Land and Hulunbuir Sandy Land), and evaluated the response relationship and influencing factors of 13 weathering indexes to climatic factors (average annual temperature and average annual precipitation). [Results and Discussions] The results showed that the same chemical weathering index (e.g. CIA) showed a poor spatial distribution law and poor correlation with climatic factors in different sandy lands (the correlation coefficient was generally less than 0.4), but different weathering indicators showed a good correlation with climatic factors in different sandy lands (the correlation coefficient was generally greater than 0.6). This indicates that the sensitivity of different weathering indicators to climate varies significantly in different regions. The chemical weathering of the sandy land in Northeast China measured by different indexes is generally controlled by climatic factors, but there are still obvious differences in the correlation between the chemical weathering intensity and temperature and precipitation in different sandy lands. The chemical weathering intensity of Hunshandake Sandy Land was generally low under the influence of precipitation, which was mainly controlled by river action and monsoon precipitation. The weathering intensity in the eastern part of the sandy land is affected by precipitation, which is mainly controlled by topography, monsoon, water vapor transport and element migration, while the weathering intensity in the western part of the sandy land is affected by temperature, which is mainly affected by the topography and high annual average temperature. The southern part of the Songnen Sandy Land has a high weathering rate and is most significantly affected by precipitation, which is mainly affected by geographical location, monsoon precipitation, distribution of multiple rivers and vegetation coverage. The weathering intensity of Hulunbuir Sandy Land is at a moderate level and is relatively weak due to temperature and precipitation, which is mainly controlled by topography, wind erosion, physical weathering and vegetation coverage. [Conclusions] In general, in addition to climatic conditions, the effects of river development, topography and regional geographical characteristics on chemical weathering intensity are equally important, so it is necessary to choose carefully when using sediment chemical weathering indicators for paleoclimate reconstruction, and this study also provides a new idea for sandy land environmental management in Northeast China.
[Objective] Chemical weathering is a key geological process that regulates the long-term climate of the earth and participates in the global carbon cycle, and is particularly important for the evolution of terrestrial climate and reconstruction of paleoclimate. [Methods] In this study, 89 aeolian sand and river sand fine-grained components (<63 μm), revealed the spatial distribution characteristics of chemical weathering in the four major sandy lands in Northeast China (Hunshandake Sandy Land, Horqin Sandy Land, Songnen Sandy Land and Hulunbuir Sandy Land), and evaluated the response relationship and influencing factors of 13 weathering indexes to climatic factors (average annual temperature and average annual precipitation). [Results and Discussions] The results showed that the same chemical weathering index (e.g. CIA) showed a poor spatial distribution law and poor correlation with climatic factors in different sandy lands (the correlation coefficient was generally less than 0.4), but different weathering indicators showed a good correlation with climatic factors in different sandy lands (the correlation coefficient was generally greater than 0.6). This indicates that the sensitivity of different weathering indicators to climate varies significantly in different regions. The chemical weathering of the sandy land in Northeast China measured by different indexes is generally controlled by climatic factors, but there are still obvious differences in the correlation between the chemical weathering intensity and temperature and precipitation in different sandy lands. The chemical weathering intensity of Hunshandake Sandy Land was generally low under the influence of precipitation, which was mainly controlled by river action and monsoon precipitation. The weathering intensity in the eastern part of the sandy land is affected by precipitation, which is mainly controlled by topography, monsoon, water vapor transport and element migration, while the weathering intensity in the western part of the sandy land is affected by temperature, which is mainly affected by the topography and high annual average temperature. The southern part of the Songnen Sandy Land has a high weathering rate and is most significantly affected by precipitation, which is mainly affected by geographical location, monsoon precipitation, distribution of multiple rivers and vegetation coverage. The weathering intensity of Hulunbuir Sandy Land is at a moderate level and is relatively weak due to temperature and precipitation, which is mainly controlled by topography, wind erosion, physical weathering and vegetation coverage. [Conclusions] In general, in addition to climatic conditions, the effects of river development, topography and regional geographical characteristics on chemical weathering intensity are equally important, so it is necessary to choose carefully when using sediment chemical weathering indicators for paleoclimate reconstruction, and this study also provides a new idea for sandy land environmental management in Northeast China.
Abstract:
The coal-bearing strata of Carboniferous Taiyuan Formation are widely distributed in Dawangzhuang area, Jiyang depression, and the high-quality reservoir control factors in the coal strata have an important influence on oil and gas exploration. Combined with burial history, tectonic evolution history, multi-proxy analyses, including the cast thin sections, fluorescence, cathodoluminescence, scanning electron microscopy and energy spectrum, petrography of fluid inclusion and homogeneous temperature, and laser ablation inductively coupled plasma mass spectrometry, were conducted to systematically study the characteristics and genetic model of high-quality reservoir of clastic rocks in coal-bearing strata of Carboniferous Taiyuan Formation(C3t) in Dawangzhuang area, Jiyang depression. The clastic reservoir of Taiyuan Formation coal measure strata in Dawangzhuang area is mainly composed of lithic quartz sandstone. The high-quality reservoir space is dominated by secondary pores, and the dissolution is strong. It is mainly filled with interstitial materials dissolution pores and feldspar dissolution pores formed by atmospheric fresh water and organic acid dissolution. The porosity of high-quality reservoir is more than 8 %, and the permeability is more than 5 × 10-3 μm2. And two phases of quartz overgrowth and two phases of carbonate cements are developed, dominated by carbonate cements. The first phase of quartz overgrowth mainly derives from pressure dissolution of quartz particles, the second phase of quartz overgrowth is mainly sourced from the feldspar dissolution. Siderite is mainly formed by pore water precipitation in syndepositional-early diagenesis stage, and ankerite is mainly related to organic acid decarboxylation. The evolution process of the diagenesis-accumulation system of the clastic rock reservoir of coal measures strata of C3t in Dawangzhuang area of Jiyang depression is: siderite → first phase of quartz overgrowth → first-stage oil in yellow fluorescence emplacement → kaolinite → ankerite →second-stage oil emplacement in blue fluorescence → second phase of quartz overgrowth and kaolinite →pyrite. High-quality reservoirs are mainly controlled by sedimentary facies, tectonic action and diagenesis. The sedimentary facies controls the distribution of lithofacies of high-quality reservoirs. The high-quality reservoirs are mainly controlled by the late uplift of atmospheric fresh water leaching dissolution and buried organic acid dissolution. At the same time, they are controlled by tectonic activities. The distance between the high-quality reservoirs and the docking faults should be far away, so as to avoid the further precipitation of CO2 produced by decarboxylation to form ankerite to destroy the reservoir properties.
The coal-bearing strata of Carboniferous Taiyuan Formation are widely distributed in Dawangzhuang area, Jiyang depression, and the high-quality reservoir control factors in the coal strata have an important influence on oil and gas exploration. Combined with burial history, tectonic evolution history, multi-proxy analyses, including the cast thin sections, fluorescence, cathodoluminescence, scanning electron microscopy and energy spectrum, petrography of fluid inclusion and homogeneous temperature, and laser ablation inductively coupled plasma mass spectrometry, were conducted to systematically study the characteristics and genetic model of high-quality reservoir of clastic rocks in coal-bearing strata of Carboniferous Taiyuan Formation(C3t) in Dawangzhuang area, Jiyang depression. The clastic reservoir of Taiyuan Formation coal measure strata in Dawangzhuang area is mainly composed of lithic quartz sandstone. The high-quality reservoir space is dominated by secondary pores, and the dissolution is strong. It is mainly filled with interstitial materials dissolution pores and feldspar dissolution pores formed by atmospheric fresh water and organic acid dissolution. The porosity of high-quality reservoir is more than 8 %, and the permeability is more than 5 × 10-3 μm2. And two phases of quartz overgrowth and two phases of carbonate cements are developed, dominated by carbonate cements. The first phase of quartz overgrowth mainly derives from pressure dissolution of quartz particles, the second phase of quartz overgrowth is mainly sourced from the feldspar dissolution. Siderite is mainly formed by pore water precipitation in syndepositional-early diagenesis stage, and ankerite is mainly related to organic acid decarboxylation. The evolution process of the diagenesis-accumulation system of the clastic rock reservoir of coal measures strata of C3t in Dawangzhuang area of Jiyang depression is: siderite → first phase of quartz overgrowth → first-stage oil in yellow fluorescence emplacement → kaolinite → ankerite →second-stage oil emplacement in blue fluorescence → second phase of quartz overgrowth and kaolinite →pyrite. High-quality reservoirs are mainly controlled by sedimentary facies, tectonic action and diagenesis. The sedimentary facies controls the distribution of lithofacies of high-quality reservoirs. The high-quality reservoirs are mainly controlled by the late uplift of atmospheric fresh water leaching dissolution and buried organic acid dissolution. At the same time, they are controlled by tectonic activities. The distance between the high-quality reservoirs and the docking faults should be far away, so as to avoid the further precipitation of CO2 produced by decarboxylation to form ankerite to destroy the reservoir properties.
Abstract:
Abstract: [Objective] In this study, to redetermine the stratigraphic boundary of the Carboniferous-Permian Taiyuan and Shanxi formations in the Yichuan area of the Ordos Basin and to solve the problem of sedimentary age attribution of coal-bearing natural gas mudstone section near the boundary of the Shanxi-Taiyuan Formation. [Methods] We selected the sandstone and mudstone samples of the transition layer between the Taiyuan and Shanxi formations in the typical coring well Yi 120 to conduct the U-Pb dating of detrital zircon and we used the maximum depositional age ( MDA ) estimation method, combined with previous research results on the zircon age of the Taiyuan Formation-Shanxi Formation in the North China Plate, to constrain the depositional age of the study interval. [Results] Experiments show that the maximum likelihood age (MLA) of the sandstone and mudstone at the top of the Taiyuan Formation is 298±2 Ma, which represents the age of the latest deposition of the strata. This interval was deposited in the Early Asselian period, which is consistent with the Asselian sedimentary age determined by conodont. The MLAs of the sandstone samples at the bottom of the Shanxi Formation is 295±1 Ma, representing the age of the earliest deposition, which was deposited in the Middle-Late Arthurian period. [Conclusions] Based on the above research and analysis, we conclude that the boundary between the Taiyuan and Shanxi formations in the study area should be above the sand-mudstone section at the top of the Taiyuan Formation; that is, the marine sand-mudstone layer at the top of the Taiyuan Formation in the study area should belong to the Taiyuan Formation, which provides a certain basis for the stratigraphic division of the Shanxi-Taiyuan Formation in the study area.
Abstract: [Objective] In this study, to redetermine the stratigraphic boundary of the Carboniferous-Permian Taiyuan and Shanxi formations in the Yichuan area of the Ordos Basin and to solve the problem of sedimentary age attribution of coal-bearing natural gas mudstone section near the boundary of the Shanxi-Taiyuan Formation. [Methods] We selected the sandstone and mudstone samples of the transition layer between the Taiyuan and Shanxi formations in the typical coring well Yi 120 to conduct the U-Pb dating of detrital zircon and we used the maximum depositional age ( MDA ) estimation method, combined with previous research results on the zircon age of the Taiyuan Formation-Shanxi Formation in the North China Plate, to constrain the depositional age of the study interval. [Results] Experiments show that the maximum likelihood age (MLA) of the sandstone and mudstone at the top of the Taiyuan Formation is 298±2 Ma, which represents the age of the latest deposition of the strata. This interval was deposited in the Early Asselian period, which is consistent with the Asselian sedimentary age determined by conodont. The MLAs of the sandstone samples at the bottom of the Shanxi Formation is 295±1 Ma, representing the age of the earliest deposition, which was deposited in the Middle-Late Arthurian period. [Conclusions] Based on the above research and analysis, we conclude that the boundary between the Taiyuan and Shanxi formations in the study area should be above the sand-mudstone section at the top of the Taiyuan Formation; that is, the marine sand-mudstone layer at the top of the Taiyuan Formation in the study area should belong to the Taiyuan Formation, which provides a certain basis for the stratigraphic division of the Shanxi-Taiyuan Formation in the study area.
Abstract:
China possesses abundant terrestrial shale oil resources, exhibiting significant potential for exploration. This study focuses on the black shale of the Shahejie Formation(Es1) in the Jiyang Depression as its research subject. By employing XRD, rock pyrolysis, fluorescence analysis, scanning electron microscopy, and low-temperature gas adsorption techniques, we comprehensively investigate the laminated black shale layer types, layer combinations, pore types, and structural characteristics of the Es1 section within the southern Bohai Bay Basin. The findings reveal a diverse range of mineral types present in the Es1 section black shales. Based on their distinct compositions, these black shale layers are classified into five categories: feldspar-quartz lamina, clay mineral-rich lamina, aragonite lamina, micritic calcite-dominated lamina, and organic-rich lamina. Furthermore, the vertical stacking relationships allow for their division into three binary layer combinations: "organic-rich + micritic calcite", "organic-rich + aragonite" and "organic-rich + feldspar-quartz". Among these, the porosity of "organic-rich + aragonite" and "organic-rich + feldspar-quartz" binary lamina combination shales was relatively higher, with superior pore structure and connectivity compared to those of "organic-rich + micritic calcite" binary lamina combination shales. In the "organic-rich + aragonite" binary lamina combination shale, shale oil is present in a free state within interlayer crevices, exhibiting optimal mobility. The coexistence of free oil and adsorbed oil in the "organic-rich + aragonite" binary lamina combination shale results in relatively poor mobility. However, in the "organic-rich + feldspar-quartz" binary lamina combination shale, shale oil primarily exists in an adsorbed form, demonstrating the lowest mobility. The research findings elucidate the heterogeneity in reservoir properties among different lamina combinations and establish the pivotal influence of diverse lamina combinations on balck shale's porosity, pore structure, and hydrocarbon storage capacity. Based on these discoveries, we have developed shale oil storage models tailored to various lamina combination black shales, thereby providing a scientific foundation for future extraction of shale oil and gas.
China possesses abundant terrestrial shale oil resources, exhibiting significant potential for exploration. This study focuses on the black shale of the Shahejie Formation(Es1) in the Jiyang Depression as its research subject. By employing XRD, rock pyrolysis, fluorescence analysis, scanning electron microscopy, and low-temperature gas adsorption techniques, we comprehensively investigate the laminated black shale layer types, layer combinations, pore types, and structural characteristics of the Es1 section within the southern Bohai Bay Basin. The findings reveal a diverse range of mineral types present in the Es1 section black shales. Based on their distinct compositions, these black shale layers are classified into five categories: feldspar-quartz lamina, clay mineral-rich lamina, aragonite lamina, micritic calcite-dominated lamina, and organic-rich lamina. Furthermore, the vertical stacking relationships allow for their division into three binary layer combinations: "organic-rich + micritic calcite", "organic-rich + aragonite" and "organic-rich + feldspar-quartz". Among these, the porosity of "organic-rich + aragonite" and "organic-rich + feldspar-quartz" binary lamina combination shales was relatively higher, with superior pore structure and connectivity compared to those of "organic-rich + micritic calcite" binary lamina combination shales. In the "organic-rich + aragonite" binary lamina combination shale, shale oil is present in a free state within interlayer crevices, exhibiting optimal mobility. The coexistence of free oil and adsorbed oil in the "organic-rich + aragonite" binary lamina combination shale results in relatively poor mobility. However, in the "organic-rich + feldspar-quartz" binary lamina combination shale, shale oil primarily exists in an adsorbed form, demonstrating the lowest mobility. The research findings elucidate the heterogeneity in reservoir properties among different lamina combinations and establish the pivotal influence of diverse lamina combinations on balck shale's porosity, pore structure, and hydrocarbon storage capacity. Based on these discoveries, we have developed shale oil storage models tailored to various lamina combination black shales, thereby providing a scientific foundation for future extraction of shale oil and gas.
Abstract:
[Objective] To investigate the sorting movement and sedimentary characteristics of fine-grained sediments under the action of turbidity currents, and analyze the controlled factors of their transport distance and sediments spatial distribution. [Methods] Based on circular flume simulation experiment, the transport and deposition process of fine-grained sediments carried by turbidity currents were simulated and analyzed by controlling three conditions: initial fluid velocity, sediment concentration, and sand mud ratio, and the sedimentary dynamic mechanism was explored. [Results] The simulation results indicate that: (1) Fine-grained sediments transported by turbidity currents will experience experimental phenomena such as “water jump”, “double flow segmentation”, “lofting”, “head lifting”, and “new head” during the flow process. (2) During fluid transportation, the movement speed and distance of fine-grained sediments are influenced by the concentration difference between the fluid and the environmental fluid. (3) Factors such as initial flow velocity, water jump, and lofting control fluid flow velocity, fine-grained sediments transport distance, and spatial distribution. (4) The “new head” phenomenon causes the sand bodies carried by the fluid to become discontinuous, isolated or dispersed. [Conclusions] According to the “new head” phenomenon in the simulation process, the causes of dispersed sand bodies are speculated, which has certain guiding significance for the study of the formation and distribution of dispersed sand bodies.
[Objective] To investigate the sorting movement and sedimentary characteristics of fine-grained sediments under the action of turbidity currents, and analyze the controlled factors of their transport distance and sediments spatial distribution. [Methods] Based on circular flume simulation experiment, the transport and deposition process of fine-grained sediments carried by turbidity currents were simulated and analyzed by controlling three conditions: initial fluid velocity, sediment concentration, and sand mud ratio, and the sedimentary dynamic mechanism was explored. [Results] The simulation results indicate that: (1) Fine-grained sediments transported by turbidity currents will experience experimental phenomena such as “water jump”, “double flow segmentation”, “lofting”, “head lifting”, and “new head” during the flow process. (2) During fluid transportation, the movement speed and distance of fine-grained sediments are influenced by the concentration difference between the fluid and the environmental fluid. (3) Factors such as initial flow velocity, water jump, and lofting control fluid flow velocity, fine-grained sediments transport distance, and spatial distribution. (4) The “new head” phenomenon causes the sand bodies carried by the fluid to become discontinuous, isolated or dispersed. [Conclusions] According to the “new head” phenomenon in the simulation process, the causes of dispersed sand bodies are speculated, which has certain guiding significance for the study of the formation and distribution of dispersed sand bodies.
Abstract:
[Objective] The Late Paleozoic Ice Age is the most remarkable icehouse period since the flourish of the terrestrial ecosystem and is characterized by multiple discrete glacial and interglacial periods. Several global warming events occurred during the Late Paleozoic Ice Age, which have received wide attention in recent years. An abrupt negative excursion in carbon isotopes (δ13C) has been recorded near the Late Pennsylvanian Kasimovian-Gzhelian Boundary (KGB), accompanied by significant global warming. The KGB warming event under the background of interglacial period of the icehouse climate is of great interest, but the study on this warming event is still in the initial stage. [Methods] In this paper, detailed sedimentological and comprehensive stratigraphic studies were carried out on the ~20-m-thick strata across the KGB in the Naqing, Shanglong, and Narao sections of the Luodian Basin, South China. [Results and Discussions] Four sedimentary lithofacies are identified, including the lime mudstone facies, bioclastic wacke- to packstone facies, normal-graded packstone facies, and dark calcareous mudstone facies, indicating a deep-water slope environment with frequent sea-level fluctuations. The newly obtained carbonate δ13C record from the Shanglong section can be well compared with the previously published records from the Naqing and Narao sections, and the negative excursion in δ13C across the KGB is recorded around the world. Three cycles of paleo-water-depth variation at the Heckelina eudoraensis zone, Idiognathodus naraoensis zone, and the bottom of H. simulator zone in the study interval show a similar pace with the astronomical cycles and can be correlated to those of the Mid-continent from North America. [Conclusions] The studied successions of the Luodian Basin provide an important reference for the study of the KGB warming event.
[Objective] The Late Paleozoic Ice Age is the most remarkable icehouse period since the flourish of the terrestrial ecosystem and is characterized by multiple discrete glacial and interglacial periods. Several global warming events occurred during the Late Paleozoic Ice Age, which have received wide attention in recent years. An abrupt negative excursion in carbon isotopes (δ13C) has been recorded near the Late Pennsylvanian Kasimovian-Gzhelian Boundary (KGB), accompanied by significant global warming. The KGB warming event under the background of interglacial period of the icehouse climate is of great interest, but the study on this warming event is still in the initial stage. [Methods] In this paper, detailed sedimentological and comprehensive stratigraphic studies were carried out on the ~20-m-thick strata across the KGB in the Naqing, Shanglong, and Narao sections of the Luodian Basin, South China. [Results and Discussions] Four sedimentary lithofacies are identified, including the lime mudstone facies, bioclastic wacke- to packstone facies, normal-graded packstone facies, and dark calcareous mudstone facies, indicating a deep-water slope environment with frequent sea-level fluctuations. The newly obtained carbonate δ13C record from the Shanglong section can be well compared with the previously published records from the Naqing and Narao sections, and the negative excursion in δ13C across the KGB is recorded around the world. Three cycles of paleo-water-depth variation at the Heckelina eudoraensis zone, Idiognathodus naraoensis zone, and the bottom of H. simulator zone in the study interval show a similar pace with the astronomical cycles and can be correlated to those of the Mid-continent from North America. [Conclusions] The studied successions of the Luodian Basin provide an important reference for the study of the KGB warming event.
Abstract:
[Objective] Selective dissolution is common in marine carbonates, and its origin is typically to be related to meteoric fluids, while other possible origins lack further discussion. [Methods] In this study, the origin of marine selective dissolution of Buqu Formation of well GK-1 in the south Qiangtang basin is investigated based on petrography, stable carbon and oxygen isotopes, and elemental geochemistry. [Results] Eight sedimentary cycles (C1 to C8 from bottom to top) were recognized from the studied Buqu Formation, each cycle with limestone in the lower part and dolostone in the upper part. These eight cycles can be divided into two types (A and B) according to different carbonate components. The limestone in type A cycle (C1-C4) is dominated by bioclastic packstone and grainstone, while in type B cycle (C5-C8) is dominated by bioclastic wackstone and packstone. Upwards from type A cycle to the type B cycle, the content of aragonite fossils (gastropods and bivalves) in the limestone decreases and the content of peloids increases. The dolomite in both type A and type B cycles is crystalline dolomite with ooid ghosts showing selective dissolution pores. Importantly, the overall percentage of selective dissolution pores in type A cycles is significantly higher than that in type B cycles. In terms of geochemistry, the carbon and oxygen isotopes of dolostone are relatively higher compared to those of limestone in each cycle. Rare earth elements and yttrium concentrations (0.44~7.25 ppm) of dolostone and limestone are extremely low and the Y/Ho ratios (35.63~75.55) are basically within the range of modern seawater. Dolostone exhibits a seawater-like PAAS-normalized REE+ Y pattern, showing a left leaning style with relatively LREE depletion and HREE enrichment, while PAAS-normalized REE+ Y pattern of limestone is relatively flat; δCe values of dolostone range from 0.55 to 0.78 (average 0.63) and δCe value of limestoe range from 0.80 to 0.88 (average 0.84); The concentrations of redox sensitive elements (U, Mo, V) are very low, and the V/V+Ni ratios range from 0.04 to 0.45. In each cycle, both Cu and Zn content in dolostone is higher than limestone, and type A cycles overall have higher Cu and Zn contents than type B cycles. [Conclusions] Based on lithology and sedimentary components, the Buqu Formation of GK-1 Well was likely deposited in shallow marine grain-shoal settings, with sea water becoming restricted from type A cycles to type B cycles. Based on the comprehensive petrological and geochemical analysis, selective dissolution herein is interpreted to be produced by early marine diagenesis rather than meteoric diagenesis or deep burial. During early marine diagenesis, aragonite may be selectively dissolved by undersaturated pore fluids via organic matter decomposition. In the sedimentary cycles, the differential development of selective dissolution is probably controlled by aragonite content, paleoproductivity, and early marine diagenetic redox boundary: i) in a single cycle, dolostone interval is characterized by higher paleoproductivity and more oxic pore water than limestone interval during early diagenesis, favoring the production of undersaturated fluids and the formation of selective dissolution pores; ii) in comparison between type A and type B cycles, type A cycles have higher content of aragonite, higher paleoproductivity and lower early marine diagenetic redox boundary, therefore resulting in a better development of selective dissolution.
[Objective] Selective dissolution is common in marine carbonates, and its origin is typically to be related to meteoric fluids, while other possible origins lack further discussion. [Methods] In this study, the origin of marine selective dissolution of Buqu Formation of well GK-1 in the south Qiangtang basin is investigated based on petrography, stable carbon and oxygen isotopes, and elemental geochemistry. [Results] Eight sedimentary cycles (C1 to C8 from bottom to top) were recognized from the studied Buqu Formation, each cycle with limestone in the lower part and dolostone in the upper part. These eight cycles can be divided into two types (A and B) according to different carbonate components. The limestone in type A cycle (C1-C4) is dominated by bioclastic packstone and grainstone, while in type B cycle (C5-C8) is dominated by bioclastic wackstone and packstone. Upwards from type A cycle to the type B cycle, the content of aragonite fossils (gastropods and bivalves) in the limestone decreases and the content of peloids increases. The dolomite in both type A and type B cycles is crystalline dolomite with ooid ghosts showing selective dissolution pores. Importantly, the overall percentage of selective dissolution pores in type A cycles is significantly higher than that in type B cycles. In terms of geochemistry, the carbon and oxygen isotopes of dolostone are relatively higher compared to those of limestone in each cycle. Rare earth elements and yttrium concentrations (0.44~7.25 ppm) of dolostone and limestone are extremely low and the Y/Ho ratios (35.63~75.55) are basically within the range of modern seawater. Dolostone exhibits a seawater-like PAAS-normalized REE+ Y pattern, showing a left leaning style with relatively LREE depletion and HREE enrichment, while PAAS-normalized REE+ Y pattern of limestone is relatively flat; δCe values of dolostone range from 0.55 to 0.78 (average 0.63) and δCe value of limestoe range from 0.80 to 0.88 (average 0.84); The concentrations of redox sensitive elements (U, Mo, V) are very low, and the V/V+Ni ratios range from 0.04 to 0.45. In each cycle, both Cu and Zn content in dolostone is higher than limestone, and type A cycles overall have higher Cu and Zn contents than type B cycles. [Conclusions] Based on lithology and sedimentary components, the Buqu Formation of GK-1 Well was likely deposited in shallow marine grain-shoal settings, with sea water becoming restricted from type A cycles to type B cycles. Based on the comprehensive petrological and geochemical analysis, selective dissolution herein is interpreted to be produced by early marine diagenesis rather than meteoric diagenesis or deep burial. During early marine diagenesis, aragonite may be selectively dissolved by undersaturated pore fluids via organic matter decomposition. In the sedimentary cycles, the differential development of selective dissolution is probably controlled by aragonite content, paleoproductivity, and early marine diagenetic redox boundary: i) in a single cycle, dolostone interval is characterized by higher paleoproductivity and more oxic pore water than limestone interval during early diagenesis, favoring the production of undersaturated fluids and the formation of selective dissolution pores; ii) in comparison between type A and type B cycles, type A cycles have higher content of aragonite, higher paleoproductivity and lower early marine diagenetic redox boundary, therefore resulting in a better development of selective dissolution.
Abstract:
[Objective]The lacustrine fine-grained sedimentary rock mixed with clay, felsic, carbonate and analcite minerals develops in the fourth member of Shahejie Formation of the Leijia area in the western sag of the Liaohe Depression in the Bohai Bay Basin and is the main carrier for the occurrence of oil and gas. Due to the complex composition and rapid lateral changes of mixed fine-grained rocks, the reservoirs are highly heterogeneous, which brings certain difficulties to the prediction of high-quality reservoirs. [Methods] Taking the Lei 15 well, the Lei 14 well and the Lei 61 well in the Leijia area of the western sag as an example, based on time series analysis method, high-precision carbonate U-Pb dating and natural gamma logging data, the mixed fine-grained rocks of the the fourth member of Shahejie Formation were analyzed by cyclostratigraphy. [Results and Discussions] 1) The optimal sedimentation rates of Well Lei 15, Well Lei 14 and Well Lei 61 were estimated by COCO, and it was found that the optimal sedimentation rates increased sequentially and were 10.57 cm/kyr, 11.4 cm/kyr and 13.93 cm respectively; Perform spectrum analysis on the paleoclimate proxy indicator (GR) and compare it with the data spectrum analysis results of the standard ETP curve (eccentricity, slope, precession composite curve), identify astronomical cycle signals in mixed fine-grained rocks in Wells Lei 15, Lei 14 and Lei 61, And use the 405 kyr long eccentricity for astronomical tuning, and use the age 43.4±1.7 Ma at 2766.61m in Well Lei 14 as the anchor point to establish an absolute astronomical time scale. [Conclusions] By conducting cyclostratigraphic research on the fourth member of Shahejie Formation in the Leijia area, astronomical cycle signals in the fourth member of Shahejie Formation can be effectively identified. This method quantitatively establishes a fine stratigraphic division and comparison framework with time attributes, which plays an important role in guiding further oil and gas exploration in the area and broadens the applicability of cycle stratigraphy in the Bohai Bay Basin.
[Objective]The lacustrine fine-grained sedimentary rock mixed with clay, felsic, carbonate and analcite minerals develops in the fourth member of Shahejie Formation of the Leijia area in the western sag of the Liaohe Depression in the Bohai Bay Basin and is the main carrier for the occurrence of oil and gas. Due to the complex composition and rapid lateral changes of mixed fine-grained rocks, the reservoirs are highly heterogeneous, which brings certain difficulties to the prediction of high-quality reservoirs. [Methods] Taking the Lei 15 well, the Lei 14 well and the Lei 61 well in the Leijia area of the western sag as an example, based on time series analysis method, high-precision carbonate U-Pb dating and natural gamma logging data, the mixed fine-grained rocks of the the fourth member of Shahejie Formation were analyzed by cyclostratigraphy. [Results and Discussions] 1) The optimal sedimentation rates of Well Lei 15, Well Lei 14 and Well Lei 61 were estimated by COCO, and it was found that the optimal sedimentation rates increased sequentially and were 10.57 cm/kyr, 11.4 cm/kyr and 13.93 cm respectively; Perform spectrum analysis on the paleoclimate proxy indicator (GR) and compare it with the data spectrum analysis results of the standard ETP curve (eccentricity, slope, precession composite curve), identify astronomical cycle signals in mixed fine-grained rocks in Wells Lei 15, Lei 14 and Lei 61, And use the 405 kyr long eccentricity for astronomical tuning, and use the age 43.4±1.7 Ma at 2766.61m in Well Lei 14 as the anchor point to establish an absolute astronomical time scale. [Conclusions] By conducting cyclostratigraphic research on the fourth member of Shahejie Formation in the Leijia area, astronomical cycle signals in the fourth member of Shahejie Formation can be effectively identified. This method quantitatively establishes a fine stratigraphic division and comparison framework with time attributes, which plays an important role in guiding further oil and gas exploration in the area and broadens the applicability of cycle stratigraphy in the Bohai Bay Basin.
Abstract:
[Objective] The Shaximiao Formation in the Middle Jurassic of the Sichuan Basin is an important tight gas exploration and development layer. Currently, the exploration and development of the first Member of the Shaximiao Formation is in its initial stage, with weak overall research, especially the lack of a systematic understanding of the controlling role of high-quality sand body distribution. [Methods] Based on petrological analysis and geochemistry, this article studied the provenance of the first Member of the Shaximiao Formation in the central Sichuan region. [Results] The results are as follows: (1) The sandstone of the first Member of the Shaximiao Formation in the central Sichuan region is mainly composed of feldspar litharenite and lithic feldspar sandstone. Igneous rock lithic fragments are mainly andesite, which are less developed in the underlying formations but commonly found in the northeast and southeast of Sichuan. (2) The dominant heavy minerals in the first Member of the Shaximiao Formation in the central Sichuan region are garnet and epidote. Epidote is rare in the underlying formations but highly developed in the northeast and southeast of Sichuan. (3) Discrimination diagrams, including F1-F2, SiO2-TiO2, La/Th-Hf, and Co/Th-La/Sc, show that the provenance of the first Member of the Shaximiao Formation in the central Sichuan region is mainly felsic volcanic rocks with a small amount of sedimentary rocks. [Conclusion] Based on the above analysis, the sandstone provenance of the first Member of the Shaximiao Formation in the central Sichuan Basin is mainly derived from the Daba Mountains in the northeast of Sichuan Basin, while other directions around the basin have limited provenance supply. These results provide strong support for the division of favorable areas for tight gas in the Sichuan Basin and for exploration and development activities.
[Objective] The Shaximiao Formation in the Middle Jurassic of the Sichuan Basin is an important tight gas exploration and development layer. Currently, the exploration and development of the first Member of the Shaximiao Formation is in its initial stage, with weak overall research, especially the lack of a systematic understanding of the controlling role of high-quality sand body distribution. [Methods] Based on petrological analysis and geochemistry, this article studied the provenance of the first Member of the Shaximiao Formation in the central Sichuan region. [Results] The results are as follows: (1) The sandstone of the first Member of the Shaximiao Formation in the central Sichuan region is mainly composed of feldspar litharenite and lithic feldspar sandstone. Igneous rock lithic fragments are mainly andesite, which are less developed in the underlying formations but commonly found in the northeast and southeast of Sichuan. (2) The dominant heavy minerals in the first Member of the Shaximiao Formation in the central Sichuan region are garnet and epidote. Epidote is rare in the underlying formations but highly developed in the northeast and southeast of Sichuan. (3) Discrimination diagrams, including F1-F2, SiO2-TiO2, La/Th-Hf, and Co/Th-La/Sc, show that the provenance of the first Member of the Shaximiao Formation in the central Sichuan region is mainly felsic volcanic rocks with a small amount of sedimentary rocks. [Conclusion] Based on the above analysis, the sandstone provenance of the first Member of the Shaximiao Formation in the central Sichuan Basin is mainly derived from the Daba Mountains in the northeast of Sichuan Basin, while other directions around the basin have limited provenance supply. These results provide strong support for the division of favorable areas for tight gas in the Sichuan Basin and for exploration and development activities.
Abstract:
Calcite containing hydrocarbon and asphalt inclusions developed in the Ordovician Majiagou Formation subsalt carbonate reservoir in the Wusenqi area of Ordos Basin, which is an important indicator of fluid source and hydrocarbon accumulation process. Through core observation, rock thin section identification, cathodoluminescence, rare earth elements, C, O, Sr isotopes, microfluorescence and laser Raman spectroscopy analysis, the calcite development stages were divided, the sources of vein forming fluids were analyzed, and the fluid inclusions were studied to reveal the significance of hydrocarbon activities on oil and gas accumulation. The results show that 4 stages of calcite veins (C1, C2, C3, C4) are developed in the carbonate reservoir in Wushenqi area, and the characteristics and sources of secondary calcite veins are different in different periods. The C1 and C4 vein forming fluids are derived from the dissolved surrounding rocks, and their isotopes of strontium carbon and oxygen are consistent with those of Ordovician seawater, and the rare earth partition pattern is characteristic of seawater. C2 calcite veins have very negative carbon isotope values, high 87Sr/86Sr values and total rare earth content, positive Eu anomaly, and the fluid comes from external fluids. C3 calcite has a negative carbon isotope value, higher 87Sr/86Sr values and total rare earth content, and the fluid is derived from external fluids. In addition, asphaltic inclusions developed on calcite veins of C2 and C3 stages, indicating that oil and gas cracked after entering the reservoir. The geochemical characteristics of calcite veins in the study area provide a theoretical basis for oil and gas accumulation in Ordos Basin and other basins.
Calcite containing hydrocarbon and asphalt inclusions developed in the Ordovician Majiagou Formation subsalt carbonate reservoir in the Wusenqi area of Ordos Basin, which is an important indicator of fluid source and hydrocarbon accumulation process. Through core observation, rock thin section identification, cathodoluminescence, rare earth elements, C, O, Sr isotopes, microfluorescence and laser Raman spectroscopy analysis, the calcite development stages were divided, the sources of vein forming fluids were analyzed, and the fluid inclusions were studied to reveal the significance of hydrocarbon activities on oil and gas accumulation. The results show that 4 stages of calcite veins (C1, C2, C3, C4) are developed in the carbonate reservoir in Wushenqi area, and the characteristics and sources of secondary calcite veins are different in different periods. The C1 and C4 vein forming fluids are derived from the dissolved surrounding rocks, and their isotopes of strontium carbon and oxygen are consistent with those of Ordovician seawater, and the rare earth partition pattern is characteristic of seawater. C2 calcite veins have very negative carbon isotope values, high 87Sr/86Sr values and total rare earth content, positive Eu anomaly, and the fluid comes from external fluids. C3 calcite has a negative carbon isotope value, higher 87Sr/86Sr values and total rare earth content, and the fluid is derived from external fluids. In addition, asphaltic inclusions developed on calcite veins of C2 and C3 stages, indicating that oil and gas cracked after entering the reservoir. The geochemical characteristics of calcite veins in the study area provide a theoretical basis for oil and gas accumulation in Ordos Basin and other basins.
Abstract:
[Objective] The Dianqianbei depression is not only an important exploration area and producing area of marine shale gas in southern China, but also an important large-super large MVT type lead-zinc metallogenic area associated with key metals in China. Asphalt or ancient reservoirs with high Pb and Zn contents are constantly found in lead-zinc deposits. In this paper, the geochemical characteristics of elements in black shale kerogen are used to study the material contribution of mineralization and the sedimentary environment of black shale. [Methods] The black shale outcrops in the Dashiban, Liangfengao and Maoba areas in the eastern part of the northern Yunnan-Guizhou depression were taken as the research objects. The kerogen in the black shale was pretreated by microwave digestion, and the trace elements in the black shale and kerogen were analyzed and tested in combination with petrographic and mineralographic observations. [Results] Three redox indicators (U/Th ,Ni/Co, V/Cr) in the kerogen of the Wufeng Formation-Longmaxi Formation showed that the Wufeng Formation was oxygen-poor-anoxic, and the Longmaxi Formation was oxygen-rich-oxygen-poor environment ; the ancient water depth calculated by Co element in the study area is 6.85 ~ 54.37 m. The paleoclimate reflected by Sr / Cu is warm and humid, and the Sr / Ba value is less than 0.5, which represents the sedimentary environment of brackish water. At the same time, in terms of paleoproductivity, Wufeng Formation is greater than Longmaxi Formation. The contents of Pb, Zn, Cd, Bi, Sb, V, Cr and Ni in the whole rock are higher than those in the kerogen, and the contents of Ag, Ge, U and Th in the kerogen are higher than those in the whole rock. The light rare earth elements in the whole rock and kerogen are relatively enriched, and the heavy rare earth elements are relatively depleted. The Eu and some Ce in the whole rock show weak negative anomalies. The kerogen shows strong Ce negative anomaly, Eu weak negative anomaly, and the total rare earth content is higher than that of the whole rock. [Conclusions] The Wufeng Formation-Longmaxi Formation in the study area is generally an oxygen-rich-oxygen-poor turbulent sedimentary environment, with a warm and humid climate of brackish water shallow shelf facies sedimentary characteristics. Trace elements in black shale kerogen can provide a basis for regional prospecting.
[Objective] The Dianqianbei depression is not only an important exploration area and producing area of marine shale gas in southern China, but also an important large-super large MVT type lead-zinc metallogenic area associated with key metals in China. Asphalt or ancient reservoirs with high Pb and Zn contents are constantly found in lead-zinc deposits. In this paper, the geochemical characteristics of elements in black shale kerogen are used to study the material contribution of mineralization and the sedimentary environment of black shale. [Methods] The black shale outcrops in the Dashiban, Liangfengao and Maoba areas in the eastern part of the northern Yunnan-Guizhou depression were taken as the research objects. The kerogen in the black shale was pretreated by microwave digestion, and the trace elements in the black shale and kerogen were analyzed and tested in combination with petrographic and mineralographic observations. [Results] Three redox indicators (U/Th ,Ni/Co, V/Cr) in the kerogen of the Wufeng Formation-Longmaxi Formation showed that the Wufeng Formation was oxygen-poor-anoxic, and the Longmaxi Formation was oxygen-rich-oxygen-poor environment ; the ancient water depth calculated by Co element in the study area is 6.85 ~ 54.37 m. The paleoclimate reflected by Sr / Cu is warm and humid, and the Sr / Ba value is less than 0.5, which represents the sedimentary environment of brackish water. At the same time, in terms of paleoproductivity, Wufeng Formation is greater than Longmaxi Formation. The contents of Pb, Zn, Cd, Bi, Sb, V, Cr and Ni in the whole rock are higher than those in the kerogen, and the contents of Ag, Ge, U and Th in the kerogen are higher than those in the whole rock. The light rare earth elements in the whole rock and kerogen are relatively enriched, and the heavy rare earth elements are relatively depleted. The Eu and some Ce in the whole rock show weak negative anomalies. The kerogen shows strong Ce negative anomaly, Eu weak negative anomaly, and the total rare earth content is higher than that of the whole rock. [Conclusions] The Wufeng Formation-Longmaxi Formation in the study area is generally an oxygen-rich-oxygen-poor turbulent sedimentary environment, with a warm and humid climate of brackish water shallow shelf facies sedimentary characteristics. Trace elements in black shale kerogen can provide a basis for regional prospecting.
Abstract:
Peperite is a kind of transitional rock formed by the syngenetic mixing of hot magmatic materials and wet and cold unconsolidated sediments, which has important paleoenvironmental implications. Based on outcrop geological survey and microscopic petrological analysis, typical peperites are recognized in Ediacaran basic volcanic rocks in northwestern Tarim Basin, which mainly include blocky peperites and fluidal peperites, and their host is purplish red sandy sediments. The peperites were mainly formed by the intrusion of magma into the water-rich unconsolidated sandy sediments or by the flow of magma on the surface of the water-rich unconsolidated sandy sediments. Among them, the thinner magmatic intrusion and the bottom of the surface flood basalt mainly formed the fluidal peperites, while the thicker magmatic intrusion developed the blocky peperites. It is concluded that the northern margin of the Tarim craton was still in an intraplate rift setting related to the breakup of the Rodinia supercontinent during the early Ediacaran, and the development of peperite indicates that the basalt eruption in this area was mainly in a littoral subaqueous sedimentary environment; with the end of volcanic eruption, the northern Tarim Craton transformed into a relatively stable passive continental margin basin or a cratonic basin during the late Ediacaran.
Peperite is a kind of transitional rock formed by the syngenetic mixing of hot magmatic materials and wet and cold unconsolidated sediments, which has important paleoenvironmental implications. Based on outcrop geological survey and microscopic petrological analysis, typical peperites are recognized in Ediacaran basic volcanic rocks in northwestern Tarim Basin, which mainly include blocky peperites and fluidal peperites, and their host is purplish red sandy sediments. The peperites were mainly formed by the intrusion of magma into the water-rich unconsolidated sandy sediments or by the flow of magma on the surface of the water-rich unconsolidated sandy sediments. Among them, the thinner magmatic intrusion and the bottom of the surface flood basalt mainly formed the fluidal peperites, while the thicker magmatic intrusion developed the blocky peperites. It is concluded that the northern margin of the Tarim craton was still in an intraplate rift setting related to the breakup of the Rodinia supercontinent during the early Ediacaran, and the development of peperite indicates that the basalt eruption in this area was mainly in a littoral subaqueous sedimentary environment; with the end of volcanic eruption, the northern Tarim Craton transformed into a relatively stable passive continental margin basin or a cratonic basin during the late Ediacaran.
Abstract:
Mangrove is an important coastal blue carbon ecosystem, which has a strong carbon sink function and has a profound impact on the global carbon cycle. In this study, the mangrove forest in Yanpu Bay was selected as the study area, and the high-resolution chronostratigraphic framework was established by 210Pb dating technology to analyze the sediment mass burial rate (SAR), organic carbon burial flux (OCAR) and potential sources of organic carbon. The results showed that the sedimentation rate of mangrove was about 2.2cm/a. The sediment was mainly silt and clay, the particle size was basically stable with depth, and there was a good correlation between excess 210Pb activity and depth, indicating that the sedimentary environment was relatively stable. The SAR values of the sediments ranged from 52.03~233.61g/(cm2·a), and the OCAR values ranged from 112.78~473.97g/(m2·a). The higher SAR values were conducive to the deposition and burial of organic carbon. Based on the distribution characteristics of stable carbon and nitrogen isotopes and the Bayesian mixing model (MixSIAR), it can be seen that sediment organic carbon was a mixed source of sea and land, in which the average contribution rate of mangrove litter was 59.70% and suspended organic particles (POM) is 25.68%. Therefore, mangrove areas and POM delivery are important factors affecting sediment organic carbon burial. At the same time, extreme weather, natural disasters, water conservancy projects and other factors further promote the complexity of organic carbon source changes.
Mangrove is an important coastal blue carbon ecosystem, which has a strong carbon sink function and has a profound impact on the global carbon cycle. In this study, the mangrove forest in Yanpu Bay was selected as the study area, and the high-resolution chronostratigraphic framework was established by 210Pb dating technology to analyze the sediment mass burial rate (SAR), organic carbon burial flux (OCAR) and potential sources of organic carbon. The results showed that the sedimentation rate of mangrove was about 2.2cm/a. The sediment was mainly silt and clay, the particle size was basically stable with depth, and there was a good correlation between excess 210Pb activity and depth, indicating that the sedimentary environment was relatively stable. The SAR values of the sediments ranged from 52.03~233.61g/(cm2·a), and the OCAR values ranged from 112.78~473.97g/(m2·a). The higher SAR values were conducive to the deposition and burial of organic carbon. Based on the distribution characteristics of stable carbon and nitrogen isotopes and the Bayesian mixing model (MixSIAR), it can be seen that sediment organic carbon was a mixed source of sea and land, in which the average contribution rate of mangrove litter was 59.70% and suspended organic particles (POM) is 25.68%. Therefore, mangrove areas and POM delivery are important factors affecting sediment organic carbon burial. At the same time, extreme weather, natural disasters, water conservancy projects and other factors further promote the complexity of organic carbon source changes.
Abstract:
【Objective】Significant breakthroughs have been made in the exploration of Jurassic continental shale oil in the Sichuan Basin. Due to the small grain size, rapid facies changes, and strong heterogeneity of continental mud shale facies, it is urgently necessary to systematically study the development rules of lithofacies and organic matter enrichment characteristics in the Dongyuemiao Member.【Methods】Taking the Dongyuemiao Member of the Ziliujing Formation in the eastern part of the Sichuan Basin as an example, based on core data, non-core lithofacies interpretation from well logging, and utilizing theory of cyclic stratigraphy, various methods such as data preprocessing, power spectral analysis, evolutionary spectral analysis, filtering of data, correlation coefficient analysis, and astronomical tuning were employed to establish a 4-5 level high frequency stratigraphic framework for the study area. Through the sedimentary response of astronomical cycles, the development rules of mud shale lithofacies and organic matter enrichment characteristics under high-frequency chronostratigraphic framework were discussed. 【Results】 ① The Dongyuemiao Member shows a good astronomical cycle signal,and the long eccentricity (405 ka), short eccentricity (128 ka), obliquity (43 ka), and precession (21 ka) astronomical cycles were extracted. There are four long eccentricity cycles and fifteen short eccentricity cycles. The long eccentricity cycle and short eccentricity cycle were used as the subdivision units of the fourth-order and fifth-order sequences, establishing a 4-5 level chronostratigraphic framework for the Dongyuemiao Member in the study area. ②Taking into account rock thins, X-ray diffraction whole-rock analysis, and well logging data, the principle of structure first is employed, with components and sedimentary structures as the primary basis The Dongyuemiao Member is divided into two lithofacies types: indigenous organic-rich laminated mudstone facies , exogenous shell-bearing mudstone and shell limestone facies and seven lithofacies types including laminated silty-rich argillaceous mudstone facies, massive silt-rich argillaceous mudstone facies, laminated mixed mudstone facies, laminated shell-bearing silty-rich argillaceous mudstone facies, laminated silt-bearing shell-rich argillaceous mudstone facies, laminated silt-bearing clay-rich shelly mudstone facies, massive argillaceous shell limestone facies, massive argillaceous shell limestone facies. ③ The coupling relationship between paleoclimate, mineral composition, and eccentricity revealed that during periods of high eccentricity and its maximum amplitude, the climate was humid and hot with significant seasonal variations. This led to the input of a large amount of fine-grained material and organic matter from the land and the development of indigenous organic-rich laminated mud shale facies. During periods of low eccentricity and its minimum amplitude, the climate was dry and cold with less input of terrigenous materials. The clay mineral and detrital mineral content were lower, and the lithofacies were dominated by exogenous shell-bearing mudstone facies, which affected the development of organic matter. The Dongyuemiao Member is mainly controlled by eccentricity cycles, and the deposition of lacustrine shelly mud shale is controlled by the climate changes driven by the 405 ka and 128 ka eccentricity cycles.【Conclusion】Long eccentricity is a key factor controlling the distribution of lithofacies and organic matter enrichment. It controls the ordered development of indigenous organic-rich laminated mud shale facies and exogenous shell-bearing mudstone and shell-bearing limestone facies. Short eccentricity has a limited impact on organic matter enrichment but significantly controls the lithofacies composition of exogenous shell-bearing mudstone.
【Objective】Significant breakthroughs have been made in the exploration of Jurassic continental shale oil in the Sichuan Basin. Due to the small grain size, rapid facies changes, and strong heterogeneity of continental mud shale facies, it is urgently necessary to systematically study the development rules of lithofacies and organic matter enrichment characteristics in the Dongyuemiao Member.【Methods】Taking the Dongyuemiao Member of the Ziliujing Formation in the eastern part of the Sichuan Basin as an example, based on core data, non-core lithofacies interpretation from well logging, and utilizing theory of cyclic stratigraphy, various methods such as data preprocessing, power spectral analysis, evolutionary spectral analysis, filtering of data, correlation coefficient analysis, and astronomical tuning were employed to establish a 4-5 level high frequency stratigraphic framework for the study area. Through the sedimentary response of astronomical cycles, the development rules of mud shale lithofacies and organic matter enrichment characteristics under high-frequency chronostratigraphic framework were discussed. 【Results】 ① The Dongyuemiao Member shows a good astronomical cycle signal,and the long eccentricity (405 ka), short eccentricity (128 ka), obliquity (43 ka), and precession (21 ka) astronomical cycles were extracted. There are four long eccentricity cycles and fifteen short eccentricity cycles. The long eccentricity cycle and short eccentricity cycle were used as the subdivision units of the fourth-order and fifth-order sequences, establishing a 4-5 level chronostratigraphic framework for the Dongyuemiao Member in the study area. ②Taking into account rock thins, X-ray diffraction whole-rock analysis, and well logging data, the principle of structure first is employed, with components and sedimentary structures as the primary basis The Dongyuemiao Member is divided into two lithofacies types: indigenous organic-rich laminated mudstone facies , exogenous shell-bearing mudstone and shell limestone facies and seven lithofacies types including laminated silty-rich argillaceous mudstone facies, massive silt-rich argillaceous mudstone facies, laminated mixed mudstone facies, laminated shell-bearing silty-rich argillaceous mudstone facies, laminated silt-bearing shell-rich argillaceous mudstone facies, laminated silt-bearing clay-rich shelly mudstone facies, massive argillaceous shell limestone facies, massive argillaceous shell limestone facies. ③ The coupling relationship between paleoclimate, mineral composition, and eccentricity revealed that during periods of high eccentricity and its maximum amplitude, the climate was humid and hot with significant seasonal variations. This led to the input of a large amount of fine-grained material and organic matter from the land and the development of indigenous organic-rich laminated mud shale facies. During periods of low eccentricity and its minimum amplitude, the climate was dry and cold with less input of terrigenous materials. The clay mineral and detrital mineral content were lower, and the lithofacies were dominated by exogenous shell-bearing mudstone facies, which affected the development of organic matter. The Dongyuemiao Member is mainly controlled by eccentricity cycles, and the deposition of lacustrine shelly mud shale is controlled by the climate changes driven by the 405 ka and 128 ka eccentricity cycles.【Conclusion】Long eccentricity is a key factor controlling the distribution of lithofacies and organic matter enrichment. It controls the ordered development of indigenous organic-rich laminated mud shale facies and exogenous shell-bearing mudstone and shell-bearing limestone facies. Short eccentricity has a limited impact on organic matter enrichment but significantly controls the lithofacies composition of exogenous shell-bearing mudstone.
Abstract:
Designing a reliable and rapid method for determining shale facies while scientifically constructing a framework for shale facies combination is of great significance for studying the vertical and horizontal changes of shale facies combinations. Accurately calculate the composition of shale minerals through methods such as X-ray diffraction analysis, lithology logging, multi mineral model, and Ipsom neural network, and use Python software to quickly divide the "three terminal element" lithofacies; Extracting high-frequency stratigraphic cycles as a framework for shale facies combination through time series analysis methods such as spectral analysis, optimal sedimentation rate estimation, and Gaussian filtering. The results show that there are 12 types of lithofacies developed in the strata, and the fifth order cycle is divided into five order sequences with good correspondence with vertical lithofacies changes. The fourth order cycle defines the fourth order sequence and divides the strata into eight 405kyr sedimentary lithofacies combinations (E1-E8). The Guanyinqiao Formation is used as a time anchor to calculate the starting and ending depths of each well lithofacies combination, and to build an isochronous ithofacies combination framework; Through comparative study of lithofacies combinations, it was found that the E1 to E4 lithofacies combinations at the bottom of the Longyi Formation have the characteristics of multiple types of lithofacies, rapid changes in vertical and horizontal lithofacies. The lithofacies types of the E5 to E8 lithofacies combinations are relatively simple, and the lateral changes are small; From the low point to the high point of the ancient structure, the E1 lithofacies combination shows a continuous decreasing trend of siliceous shale content, the E2-E4 lithofacies combination shows a significant decrease in mixed shale content, the E5-E8 lithofacies combination shows a decrease in siliceous shale content, and the siliceous/muddy mixed shale content significantly increases. Overall, the shale lithofacies combination framework built based on time series analysis methods, combined with new lithofacies judgment methods, can accurately describe the differences in stratigraphic lithofacies combinations in different regions during the same period, providing new ideas for quantitative analysis of shale lithofacies heterogeneity and its changing trends.
Designing a reliable and rapid method for determining shale facies while scientifically constructing a framework for shale facies combination is of great significance for studying the vertical and horizontal changes of shale facies combinations. Accurately calculate the composition of shale minerals through methods such as X-ray diffraction analysis, lithology logging, multi mineral model, and Ipsom neural network, and use Python software to quickly divide the "three terminal element" lithofacies; Extracting high-frequency stratigraphic cycles as a framework for shale facies combination through time series analysis methods such as spectral analysis, optimal sedimentation rate estimation, and Gaussian filtering. The results show that there are 12 types of lithofacies developed in the strata, and the fifth order cycle is divided into five order sequences with good correspondence with vertical lithofacies changes. The fourth order cycle defines the fourth order sequence and divides the strata into eight 405kyr sedimentary lithofacies combinations (E1-E8). The Guanyinqiao Formation is used as a time anchor to calculate the starting and ending depths of each well lithofacies combination, and to build an isochronous ithofacies combination framework; Through comparative study of lithofacies combinations, it was found that the E1 to E4 lithofacies combinations at the bottom of the Longyi Formation have the characteristics of multiple types of lithofacies, rapid changes in vertical and horizontal lithofacies. The lithofacies types of the E5 to E8 lithofacies combinations are relatively simple, and the lateral changes are small; From the low point to the high point of the ancient structure, the E1 lithofacies combination shows a continuous decreasing trend of siliceous shale content, the E2-E4 lithofacies combination shows a significant decrease in mixed shale content, the E5-E8 lithofacies combination shows a decrease in siliceous shale content, and the siliceous/muddy mixed shale content significantly increases. Overall, the shale lithofacies combination framework built based on time series analysis methods, combined with new lithofacies judgment methods, can accurately describe the differences in stratigraphic lithofacies combinations in different regions during the same period, providing new ideas for quantitative analysis of shale lithofacies heterogeneity and its changing trends.
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Abstract : In order to deeply evaluate the natural gas exploration prospect and predict the favorable exploration zone and exploration target of the shore-shallow lake beach-bar sand body of the Quaternary Qigequan Formation in Tainan area, eastern Qaidam Basin, based on the comprehensive analysis of core observation and drilling ( logging ) data, combined with the analysis results of rock thin section, grain size-standard deviation, grain size cumulative probability curve, environmental sensitive grain size composition and other parameters, the grain size variation characteristics and hydrodynamic significance of the shore-shallow lake beach-bar sand body of Qigequan Formation in this area were studied in detail. The results show that : First, The sedimentary period of Qigequan in Tainan area is the sedimentary environment of shore-shallow lake. The beach-bar sand body is developed, the rock is loose, the cementation is poor, easy to break, and the grain size is fine. The lithology is mainly lithic feldspar fine sandstone-siltstone, the composition maturity is medium-poor, and the sorting roundness is medium-poor. Second,During the sedimentary period of Qigequan Formation, the cumulative probability curve of grain size of beach-bar sand bodies in the study area showed six patterns, mainly one-hop one-suspension type ( 64.4% ), followed by multi-segment type ( 11.9% ), and the third is two-hop one-suspension type ( 7.5% ). Third, During the sedimentary period of Qigequan Formation, the grain size-standard deviation diagram of beach-bar sand bodies in the study area showed four patterns, mainly multimodal ( 50.0% ), followed by bimodal ( 33.4% ), unimodal and trimodal ( both 8.3% ). Combined with the cumulative curve of grain size probability and paleogeomorphology analysis, four environmentally sensitive grain size components were determined, which represented suspension transport, wave, coastal current and storm wave, respectively. Among them, wave was the main hydrodynamic type controlling the formation and development of beach-bar sand bodies, and the average value of environmentally sensitive grain size components accounted for 27.9% of the total grain size. Followed by the suspension effect ( average of 15.3% ) and the coastal current ( average of 11.4% ), the storm wave effect is the weakest ( average of 2.3% ). Forth, Through the study of the plane distribution characteristics of the percentage content of environmentally sensitive grain size components, it is shown that the influence of waves on the formation and development of beach-bar sand bodies is weakened from the core to the wing of the anticline, while the suspension effect is just the opposite, and the influence of coastal flow on beach-bar sand bodies is concentrated on the east and west wings of the anticline.
Abstract : In order to deeply evaluate the natural gas exploration prospect and predict the favorable exploration zone and exploration target of the shore-shallow lake beach-bar sand body of the Quaternary Qigequan Formation in Tainan area, eastern Qaidam Basin, based on the comprehensive analysis of core observation and drilling ( logging ) data, combined with the analysis results of rock thin section, grain size-standard deviation, grain size cumulative probability curve, environmental sensitive grain size composition and other parameters, the grain size variation characteristics and hydrodynamic significance of the shore-shallow lake beach-bar sand body of Qigequan Formation in this area were studied in detail. The results show that : First, The sedimentary period of Qigequan in Tainan area is the sedimentary environment of shore-shallow lake. The beach-bar sand body is developed, the rock is loose, the cementation is poor, easy to break, and the grain size is fine. The lithology is mainly lithic feldspar fine sandstone-siltstone, the composition maturity is medium-poor, and the sorting roundness is medium-poor. Second,During the sedimentary period of Qigequan Formation, the cumulative probability curve of grain size of beach-bar sand bodies in the study area showed six patterns, mainly one-hop one-suspension type ( 64.4% ), followed by multi-segment type ( 11.9% ), and the third is two-hop one-suspension type ( 7.5% ). Third, During the sedimentary period of Qigequan Formation, the grain size-standard deviation diagram of beach-bar sand bodies in the study area showed four patterns, mainly multimodal ( 50.0% ), followed by bimodal ( 33.4% ), unimodal and trimodal ( both 8.3% ). Combined with the cumulative curve of grain size probability and paleogeomorphology analysis, four environmentally sensitive grain size components were determined, which represented suspension transport, wave, coastal current and storm wave, respectively. Among them, wave was the main hydrodynamic type controlling the formation and development of beach-bar sand bodies, and the average value of environmentally sensitive grain size components accounted for 27.9% of the total grain size. Followed by the suspension effect ( average of 15.3% ) and the coastal current ( average of 11.4% ), the storm wave effect is the weakest ( average of 2.3% ). Forth, Through the study of the plane distribution characteristics of the percentage content of environmentally sensitive grain size components, it is shown that the influence of waves on the formation and development of beach-bar sand bodies is weakened from the core to the wing of the anticline, while the suspension effect is just the opposite, and the influence of coastal flow on beach-bar sand bodies is concentrated on the east and west wings of the anticline.
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To investigate the degradation characteristics of n-hexadecane, a major component of petroleum, by microorganisms isolated from petroleum-contaminated soil in the Changqing oilfield, we employed petroleum-contaminated soil as the source of bacteria. Our objectives were to isolate strains with highly efficient n-hexadecane degradation capabilities, implement a salinization approach to achieve salinity-resistant degradation, and elucidate the kinetics and associated metabolic mechanisms of degradation. Through morphological characterization, Gram staining, biochemical and physicochemical tests, as well as 16S rDNA sequence analysis, we identified the isolated strain as Acinetobacter sp.5-5. The optimal degradation conditions for Acinetobacter sp.5-5 were determined through a resistance experiment spanning 14 days. It was found that, under specific conditions of n-hexadecane concentration (0.5% (V/V)), salinity (0.5%), and pH (7.0), the petroleum hydrocarbon-degrading bacteria achieved a remarkable total degradation of n-hexadecane, reaching 99.24%, with rapid degradation completed within two days (82.13%). Subsequently, the kinetics of n-hexadecane degradation were explored using zero-, quasi-primary, and quasi-secondary kinetic models. The results revealed that the quasi-primary model provided the best fit for describing the degradation process of n-hexadecane. Furthermore, in conjunction with the analysis of culture solution pH and degradation product profiles, our preliminary assessment of the n-hexadecane degradation pathway within this microbial degradation system indicated a process involving chain cleavage and acid production. This study underscores the high degradation potential of petroleum hydrocarbon-degrading bacteria, including their resilience to saline and alkaline conditions, particularly in the context of n-hexadecane. These findings hold promise for their widespread application in the remediation of salinized petroleum-contaminated soils.
To investigate the degradation characteristics of n-hexadecane, a major component of petroleum, by microorganisms isolated from petroleum-contaminated soil in the Changqing oilfield, we employed petroleum-contaminated soil as the source of bacteria. Our objectives were to isolate strains with highly efficient n-hexadecane degradation capabilities, implement a salinization approach to achieve salinity-resistant degradation, and elucidate the kinetics and associated metabolic mechanisms of degradation. Through morphological characterization, Gram staining, biochemical and physicochemical tests, as well as 16S rDNA sequence analysis, we identified the isolated strain as Acinetobacter sp.5-5. The optimal degradation conditions for Acinetobacter sp.5-5 were determined through a resistance experiment spanning 14 days. It was found that, under specific conditions of n-hexadecane concentration (0.5% (V/V)), salinity (0.5%), and pH (7.0), the petroleum hydrocarbon-degrading bacteria achieved a remarkable total degradation of n-hexadecane, reaching 99.24%, with rapid degradation completed within two days (82.13%). Subsequently, the kinetics of n-hexadecane degradation were explored using zero-, quasi-primary, and quasi-secondary kinetic models. The results revealed that the quasi-primary model provided the best fit for describing the degradation process of n-hexadecane. Furthermore, in conjunction with the analysis of culture solution pH and degradation product profiles, our preliminary assessment of the n-hexadecane degradation pathway within this microbial degradation system indicated a process involving chain cleavage and acid production. This study underscores the high degradation potential of petroleum hydrocarbon-degrading bacteria, including their resilience to saline and alkaline conditions, particularly in the context of n-hexadecane. These findings hold promise for their widespread application in the remediation of salinized petroleum-contaminated soils.
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[Objective] Recently, the shale gas exploration of the Lower Cambrian Qiongzhusi Formation in the Sichuan Basin marked a significant breakthrough, which has aroused widespread attention towards the redox conditions and the organic matter enrichment mechanisms of the Qiongzhusi Formation during its sedimentary period. Redox conditions of water column play a pivotal role in controlling the enrichment of organic matter. The particle sizes and distribution of framboidal pyrites serve as powerful redox indicators. These proxies, when combined with relevant geochemical data, enable the reconstruction of the ancient oceanic redox environment. Furthermore, the assemblage of pyrite morphological characteristics may correspond to changes in redox conditions. However, a detailed comparison between the pyrite morphological characteristics and redox conditions revealed by other geochemical markers remains limited. [Methods] This study focuses on the black shale of the Lower Cambrian Qiongzhusi Formation from well W207 in the Sichuan Basin. We conducted a comprehensive analysis of the particle sizes and distribution patterns of the framboidal pyrites. Using this method, in combination with total organic carbon (TOC), total sulfur (TS), pyrite content and previously published iron speciation data, we aimed to reconstruct the paleo-marine redox environment of the Qiongzhusi Formation during its sedimentary period. On this basis, the relationship between the assemblage of pyrite morphological characteristics and redox condition changes is discussed. [Results and Discussions] The redox environmental evolution of the Qiongzhusi Formation can be divided into three stages, i.e., strongly euxinic, intermittently euxinic and dysoxic from the bottom to the top. The morphology of pyrite is abundant, mainly framboidal pyrites, accompanied by a few pyrite microcrystals and euhedral pyrites. The framboidal pyrites are generally small in size, ranging from 2.2 to 18.4 μm with an average value of 6.39 ± 1.7 μm. More than 80% of the particle sizes are in the range of 3 – 8 μm, reflecting that framboidal pyrites were mainly formed in the water bodies of the synsedimentary period. In addition, a robust positive correlation between pyrite content and TOC and TS contents was observed. Pyrite morphology varies in different redox conditions. Specifically, in euxinic environment, the pyrite content is notably high, mainly contributed by abundant framboidal pyrites. In this setting, spherulitic microcrystals are dominant, while pyrite microcrystals and well-defined euhedral pyrites with clear edges are rare. As the redox environment gradually shifted to a more oxidized state, there was a decline in both the pyrite content and the quantity of framboidal pyrites. Concurrently, the microcrystals of the framboidal pyrites evolved from octahedral to cubic forms. At this stage, the pyrite microcrystals and euhedral pyrites both increase in quantity, with the former often exhibiting aggregates and the latter featuring irregular edges. [Conclusions] In conclusion, the observed changes in redox conditions during the sedimentation of the Qiongzhusi Formation reflect a gradual oxidation process in the inner shelf areas of South China. This aligns with the rise in atmospheric oxygen level during the early Cambrian. Notably, sedimentary pyrite displays distinct variations in the distribution of particle sizes and the assemblage of pyrite morphological characteristics as a function of redox conditions. These differences can serve as valuable supplementary indicators for assessing redox conditions in subsequent studies.
[Objective] Recently, the shale gas exploration of the Lower Cambrian Qiongzhusi Formation in the Sichuan Basin marked a significant breakthrough, which has aroused widespread attention towards the redox conditions and the organic matter enrichment mechanisms of the Qiongzhusi Formation during its sedimentary period. Redox conditions of water column play a pivotal role in controlling the enrichment of organic matter. The particle sizes and distribution of framboidal pyrites serve as powerful redox indicators. These proxies, when combined with relevant geochemical data, enable the reconstruction of the ancient oceanic redox environment. Furthermore, the assemblage of pyrite morphological characteristics may correspond to changes in redox conditions. However, a detailed comparison between the pyrite morphological characteristics and redox conditions revealed by other geochemical markers remains limited. [Methods] This study focuses on the black shale of the Lower Cambrian Qiongzhusi Formation from well W207 in the Sichuan Basin. We conducted a comprehensive analysis of the particle sizes and distribution patterns of the framboidal pyrites. Using this method, in combination with total organic carbon (TOC), total sulfur (TS), pyrite content and previously published iron speciation data, we aimed to reconstruct the paleo-marine redox environment of the Qiongzhusi Formation during its sedimentary period. On this basis, the relationship between the assemblage of pyrite morphological characteristics and redox condition changes is discussed. [Results and Discussions] The redox environmental evolution of the Qiongzhusi Formation can be divided into three stages, i.e., strongly euxinic, intermittently euxinic and dysoxic from the bottom to the top. The morphology of pyrite is abundant, mainly framboidal pyrites, accompanied by a few pyrite microcrystals and euhedral pyrites. The framboidal pyrites are generally small in size, ranging from 2.2 to 18.4 μm with an average value of 6.39 ± 1.7 μm. More than 80% of the particle sizes are in the range of 3 – 8 μm, reflecting that framboidal pyrites were mainly formed in the water bodies of the synsedimentary period. In addition, a robust positive correlation between pyrite content and TOC and TS contents was observed. Pyrite morphology varies in different redox conditions. Specifically, in euxinic environment, the pyrite content is notably high, mainly contributed by abundant framboidal pyrites. In this setting, spherulitic microcrystals are dominant, while pyrite microcrystals and well-defined euhedral pyrites with clear edges are rare. As the redox environment gradually shifted to a more oxidized state, there was a decline in both the pyrite content and the quantity of framboidal pyrites. Concurrently, the microcrystals of the framboidal pyrites evolved from octahedral to cubic forms. At this stage, the pyrite microcrystals and euhedral pyrites both increase in quantity, with the former often exhibiting aggregates and the latter featuring irregular edges. [Conclusions] In conclusion, the observed changes in redox conditions during the sedimentation of the Qiongzhusi Formation reflect a gradual oxidation process in the inner shelf areas of South China. This aligns with the rise in atmospheric oxygen level during the early Cambrian. Notably, sedimentary pyrite displays distinct variations in the distribution of particle sizes and the assemblage of pyrite morphological characteristics as a function of redox conditions. These differences can serve as valuable supplementary indicators for assessing redox conditions in subsequent studies.
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Abstract: [Objective]Currently, research on the Early Jurassic Toarcian Oceanic Anoxic Event (T-OAE; ~183 Ma) in the Ordos Basin mainly focuses on paleoclimate conditions, sedimentary environment evolution, and biodiversity changes, while the mechanisms of sulfur cycling during the T-OAE period in lakes remain unclear.[Methods]In order to further elucidate the sulfur cycling mechanism, Petrology and Geochemistry analyses were conducted on mudstone and black shale samples from the Anya section. The mechanisms of sulfur isotope fractionation during the T-OAE period were explored using major and trace elements and pyrite sulfur isotopes (δ34Spy).[Results and discussions]The pyrite in the Anya section samples mainly exists in the form of tetrahedral crystals, forming framboidal pyrite. The δ34Spy values of the samples exhibit anomalously positive values (ranging from 2.7 to 14.1‰, with an average of 8.3‰). Based on the variations in δ34Spy and total organic carbon (TOC) in conjunction with geochemical indicators (δ13C, TS, Corg/P, (La/Th)N), the evolution of the lake sedimentary environment during the T-OAE period was divided into four stages (high organic matter stages I and II, low organic matter stages I and II). [Conclusions] The δ34Spy values during the T-OAE period in the Anya section of the Ordos Basin coincide with atmospheric precipitation and surface runoff, indicating that the main source of sulfur in the lake is sulfate in the water mass. The sulfur isotopes of the samples are mainly controlled by the redox conditions of the lake bottom water and organic matter, and are independent of sedimentation rate and sulfate concentration. When the dissolved oxygen in the basin bottom water is low and the organic matter content is high, dissolved oxygen infiltrates into the sediment, activating anaerobic oxidants and promoting the reoxidation of H2S, resulting in positive δ34Spy values through Rayleigh fractionation. When the bottom water environment of the lake is oxygen-rich and the organic matter content is low, dissolved oxygen infiltrates into sediments, activating anaerobic oxidants and promoting H2S reoxidation, leading to a positive δ34Spy shift through the Rayleigh fractionation model. When the bottom water environment of the lake is oxygen-deficient and the organic matter content is high, the activity of sulfate-reducing bacteria is enhanced, promoting the MSR reaction and preferentially incorporating 32S, resulting in a negative δ34Spy shift. The sulfur cycle during the T-OAE period in the Anya section is mainly controlled by local/regional sedimentary environments, but the sulfur cycle is also influenced by global warming and intensified hydrological circulation during the T-OAE period
Abstract: [Objective]Currently, research on the Early Jurassic Toarcian Oceanic Anoxic Event (T-OAE; ~183 Ma) in the Ordos Basin mainly focuses on paleoclimate conditions, sedimentary environment evolution, and biodiversity changes, while the mechanisms of sulfur cycling during the T-OAE period in lakes remain unclear.[Methods]In order to further elucidate the sulfur cycling mechanism, Petrology and Geochemistry analyses were conducted on mudstone and black shale samples from the Anya section. The mechanisms of sulfur isotope fractionation during the T-OAE period were explored using major and trace elements and pyrite sulfur isotopes (δ34Spy).[Results and discussions]The pyrite in the Anya section samples mainly exists in the form of tetrahedral crystals, forming framboidal pyrite. The δ34Spy values of the samples exhibit anomalously positive values (ranging from 2.7 to 14.1‰, with an average of 8.3‰). Based on the variations in δ34Spy and total organic carbon (TOC) in conjunction with geochemical indicators (δ13C, TS, Corg/P, (La/Th)N), the evolution of the lake sedimentary environment during the T-OAE period was divided into four stages (high organic matter stages I and II, low organic matter stages I and II). [Conclusions] The δ34Spy values during the T-OAE period in the Anya section of the Ordos Basin coincide with atmospheric precipitation and surface runoff, indicating that the main source of sulfur in the lake is sulfate in the water mass. The sulfur isotopes of the samples are mainly controlled by the redox conditions of the lake bottom water and organic matter, and are independent of sedimentation rate and sulfate concentration. When the dissolved oxygen in the basin bottom water is low and the organic matter content is high, dissolved oxygen infiltrates into the sediment, activating anaerobic oxidants and promoting the reoxidation of H2S, resulting in positive δ34Spy values through Rayleigh fractionation. When the bottom water environment of the lake is oxygen-rich and the organic matter content is low, dissolved oxygen infiltrates into sediments, activating anaerobic oxidants and promoting H2S reoxidation, leading to a positive δ34Spy shift through the Rayleigh fractionation model. When the bottom water environment of the lake is oxygen-deficient and the organic matter content is high, the activity of sulfate-reducing bacteria is enhanced, promoting the MSR reaction and preferentially incorporating 32S, resulting in a negative δ34Spy shift. The sulfur cycle during the T-OAE period in the Anya section is mainly controlled by local/regional sedimentary environments, but the sulfur cycle is also influenced by global warming and intensified hydrological circulation during the T-OAE period
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Abstract: Through detailed field investigation in the Zoige Basin, complete stratigraphic profile of sedimentary sequence was found and systematically sampled on the high platform north of the hydrological station at the northern end of the old bridge of the Yellow River in Maqu County at the front of the glacial fans and alluvial fans. Through grain size analysis and Optically Stimulated Luminescence (OSL) dating, the sedimentary environment and surface process changes since the last deglaciation in Zoige Basin were studied. The results showed that during the last glacial before 14.5ka, the ice meltwater and mountain flood process in the Warihe River in the eastern end of the Jishi Mountain were active and accumulation rapidly in the foothill, forming a thick glacial- alluvial fan sand and gravel layer. During the B?lling-Aller?d warm period of 14.7-11.7 ka, the glaciers melted, and the depression in the front of the glacial fans and alluvial fans layer formed a muddy swamp environment with the accumulation of gray-green sandy sediments. However, the climate changed abruptly and worsened during the Younger Dryas period, the upper part of the gray-green bog soil layer was folded and deformed due to surface freeze-thaw action.In the early Holocene (11.7-8.5ka), the prevaling aeolian activities made the shallow depression in this area accumulate to form the interlayer of aeolian sand and mud soil. During the warm and humid period of 8.5-3.1 ka, the palaeosol of swamp meadow black soil was formed in this area. In the late Holocene since 3.1 ka BP, the climate was relatively dry, and the sandstorm deposits were transformed into subalpine meadow paleosols. The results are of great significance to reveal the response of surface processes to environmental changes since the last deglaciation in the Zoige Basin, and to further understand the environmental changes and surface processes in the Tibetan Plateau for global changes.
Abstract: Through detailed field investigation in the Zoige Basin, complete stratigraphic profile of sedimentary sequence was found and systematically sampled on the high platform north of the hydrological station at the northern end of the old bridge of the Yellow River in Maqu County at the front of the glacial fans and alluvial fans. Through grain size analysis and Optically Stimulated Luminescence (OSL) dating, the sedimentary environment and surface process changes since the last deglaciation in Zoige Basin were studied. The results showed that during the last glacial before 14.5ka, the ice meltwater and mountain flood process in the Warihe River in the eastern end of the Jishi Mountain were active and accumulation rapidly in the foothill, forming a thick glacial- alluvial fan sand and gravel layer. During the B?lling-Aller?d warm period of 14.7-11.7 ka, the glaciers melted, and the depression in the front of the glacial fans and alluvial fans layer formed a muddy swamp environment with the accumulation of gray-green sandy sediments. However, the climate changed abruptly and worsened during the Younger Dryas period, the upper part of the gray-green bog soil layer was folded and deformed due to surface freeze-thaw action.In the early Holocene (11.7-8.5ka), the prevaling aeolian activities made the shallow depression in this area accumulate to form the interlayer of aeolian sand and mud soil. During the warm and humid period of 8.5-3.1 ka, the palaeosol of swamp meadow black soil was formed in this area. In the late Holocene since 3.1 ka BP, the climate was relatively dry, and the sandstorm deposits were transformed into subalpine meadow paleosols. The results are of great significance to reveal the response of surface processes to environmental changes since the last deglaciation in the Zoige Basin, and to further understand the environmental changes and surface processes in the Tibetan Plateau for global changes.
Abstract:
[Objective] The second member of the Permian Lucaogou Formation (P2l2) is the main source rock in the Malang Sag of the Santanghu Basin, with high abundance of β-carotane, but its content shows great differences in the section. In order to further clarify the longitudinal variation of β-carotane in P2l2, and then to explore the main controlling factors of its enrichment and its distribution on the plane. [Methods] In this study, organic geochemical analysis was carried out and the source rocks investigated were divided into groups I, II and III from bottom to top according to the β-carotane index. The β-carotane index was relatively low in group I, and gradually increased from bottom to top in group II, while the β-carotane index in group III fluctuated greatly. [Results and Discussions] The results show that the relative content of β-carotane is an effective index to reflect the quality of source rocks in the study area. The organic matter of P2l2 source rocks in Malang Sag is mainly composed of lower aquatic organisms. However, compared with the group I, the group II and group III have a richer supply of prokaryote organic matter. The ratios of Steranes/Hopanes, C28 steranes/C29 steranes and (Pr+Ph)/(nC17+ nC18) indicated that the precursors of β-carotane in groups II and III might be algae with phytol side chains of chlorophyll a, b and c and bacteri. According to the parameters of Pr/Ph, C35 hopanes/C34 hopanes and ETR, it can be concluded that the water salinity of source rocks in groups II and III is high, mainly in a reducing environment. Compared with the fluctuating environment of weak oxidation-weak reduction during the deposition of group I and the relatively low salinity of water, it is more conducive to the preservation of β-carotane. A certain intensity of hydrothermal activity occurred during the deposition of group III source rocks, resulting in a large fluctuation of β-carotane content. [Conclusions] Therefore, the enrichment of P2l2 β-carotane in Malang Sag is mainly controlled by the source of organic matter and sedimentary environment.
[Objective] The second member of the Permian Lucaogou Formation (P2l2) is the main source rock in the Malang Sag of the Santanghu Basin, with high abundance of β-carotane, but its content shows great differences in the section. In order to further clarify the longitudinal variation of β-carotane in P2l2, and then to explore the main controlling factors of its enrichment and its distribution on the plane. [Methods] In this study, organic geochemical analysis was carried out and the source rocks investigated were divided into groups I, II and III from bottom to top according to the β-carotane index. The β-carotane index was relatively low in group I, and gradually increased from bottom to top in group II, while the β-carotane index in group III fluctuated greatly. [Results and Discussions] The results show that the relative content of β-carotane is an effective index to reflect the quality of source rocks in the study area. The organic matter of P2l2 source rocks in Malang Sag is mainly composed of lower aquatic organisms. However, compared with the group I, the group II and group III have a richer supply of prokaryote organic matter. The ratios of Steranes/Hopanes, C28 steranes/C29 steranes and (Pr+Ph)/(nC17+ nC18) indicated that the precursors of β-carotane in groups II and III might be algae with phytol side chains of chlorophyll a, b and c and bacteri. According to the parameters of Pr/Ph, C35 hopanes/C34 hopanes and ETR, it can be concluded that the water salinity of source rocks in groups II and III is high, mainly in a reducing environment. Compared with the fluctuating environment of weak oxidation-weak reduction during the deposition of group I and the relatively low salinity of water, it is more conducive to the preservation of β-carotane. A certain intensity of hydrothermal activity occurred during the deposition of group III source rocks, resulting in a large fluctuation of β-carotane content. [Conclusions] Therefore, the enrichment of P2l2 β-carotane in Malang Sag is mainly controlled by the source of organic matter and sedimentary environment.
Abstract:
[Objective] The beach-bar sand body is an important reservoir developed in the coastal or lakeshore area. Currently, there are more studies on the architecture of lakeshore beach-bar sand body, while there are differences in the depositional environments between the coastal and lakeshore, and there are differences in the sedimentation patterns of beach-bar, so the research on the architecture of beach-bar sand body needs to be deepened. [Methods] In this paper, based on a large amount of literature research on marine beach-bar deposits, the results are summarised in terms of the sedimentary characteristics and the hydrodynamic mechanism of marine beach-bar sand, the factors influencing the architecture, and the architecture pattern and characterization of it. [Results and discussion] The results show that the beach-bar deposits is dominated by sandbar, the development of sandbar is controlled by a variety of hydrodynamics such as nearshore spiral current, longshore current, rip current, swash current, and backward current in the seafloor, a variety types of sandbar have been formed under multiple types of hydrodynamic action, such as linear sandbar, coastal sandbar, sandbar spits, plume sandbar, tongue-like sandbar, oblique sandbar, etc. There are differences in the architecture characteristics and genesis of different types of sandbar. The sedimentary architecture of the sandbar is controlled by multiple factors. Shoreline morphology and wave interaction processes determine the mode of wave action, the supply of sediment sources and changes in relative sea level affect the development and stacking pattern of the sandbar, and tectonics and sedimentary palaeomorphology control the distribution of the sandbar. The sedimentary architecture of the beach-bar was characterized according to three levels: composite beach-bar, single bar and intra-bar accretionary body, and a preliminary beach-bar architecture model and characterization method were established. [Conclusions] Architecture prototypes should be modelled using various methods such as field outcrops, modern sedimentation, subsurface well datas and sediment simulation, which can help enrich the sedimentological theory of marine beach-bar reservoirs and more effectively guide the development of marine beach-bar oil and gas reservoirs.
[Objective] The beach-bar sand body is an important reservoir developed in the coastal or lakeshore area. Currently, there are more studies on the architecture of lakeshore beach-bar sand body, while there are differences in the depositional environments between the coastal and lakeshore, and there are differences in the sedimentation patterns of beach-bar, so the research on the architecture of beach-bar sand body needs to be deepened. [Methods] In this paper, based on a large amount of literature research on marine beach-bar deposits, the results are summarised in terms of the sedimentary characteristics and the hydrodynamic mechanism of marine beach-bar sand, the factors influencing the architecture, and the architecture pattern and characterization of it. [Results and discussion] The results show that the beach-bar deposits is dominated by sandbar, the development of sandbar is controlled by a variety of hydrodynamics such as nearshore spiral current, longshore current, rip current, swash current, and backward current in the seafloor, a variety types of sandbar have been formed under multiple types of hydrodynamic action, such as linear sandbar, coastal sandbar, sandbar spits, plume sandbar, tongue-like sandbar, oblique sandbar, etc. There are differences in the architecture characteristics and genesis of different types of sandbar. The sedimentary architecture of the sandbar is controlled by multiple factors. Shoreline morphology and wave interaction processes determine the mode of wave action, the supply of sediment sources and changes in relative sea level affect the development and stacking pattern of the sandbar, and tectonics and sedimentary palaeomorphology control the distribution of the sandbar. The sedimentary architecture of the beach-bar was characterized according to three levels: composite beach-bar, single bar and intra-bar accretionary body, and a preliminary beach-bar architecture model and characterization method were established. [Conclusions] Architecture prototypes should be modelled using various methods such as field outcrops, modern sedimentation, subsurface well datas and sediment simulation, which can help enrich the sedimentological theory of marine beach-bar reservoirs and more effectively guide the development of marine beach-bar oil and gas reservoirs.
Abstract:
[Objective] Different reservoir diagenesis has a significant effect on reservoir heterogeneity, and limits the ability to predict the presence of oil and gas in tight sandstone reservoirs. [Methods] In the study area, the constraints of lithofacies combinations causing differences in diagenesis in Chang 8 tight sandstone in the Zhijing-Ansai area were clarified by observation and identification from thin sections, cathodoluminescence (CL), scanning electron microscopy (SEM), C and O isotope analysis, and laser ablation. [Results and discussion] The reservoir sandstone comprises three lithofacies combinations: type I is siltstone or fine sandstone interbedded with argillaceous rock; type II is fine-to-medium sandstone; and type III is fine sandstone/siltstone/argillaceous rock. The fine particles of the siltstone facies have high mica content, and the rock is strongly compacted. The reservoir contains a large amount of near-argillaceous calcite cement that was developed early. The mudstone is rich in pore water with high concentrations of calcium ions and bicarbonate ions. When the mudstone overlying and underlying the reservoir sandstone is deeply buried, overcompaction causes the muddy and clayey sediments to discharge mineralized water into the sandstone, affecting its diagenesis. The supersaturated calcium carbonate thus forms a dense carbonate cement at the sandstone-mudstone interface. The calcite cement developed in the type II sandstone facies combination was formed later: this is mainly due to the later evolution of organic matter influenced by the decarboxylation of organic matter in the source rocks. The conversion of clay minerals in source rocks occurs when the pore water containing calcium ions undergoes lateral advection along highly permeable pathways, entering the reservoir and providing a material source for the development of calcite in the thick sandstone. Quartz cement is usually developed within the type I lithofacies and is mainly provided by the dissolution of feldspars and the transformation of clay minerals which are the source of silica. The dissolution process usually develops in regions of the rock with relatively coarse particle size and low plastic particle content, thus providing good fluid migration channels. [Conclusions] The differences and origin of diagenesis in the study area are clarified, providing an important basis for further research on the origin of reservoir heterogeneity.
[Objective] Different reservoir diagenesis has a significant effect on reservoir heterogeneity, and limits the ability to predict the presence of oil and gas in tight sandstone reservoirs. [Methods] In the study area, the constraints of lithofacies combinations causing differences in diagenesis in Chang 8 tight sandstone in the Zhijing-Ansai area were clarified by observation and identification from thin sections, cathodoluminescence (CL), scanning electron microscopy (SEM), C and O isotope analysis, and laser ablation. [Results and discussion] The reservoir sandstone comprises three lithofacies combinations: type I is siltstone or fine sandstone interbedded with argillaceous rock; type II is fine-to-medium sandstone; and type III is fine sandstone/siltstone/argillaceous rock. The fine particles of the siltstone facies have high mica content, and the rock is strongly compacted. The reservoir contains a large amount of near-argillaceous calcite cement that was developed early. The mudstone is rich in pore water with high concentrations of calcium ions and bicarbonate ions. When the mudstone overlying and underlying the reservoir sandstone is deeply buried, overcompaction causes the muddy and clayey sediments to discharge mineralized water into the sandstone, affecting its diagenesis. The supersaturated calcium carbonate thus forms a dense carbonate cement at the sandstone-mudstone interface. The calcite cement developed in the type II sandstone facies combination was formed later: this is mainly due to the later evolution of organic matter influenced by the decarboxylation of organic matter in the source rocks. The conversion of clay minerals in source rocks occurs when the pore water containing calcium ions undergoes lateral advection along highly permeable pathways, entering the reservoir and providing a material source for the development of calcite in the thick sandstone. Quartz cement is usually developed within the type I lithofacies and is mainly provided by the dissolution of feldspars and the transformation of clay minerals which are the source of silica. The dissolution process usually develops in regions of the rock with relatively coarse particle size and low plastic particle content, thus providing good fluid migration channels. [Conclusions] The differences and origin of diagenesis in the study area are clarified, providing an important basis for further research on the origin of reservoir heterogeneity.
Abstract:
[Objective] The dissolution of quartz particles in tight sandstone has attracted more and more attention. There is a clear correlation between the dissolution boundary characteristics of quartz particles and the dissolution mechanism, but the coupling relationship has not been systematically summarized to determine the types and characteristics of quartz dissolution. In order to clarify the relationship between the dissolution characteristics of quartz particle boundary and the dissolution mechanism. [Method] Based on the methods of thin section identification, cathodoluminescence, and scanning electron microscopy, combined with the test and analysis data, the fine observation and statistical analysis of the quartz boundary dissolution characteristics of the second member of Xujiahe Formation in western Sichuan are carried out. By establishing different types of quartz boundary dissolution, the dissolution process of quartz is determined, and the dissolution mechanism is analyzed. It can provide new ideas and references for the dissolution analysis of sandstone skeleton particles and the genesis of pores in tight sandstone. [Result] The boundary dissolution characteristics of quartz particles are divided into two categories: 1 smooth boundary-dissolved pore-increasing type, which shows that the boundary of quartz particles is smooth and clear, and pores are formed after dissolution; the fuzzy boundary-dissolution metasomatism type is characterized by the fuzzy and rough boundary of quartz particles, which is the result of dissolution and metasomatism of carbonate minerals and clay minerals. According to the different metasomatism minerals, it is further divided into boundary fuzzy-dissolution-carbonate metasomatism type and boundary fuzzy-dissolution-clay mineral metasomatism type. The smooth boundary-dissolution pore-increasing type is the result of organic acid dissolution under acidic conditions. The fuzzy boundary-dissolution-carbonate metasomatism type is the result of metasomatism between carbonate ions and quartz particles due to the difference in ion concentration under alkaline conditions. The boundary fuzzy-dissolution-clay mineral metasomatism type is that under alkaline conditions, clay minerals release alkali metal ions, produce a “salt effect”, accelerate the dissolution rate of quartz particles, and metasomatized quartz particles through clay film. The evolution of quartz particle dissolution boundary tends to change from smooth boundary-dissolution pore-increasing type to fuzzy boundary-dissolution metasomatic type, which not only reveals the characteristics of smooth boundary-dissolution pore-increasing type but also reflects that the evolution of quartz particle boundary is in the direction of favorable reservoir. Among the quartz particles corroded in the second member of the Xujiahe Formation in the study area, the corrosion loss part accounts for 4.33 % ~ 8.67 % of the quartz particle area, with an average of 6.37 %. The proportion of dissolved quartz particles to all quartz particles reached more than 55.33 %, with a maximum of about 72 % and an average of 63.02 %. The content of quartz in the thin section is about 45 % -96 %, with an average of 75.3 %. Therefore, the statistical results of quartz dissolution surface porosity are between 2.05 % and 4.09 %, with an average of 3.19 %. [Conclusion] The dissolution of quartz particles is carried out in a favorable direction for the reservoir and can provide a certain amount of secondary pores, increase the oil and gas reservoir space, and effectively improve the pore structure of tight sandstone.
[Objective] The dissolution of quartz particles in tight sandstone has attracted more and more attention. There is a clear correlation between the dissolution boundary characteristics of quartz particles and the dissolution mechanism, but the coupling relationship has not been systematically summarized to determine the types and characteristics of quartz dissolution. In order to clarify the relationship between the dissolution characteristics of quartz particle boundary and the dissolution mechanism. [Method] Based on the methods of thin section identification, cathodoluminescence, and scanning electron microscopy, combined with the test and analysis data, the fine observation and statistical analysis of the quartz boundary dissolution characteristics of the second member of Xujiahe Formation in western Sichuan are carried out. By establishing different types of quartz boundary dissolution, the dissolution process of quartz is determined, and the dissolution mechanism is analyzed. It can provide new ideas and references for the dissolution analysis of sandstone skeleton particles and the genesis of pores in tight sandstone. [Result] The boundary dissolution characteristics of quartz particles are divided into two categories: 1 smooth boundary-dissolved pore-increasing type, which shows that the boundary of quartz particles is smooth and clear, and pores are formed after dissolution; the fuzzy boundary-dissolution metasomatism type is characterized by the fuzzy and rough boundary of quartz particles, which is the result of dissolution and metasomatism of carbonate minerals and clay minerals. According to the different metasomatism minerals, it is further divided into boundary fuzzy-dissolution-carbonate metasomatism type and boundary fuzzy-dissolution-clay mineral metasomatism type. The smooth boundary-dissolution pore-increasing type is the result of organic acid dissolution under acidic conditions. The fuzzy boundary-dissolution-carbonate metasomatism type is the result of metasomatism between carbonate ions and quartz particles due to the difference in ion concentration under alkaline conditions. The boundary fuzzy-dissolution-clay mineral metasomatism type is that under alkaline conditions, clay minerals release alkali metal ions, produce a “salt effect”, accelerate the dissolution rate of quartz particles, and metasomatized quartz particles through clay film. The evolution of quartz particle dissolution boundary tends to change from smooth boundary-dissolution pore-increasing type to fuzzy boundary-dissolution metasomatic type, which not only reveals the characteristics of smooth boundary-dissolution pore-increasing type but also reflects that the evolution of quartz particle boundary is in the direction of favorable reservoir. Among the quartz particles corroded in the second member of the Xujiahe Formation in the study area, the corrosion loss part accounts for 4.33 % ~ 8.67 % of the quartz particle area, with an average of 6.37 %. The proportion of dissolved quartz particles to all quartz particles reached more than 55.33 %, with a maximum of about 72 % and an average of 63.02 %. The content of quartz in the thin section is about 45 % -96 %, with an average of 75.3 %. Therefore, the statistical results of quartz dissolution surface porosity are between 2.05 % and 4.09 %, with an average of 3.19 %. [Conclusion] The dissolution of quartz particles is carried out in a favorable direction for the reservoir and can provide a certain amount of secondary pores, increase the oil and gas reservoir space, and effectively improve the pore structure of tight sandstone.
Abstract:
[Objective] The Upper Carboniferous Benxi Formation in the Ordos Basin is the first set of sea-land interaction coal-bearing strata after the Caledonian movement, and has great exploration potential, but the coupling relationship between the basin and mountains under the influence of the north-south source system and multi-source composite in the eastern part of the basin is still controversial due to the tectonic activity of the periphery orogenic belt. [Method] In order to further trace the source system and restore the paleogeographical pattern, the sedimentary source filling process of the Benxi Formation in the eastern Ordos Basin was discussed by analyzing the characteristics of the rock chip components, rare earth elements and the U-Pb age characteristics of clastic zircon, combined with the tectonic background and lithological characteristics of the host rock. [Results] The sediments in the northern part of the study area were mainly derived from the Inner Mongolia uplift (Seltenshan, Wula-Daqingshan, Jining area) and the Central Asian orogenic belt in the active continental margin tectonic background. The southern part is mainly supplied by clastic material from the North Qinling, and the tectonic background of the source area is relatively complex, which is mainly a mixture of passive continental margin and continental island arc. In the North Qinling, the tectonic environment of stretching and stretching to collision and extrusion under the background of trench-arc-basin is formed. The parent rocks in the northern and southern source areas are the mixture of granitic rock and alkaline basalt, and the northern and southern provenance systems converge in the Lian45-Chengjiagou area. [Conclusion] As a whole, the Central Asian orogenic belt of Benxi Age has a high degree of uplift and denudation on both sides of the study area, which reflects the characteristics of irregular oblique collision in the northern part of the North China Plate. The northern margin of the North China Plate has a high uplift, which provides the main provenance for the northern part of the study area, and is dominated by the development of a large tide-delta complex system. Under the influence of strong source supply, the sand body extends farther in the northeast of the study area. Compared with the northern provenance, the overall provenance supply in the south was weaker, with the North Qinling Mountain as the main source area, and the southern margin of the North China Plate was uplifted in low amplitude at this time, and the sedimentary system of the barrier coast was mainly developed. In the area where the north and south sources meet, more detrital materials from the Northern Qinling Mountains are accepted, and a large number of tidal sand dams are deposited due to the transformation of eastward and north-east currents.
[Objective] The Upper Carboniferous Benxi Formation in the Ordos Basin is the first set of sea-land interaction coal-bearing strata after the Caledonian movement, and has great exploration potential, but the coupling relationship between the basin and mountains under the influence of the north-south source system and multi-source composite in the eastern part of the basin is still controversial due to the tectonic activity of the periphery orogenic belt. [Method] In order to further trace the source system and restore the paleogeographical pattern, the sedimentary source filling process of the Benxi Formation in the eastern Ordos Basin was discussed by analyzing the characteristics of the rock chip components, rare earth elements and the U-Pb age characteristics of clastic zircon, combined with the tectonic background and lithological characteristics of the host rock. [Results] The sediments in the northern part of the study area were mainly derived from the Inner Mongolia uplift (Seltenshan, Wula-Daqingshan, Jining area) and the Central Asian orogenic belt in the active continental margin tectonic background. The southern part is mainly supplied by clastic material from the North Qinling, and the tectonic background of the source area is relatively complex, which is mainly a mixture of passive continental margin and continental island arc. In the North Qinling, the tectonic environment of stretching and stretching to collision and extrusion under the background of trench-arc-basin is formed. The parent rocks in the northern and southern source areas are the mixture of granitic rock and alkaline basalt, and the northern and southern provenance systems converge in the Lian45-Chengjiagou area. [Conclusion] As a whole, the Central Asian orogenic belt of Benxi Age has a high degree of uplift and denudation on both sides of the study area, which reflects the characteristics of irregular oblique collision in the northern part of the North China Plate. The northern margin of the North China Plate has a high uplift, which provides the main provenance for the northern part of the study area, and is dominated by the development of a large tide-delta complex system. Under the influence of strong source supply, the sand body extends farther in the northeast of the study area. Compared with the northern provenance, the overall provenance supply in the south was weaker, with the North Qinling Mountain as the main source area, and the southern margin of the North China Plate was uplifted in low amplitude at this time, and the sedimentary system of the barrier coast was mainly developed. In the area where the north and south sources meet, more detrital materials from the Northern Qinling Mountains are accepted, and a large number of tidal sand dams are deposited due to the transformation of eastward and north-east currents.
Abstract:
The Permian Upper Urho Formation in the eastern slope area of Fukang Sag is an important oil and gas exploration formation in the Junggar Basin. However, the deep conglomerate reservoir is tight, and the unclear reservoir characteristics and genesis restrict the process of oil and gas exploration and development. Through core observation, casting thin section, physical property analysis, scanning electron microscope, high-pressure mercury injection curve and other data, the petrology characteristics, physical property characteristics, pore characteristics and reservoir genetic mechanism of the tight conglomerate reservoir of the Upper Urho Formation in the slope area of Fukang Sag were studied. The results indicate that: ① the reservoir is an ultra-low porosity and ultra-low permeability lithic sandstone reservoir; ② The pore types are mainly micropores and fractures, and the pore structure is mainly small pores and micro throats, with poor connectivity; ③ Sedimentary microfacies are the basis for the differential development of reservoir physical properties. Conglomerates deposited in clastic flow channels, and fine sandstones deposited in far sand bars have high shale content and poor physical properties, while underwater distributary channels have relatively good physical properties of conglomeratic sandstones; Diagenetic compaction and clay illitization are the main factors causing the tightness and low permeability of the reservoir; Fractures and high pressure are the main reasons for higher initial oil and gas production; ④ The conglomeratic sandstone in the underwater distributary channel at the top of P3w1 and bottom of P3w2 is an important layer for stable oil production, and the Fubei area, far from the influence of provenance of the Xiquan uplift, is a favorable area for further oil and gas exploration.
The Permian Upper Urho Formation in the eastern slope area of Fukang Sag is an important oil and gas exploration formation in the Junggar Basin. However, the deep conglomerate reservoir is tight, and the unclear reservoir characteristics and genesis restrict the process of oil and gas exploration and development. Through core observation, casting thin section, physical property analysis, scanning electron microscope, high-pressure mercury injection curve and other data, the petrology characteristics, physical property characteristics, pore characteristics and reservoir genetic mechanism of the tight conglomerate reservoir of the Upper Urho Formation in the slope area of Fukang Sag were studied. The results indicate that: ① the reservoir is an ultra-low porosity and ultra-low permeability lithic sandstone reservoir; ② The pore types are mainly micropores and fractures, and the pore structure is mainly small pores and micro throats, with poor connectivity; ③ Sedimentary microfacies are the basis for the differential development of reservoir physical properties. Conglomerates deposited in clastic flow channels, and fine sandstones deposited in far sand bars have high shale content and poor physical properties, while underwater distributary channels have relatively good physical properties of conglomeratic sandstones; Diagenetic compaction and clay illitization are the main factors causing the tightness and low permeability of the reservoir; Fractures and high pressure are the main reasons for higher initial oil and gas production; ④ The conglomeratic sandstone in the underwater distributary channel at the top of P3w1 and bottom of P3w2 is an important layer for stable oil production, and the Fubei area, far from the influence of provenance of the Xiquan uplift, is a favorable area for further oil and gas exploration.
Abstract:
There are several provenance systems in the southern Ordos Region, such as Qinling and Qilian orogenic belt, and the quantitative characterization of the elements of each source-to-sink system is relatively weak, which restricts the study of the differences of different source-to-sink systems and the structure-sedimentary filling process constrained by them. Taking the Shanxi Formation of Lower Permian as the object of study, the differences of unit elements such as tectonic setting, paleo-slope and depositional system of each source-to-sink system are elucidated by means of sedimentology, geochemistry and detrital zircon dating, etc., and the structure-sedimentary model of the Shanxi Formation under the combined influence of multiple source-to-sink systems in the southern basin is reconstructed. The results show that: (1) There are three major source-to-sink systems in the southern Ordos area: North Qilian, West North Qinling and East North Qinling during the sedimentary period of Shanxi Formation. The North Qilian source-to-sink system is relatively rich in light REE, the mean δEu is 0.60, and the mean paleo-slope along the source direction is 0.045°. Light REE are obviously enriched in the source-to-sink system in the western part of the North Qinling, with an average δEu of 0.75 and an average paleo-slope of 0.04°. The source-to-sink system in the eastern part of the North Qinling is rich in light REE, with an average δEu value of 1.05 and an average paleo-slope of 0.048°; (2) The source-to-sink systems are derived from the Central Asian orogenic belt, the North China Craton basement, the east and west of the North Qinling and the North Qilian orogenic belt, but the North China Craton basement is the main source; (3) Active continental margin dominates the tectonic background of provenance regions in all source-to-sink systems, which followed by passive continental margin. Due to Mianlue Ocean subduction, the southern part of Ordos is an active continental margin tectonic setting with continuous plate convergence. The source area of the source-to-sink system in the eastern part of the North Qinling has the highest uplift degree, and the late Shanxi is relatively sand-rich, dominated by transitional deposits from the delta plain to the front, with the smallest extension scale. The source region of the source-to-sink system in the west part of the North Qinling has the lowest uplift degree, rich sand in the early stage and poor sandy sediments in the late stage. The source region of the North Qilian source-to-sink system has a moderate uplift degree, and is dominated by the delta plain transiting deposits to the front margin.
There are several provenance systems in the southern Ordos Region, such as Qinling and Qilian orogenic belt, and the quantitative characterization of the elements of each source-to-sink system is relatively weak, which restricts the study of the differences of different source-to-sink systems and the structure-sedimentary filling process constrained by them. Taking the Shanxi Formation of Lower Permian as the object of study, the differences of unit elements such as tectonic setting, paleo-slope and depositional system of each source-to-sink system are elucidated by means of sedimentology, geochemistry and detrital zircon dating, etc., and the structure-sedimentary model of the Shanxi Formation under the combined influence of multiple source-to-sink systems in the southern basin is reconstructed. The results show that: (1) There are three major source-to-sink systems in the southern Ordos area: North Qilian, West North Qinling and East North Qinling during the sedimentary period of Shanxi Formation. The North Qilian source-to-sink system is relatively rich in light REE, the mean δEu is 0.60, and the mean paleo-slope along the source direction is 0.045°. Light REE are obviously enriched in the source-to-sink system in the western part of the North Qinling, with an average δEu of 0.75 and an average paleo-slope of 0.04°. The source-to-sink system in the eastern part of the North Qinling is rich in light REE, with an average δEu value of 1.05 and an average paleo-slope of 0.048°; (2) The source-to-sink systems are derived from the Central Asian orogenic belt, the North China Craton basement, the east and west of the North Qinling and the North Qilian orogenic belt, but the North China Craton basement is the main source; (3) Active continental margin dominates the tectonic background of provenance regions in all source-to-sink systems, which followed by passive continental margin. Due to Mianlue Ocean subduction, the southern part of Ordos is an active continental margin tectonic setting with continuous plate convergence. The source area of the source-to-sink system in the eastern part of the North Qinling has the highest uplift degree, and the late Shanxi is relatively sand-rich, dominated by transitional deposits from the delta plain to the front, with the smallest extension scale. The source region of the source-to-sink system in the west part of the North Qinling has the lowest uplift degree, rich sand in the early stage and poor sandy sediments in the late stage. The source region of the North Qilian source-to-sink system has a moderate uplift degree, and is dominated by the delta plain transiting deposits to the front margin.
Abstract:
[Objective] The direct relationship between sedimentary environment and seismic elastic response of organic shale is very important for reservoir quality evaluation and geological modeling of unconventional oil and gas reservoirs. [Methods] The sedimentary characteristics and lithofacies of the Longmaxi Shale in the Zigong area are characterized, and four depositional units (I-A, I-B, I-C and II) are identified, the influence of sedimentary environment on the elastic characteristics of shale of Longmaxi Formation in Zigong area, Sichuan Basin is analyzed. [Results] The results show that the sedimentary environment mainly controls the elastic characteristics of the shale of the Longmaxi Formation in two aspects: first, the difference of rock structure caused by hydrodynamic action; The elastic characteristics of shale in the deep water shelf environment are obviously different from those of argillaceous siltstone in the overlying turbidite environment, the variation of elastic characteristics is mainly controlled by the precession system and water depth.In addition, it is found that quartz and TOC content have a competitive relationship in influencing the elastic characteristics of the reservoir. Finally, the prediction ability of pre-stack AVO inversion to seismic elastic attributes is used to trace the sedimentary evolution process, which provides an insight for directly characterizing sedimentary facies of unconventional shale reservoirs by geophysical attributes. [Conclusions] The sedimentary environment affects the elastic characteristics of shale reservoirs by controlling the structure and composition of rocks. For the influence of quartz and TOC content on reservoir elasticity, the softening effect caused by organic matter is dominant at low quartz content, and the hardening effect of quartz grains is dominant at high quartz content.
[Objective] The direct relationship between sedimentary environment and seismic elastic response of organic shale is very important for reservoir quality evaluation and geological modeling of unconventional oil and gas reservoirs. [Methods] The sedimentary characteristics and lithofacies of the Longmaxi Shale in the Zigong area are characterized, and four depositional units (I-A, I-B, I-C and II) are identified, the influence of sedimentary environment on the elastic characteristics of shale of Longmaxi Formation in Zigong area, Sichuan Basin is analyzed. [Results] The results show that the sedimentary environment mainly controls the elastic characteristics of the shale of the Longmaxi Formation in two aspects: first, the difference of rock structure caused by hydrodynamic action; The elastic characteristics of shale in the deep water shelf environment are obviously different from those of argillaceous siltstone in the overlying turbidite environment, the variation of elastic characteristics is mainly controlled by the precession system and water depth.In addition, it is found that quartz and TOC content have a competitive relationship in influencing the elastic characteristics of the reservoir. Finally, the prediction ability of pre-stack AVO inversion to seismic elastic attributes is used to trace the sedimentary evolution process, which provides an insight for directly characterizing sedimentary facies of unconventional shale reservoirs by geophysical attributes. [Conclusions] The sedimentary environment affects the elastic characteristics of shale reservoirs by controlling the structure and composition of rocks. For the influence of quartz and TOC content on reservoir elasticity, the softening effect caused by organic matter is dominant at low quartz content, and the hardening effect of quartz grains is dominant at high quartz content.
Abstract:
[Objective] Among the past ice chamber climate records, the Late Paleozoic ice age, which developed mainly in the Gondwana continent, is the most similar to the current climate evolution It has become a hot target for comparative studies of Quaternary ice ages and ice chamber climate studies. The Late Paleozoic ice age, as the glacial event with the widest influence range and the richest geological record since the Phanerozoic, recorded the complete greenhouse-icehouse-greenhouse climate change process, which is of great significance for us to understand the evolution of earth climate. The Lhasa Block originated from the Gondwana continent and was located at the northeastern margin of the Gondwana continent during the Late Paleozoic period. Although a lot of studies have been conducted on the spatial and temporal evolution and controlling factors of the Late Paleozoic ice age, the sedimentary evolution history of the Lhasa Block during the Late Paleozoic ice age is still unclear and needs to be strengthened. [Methods] In view of this, this study selected the Late Paleozoic strata in the Xainza area of the Lhasa Block to carry out a 1:200 scale profile survey, which includes rock color, lithological characteristics, rock thickness, sedimentary structures, fossils and contact relationships. Lithofacies and lithofacies combinations were classified for glacial development, and sedimentary architecture analysis was applied to find the lateral and vertical changes of sedimentary facies to identify the sedimentary environment and recover the glacial sedimentary system. [Results and Discussions] The study shows that the Late Paleozoic ice age records of Lhasa block are mainly present at the Lagar Formation, with the age constraint of Late Carboniferous-Early Permian. According to the glacial deposits of Lagar Formation, twenty lithofacies and sixteen typical lithofacies associations are recognized, which are arranged into six sedimentary environments, including shallow sea shelf, baseline fan, subglacial, ice river, ice lake and outwash fan. [Conclusions] The Late Paleozoic glaciers in the central part of the Lhasa Block are located in the nearshore glaciomarine environment, and the glacial depositional system is mainly divided into marine and terrestrial phases. In addition, a number of small glacial-interglacial cyclones can be delineated in the early evolutionary stage and late evolutionary stage of the Lagar Formation based on the variation of glacial and non-glacial environments in the vertical direction. The sedimentary system analysis for the Lagar Formation sedimentary sequences indicates that the Late Paleozoic ice age in the Xainza area of the Lhasa Block experienced a transition from early marine to late terrestrial glaciations, indicating a global trend of gradual climate warming from the Late Carboniferous to the Early Permian, consistent with the global Late Paleozoic ice age evolutionary features. The Late Paleozoic ice age was the closest global ice age to the Quaternary ice age and is an important window for understanding future climate shifts such as glacial melting and global warming on Earth. Conducting research on the Late Paleozoic sedimentary record of the Lhasa Block is of great significance for exploring the spatial and temporal evolution, climate change and driving mechanisms of the global Late Paleozoic ice age.
[Objective] Among the past ice chamber climate records, the Late Paleozoic ice age, which developed mainly in the Gondwana continent, is the most similar to the current climate evolution It has become a hot target for comparative studies of Quaternary ice ages and ice chamber climate studies. The Late Paleozoic ice age, as the glacial event with the widest influence range and the richest geological record since the Phanerozoic, recorded the complete greenhouse-icehouse-greenhouse climate change process, which is of great significance for us to understand the evolution of earth climate. The Lhasa Block originated from the Gondwana continent and was located at the northeastern margin of the Gondwana continent during the Late Paleozoic period. Although a lot of studies have been conducted on the spatial and temporal evolution and controlling factors of the Late Paleozoic ice age, the sedimentary evolution history of the Lhasa Block during the Late Paleozoic ice age is still unclear and needs to be strengthened. [Methods] In view of this, this study selected the Late Paleozoic strata in the Xainza area of the Lhasa Block to carry out a 1:200 scale profile survey, which includes rock color, lithological characteristics, rock thickness, sedimentary structures, fossils and contact relationships. Lithofacies and lithofacies combinations were classified for glacial development, and sedimentary architecture analysis was applied to find the lateral and vertical changes of sedimentary facies to identify the sedimentary environment and recover the glacial sedimentary system. [Results and Discussions] The study shows that the Late Paleozoic ice age records of Lhasa block are mainly present at the Lagar Formation, with the age constraint of Late Carboniferous-Early Permian. According to the glacial deposits of Lagar Formation, twenty lithofacies and sixteen typical lithofacies associations are recognized, which are arranged into six sedimentary environments, including shallow sea shelf, baseline fan, subglacial, ice river, ice lake and outwash fan. [Conclusions] The Late Paleozoic glaciers in the central part of the Lhasa Block are located in the nearshore glaciomarine environment, and the glacial depositional system is mainly divided into marine and terrestrial phases. In addition, a number of small glacial-interglacial cyclones can be delineated in the early evolutionary stage and late evolutionary stage of the Lagar Formation based on the variation of glacial and non-glacial environments in the vertical direction. The sedimentary system analysis for the Lagar Formation sedimentary sequences indicates that the Late Paleozoic ice age in the Xainza area of the Lhasa Block experienced a transition from early marine to late terrestrial glaciations, indicating a global trend of gradual climate warming from the Late Carboniferous to the Early Permian, consistent with the global Late Paleozoic ice age evolutionary features. The Late Paleozoic ice age was the closest global ice age to the Quaternary ice age and is an important window for understanding future climate shifts such as glacial melting and global warming on Earth. Conducting research on the Late Paleozoic sedimentary record of the Lhasa Block is of great significance for exploring the spatial and temporal evolution, climate change and driving mechanisms of the global Late Paleozoic ice age.
Abstract:
In order to study the sedimentary characteristics and geological significance of the typical tempestites in the Lower Ordovician Fenxiang Formation in the chengkou area of the Upper Yangtze Basin. Via detailed field survey and microscopic section analysis, the sedimentary sequence of the tempestites and mode of the Fenxiang Formation are established, which reveal the geological significance. The results show that the tempestites sedimentary structures of Fenxiang Formation in Chengkou area mainly include bottom scour structure, storm gravel layer, grain sequence bedding and mound cross-bedding. At the same time, five kinds of tempestites sedimentary sequences were identified: Sequence I was mainly composed of bottom erosion, gravel layer (A), grain sequence (B) and parallel bedding segment (C), and mainly developed in the platform margin facies; Sequence II consists of grain sequence (B) and parallel bedding segment (C), which developed in the platform margin facies near the slope. Sequence III is composed of bottom erosion and gravel layer (A), grain sequence layer (B), parallel bedding (C) and argillaceous limestone segment (E), which are mainly deposited in the fore-platform slope facies zone. Sequence Ⅳ mainly consists of grain sequence segment (B) and argillaceous micrite segment (E), which are mainly deposited in the lower the fore-platform slope. Sequence V is composed of grain sequence (B), mound bedding segment (D) and argillaceous micrite segment (E), which mainly developed in the deepwater shelf. The development of tempestites indicates that the upper Yangtze platform was located in the low latitude area in the Early Ordovician, and the Chengkou area was dominated by platform margin and slope deposits. The bottom-up sedimentary environment evolved into platform margin → platform front slope → deep water shelf. The development of tempestites indicates that the Upper Yangtze platform was near the equator at low latitude during the Ordovician period. The sedimentary environment of Fenxiang Formation in the Chengkou area of the Upper Yangtze Platform is the platform margin zone. Combined with the regional geological background, it is considered that there are geological conditions for developing large-scale platform margin shoals in the chengkou area of the Yangtze Platform..
In order to study the sedimentary characteristics and geological significance of the typical tempestites in the Lower Ordovician Fenxiang Formation in the chengkou area of the Upper Yangtze Basin. Via detailed field survey and microscopic section analysis, the sedimentary sequence of the tempestites and mode of the Fenxiang Formation are established, which reveal the geological significance. The results show that the tempestites sedimentary structures of Fenxiang Formation in Chengkou area mainly include bottom scour structure, storm gravel layer, grain sequence bedding and mound cross-bedding. At the same time, five kinds of tempestites sedimentary sequences were identified: Sequence I was mainly composed of bottom erosion, gravel layer (A), grain sequence (B) and parallel bedding segment (C), and mainly developed in the platform margin facies; Sequence II consists of grain sequence (B) and parallel bedding segment (C), which developed in the platform margin facies near the slope. Sequence III is composed of bottom erosion and gravel layer (A), grain sequence layer (B), parallel bedding (C) and argillaceous limestone segment (E), which are mainly deposited in the fore-platform slope facies zone. Sequence Ⅳ mainly consists of grain sequence segment (B) and argillaceous micrite segment (E), which are mainly deposited in the lower the fore-platform slope. Sequence V is composed of grain sequence (B), mound bedding segment (D) and argillaceous micrite segment (E), which mainly developed in the deepwater shelf. The development of tempestites indicates that the upper Yangtze platform was located in the low latitude area in the Early Ordovician, and the Chengkou area was dominated by platform margin and slope deposits. The bottom-up sedimentary environment evolved into platform margin → platform front slope → deep water shelf. The development of tempestites indicates that the Upper Yangtze platform was near the equator at low latitude during the Ordovician period. The sedimentary environment of Fenxiang Formation in the Chengkou area of the Upper Yangtze Platform is the platform margin zone. Combined with the regional geological background, it is considered that there are geological conditions for developing large-scale platform margin shoals in the chengkou area of the Yangtze Platform..
Abstract:
The Early Triassic is a special geological historical period after the mass extinction of organisms. The genetic mechanism of oolites and giant oolites and the paleomarine environment they represent have been a controversial issue in the field of geology. Based on field and core observations, using petrological, mineralogical, and geochemical analyses, this paper explores the sedimentary characteristics, genesis, and paleoenvironmental significance of oolites and giant oolites from the Early Triassic Feixianguan Formation in the Yuanba area. The research shows that the oolites and giant oolites of the Feixianguan Formation in the Yuanba area are mainly developed in the platform margin zone of the Fei'er Member, and the types of oolites are mainly concentric oolites and single crystal oolites, indicating that they were formed in a shallow water environment with strong hydrodynamic forces and easy exposure; The type of giant oolites is dominated by concentric oolites, which are often thinly interbedded with oolitic limestone and micrite limestone, accompanied by the appearance of scouring surfaces, indicating that they are developed in areas affected by indirect storm action. Combined with geochemical analysis, it is found that the Sr content of the oolitic concentric ring layer is high, and the common needle or rod shaped crystal structure indicates that its original minerals are mainly aragonite deposits; However, the Sr content of the giant oolitic concentric layer is relatively low, and the irregular granular crystal structure is mainly developed, indicating that its original minerals are mainly calcite deposits. In addition, the oolitic concentric sphere has characteristics such as high Fe content, no significant Ce anomalies, positive Eu anomalies, LREE relative HREE enrichment, and V/(V+Ni)>0.6, indicating that it was formed in a ferritized weak oxygen reduction environment; Giant oolites have characteristics such as low Fe content, negative Ce anomalies, LREE relative HREE depletion, and V/(V+Ni)<0.6, indicating that they were formed in an oxidation-weak oxidation environment. According to comprehensive analysis, during the sedimentary period of the Early Triassic Feixianguan Formation, the seawater was mainly composed of anoxic aragonite sea, which was influenced by the strengthening of continental weathering, especially intermittent storms, which increased the input of terrestrial materials (especially Ca2+and oxidants), resulting in the decrease and oxidation of Mg/Ca in the shallow seawater, and the development of a transient calcite sea. This may be one of the important reasons for the improvement of the marine environment and the gradual recovery of organisms in the Early Triassic.
The Early Triassic is a special geological historical period after the mass extinction of organisms. The genetic mechanism of oolites and giant oolites and the paleomarine environment they represent have been a controversial issue in the field of geology. Based on field and core observations, using petrological, mineralogical, and geochemical analyses, this paper explores the sedimentary characteristics, genesis, and paleoenvironmental significance of oolites and giant oolites from the Early Triassic Feixianguan Formation in the Yuanba area. The research shows that the oolites and giant oolites of the Feixianguan Formation in the Yuanba area are mainly developed in the platform margin zone of the Fei'er Member, and the types of oolites are mainly concentric oolites and single crystal oolites, indicating that they were formed in a shallow water environment with strong hydrodynamic forces and easy exposure; The type of giant oolites is dominated by concentric oolites, which are often thinly interbedded with oolitic limestone and micrite limestone, accompanied by the appearance of scouring surfaces, indicating that they are developed in areas affected by indirect storm action. Combined with geochemical analysis, it is found that the Sr content of the oolitic concentric ring layer is high, and the common needle or rod shaped crystal structure indicates that its original minerals are mainly aragonite deposits; However, the Sr content of the giant oolitic concentric layer is relatively low, and the irregular granular crystal structure is mainly developed, indicating that its original minerals are mainly calcite deposits. In addition, the oolitic concentric sphere has characteristics such as high Fe content, no significant Ce anomalies, positive Eu anomalies, LREE relative HREE enrichment, and V/(V+Ni)>0.6, indicating that it was formed in a ferritized weak oxygen reduction environment; Giant oolites have characteristics such as low Fe content, negative Ce anomalies, LREE relative HREE depletion, and V/(V+Ni)<0.6, indicating that they were formed in an oxidation-weak oxidation environment. According to comprehensive analysis, during the sedimentary period of the Early Triassic Feixianguan Formation, the seawater was mainly composed of anoxic aragonite sea, which was influenced by the strengthening of continental weathering, especially intermittent storms, which increased the input of terrestrial materials (especially Ca2+and oxidants), resulting in the decrease and oxidation of Mg/Ca in the shallow seawater, and the development of a transient calcite sea. This may be one of the important reasons for the improvement of the marine environment and the gradual recovery of organisms in the Early Triassic.
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.
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.
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.
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.
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.
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2025, 43(2): 361-375.
doi: 10.14027/j.issn.1000-0550.2023.117
Abstract:
Significance The grain sizes of sediments contain information on multiple factors： transport path， depositional process， and environment. Grain-size distribution （GSD） is defined in sedimentology and geology as the frequency of occurrence of different-diameter particles. GSD is a record of the original sedimentological information. It is one aspect of the basic data used to reveal modern and ancient depositional environments in rivers， lakes， oceans， deserts， loess， etc. The traditional GSD analytical methods adopted to describe the overall features of depositional processes and environments， either qualitatively or semi-quantitatively， may not overcome problems of quantification and multiple solutions. Progress This study summarizes the range of different classification standards of grain-size scale， and compares moment and graphical frequency-curve methods of describing GSDs with morphological description standards. The applicability and usage of traditional methods of sedimentary environment analysis by GSD are reviewed， and some unconventional approaches are developed using mathematical methodology to tackle the entire range of GSD. Unsupervised clustering algorithms calculate the similarity of GSDs using their frequency， cumulative frequency or statistical parameters， then depositional environments are sorted according to the classes of clustering. Multifractal analysis is used to extract fractal parameters that represent the complexity of GSD frequency data. The different fractal structures reveal different depositional properties. When applied to multiple sedimentary processes in different sedimentary environments and dynamics and the GSD is superposed by multi-subpopulations， the corresponding frequency curve is found to be bimodal or multimodal. This implies that an inverse unmixing model of the sediments is ideally suited for obtaining genetically meaningful interpretations of these subpopulations. Two techniques are used to separate the grain-size component from GSD frequency data. To apply the statistical finite-mixture model， single-sample unmixing （SSU） uses a probability density function （normal， skew normal or Weibull distribution） to unmix the GSD by curve-fitting techniques. Each grain-size component is distributed in a unimodal fashion such that its statistical parameters （mean， sorting， skewness， kurtosis and percentage） may be calculated. The end-member modeling algorithm （EMMA） decomposes grain-size end-members from a GSD dataset. These unimodal or multimodal grain-size end-members are linearly independent and fixed within a single GSD dataset. Many improved EMMAs are available in different open-source tools. To introduce examples of the application of these unconventional methods， in this study 27 GSDs from the central bar of the Kangshan River in the Poyang Lake drainage are processed by clustering， multifractal， SSU and EMMA. Conclusions and Prospects Problems of sedimentation analysis and the big-data properties of GSDs are solved. The trend of development of the depositional significance of GSDs is proposed based on analytical methods. With the advent of various modern grain-size analysis techniques and more sophisticated artificial intelligence procedures in earth sciences， new increasingly intelligent mining methods for GSDs are emerging for understanding the spatio-temporal grain-size patterns in sediments. Some excellent sedimentological related databases have been constructed. Accordingly， an open-access database will be established for GSDs to include various kinds of data， intelligent methods and a literature of reported research. Under the background of big data， GSD big-data technology will provide a new driver for mining depositional properties intensively， and integrate them into sedimentological big data. Four phases， initial， exploratory， early development and rapid development， describe the history of GSD research. The future must hold a big-data phase for intelligent mining using sedimentological GSD information.
Significance The grain sizes of sediments contain information on multiple factors： transport path， depositional process， and environment. Grain-size distribution （GSD） is defined in sedimentology and geology as the frequency of occurrence of different-diameter particles. GSD is a record of the original sedimentological information. It is one aspect of the basic data used to reveal modern and ancient depositional environments in rivers， lakes， oceans， deserts， loess， etc. The traditional GSD analytical methods adopted to describe the overall features of depositional processes and environments， either qualitatively or semi-quantitatively， may not overcome problems of quantification and multiple solutions. Progress This study summarizes the range of different classification standards of grain-size scale， and compares moment and graphical frequency-curve methods of describing GSDs with morphological description standards. The applicability and usage of traditional methods of sedimentary environment analysis by GSD are reviewed， and some unconventional approaches are developed using mathematical methodology to tackle the entire range of GSD. Unsupervised clustering algorithms calculate the similarity of GSDs using their frequency， cumulative frequency or statistical parameters， then depositional environments are sorted according to the classes of clustering. Multifractal analysis is used to extract fractal parameters that represent the complexity of GSD frequency data. The different fractal structures reveal different depositional properties. When applied to multiple sedimentary processes in different sedimentary environments and dynamics and the GSD is superposed by multi-subpopulations， the corresponding frequency curve is found to be bimodal or multimodal. This implies that an inverse unmixing model of the sediments is ideally suited for obtaining genetically meaningful interpretations of these subpopulations. Two techniques are used to separate the grain-size component from GSD frequency data. To apply the statistical finite-mixture model， single-sample unmixing （SSU） uses a probability density function （normal， skew normal or Weibull distribution） to unmix the GSD by curve-fitting techniques. Each grain-size component is distributed in a unimodal fashion such that its statistical parameters （mean， sorting， skewness， kurtosis and percentage） may be calculated. The end-member modeling algorithm （EMMA） decomposes grain-size end-members from a GSD dataset. These unimodal or multimodal grain-size end-members are linearly independent and fixed within a single GSD dataset. Many improved EMMAs are available in different open-source tools. To introduce examples of the application of these unconventional methods， in this study 27 GSDs from the central bar of the Kangshan River in the Poyang Lake drainage are processed by clustering， multifractal， SSU and EMMA. Conclusions and Prospects Problems of sedimentation analysis and the big-data properties of GSDs are solved. The trend of development of the depositional significance of GSDs is proposed based on analytical methods. With the advent of various modern grain-size analysis techniques and more sophisticated artificial intelligence procedures in earth sciences， new increasingly intelligent mining methods for GSDs are emerging for understanding the spatio-temporal grain-size patterns in sediments. Some excellent sedimentological related databases have been constructed. Accordingly， an open-access database will be established for GSDs to include various kinds of data， intelligent methods and a literature of reported research. Under the background of big data， GSD big-data technology will provide a new driver for mining depositional properties intensively， and integrate them into sedimentological big data. Four phases， initial， exploratory， early development and rapid development， describe the history of GSD research. The future must hold a big-data phase for intelligent mining using sedimentological GSD information.
2025, 43(2): 376-386.
doi: 10.14027/j.issn.1000-0550.2023.073
Abstract:
Objective As an important component of unconventional oil and gas resources， the basic research of shale oil and gas resources has gradually gained momentum. With the continuous microscopization of the study scale， it is increasingly important to study the microstructures of clay sediments. Microstructures of clay sediments have an impact on shale foliation and lamination structure， thus influencing the shale reservoir capacity and development effect. Therefore， further understanding of clay sediments microstructures is conducive to the distribution prediction and exploitation of shale oil and gas resources. Methods In addition to being affected to rows and columns by physical action， clay particles also undergo chemical adsorption and flocculation to form floccules with varying degrees. The basic floccule unit is tabular particles or domains， further forming flocs or chains， before finally forming a card house structure under the electric charge. There are many types of structures， reflecting the difference of flocculation. 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， and organic matter. 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. Results Flocculation enables clay minerals to be deposited in high-energy hydrodynamic environment. The larger the clay particle size is， the less likely it is to flocculate. Moreover， relatively turbulent water interferes with flocculation and prevents mudstone particles from forming layers. Climatic stratification and storm pressure conduction affect the microstructure of clay deposits. Strong acidic water is conducive to the flocculation of clay particles such as kaolinite. The effects of salinity and organic matter are controversial. The sedimentary environment of shale is diverse， and the sedimentary dynamics include isobaric flow， upwelling flow， gravity flow， viscous underflow， suspended sedimentation， tsunami， and storm. However， this study is still in its infancy， and no perfect sedimentary geological model has been established； The quantitative research of floccules and other components of mudstone composite particles is insufficient， and artificial intelligence image recognition 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. Conclusions Based on the qualitative and quantitative description of microstructures of clay sediments and demonstration of sedimentary environments of mudstone composite particles， fine description of complex and changeable sedimentary environment and sedimentary micro-environment can be achieved， deepening our understanding of the differentiation characteristics of sedimentary environments of shale such as lakes and seas， further revealing the differences in shale reservoir quality within the high-precision range， and laying a foundation for the selection and development of geology and engineering "desserts" in shale； this study has great significance for the deep utilization of shale oil and gas geological resources.
Objective As an important component of unconventional oil and gas resources， the basic research of shale oil and gas resources has gradually gained momentum. With the continuous microscopization of the study scale， it is increasingly important to study the microstructures of clay sediments. Microstructures of clay sediments have an impact on shale foliation and lamination structure， thus influencing the shale reservoir capacity and development effect. Therefore， further understanding of clay sediments microstructures is conducive to the distribution prediction and exploitation of shale oil and gas resources. Methods In addition to being affected to rows and columns by physical action， clay particles also undergo chemical adsorption and flocculation to form floccules with varying degrees. The basic floccule unit is tabular particles or domains， further forming flocs or chains， before finally forming a card house structure under the electric charge. There are many types of structures， reflecting the difference of flocculation. 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， and organic matter. 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. Results Flocculation enables clay minerals to be deposited in high-energy hydrodynamic environment. The larger the clay particle size is， the less likely it is to flocculate. Moreover， relatively turbulent water interferes with flocculation and prevents mudstone particles from forming layers. Climatic stratification and storm pressure conduction affect the microstructure of clay deposits. Strong acidic water is conducive to the flocculation of clay particles such as kaolinite. The effects of salinity and organic matter are controversial. The sedimentary environment of shale is diverse， and the sedimentary dynamics include isobaric flow， upwelling flow， gravity flow， viscous underflow， suspended sedimentation， tsunami， and storm. However， this study is still in its infancy， and no perfect sedimentary geological model has been established； The quantitative research of floccules and other components of mudstone composite particles is insufficient， and artificial intelligence image recognition 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. Conclusions Based on the qualitative and quantitative description of microstructures of clay sediments and demonstration of sedimentary environments of mudstone composite particles， fine description of complex and changeable sedimentary environment and sedimentary micro-environment can be achieved， deepening our understanding of the differentiation characteristics of sedimentary environments of shale such as lakes and seas， further revealing the differences in shale reservoir quality within the high-precision range， and laying a foundation for the selection and development of geology and engineering "desserts" in shale； this study has great significance for the deep utilization of shale oil and gas geological resources.
2025, 43(2): 387-407.
doi: 10.14027/j.issn.1000-0550.2023.022
Abstract:
Objective The Guadelup-Leping boundary （PLB boundary） of the Middle-Late Permian has long been considered a difficult academic issue for geoscientists. On the one hand， the uplift movement at the turn of the Middle and Late Permian caused a sedimentary discontinuity and differential denudation， which made determining the boundary and comparing it with the global profile difficult. On the other hand， the reason several profiles recorded negative carbon isotope drift events related to the PLB boundary with different occurrence is still unclear. Methods This study selected seven sections of the late Guadalupian strata （including Sandui Town， Wangjiagou， Daliang Township） along the northwest margin of the Yangtze Plate as research object and identified the formation time limit through lithological characteristics and conodonts. Major trace and rare earth element analyses also complement the environmental evidence of regional carbon isotope drift events. Results The results show that：（1） From the Jinogondolla.postserrata to Clarkina.dukouensis zone， the field sections can be divided into four lithologic sections， bioclastic limestone （containing dolomite）， siliceous limestone （argillaceous limestone）， coal seam， and marl-bearing limestone， representing three stages of sea level： stabilization-decline-rise. （2） The characteristic key bed of the PLB boundary identified based on the paleoexposure， lithologic mutation， and first appearance surfaces of the C. dukouensis is marked as the lowest Leping boundary. （3） Two regression events were recorded in the J.postserra-J.shannini zone and J.altudaensis-J.xuanhanensis zone of the Sandui Town profile， resulting in synchronous negative deviation of Sr/Ba and Y/Ho values and relative enrichment of light rare earth elements. Conclusions The Emeishan Large Igneous Province began to move in the J. altudaensis belt， and the input of hydrothermal fluid caused a sharp increase in the total rare earth elements in the region. The biological population was affected by the extinction event in the J. postserrata belt that lasted until the PLB boundary. This study complements the profile evidence by explaining the differences in the timing and period of negative carbon isotope deviation events between the northwest margin of the Yangtze Craton and the global records.
Objective The Guadelup-Leping boundary （PLB boundary） of the Middle-Late Permian has long been considered a difficult academic issue for geoscientists. On the one hand， the uplift movement at the turn of the Middle and Late Permian caused a sedimentary discontinuity and differential denudation， which made determining the boundary and comparing it with the global profile difficult. On the other hand， the reason several profiles recorded negative carbon isotope drift events related to the PLB boundary with different occurrence is still unclear. Methods This study selected seven sections of the late Guadalupian strata （including Sandui Town， Wangjiagou， Daliang Township） along the northwest margin of the Yangtze Plate as research object and identified the formation time limit through lithological characteristics and conodonts. Major trace and rare earth element analyses also complement the environmental evidence of regional carbon isotope drift events. Results The results show that：（1） From the Jinogondolla.postserrata to Clarkina.dukouensis zone， the field sections can be divided into four lithologic sections， bioclastic limestone （containing dolomite）， siliceous limestone （argillaceous limestone）， coal seam， and marl-bearing limestone， representing three stages of sea level： stabilization-decline-rise. （2） The characteristic key bed of the PLB boundary identified based on the paleoexposure， lithologic mutation， and first appearance surfaces of the C. dukouensis is marked as the lowest Leping boundary. （3） Two regression events were recorded in the J.postserra-J.shannini zone and J.altudaensis-J.xuanhanensis zone of the Sandui Town profile， resulting in synchronous negative deviation of Sr/Ba and Y/Ho values and relative enrichment of light rare earth elements. Conclusions The Emeishan Large Igneous Province began to move in the J. altudaensis belt， and the input of hydrothermal fluid caused a sharp increase in the total rare earth elements in the region. The biological population was affected by the extinction event in the J. postserrata belt that lasted until the PLB boundary. This study complements the profile evidence by explaining the differences in the timing and period of negative carbon isotope deviation events between the northwest margin of the Yangtze Craton and the global records.
2025, 43(2): 408-422.
doi: 10.14027/j.issn.1000-0550.2023.040
Abstract:
Objective The Carboniferous deposits 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 our understanding of the regional tectono-sedimentary pattern. The rare earth element （REE） properties of argillaceous rocks are stable； therefore， analysing their geochemical characteristics is an efficient path for reconstructing the tectonic setting， material source， and sedimentary environment. Methods Inductively coupled plasma mass spectrometry （ICP-MS） has been applied to investigate REE geochemistry in the Lower Carboniferous Huaitoutala Formation （C1h） in Xiaosaishenteng Shan. Results The results indicate that the Xiaosaishenteng Shan area was likely a back-arc basin influenced by the northern subduction of the South Kunlun oceanic crust， 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. Thus， it exhibits an overall palaeogeomorphic pattern of "high in the south and low in the north， from land to sea". The orogenic belt extending west from the subduction collision zone in the north margin of Qaidam to the southeast of Xiaosaishenteng Shan was the important provenance area， providing the weathered detrital materials of parent rocks composed of granite， alkaline basalt， and sedimentary rock to the study area since the early deposition of the C1h. With the weakening of regional tectonic intensity， the clastic materials of argillaceous interlayers in the top C1h carbonates may come from the re-transport of the preexisting sediments. Overall， the sedimentary paleo-water of C1h 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 occurred in an oxidized environment. The phase sequence of “platform edge shoal ⁃ platform front slope-shelf edge- platform front slope - platform edge organic reef” was developed successively. Conclusions Our results provide a basis for the reconstruction of the regional paleogeographic pattern and our understanding of the spatiotemporal evolution of the Proto-Tethys oceans and its energy and mineral effects.
Objective The Carboniferous deposits 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 our understanding of the regional tectono-sedimentary pattern. The rare earth element （REE） properties of argillaceous rocks are stable； therefore， analysing their geochemical characteristics is an efficient path for reconstructing the tectonic setting， material source， and sedimentary environment. Methods Inductively coupled plasma mass spectrometry （ICP-MS） has been applied to investigate REE geochemistry in the Lower Carboniferous Huaitoutala Formation （C1h） in Xiaosaishenteng Shan. Results The results indicate that the Xiaosaishenteng Shan area was likely a back-arc basin influenced by the northern subduction of the South Kunlun oceanic crust， 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. Thus， it exhibits an overall palaeogeomorphic pattern of "high in the south and low in the north， from land to sea". The orogenic belt extending west from the subduction collision zone in the north margin of Qaidam to the southeast of Xiaosaishenteng Shan was the important provenance area， providing the weathered detrital materials of parent rocks composed of granite， alkaline basalt， and sedimentary rock to the study area since the early deposition of the C1h. With the weakening of regional tectonic intensity， the clastic materials of argillaceous interlayers in the top C1h carbonates may come from the re-transport of the preexisting sediments. Overall， the sedimentary paleo-water of C1h 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 occurred in an oxidized environment. The phase sequence of “platform edge shoal ⁃ platform front slope-shelf edge- platform front slope - platform edge organic reef” was developed successively. Conclusions Our results provide a basis for the reconstruction of the regional paleogeographic pattern and our understanding of the spatiotemporal evolution of the Proto-Tethys oceans and its energy and mineral effects.
2025, 43(2): 423-438.
doi: 10.14027/j.issn.1000-0550.2023.012
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Objective The Dagushi Formation of the Mesoproterozoic Xiong’er Group is the earliest sedimentary unit overlying the metamorphic crystalline basement at the southern margin of the North China Craton. Studies of the depositional environment and formation processes are highly significant for an understanding of the breakup of the Columbia supercontinent and the sedimentary environment and tectonic setting of the early Xiong’er Group. However， systematic research on the sediment provenance and paleoenvironment of the Dagushi Formation is still lacking. Methods The provenance， sedimentary environment and tectonic setting of the Dagushi Formation were studied by analysis of major- and trace elements in the Dagushi Formation of the Xiong’er Group， Xiaogoubei area， Jiyuan， Henan Province. Results For the major elements， the results show that the fine-grained clastic rocks of the Dagushi Formation are close to their source， with the compositional maturity gradually decreasing upwards from the bottom. From bottom to top， the sediments are mainly erosional products of a mixture of mafic and felsic rocks， gradually changing from granites to felsic volcanic rocks， then to intermediate rocks. The composition of the ancient sediments in the upper member gradually increases. The Dagushi Formation was deposited in a warm， humid climate， with evidence of several climate fluctuations during that time. Analysis of trace elements and REE show that the lower Dagushi Formation was formed in a relatively stable tectonic setting， and that the middle and upper segments were formed in an active tectonic setting. Conclusions Together with the evidence from 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 was associated with crust activation and associated tectono-thermal events. A mantle plume uplifted and activated the crust， gradually developing the southern margin of the North China Craton into an active tectonic setting. The deposition of the Dagushi Formation occurred in a local depression. Early volcanism of the Xiong’er Group provided the sedimentary provenance for the Dagushi Formation. This study provides new evidence for a better understanding of the evolution of Early Mesoproterozoic tectonism and deposition in the North China Craton.
Objective The Dagushi Formation of the Mesoproterozoic Xiong’er Group is the earliest sedimentary unit overlying the metamorphic crystalline basement at the southern margin of the North China Craton. Studies of the depositional environment and formation processes are highly significant for an understanding of the breakup of the Columbia supercontinent and the sedimentary environment and tectonic setting of the early Xiong’er Group. However， systematic research on the sediment provenance and paleoenvironment of the Dagushi Formation is still lacking. Methods The provenance， sedimentary environment and tectonic setting of the Dagushi Formation were studied by analysis of major- and trace elements in the Dagushi Formation of the Xiong’er Group， Xiaogoubei area， Jiyuan， Henan Province. Results For the major elements， the results show that the fine-grained clastic rocks of the Dagushi Formation are close to their source， with the compositional maturity gradually decreasing upwards from the bottom. From bottom to top， the sediments are mainly erosional products of a mixture of mafic and felsic rocks， gradually changing from granites to felsic volcanic rocks， then to intermediate rocks. The composition of the ancient sediments in the upper member gradually increases. The Dagushi Formation was deposited in a warm， humid climate， with evidence of several climate fluctuations during that time. Analysis of trace elements and REE show that the lower Dagushi Formation was formed in a relatively stable tectonic setting， and that the middle and upper segments were formed in an active tectonic setting. Conclusions Together with the evidence from 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 was associated with crust activation and associated tectono-thermal events. A mantle plume uplifted and activated the crust， gradually developing the southern margin of the North China Craton into an active tectonic setting. The deposition of the Dagushi Formation occurred in a local depression. Early volcanism of the Xiong’er Group provided the sedimentary provenance for the Dagushi Formation. This study provides new evidence for a better understanding of the evolution of Early Mesoproterozoic tectonism and deposition in the North China Craton.
2025, 43(2): 439-452.
doi: 10.14027/j.issn.1000-0550.2023.058
Abstract:
Objective Long-term and extensive glaciation occurred during the Late Carboniferous-Early Permian. In this period， the Baoshan Block， as a part of the Gondwana continental margin， experienced several transgressive-regressive cycles， preserving important information on the expansion or depletion of glaciers. This study focused on the Xiyi section， Dongshanpo section， and Woniusi section in the Baoshan area of western Yunnan， exploring the paleo-ocean redox environment from the Middle Carboniferous-Early Permian and analyzing the mechanism of anoxic events and the relationship with glaciation. Methods Pyrite framboid was 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 were mainly oxic and dysoxic but punctuated by short anoxic-dysoxic episodes. Interval Ⅳ， the early Kungurian to the middle Roadian experienced the same trace as Interval Ⅲ. In general， the redox environment of the paleo-ocean in the Baoshan area showed a trend of euxinic → anoxic → dysoxic → oxic. The Early Carboniferous was dominated by an 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 positively correlated with the positive drift of δ13Ccarb 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 likely 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 may be related to the sea level falls caused by glacial events and the temperature fall 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 Long-term and extensive glaciation occurred during the Late Carboniferous-Early Permian. In this period， the Baoshan Block， as a part of the Gondwana continental margin， experienced several transgressive-regressive cycles， preserving important information on the expansion or depletion of glaciers. This study focused on the Xiyi section， Dongshanpo section， and Woniusi section in the Baoshan area of western Yunnan， exploring the paleo-ocean redox environment from the Middle Carboniferous-Early Permian and analyzing the mechanism of anoxic events and the relationship with glaciation. Methods Pyrite framboid was 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 were mainly oxic and dysoxic but punctuated by short anoxic-dysoxic episodes. Interval Ⅳ， the early Kungurian to the middle Roadian experienced the same trace as Interval Ⅲ. In general， the redox environment of the paleo-ocean in the Baoshan area showed a trend of euxinic → anoxic → dysoxic → oxic. The Early Carboniferous was dominated by an 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 positively correlated with the positive drift of δ13Ccarb 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 likely 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 may be related to the sea level falls caused by glacial events and the temperature fall 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.
2025, 43(2): 453-466.
doi: 10.14027/j.issn.1000-0550.2023.038
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，Mccloudiacontracta，Pseudofusulina cf. wulungensis，Rugosofusulinaparagregariformis，Triticites daaoziensis，Zellia ex. gr. crassialveola，Sphaeroschwagerinaborealis，S. sp. indet.， Boultoniawills. 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. Conclusions 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，Mccloudiacontracta，Pseudofusulina cf. wulungensis，Rugosofusulinaparagregariformis，Triticites daaoziensis，Zellia ex. gr. crassialveola，Sphaeroschwagerinaborealis，S. sp. indet.， Boultoniawills. 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. Conclusions 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.
2025, 43(2): 467-480.
doi: 10.14027/j.issn.1000-0550.2023.025
Abstract:
Objective The hydrothermal activities during the Early Cambrian in northwest Hunan significantly influenced the sedimentary strata at that time. However， the specific influence of the hydrothermal activities on the surrounding area remains unclear. Methods Based on the analysis of total organic carbon （TOC）， X-ray diffraction （XRD）， major and trace elements， etc.， the differences in the sedimentary geochemistry at the bottom of lower Cambrian Niutitang Formation in wells Huanye 1 （HY1）， Xiangan 1 （XA1）， and Xiangji 1 （XJ1） in northwestern Hunan were compared and analyzed. Results Research shows that combined with the sedimentary setting and structural characteristics of the early Cambrian， the specific influence and extent of hydrothermal activities on the peripheral sediments were systematically revealed. These wells were far from the hydrothermal activities， and the contribution from the hydrothermal activities is small. However， certain geochemical indicators suggest that there are both normal and hydrothermal deposition characteristics at the bottom of the Niutitang Formation black shales. XJ1 was the most affected by the hydrothermal activity， XA1 was practically unaffected， and HY1 was moderately affected. Co/Zn， LaN/CeN， ∑REE， and ∑LREE/∑HREE are indicators for showing hydrothermal activities. Ba， Mo， Ni， U and V are highly enriched in that stratum. The sedimentary environment of strong reducing or vulcanization may be the main factor for the enrichment of these 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 affected by the hydrothermal activities in turn， differ in their response of sedimentary geochemistry characteristics. XJ1 in the deep-sea basin is more dependent on the supply from the deep internal source of the remote debris. Conclusions The hydrothermal activities provide a material basis that is rich in these elements by the contrast in different wells. Furthermore， the hydrothermal activities strengthen the reducibility of the surrounding sedimentary environment， which is conducive to the further enrichment of these elements and organic matter. This influence gradually decreases with the increase of the distance from the hydrothermal activities. However， the response of hydrothermal sediment is relatively confusing and vague owing to the complex factors on the content of elements in the black shales.
Objective The hydrothermal activities during the Early Cambrian in northwest Hunan significantly influenced the sedimentary strata at that time. However， the specific influence of the hydrothermal activities on the surrounding area remains unclear. Methods Based on the analysis of total organic carbon （TOC）， X-ray diffraction （XRD）， major and trace elements， etc.， the differences in the sedimentary geochemistry at the bottom of lower Cambrian Niutitang Formation in wells Huanye 1 （HY1）， Xiangan 1 （XA1）， and Xiangji 1 （XJ1） in northwestern Hunan were compared and analyzed. Results Research shows that combined with the sedimentary setting and structural characteristics of the early Cambrian， the specific influence and extent of hydrothermal activities on the peripheral sediments were systematically revealed. These wells were far from the hydrothermal activities， and the contribution from the hydrothermal activities is small. However， certain geochemical indicators suggest that there are both normal and hydrothermal deposition characteristics at the bottom of the Niutitang Formation black shales. XJ1 was the most affected by the hydrothermal activity， XA1 was practically unaffected， and HY1 was moderately affected. Co/Zn， LaN/CeN， ∑REE， and ∑LREE/∑HREE are indicators for showing hydrothermal activities. Ba， Mo， Ni， U and V are highly enriched in that stratum. The sedimentary environment of strong reducing or vulcanization may be the main factor for the enrichment of these 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 affected by the hydrothermal activities in turn， differ in their response of sedimentary geochemistry characteristics. XJ1 in the deep-sea basin is more dependent on the supply from the deep internal source of the remote debris. Conclusions The hydrothermal activities provide a material basis that is rich in these elements by the contrast in different wells. Furthermore， the hydrothermal activities strengthen the reducibility of the surrounding sedimentary environment， which is conducive to the further enrichment of these elements and organic matter. This influence gradually decreases with the increase of the distance from the hydrothermal activities. However， the response of hydrothermal sediment is relatively confusing and vague owing to the complex factors on the content of elements in the black shales.
2025, 43(2): 481-499.
doi: 10.14027/j.issn.1000-0550.2024.066
Abstract:
Objective Lithium constitutes a critical strategic and new energy metal within China. The Ordos Basin features a widespread distribution of bauxite deposits. Recent years have seen a major breakthrough in bauxite gas exploration within the Longdong area of the Ordos Basin. Exploration has uncovered considerable reserves of Li resources associated with the bauxite deposits. Consideration of the occurrence and enrichment patterns of Li in bauxite deposits has significant academic value for studying paleoclimate and paleoenvironments， and also offers robust support for the exploration and development of Li resources. Methods Focusing on the Al-bearing rock series of the Benxi Formation in the central and eastern Ordos Basin， this study builds upon classical understandings and recent research advancements to investigate the fundamental characteristics， modes of occurrence and enrichment patterns of Li， employing core observation， drilling data and geochemical testing. Results The findings reveal that Li is unevenly distributed in the bauxite deposits， with a substantial range of variation. Generally， Li is most highly concentrated in the middle and upper segments of the deposits. It is predominantly concentrated in bauxite clay rock and bauxite rock， but is comparatively rare in bauxite iron ore. Initially， Li is positively correlated with Al2O3， SiO2 and the Al2O3/SiO2 ratio， which subsequently transitions to a negative correlation. Conclusions The hot， humid and high rainfall conditions of the paleoclimate together with an alkaline environment facilitated the formation of clay minerals and enhanced the isomorphic substitution of Li+ for Al3+ and Mg2+， but as desilication and aluminum enrichment intensify the Li content of bauxite rock sharply decreases， attributable to the lack of clay minerals.
Objective Lithium constitutes a critical strategic and new energy metal within China. The Ordos Basin features a widespread distribution of bauxite deposits. Recent years have seen a major breakthrough in bauxite gas exploration within the Longdong area of the Ordos Basin. Exploration has uncovered considerable reserves of Li resources associated with the bauxite deposits. Consideration of the occurrence and enrichment patterns of Li in bauxite deposits has significant academic value for studying paleoclimate and paleoenvironments， and also offers robust support for the exploration and development of Li resources. Methods Focusing on the Al-bearing rock series of the Benxi Formation in the central and eastern Ordos Basin， this study builds upon classical understandings and recent research advancements to investigate the fundamental characteristics， modes of occurrence and enrichment patterns of Li， employing core observation， drilling data and geochemical testing. Results The findings reveal that Li is unevenly distributed in the bauxite deposits， with a substantial range of variation. Generally， Li is most highly concentrated in the middle and upper segments of the deposits. It is predominantly concentrated in bauxite clay rock and bauxite rock， but is comparatively rare in bauxite iron ore. Initially， Li is positively correlated with Al2O3， SiO2 and the Al2O3/SiO2 ratio， which subsequently transitions to a negative correlation. Conclusions The hot， humid and high rainfall conditions of the paleoclimate together with an alkaline environment facilitated the formation of clay minerals and enhanced the isomorphic substitution of Li+ for Al3+ and Mg2+， but as desilication and aluminum enrichment intensify the Li content of bauxite rock sharply decreases， attributable to the lack of clay minerals.
2025, 43(2): 500-512.
doi: 10.14027/j.issn.1000-0550.2023.034
Abstract:
Objective Recently， a breakthrough has been made in the gas exploration of the aluminiferous rock series from the Taiyuan Formation in Longdong area of Ordos Basin. However， the mineralogical studies of aluminous rock series are still relatively weak due to the constraints of conventional optical microscopy. This study aims to identify the mineral composition and its occurrence state， determine the elemental types and content of minerals in the ore in detail， discuss their mineral genesis， and summarize the mineral evolution sequence. Methods The aluminiferous rock series in this area was selected as the object of study. The mineralogical characteristics of the aluminiferous rock series were studied by using TIMA （TESCAN Integrated Mineral Analyzer）， a fully automatic mineral analysis system of Czech Republic， combined with thin section observation and other means. Results The study shows that the main mineral components of the aluminiferous rock series in the Longdong area include diaspore， siderite， pyrite， illite， kaolinite， and oolitic chlorite. The main body of illite is the product of fluid alteration， the early sedimentary kaolinite is the product of weathering， 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 later 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 by： surface weathering， metallogenic， and epigenetic periods. Conclusions For samples of the aluminum rock series with complex mineral composition and small grains that are not easily observed by optical microscopy， TIMA based on scanning electron microscopy and energy spectrum analysis can quickly and effectively identify the mineral composition of the aluminiferous rock series， obtain mineral composition and elemental information， and identify the symbiotic， attachment， and encapsulated relationship between different minerals.
Objective Recently， a breakthrough has been made in the gas exploration of the aluminiferous rock series from the Taiyuan Formation in Longdong area of Ordos Basin. However， the mineralogical studies of aluminous rock series are still relatively weak due to the constraints of conventional optical microscopy. This study aims to identify the mineral composition and its occurrence state， determine the elemental types and content of minerals in the ore in detail， discuss their mineral genesis， and summarize the mineral evolution sequence. Methods The aluminiferous rock series in this area was selected as the object of study. The mineralogical characteristics of the aluminiferous rock series were studied by using TIMA （TESCAN Integrated Mineral Analyzer）， a fully automatic mineral analysis system of Czech Republic， combined with thin section observation and other means. Results The study shows that the main mineral components of the aluminiferous rock series in the Longdong area include diaspore， siderite， pyrite， illite， kaolinite， and oolitic chlorite. The main body of illite is the product of fluid alteration， the early sedimentary kaolinite is the product of weathering， 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 later 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 by： surface weathering， metallogenic， and epigenetic periods. Conclusions For samples of the aluminum rock series with complex mineral composition and small grains that are not easily observed by optical microscopy， TIMA based on scanning electron microscopy and energy spectrum analysis can quickly and effectively identify the mineral composition of the aluminiferous rock series， obtain mineral composition and elemental information， and identify the symbiotic， attachment， and encapsulated relationship between different minerals.
2025, 43(2): 513-526.
doi: 10.14027/j.issn.1000-0550.2023.035
Abstract:
Objective Shelf-marginal sea， under land-sea interaction， is a key region with important information regarding climate， sea-level change， biogeochemical cycles， and human activities. To discuss the phased characteristics and influencing factors of organic carbon burial in the background of sedimentary environment evolution since the last deglaciation， Methods we analyzed AMS14C dating， the sediment grain size， total organic carbon （TOC）， total nitrogen （TN）， and stable carbon isotopes （δ13C） of core H12 in the eastern side of central south Yellow Sea mud. Results The results show that the hard clay layer developed during the period of relatively low sea level （17-12.6 ka B.P.） with relatively high TOC-MAR （TOC-Mass Accumulation Rate） 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 signi-ficantly high value around 8 ka B.P.， similar to the obviously increasing sedimentation rate， which may be related to the change of sediment transport mode driven by monsoon. During the high sea level period （beginning 7.8 ka B.P.）， the main contribution is marine sources. In particular， from 5-2 ka B.P.， the relative variation of TOC content on the centennial scale is large， consistent with the weakening stage of the Kuroshio Current and the strong period of the East Asian winter monsoon， which may reflect the enhancement of Yellow Sea warm current driven by the East Asian winter monsoon， leading to changes in marine primary productivity and water environment and thus affecting the burial of TOC. Since 2 ka B.P.， the variation of TOC content has decreased， and the contribution of organic matter from marine sources has increased， which may be related to the strengthening of ENSO （El Nino-Southern Oscillation） activities. Conclusions 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 periodic changes of TOC sedimentary records from high sea level may be related to the changes of the Yellow Sea warm current under the influence of the East Asian winter monsoon and ENSO activities.
Objective Shelf-marginal sea， under land-sea interaction， is a key region with important information regarding climate， sea-level change， biogeochemical cycles， and human activities. To discuss the phased characteristics and influencing factors of organic carbon burial in the background of sedimentary environment evolution since the last deglaciation， Methods we analyzed AMS14C dating， the sediment grain size， total organic carbon （TOC）， total nitrogen （TN）， and stable carbon isotopes （δ13C） of core H12 in the eastern side of central south Yellow Sea mud. Results The results show that the hard clay layer developed during the period of relatively low sea level （17-12.6 ka B.P.） with relatively high TOC-MAR （TOC-Mass Accumulation Rate） 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 signi-ficantly high value around 8 ka B.P.， similar to the obviously increasing sedimentation rate， which may be related to the change of sediment transport mode driven by monsoon. During the high sea level period （beginning 7.8 ka B.P.）， the main contribution is marine sources. In particular， from 5-2 ka B.P.， the relative variation of TOC content on the centennial scale is large， consistent with the weakening stage of the Kuroshio Current and the strong period of the East Asian winter monsoon， which may reflect the enhancement of Yellow Sea warm current driven by the East Asian winter monsoon， leading to changes in marine primary productivity and water environment and thus affecting the burial of TOC. Since 2 ka B.P.， the variation of TOC content has decreased， and the contribution of organic matter from marine sources has increased， which may be related to the strengthening of ENSO （El Nino-Southern Oscillation） activities. Conclusions 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 periodic changes of TOC sedimentary records from high sea level may be related to the changes of the Yellow Sea warm current under the influence of the East Asian winter monsoon and ENSO activities.
2025, 43(2): 527-538.
doi: 10.14027/j.issn.1000-0550.2023.024
Abstract:
Objective The Mangshan loess deposits located in central China Plain， along 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. To explore the mechanism of Mangshan loess formation， as well as the difference and mechanism of the formation process between Mangshan loess and paleosol during the glacial and interglacial periods. Methods In this study， sixteen samples， including 4 202 detrital zircon particles， comprising the steps of particle separation， target preparation， laser ablation， mass spectrometer testing， lead correction and the like， are analyzed for U-Pb dating from the Mangshan loess-paleosol sequence of the last glacial-interglacial cycle. Results The results reveal that the main age spectra peaked at 240 Ma， 440 Ma， 800-1 000 Ma， 1 800-2 000 Ma， and 2 500 Ma， indicating that the provenances of Mangshan loess were located in 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 increased， and the eroded sediments were carried by fluvial runoff to the lower reaches of the Yellow River， closing to the Mangshan loess deposit site. During the interglacial period， the contribution of the proximal source materials to the Mangshan loess deposits intensified， and the contribution increased by 10%. Conclusions Investigation of the 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.
Objective The Mangshan loess deposits located in central China Plain， along 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. To explore the mechanism of Mangshan loess formation， as well as the difference and mechanism of the formation process between Mangshan loess and paleosol during the glacial and interglacial periods. Methods In this study， sixteen samples， including 4 202 detrital zircon particles， comprising the steps of particle separation， target preparation， laser ablation， mass spectrometer testing， lead correction and the like， are analyzed for U-Pb dating from the Mangshan loess-paleosol sequence of the last glacial-interglacial cycle. Results The results reveal that the main age spectra peaked at 240 Ma， 440 Ma， 800-1 000 Ma， 1 800-2 000 Ma， and 2 500 Ma， indicating that the provenances of Mangshan loess were located in 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 increased， and the eroded sediments were carried by fluvial runoff to the lower reaches of the Yellow River， closing to the Mangshan loess deposit site. During the interglacial period， the contribution of the proximal source materials to the Mangshan loess deposits intensified， and the contribution increased by 10%. Conclusions Investigation of the 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.
2025, 43(2): 539-554.
doi: 10.14027/j.issn.1000-0550.2023.042
Abstract:
Objective In sedimentological studies， effectively distinguishing the aeolian and hydrogenic deposits has long garnered series academic attention； however， it remains difficult. Although certain macro-scale sedimentary features （such as wind-ripple marks， wind-ripple strata， and pin stripe laminations） can provide favorable support for the identification of aeolian deposits， owing to the differences in outcrops exposure conditions， the features mentioned above are difficult to accurately recognize. In contrast， the characteristic microtextures of aeolian deposits， such as high composition， structural maturity， and stable mineral surface morphology， are not limited by outcrop conditions， which provides an effective method for identifying aeolian deposits. Methods In this study， taking Late Jurassic aeolian and hydrogenic deposits from the Ningwu-Jingle basin of Shanxi Province as an example， a series of micro-scale analyses were conducted on the two types of sandstones. [Results and Conclusions] The aeolian sandstone has high composition and structural maturity compared to fluvial sandstone， between different aeolian strate with varying grain size characteristics， microscopic structures such as dished pits， crescentic percussion marks and upturned plates on the surface of mineral particles indicate the aeolian origin of the sandstone， additionally， aeolian quartz particles exhibit high levels of ferrum and manganese. Based on the combined of thin section analysis， grain size analysis， scanning electron microscopy， and energy spectrum analysis， we propose that the dished pits on the surface of mineral particles and wind-ripple strata with inverse grain size grading can be used as the unique identification indicators of aeolian deposits. Owing to the explanatory ambiguity of the microscopic characteristics of most aeolian deposits， we recommend adopting a multi-index combined method to analyze the genesis of aeolian deposits.
Objective In sedimentological studies， effectively distinguishing the aeolian and hydrogenic deposits has long garnered series academic attention； however， it remains difficult. Although certain macro-scale sedimentary features （such as wind-ripple marks， wind-ripple strata， and pin stripe laminations） can provide favorable support for the identification of aeolian deposits， owing to the differences in outcrops exposure conditions， the features mentioned above are difficult to accurately recognize. In contrast， the characteristic microtextures of aeolian deposits， such as high composition， structural maturity， and stable mineral surface morphology， are not limited by outcrop conditions， which provides an effective method for identifying aeolian deposits. Methods In this study， taking Late Jurassic aeolian and hydrogenic deposits from the Ningwu-Jingle basin of Shanxi Province as an example， a series of micro-scale analyses were conducted on the two types of sandstones. [Results and Conclusions] The aeolian sandstone has high composition and structural maturity compared to fluvial sandstone， between different aeolian strate with varying grain size characteristics， microscopic structures such as dished pits， crescentic percussion marks and upturned plates on the surface of mineral particles indicate the aeolian origin of the sandstone， additionally， aeolian quartz particles exhibit high levels of ferrum and manganese. Based on the combined of thin section analysis， grain size analysis， scanning electron microscopy， and energy spectrum analysis， we propose that the dished pits on the surface of mineral particles and wind-ripple strata with inverse grain size grading can be used as the unique identification indicators of aeolian deposits. Owing to the explanatory ambiguity of the microscopic characteristics of most aeolian deposits， we recommend adopting a multi-index combined method to analyze the genesis of aeolian deposits.
2025, 43(2): 555-575.
doi: 10.14027/j.issn.1000-0550.2023.021
Abstract:
Objective This study aimed 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. Methods Taking the Triassic Karamay Formation in the midwestern Taibei Sag as an example， the petrological characteristics of the Triassic Karamay Formation reservoir were studied by field outcrop， core observation， particle size analysis， and rock thin section identification. The paleogeomorphology and tectonic evolution characteristics were restored by impression method. The paleogeomorphology analysis was conducted by heavy mineral combination method， and the paleosedimentary environment was analyzed by trace elements. Under the constraint of sequence stratigraphic framework， comprehensive utilization of field outcrops， drilling cores， logging and mud logging， and a variety of analysis and testing data were applied to summarize the rock facies marks， logging facies marks， and other characteristics and determine the sedimentary facies type. Based on the study of sedimentary facies types， the research idea of ' point-line-surface-body ' was adopted， and the sedimentary facies distribution law of the Triassic Karamay Formation was studied using single well core sedimentology analysis， sandstone thickness contour map， sandstone percentage contour map， and profile facies analysis. Based on the study of sedimentary system distribution and favorable reservoir facies belt， the favorable direction and zone of oil and gas exploration in the Triassic Karamay Formation of the Taibei Sag in the Turpan-Hami Basin are analyzed based on a fuzzy mathematics algorithm combined with the hydrocarbon generation and structural zones. [Results and Conclusions] The reservoir rocks of the Triassic Karamay Formation are mainly glutenite， sandstone， and mudstone， with low compositional maturity， showing characteristics of near-source deposition. The thickness of the residual strata in the sedimentary period of the Triassic Karamay Formation showed a trend of gradual thinning from north to south and from the middle to both sides， indicating that the northern part of the Triassic in the Taibei Sag was the sedimentary center. The overall paleotopography in the central and western parts of the Taibei Sag is relatively slow， the paleocurrent is relatively slow， the hydrodynamic force is relatively weak， and the wide-covered braided river delta deposit is developed. The Karamay Formation is a braided river delta front deposit， which is distributed along the edge of the basin. The sediment source mainly comes from the ancient uplift in the south， and the ZTR （Zircon， Tourmaline， Rutile） index in the north of the basin increases from south to north， indicating that the source migrates from south to north. The sedimentary environment is a semi-humid， anaerobic reduction salt lake environment. Affected by the paleogeomorphology， the sand bodies in the central and western parts of the Taibei Sag are relatively developed， with large thickness and wide distribution. The T2-3k1 period was a braided river delta front deposition， which is distributed in a sheet along the edge of the basin. During the T2-3k2 period， the braided river delta front deposition was developed and distributed in a sheet along the edge of the basin. Based on the sandstone thickness， sedimentary microfacies parameters （sand ratio）， physical parameters （ porosity and permeability）， etc.， the comprehensive evaluation of the reservoir was conducted using fuzzy evaluation. The braided river delta front is the favorable sedimentary facies zone of the high-quality reservoir of the Karamay Formation. The conditions of migration and accumulation are good， and it is a favorable oil and gas exploration zone.
Objective This study aimed 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. Methods Taking the Triassic Karamay Formation in the midwestern Taibei Sag as an example， the petrological characteristics of the Triassic Karamay Formation reservoir were studied by field outcrop， core observation， particle size analysis， and rock thin section identification. The paleogeomorphology and tectonic evolution characteristics were restored by impression method. The paleogeomorphology analysis was conducted by heavy mineral combination method， and the paleosedimentary environment was analyzed by trace elements. Under the constraint of sequence stratigraphic framework， comprehensive utilization of field outcrops， drilling cores， logging and mud logging， and a variety of analysis and testing data were applied to summarize the rock facies marks， logging facies marks， and other characteristics and determine the sedimentary facies type. Based on the study of sedimentary facies types， the research idea of ' point-line-surface-body ' was adopted， and the sedimentary facies distribution law of the Triassic Karamay Formation was studied using single well core sedimentology analysis， sandstone thickness contour map， sandstone percentage contour map， and profile facies analysis. Based on the study of sedimentary system distribution and favorable reservoir facies belt， the favorable direction and zone of oil and gas exploration in the Triassic Karamay Formation of the Taibei Sag in the Turpan-Hami Basin are analyzed based on a fuzzy mathematics algorithm combined with the hydrocarbon generation and structural zones. [Results and Conclusions] The reservoir rocks of the Triassic Karamay Formation are mainly glutenite， sandstone， and mudstone， with low compositional maturity， showing characteristics of near-source deposition. The thickness of the residual strata in the sedimentary period of the Triassic Karamay Formation showed a trend of gradual thinning from north to south and from the middle to both sides， indicating that the northern part of the Triassic in the Taibei Sag was the sedimentary center. The overall paleotopography in the central and western parts of the Taibei Sag is relatively slow， the paleocurrent is relatively slow， the hydrodynamic force is relatively weak， and the wide-covered braided river delta deposit is developed. The Karamay Formation is a braided river delta front deposit， which is distributed along the edge of the basin. The sediment source mainly comes from the ancient uplift in the south， and the ZTR （Zircon， Tourmaline， Rutile） index in the north of the basin increases from south to north， indicating that the source migrates from south to north. The sedimentary environment is a semi-humid， anaerobic reduction salt lake environment. Affected by the paleogeomorphology， the sand bodies in the central and western parts of the Taibei Sag are relatively developed， with large thickness and wide distribution. The T2-3k1 period was a braided river delta front deposition， which is distributed in a sheet along the edge of the basin. During the T2-3k2 period， the braided river delta front deposition was developed and distributed in a sheet along the edge of the basin. Based on the sandstone thickness， sedimentary microfacies parameters （sand ratio）， physical parameters （ porosity and permeability）， etc.， the comprehensive evaluation of the reservoir was conducted using fuzzy evaluation. The braided river delta front is the favorable sedimentary facies zone of the high-quality reservoir of the Karamay Formation. The conditions of migration and accumulation are good， and it is a favorable oil and gas exploration zone.
2025, 43(2): 576-594.
doi: 10.14027/j.issn.1000-0550.2023.043
Abstract:
Objective In recent years， a growing number of scholars have focused on deep-water deposition， which can form coarse clastic sand bodies and fine-grained sediments along submarine slopes， abyssal plains， and abyssal lakes. However， the understanding of the development law and sedimentary model remains controversial. Methods Taking the Lower Cretaceous Laiyang Formation in the Lingshan Island of Riqingwei Basin as an example， with the help of core observations of well LK-1， thin-section microscopic identification， and outcrop exploration， the deep-water sedimentary process was evaluated using lithofacies assemblage， sedimentary types， genetic mechanism， fluid evolution characteristics， and sedimentary model. Results （1） The Early Cretaceous deep-water sedimentary lithofacies in the study area can be divided into 9 types： layered shale， deformed structural mudstone， deformed structural argillaceous siltstone， parallel bedding siltstone， argillaceous clastic siltstone， sequence-bedding fine sandstone， massive bedding fine sandstone， cross-bedding fine sandstone， and massive bedding pebbled sandstone facies. Five types of lithofacies association are summarized based on the development situation. （2） Based on the lithofacies assemblages， six sedimentary types were identified， including slump， sandy debris flow， turbidity current， hybrid event bed， bottom current， and deep-water suspended deposits. （3） Considering the tectonic setting of the basin， distribution law of deep-water sediments， and triggering mechanism of gravity flow， gravity flow was found to present evolutionary characteristics of sandy debris flow to sandy debris flow-turbidity flow to turbidity flow from the continental slope to the basin floor. Thus， the Early Cretaceous deep-water sedimentary model dominated by deep-water gravity flow in the Lingshan Island was established. Conclusions 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 the paleoenvironment and paleogeography during the Early Cretaceous in this area.
Objective In recent years， a growing number of scholars have focused on deep-water deposition， which can form coarse clastic sand bodies and fine-grained sediments along submarine slopes， abyssal plains， and abyssal lakes. However， the understanding of the development law and sedimentary model remains controversial. Methods Taking the Lower Cretaceous Laiyang Formation in the Lingshan Island of Riqingwei Basin as an example， with the help of core observations of well LK-1， thin-section microscopic identification， and outcrop exploration， the deep-water sedimentary process was evaluated using lithofacies assemblage， sedimentary types， genetic mechanism， fluid evolution characteristics， and sedimentary model. Results （1） The Early Cretaceous deep-water sedimentary lithofacies in the study area can be divided into 9 types： layered shale， deformed structural mudstone， deformed structural argillaceous siltstone， parallel bedding siltstone， argillaceous clastic siltstone， sequence-bedding fine sandstone， massive bedding fine sandstone， cross-bedding fine sandstone， and massive bedding pebbled sandstone facies. Five types of lithofacies association are summarized based on the development situation. （2） Based on the lithofacies assemblages， six sedimentary types were identified， including slump， sandy debris flow， turbidity current， hybrid event bed， bottom current， and deep-water suspended deposits. （3） Considering the tectonic setting of the basin， distribution law of deep-water sediments， and triggering mechanism of gravity flow， gravity flow was found to present evolutionary characteristics of sandy debris flow to sandy debris flow-turbidity flow to turbidity flow from the continental slope to the basin floor. Thus， the Early Cretaceous deep-water sedimentary model dominated by deep-water gravity flow in the Lingshan Island was established. Conclusions 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 the paleoenvironment and paleogeography during the Early Cretaceous in this area.
2025, 43(2): 595-608.
doi: 10.14027/j.issn.1000-0550.2024.048
Abstract:
Objective This study aimed to reveal the sedimentary characteristics and formation mechanism of the argillaceous delta of the Damoguaihe Formation in Hailaer Basin. Methods The lithology， grain size， sedimentary structure， vertical sequence， fossil types， seismic reflection characteristics， stratigraphic structure， and distribution law of the Damoguaihe Formation were analyzed in detail by studying core， outcrop， logging， logging， and seismic data. Results The results show that the Damoguaihe Formation in Hailaer Basin has the typical three-fold structure of a Gilbert delta. The rock types of the Damoguaihe Formation are mainly mudstone， silty mudstone， argillaceous siltstone， siltstone， and fine sandstone， with a small amount of thin conglomerate. The Second member of the Damoguaihe Formation has thin coal seam deposits， and no chemical rock deposits. The vertical sequence of the single well lithology is composed of composite cycle deposits. The clastic particles are suspended and jumping populations. The suspension population is more than 70%， and the jump population is less than 30%. There is a transitional zone between the suspension and jump populations that reflects the influence of river and wave action. The stratification structures formed by fluvial sedimentation and wave transformation， such as parallel stratified siltstone reacting to fluvial deposition and wave-like stratified siltstone reacting to wave action， and sand-mud interaction sedimentation with lenticular stratification， are well developed. Multi-phase "S" type foredeposits can be identified from the second section of three-dimensinal seismic data. These foredeposits are characterized by good continuity of in-phase axis and distribution of imbricated foredeposits at small angles. The isochronous section tracing of strata indicates that these foredeposits are foliated on the plane and are distributed from the edge of the depression to the center. The distribution of the foredeposits from the Damoguaihe Formation in Hailaer Basin is different from those deposited in the slope zone， which are mostly distributed in strips parallel to the slope break zone. Fault activity in the second member of Hailaer Basin was primarily stable during the depositional period. In a specific period of tectonic evolution， there was no strong fault activity in Hailaer Basin， thus restraining the influx of coarse clastic materials. However， the overall tilt and subsidence occurred in the northeast and southwest of the basin， and a broad NE-SW trending water system was formed roughly. There may be a local SW-NE drainage pattern in the basin. In addition， the mud-dominated foredeposits in the delta of the Damoguaihe Formation are associated with many low-energy meandering rivers that mainly transport fine-grained sediments. The channel image of a meander river in the study area was identified by isochronous slices of stratigraphic dynamics， and the analysis of sediment grain size showed that the muddy delta of the Damoguaihe Formation in Hailaer Basin was weak in the sedimentary period and was mainly controlled by provenance and hydrodynamic conditions. Conclusions The above research results confirm that the mud-rich sand-poor deposits in the Second member of the Damoguaihe Formation in Hailaer Basin belong to the muddy delta deposits， and the formation of the muddy delta in this area is controlled by the fine grain source and the low energy and high bending meander river with weak hydrodynamic characteristics， which provides a theoretical basis for clarifying the sedimentary characteristics and formation mechanism of the muddy delta in the study area.
Objective This study aimed to reveal the sedimentary characteristics and formation mechanism of the argillaceous delta of the Damoguaihe Formation in Hailaer Basin. Methods The lithology， grain size， sedimentary structure， vertical sequence， fossil types， seismic reflection characteristics， stratigraphic structure， and distribution law of the Damoguaihe Formation were analyzed in detail by studying core， outcrop， logging， logging， and seismic data. Results The results show that the Damoguaihe Formation in Hailaer Basin has the typical three-fold structure of a Gilbert delta. The rock types of the Damoguaihe Formation are mainly mudstone， silty mudstone， argillaceous siltstone， siltstone， and fine sandstone， with a small amount of thin conglomerate. The Second member of the Damoguaihe Formation has thin coal seam deposits， and no chemical rock deposits. The vertical sequence of the single well lithology is composed of composite cycle deposits. The clastic particles are suspended and jumping populations. The suspension population is more than 70%， and the jump population is less than 30%. There is a transitional zone between the suspension and jump populations that reflects the influence of river and wave action. The stratification structures formed by fluvial sedimentation and wave transformation， such as parallel stratified siltstone reacting to fluvial deposition and wave-like stratified siltstone reacting to wave action， and sand-mud interaction sedimentation with lenticular stratification， are well developed. Multi-phase "S" type foredeposits can be identified from the second section of three-dimensinal seismic data. These foredeposits are characterized by good continuity of in-phase axis and distribution of imbricated foredeposits at small angles. The isochronous section tracing of strata indicates that these foredeposits are foliated on the plane and are distributed from the edge of the depression to the center. The distribution of the foredeposits from the Damoguaihe Formation in Hailaer Basin is different from those deposited in the slope zone， which are mostly distributed in strips parallel to the slope break zone. Fault activity in the second member of Hailaer Basin was primarily stable during the depositional period. In a specific period of tectonic evolution， there was no strong fault activity in Hailaer Basin， thus restraining the influx of coarse clastic materials. However， the overall tilt and subsidence occurred in the northeast and southwest of the basin， and a broad NE-SW trending water system was formed roughly. There may be a local SW-NE drainage pattern in the basin. In addition， the mud-dominated foredeposits in the delta of the Damoguaihe Formation are associated with many low-energy meandering rivers that mainly transport fine-grained sediments. The channel image of a meander river in the study area was identified by isochronous slices of stratigraphic dynamics， and the analysis of sediment grain size showed that the muddy delta of the Damoguaihe Formation in Hailaer Basin was weak in the sedimentary period and was mainly controlled by provenance and hydrodynamic conditions. Conclusions The above research results confirm that the mud-rich sand-poor deposits in the Second member of the Damoguaihe Formation in Hailaer Basin belong to the muddy delta deposits， and the formation of the muddy delta in this area is controlled by the fine grain source and the low energy and high bending meander river with weak hydrodynamic characteristics， which provides a theoretical basis for clarifying the sedimentary characteristics and formation mechanism of the muddy delta in the study area.
2025, 43(2): 609-621.
doi: 10.14027/j.issn.1000-0550.2024.082
Abstract:
Objective By studying the distribution law of the river network plane of modern distributive fluvial system， the reservoir distribution of underground fluvial sand-bodies is predicted， providing a knowledge base for reservoir modeling and guiding oil and gas exploration and development. Methods Using modern geographic information software such as Google Earth， Global Mapper， and 91Satellite Map Assistant， the number and width of the Golmud fluvial fan channels were collected using equal interval survey lines， the drainage density of Golmud fluvial fan was calculated， the variation of the drainage density of Golmud fluvial fan was summarized， and the main controlling factors of drainage density were analyzed. Results （1） The characteristics of the distribution of drainage density are consistent with the process of river-pattern transition； it can be roughly divided into three stages： proximal， middle and distal. The proximal drainage density ranges from 0.089 to 0.198， with an average drainage density of 0.143； the middle drainage density ranges from 0.136 to 0.190， with an average drainage density of 0.164； and the distal drainage density ranges from 0.164 to 0.372， with an average drainage density of 0.254. （2） The drainage density is controlled by slope and geomorphological factors， with the average drainage density gradually increasing as the slope decreases from the proximal to the distal end； spring lines contribute to the growth of the drainage density， whereas the Gobi， deserts and lakes cause the drainage density to decrease. （3） By studying the drainage density of the Golmud fluvial fan， the measurements can provide data support for three-dimensional （3D） geological modeling of subsurface sand bodies. Conclusions The drainage density responds to the change rule of the channel width along the course within the river fan. By portraying the drainage density within the range of the modern depositional system， it can provide a reference basis for the density of the sandstone and the area ratio of the sand body on the subsurface depositional transects.
Objective By studying the distribution law of the river network plane of modern distributive fluvial system， the reservoir distribution of underground fluvial sand-bodies is predicted， providing a knowledge base for reservoir modeling and guiding oil and gas exploration and development. Methods Using modern geographic information software such as Google Earth， Global Mapper， and 91Satellite Map Assistant， the number and width of the Golmud fluvial fan channels were collected using equal interval survey lines， the drainage density of Golmud fluvial fan was calculated， the variation of the drainage density of Golmud fluvial fan was summarized， and the main controlling factors of drainage density were analyzed. Results （1） The characteristics of the distribution of drainage density are consistent with the process of river-pattern transition； it can be roughly divided into three stages： proximal， middle and distal. The proximal drainage density ranges from 0.089 to 0.198， with an average drainage density of 0.143； the middle drainage density ranges from 0.136 to 0.190， with an average drainage density of 0.164； and the distal drainage density ranges from 0.164 to 0.372， with an average drainage density of 0.254. （2） The drainage density is controlled by slope and geomorphological factors， with the average drainage density gradually increasing as the slope decreases from the proximal to the distal end； spring lines contribute to the growth of the drainage density， whereas the Gobi， deserts and lakes cause the drainage density to decrease. （3） By studying the drainage density of the Golmud fluvial fan， the measurements can provide data support for three-dimensional （3D） geological modeling of subsurface sand bodies. Conclusions The drainage density responds to the change rule of the channel width along the course within the river fan. By portraying the drainage density within the range of the modern depositional system， it can provide a reference basis for the density of the sandstone and the area ratio of the sand body on the subsurface depositional transects.
2025, 43(2): 622-634.
doi: 10.14027/j.issn.1000-0550.2023.039
Abstract:
Objective The offshore Indus Basin was located in the equatorial region during the Paleocene-Eocene period， and a large-scale carbonate platform was developed. However， limited by the quality and quantity of two-dimensional （2D） seismic data， the sedimentary characteristics and evolution of the carbonate platform are not clear， and the internal structure of the platform is not depicted sufficiently， which further restricts the deepening of oil and gas exploration in this area. Methods Through the collection of previous and newly acquired 2D seismic and drilling data， the seismic facies identification of the Paleocene-Eocene carbonate platform in the offshore Indus Basin was performed， 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， six 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 facies， with good reservoir physical properties. Based on seismic facies analysis， the carbonate platform in the study area is divided into four sedimentary evolution stages， including initial development， prosperity， recession， and inundation stages. 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 the 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 were further reduced， and the reef and shoal facies were deposited， and the platform was gradually inundated by seawater in the late stage. Conclusions 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 Paleocene-Eocene period， and sea level rise and fall and paleoclimate evolution affect the platform shape. In the petroleum accumulation process of the reef reservoir， 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 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 northeast （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， as well as support for oil and gas exploration in the region.
Objective The offshore Indus Basin was located in the equatorial region during the Paleocene-Eocene period， and a large-scale carbonate platform was developed. However， limited by the quality and quantity of two-dimensional （2D） seismic data， the sedimentary characteristics and evolution of the carbonate platform are not clear， and the internal structure of the platform is not depicted sufficiently， which further restricts the deepening of oil and gas exploration in this area. Methods Through the collection of previous and newly acquired 2D seismic and drilling data， the seismic facies identification of the Paleocene-Eocene carbonate platform in the offshore Indus Basin was performed， 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， six 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 facies， with good reservoir physical properties. Based on seismic facies analysis， the carbonate platform in the study area is divided into four sedimentary evolution stages， including initial development， prosperity， recession， and inundation stages. 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 the 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 were further reduced， and the reef and shoal facies were deposited， and the platform was gradually inundated by seawater in the late stage. Conclusions 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 Paleocene-Eocene period， and sea level rise and fall and paleoclimate evolution affect the platform shape. In the petroleum accumulation process of the reef reservoir， 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 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 northeast （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， as well as support for oil and gas exploration in the region.
2025, 43(2): 635-652.
doi: 10.14027/j.issn.1000-0550.2023.030
Abstract:
Objective Mixed siliciclastic-carbonate reservoirs are a new target reservoir for hydrocarbon exploration； however， the heterogeneities can lead to unanswered questions. Previous studies have focused on “strata mixing” sediments， with little attention giben to the “compositional mixing” type. In recent years， typical “compositional mixing” sedimentation has been discovered in medium-deep Paleogene deposits in the Bohai Sea with breakthroughs in oil and gas exploration， providing an ideal case to explore the heterogeneity within “compositional mixing” deposits. Methods Abundant drilling data were used for detailed studies on the characteristics and main controlling factors of the heterogeneities associated with “compositional mixing”. Results Two principal reservoir types were recognized in this study： biological and debris-flows mixing shores. The two types have significant heterogeneities in petrofabric and spatial distribution owing to a complex interplay of controlling factors. The biological mixing shore reservoir is distributed in the flanks of detrital deposition and/or a higher position of structural units t\controlled by paleoclimate. Lake-level changes influence the vertical stacking of different genetic facies within this reservoir type.. The debris-flows mixing shoal reservoir has later distribution on the proximal area of nearby uplift because this type can be controlled by the interplay of paleoclimate and paleo water-depth. Furthermore， the vertical patterns are heterolithic and are related to the variational hydrodynamic strength of gravity-driven depositional processes. The complex heterogeneity of the reservoir physical properties and pore structure is attributed to the mutual influence of clastic components supply， selective dissolution， dolomitization， cement type， and quantity. Conclusions Finally， a formation model of “compositional mixing” heterogeneity was developed， with significance for the further reservoir prediction and evaluation of worldwide mixed sediments reservoirs.
Objective Mixed siliciclastic-carbonate reservoirs are a new target reservoir for hydrocarbon exploration； however， the heterogeneities can lead to unanswered questions. Previous studies have focused on “strata mixing” sediments， with little attention giben to the “compositional mixing” type. In recent years， typical “compositional mixing” sedimentation has been discovered in medium-deep Paleogene deposits in the Bohai Sea with breakthroughs in oil and gas exploration， providing an ideal case to explore the heterogeneity within “compositional mixing” deposits. Methods Abundant drilling data were used for detailed studies on the characteristics and main controlling factors of the heterogeneities associated with “compositional mixing”. Results Two principal reservoir types were recognized in this study： biological and debris-flows mixing shores. The two types have significant heterogeneities in petrofabric and spatial distribution owing to a complex interplay of controlling factors. The biological mixing shore reservoir is distributed in the flanks of detrital deposition and/or a higher position of structural units t\controlled by paleoclimate. Lake-level changes influence the vertical stacking of different genetic facies within this reservoir type.. The debris-flows mixing shoal reservoir has later distribution on the proximal area of nearby uplift because this type can be controlled by the interplay of paleoclimate and paleo water-depth. Furthermore， the vertical patterns are heterolithic and are related to the variational hydrodynamic strength of gravity-driven depositional processes. The complex heterogeneity of the reservoir physical properties and pore structure is attributed to the mutual influence of clastic components supply， selective dissolution， dolomitization， cement type， and quantity. Conclusions Finally， a formation model of “compositional mixing” heterogeneity was developed， with significance for the further reservoir prediction and evaluation of worldwide mixed sediments reservoirs.
2025, 43(2): 653-667.
doi: 10.14027/j.issn.1000-0550.2023.055
Abstract:
Objective The typical "mixed sediments" of the Wujiapingian age of Permian in the northwest of Sichuan Basin exhibits great potential exploration， but the research on its diagenesis and pore evolution is relatively weak. Methods Based on the data of field profile， core， thin section， cathodoluminescence and geochemical analysis， the petrological characteristics， diagenesis and pore evolution of the Upper Permian Wujiaping Formation in the northwest of Sichuan Basin are studied. Results The Wujiaping Formation in the northwest of Sichuan develops four major rocks and diverse lithology， but mainly carbonate rocks， and the First to Third members of Wujiaping Formation are developed. Volcanic clastic rocks are mainly developed in the middle of Wu2 member in well Shuangtan 1 area， and siliceous rocks are mainly produced in thin layers from the lower part of Wu1 member to the middle part of Wu2 member. The clastic rocks are mainly shale （mudstone）， which are distributed at the bottom of the First member of Wujiaping Formation， with undeveloped pores. The dissolution and metasomatism experienced by various rocks are obviously different. The manifestation and intensity of dissolution in different lithology are different. Carbonate rocks are the most developed and the dissolution between grains/crystalline grain is the most common， followed by pyroclastic rocks， and the dissolution of siliceous rocks is the weakest， which is only seen in the dissolution of the non-silicified carbonate components. There are many types of metasomatism in different lithology： dolomitization and silicification are common in carbonate rocks； Pyroclastic rocks are devitrification， while siliceous rocks are silicification and a small amount of dolomitization. The key diagenetic stages and functions conducive to the development of pores in various rocks are different： the interparticle/intergranular dissolved pores and fractures mainly developed in carbonate rocks are controlled by the dissolution of meteoric water at the contemporaneous stage， the dolomitization of evaporated seawater， and the dissolution， dolomitization， and structural fracture of the burial environment. Volcanic clastic rocks are mainly interparticle shrinkage pores formed by devitrification in the early diagenetic stage， while siliceous rocks have the weakest pore development， which are mainly controlled by the residual carbonate components of meteoric water dissolution in the contemporaneous stage， fractures formed by tectonic fractures and their dissolution. Conclusions Therefore， the mixed deposition formed different lithology with different components， and the dissolution， dolomitization and tectonic fracture at different diagenetic stages had different effects on it， thus controlling the difference of pore development and evolution.
Objective The typical "mixed sediments" of the Wujiapingian age of Permian in the northwest of Sichuan Basin exhibits great potential exploration， but the research on its diagenesis and pore evolution is relatively weak. Methods Based on the data of field profile， core， thin section， cathodoluminescence and geochemical analysis， the petrological characteristics， diagenesis and pore evolution of the Upper Permian Wujiaping Formation in the northwest of Sichuan Basin are studied. Results The Wujiaping Formation in the northwest of Sichuan develops four major rocks and diverse lithology， but mainly carbonate rocks， and the First to Third members of Wujiaping Formation are developed. Volcanic clastic rocks are mainly developed in the middle of Wu2 member in well Shuangtan 1 area， and siliceous rocks are mainly produced in thin layers from the lower part of Wu1 member to the middle part of Wu2 member. The clastic rocks are mainly shale （mudstone）， which are distributed at the bottom of the First member of Wujiaping Formation， with undeveloped pores. The dissolution and metasomatism experienced by various rocks are obviously different. The manifestation and intensity of dissolution in different lithology are different. Carbonate rocks are the most developed and the dissolution between grains/crystalline grain is the most common， followed by pyroclastic rocks， and the dissolution of siliceous rocks is the weakest， which is only seen in the dissolution of the non-silicified carbonate components. There are many types of metasomatism in different lithology： dolomitization and silicification are common in carbonate rocks； Pyroclastic rocks are devitrification， while siliceous rocks are silicification and a small amount of dolomitization. The key diagenetic stages and functions conducive to the development of pores in various rocks are different： the interparticle/intergranular dissolved pores and fractures mainly developed in carbonate rocks are controlled by the dissolution of meteoric water at the contemporaneous stage， the dolomitization of evaporated seawater， and the dissolution， dolomitization， and structural fracture of the burial environment. Volcanic clastic rocks are mainly interparticle shrinkage pores formed by devitrification in the early diagenetic stage， while siliceous rocks have the weakest pore development， which are mainly controlled by the residual carbonate components of meteoric water dissolution in the contemporaneous stage， fractures formed by tectonic fractures and their dissolution. Conclusions Therefore， the mixed deposition formed different lithology with different components， and the dissolution， dolomitization and tectonic fracture at different diagenetic stages had different effects on it， thus controlling the difference of pore development and evolution.
2025, 43(2): 668-682.
doi: 10.14027/j.issn.1000-0550.2023.017
Abstract:
Objective The Precambrian Ediacaran⁃Cambrian transition period is extremely important for the evolution of early life on Earth. The explosion and radiation of multicellular life are closely related to the paleoclimate， seawater oxygen content and marine sedimentary environment during this period. In order to reveal the paleoclimate and paleomarine environment during the early eruption of life in the Cambrian， and to understand the relationship between the global paleomarine medium conditions and the co-evolution of early life in the early Cambrian， this study considers Cambrian strata in eastern Yunnan province which recorded the scenario of the eruption of life in the Cambrian. Methods The petrological and sedimentological characteristics are based on detailed descriptions of typical outcrop sections in the field. The paleo-ocean， paleoclimate and paleoenvironment of the Yuhucun Formation in Zhujiaqing area， Huize， eastern Yunnan province were reconstructed from tests and analysis of major elements， trace elements and rare earth elements. Results The Yuhucun Formation in this region was found to be mainly a set of shallow marine carbonate rocks， accompanied by a small amount of clastic rocks and phosphorite. It was formed in the tidal flat facies belt of the carbonate platform， divided between supratidal-intertidal and subtidal microfacies. The U/Th， V/Cr and V/（V+Ni） values indicate that the paleo-ocean was in an oxygen-poor-anoxic environment during the deposition of the lower Cambrian Yuhucun Formation in the Huize area， and the seawater reducibility was generally weakened. The Sr/Ca and K/Na values indicate that the paleo-ocean salinity experienced three secondary increase/decrease cycles. The Sr/Cu and SiO2/Al2O3 values indicate that the paleoclimate was generally arid， but fluctuating warming events during the period reflect dry/wet alternation in the early Cambrian. The regional sea-level change and paleoclimate are consistent with the early Cambrian. Conclusions This reconstruction of the paleomarine environment and paleoclimate during the sedimentary period of the Yuhucun Formation in eastern Yunnan reveals the co-evolution of global biological evolution and sedimentary environment in the early Cambrian Newfoundland.
Objective The Precambrian Ediacaran⁃Cambrian transition period is extremely important for the evolution of early life on Earth. The explosion and radiation of multicellular life are closely related to the paleoclimate， seawater oxygen content and marine sedimentary environment during this period. In order to reveal the paleoclimate and paleomarine environment during the early eruption of life in the Cambrian， and to understand the relationship between the global paleomarine medium conditions and the co-evolution of early life in the early Cambrian， this study considers Cambrian strata in eastern Yunnan province which recorded the scenario of the eruption of life in the Cambrian. Methods The petrological and sedimentological characteristics are based on detailed descriptions of typical outcrop sections in the field. The paleo-ocean， paleoclimate and paleoenvironment of the Yuhucun Formation in Zhujiaqing area， Huize， eastern Yunnan province were reconstructed from tests and analysis of major elements， trace elements and rare earth elements. Results The Yuhucun Formation in this region was found to be mainly a set of shallow marine carbonate rocks， accompanied by a small amount of clastic rocks and phosphorite. It was formed in the tidal flat facies belt of the carbonate platform， divided between supratidal-intertidal and subtidal microfacies. The U/Th， V/Cr and V/（V+Ni） values indicate that the paleo-ocean was in an oxygen-poor-anoxic environment during the deposition of the lower Cambrian Yuhucun Formation in the Huize area， and the seawater reducibility was generally weakened. The Sr/Ca and K/Na values indicate that the paleo-ocean salinity experienced three secondary increase/decrease cycles. The Sr/Cu and SiO2/Al2O3 values indicate that the paleoclimate was generally arid， but fluctuating warming events during the period reflect dry/wet alternation in the early Cambrian. The regional sea-level change and paleoclimate are consistent with the early Cambrian. Conclusions This reconstruction of the paleomarine environment and paleoclimate during the sedimentary period of the Yuhucun Formation in eastern Yunnan reveals the co-evolution of global biological evolution and sedimentary environment in the early Cambrian Newfoundland.
2025, 43(2): 683-700.
doi: 10.14027/j.issn.1000-0550.2024.028
Abstract:
Objective We explored the distribution pattern， composition characteristics， and main controlling factors of four types of high-abnormally high abundant rearranged hopanes in coal measure source rocks in the Ordos Basin. Methods The saturated hydrocarbons and aromatic hydrocarbons of 29 coal measure source rocks in the Upper Paleozoic of the Ordos Basin were analyzed in detail using gas chromatography-mass spectrometry （GC-MS）. Results Based on the peak order and retention time of the compounds， GC-MS analysis of the coal measure source rocks in Ordos Basin was conducted. Four types of rearranged hopanes with different abundances were systematically identified： 17α （H） -rearranged hopane series （C30*）， 18α（H） -neohopane series （Ts and C29Ts）， early-eluting rearranged hopane series （C30E）， and 28，30-dinor-21-methyl rearranged hopane series （29Nsp）. The peak order of the four types of rearranged hopane compounds is： early-eluting rearranged hopane series > 17α （H） -rearranged hopane series > 18α （H） -neohopane series > 28，30-dinor-21-methyl rearranged hopane series （29Nsp）. The study of the internal composition of these four types of rearranged hopane compounds in the coal measure source rocks in the study area shows good correlation between the same types of rearranged hopane compounds； that is， there is a good correlation between C30*/C30 hopane and C29*/C29 hopane， C29Ts/C29 hopane and Ts/Tm. The correlation between different types of rearranged hopanes is different. The correlation between C30*/C30 hopane， C30E/C30 hopane and 29Nsp/C29 hopane is good， but the correlation between C29Ts/C29 hopane and the other three is poor， indicating that the formation mechanism of different types of rearranged hopanes may differ. In addition， the relative abundance of 17α （H） -diahopane series， early elution diahopane series， and 28，30-dinor-21-methyldiahopane series （29Nsp） in the coal measure source rock samples is significantly affected by water redox and salinity conditions. With the increase of thermal evolution degree of organic matter， the relative abundance of these rearranged hopane compounds shows an approximate normal distribution. In the peak stage of oil generation （Ro is between 0.80% and 0.90%）， the relative abundance of high-abnormally high abundant rearranged hopanes compounds reaches the peak， but maturity has little effect on low abundance rearranged hopanes. Furthermore， the ratios of （C28+C29） tricyclic terpane （TT）/C30 hopane and regular sterane/C30-35 hopane in samples with high-abnormally high abundance and the ratios of rearranged hopanes to hopanes with the same carbon number （C30*/C30 hopane， C30E/C30 hopane， 29Nsp/C29 hopane） have clear positive correlations， revealing that the biogenic materials of high-abnormally high abundant rearranged hopanes compounds are primarily lower aquatic organisms and bacteria and algae compounds. Conclusions Based on the same evolution path and formation mechanism of the same types of rearranged hopanes， there are 17α （H） -rearranged hopanes with high-abnormally high abundance， early elution rearranged hopanes， and 28，30-dinor-21-methyl rearranged hopanes in the coal measure source rocks， which formed in the sedimentary environment with Pr/Ph values between 1.00 and 2.00 and a gammacerane index between 0.10 and 0.13， and the biological precursors are mainly bacterial hopanes. The formation of high-abnormally high abundance 18α （H） -neohopanes is mainly controlled by the biogenic parent material of organic matter， which may be limonene or C29 hopane compounds.
Objective We explored the distribution pattern， composition characteristics， and main controlling factors of four types of high-abnormally high abundant rearranged hopanes in coal measure source rocks in the Ordos Basin. Methods The saturated hydrocarbons and aromatic hydrocarbons of 29 coal measure source rocks in the Upper Paleozoic of the Ordos Basin were analyzed in detail using gas chromatography-mass spectrometry （GC-MS）. Results Based on the peak order and retention time of the compounds， GC-MS analysis of the coal measure source rocks in Ordos Basin was conducted. Four types of rearranged hopanes with different abundances were systematically identified： 17α （H） -rearranged hopane series （C30*）， 18α（H） -neohopane series （Ts and C29Ts）， early-eluting rearranged hopane series （C30E）， and 28，30-dinor-21-methyl rearranged hopane series （29Nsp）. The peak order of the four types of rearranged hopane compounds is： early-eluting rearranged hopane series > 17α （H） -rearranged hopane series > 18α （H） -neohopane series > 28，30-dinor-21-methyl rearranged hopane series （29Nsp）. The study of the internal composition of these four types of rearranged hopane compounds in the coal measure source rocks in the study area shows good correlation between the same types of rearranged hopane compounds； that is， there is a good correlation between C30*/C30 hopane and C29*/C29 hopane， C29Ts/C29 hopane and Ts/Tm. The correlation between different types of rearranged hopanes is different. The correlation between C30*/C30 hopane， C30E/C30 hopane and 29Nsp/C29 hopane is good， but the correlation between C29Ts/C29 hopane and the other three is poor， indicating that the formation mechanism of different types of rearranged hopanes may differ. In addition， the relative abundance of 17α （H） -diahopane series， early elution diahopane series， and 28，30-dinor-21-methyldiahopane series （29Nsp） in the coal measure source rock samples is significantly affected by water redox and salinity conditions. With the increase of thermal evolution degree of organic matter， the relative abundance of these rearranged hopane compounds shows an approximate normal distribution. In the peak stage of oil generation （Ro is between 0.80% and 0.90%）， the relative abundance of high-abnormally high abundant rearranged hopanes compounds reaches the peak， but maturity has little effect on low abundance rearranged hopanes. Furthermore， the ratios of （C28+C29） tricyclic terpane （TT）/C30 hopane and regular sterane/C30-35 hopane in samples with high-abnormally high abundance and the ratios of rearranged hopanes to hopanes with the same carbon number （C30*/C30 hopane， C30E/C30 hopane， 29Nsp/C29 hopane） have clear positive correlations， revealing that the biogenic materials of high-abnormally high abundant rearranged hopanes compounds are primarily lower aquatic organisms and bacteria and algae compounds. Conclusions Based on the same evolution path and formation mechanism of the same types of rearranged hopanes， there are 17α （H） -rearranged hopanes with high-abnormally high abundance， early elution rearranged hopanes， and 28，30-dinor-21-methyl rearranged hopanes in the coal measure source rocks， which formed in the sedimentary environment with Pr/Ph values between 1.00 and 2.00 and a gammacerane index between 0.10 and 0.13， and the biological precursors are mainly bacterial hopanes. The formation of high-abnormally high abundance 18α （H） -neohopanes is mainly controlled by the biogenic parent material of organic matter， which may be limonene or C29 hopane compounds.
2025, 43(2): 701-733.
doi: 10.14027/j.issn.1000-0550.2023.060
Abstract:
Objective The depositional environmental conditions required for the enrichment of organic matter in black shale are not only related to shale oil and gas exploration， but also to other sedimentary minerals and geosciences. For example， bauxite， phosphate rock， manganese ore， and barite ore often coexist with black shale， and the development of black shale is an important environmental or ore prospecting symbol. It is also used as an important reference for paleoclimate， and even the most important evidence of ocean anoxic events is the development of black shale； the current carbon neutralization and carbon sequestration are also required to study carbon burial. Therefore， it is imporatnt to study the development of black shale and the enrichment mechanism of the contained organic matter. It is believed that organic-rich shale develops in deep-water environments， because the deeper the water body， the stronger the reducing environment， making it conducive to the preservation of organic matter. For example， deep-water continental shelves and deep-to-semi-deep lakes can develop high-quality source rocks. However， a large number of exploration practices have proven that these views may have problems and are contrary to modern ecology. Methods For this reason， this study took the Wufeng Formation-Longmaxi Formation shale in the Sichuan Basin as an example and fully combined the spatial distribution of primary productivity and the carbon fixation rate of different water bodies. Sedimentary facies and paleogeography， fossil development， salinity and other characteristics， and the distribution characteristics of shale and its organic matter in space and time were studied. Results The study found that the development of organic-rich shale requires three characteristics： shallow， continental， and sealed. （1） "Shallow" refers to the shallow water environment. The shallower the water body is， the higher the primary productivity and carbon fixation rate； shale is symbiotic with sapropelite， humic coal， evaporite rock， and other shallow water environments； it has cross-laminated， wavy shallow-water characteristic sedimentary structures， such as laminae and grain sequence texture. Judging from the characteristics of modern peat development， organic-rich peat developed only before or at the end of the transgression； the three major ice ages （regression） from the Proterozoic to the Early Paleozoic had a good correspondence with the enrichment of organic matter， confirming that more shallow swamps and lagoons are prone to appear in the regressive environment and are rich in organic matter； during transgression or high water body sedimentation， particularly in the period of maximum flooding， it is not conducive to the enrichment of organic matter， and the dense section is not rich in organic matter. （2） "Land" has two meanings： organic-rich shale is distributed near land and far from water， and the contribution of terrigenous organic matter. Shale oil and gas have the same pattern as coal seams， the horsetail pattern： the closer to the land， the richer the organic matter， which is consistent with the modern ocean primary productivity near the land and far water； the evolution and eruption age of the organic matter types of organic-rich shale and coal is consistent with that of land. The evolution process of organisms on land is consistent. From the Proterozoic to the Early Paleozoic， the lower organisms dominated the land， and the shale and coal were sapropelic. After the outbreak of higher plants on land， the organic matter type was mainly humic. （3） "Seal" means that the water body is well sealed. Closed lagoons and bays that are less affected by tidal currents and ocean currents are conducive to the enrichment of organic matter and most minerals， and this environment is a low-energy， stagnant， and strongly reducing environment. The more closed the water body is， the higher the carbon fixation rate， and most oil and gas shales are developed in restricted low-salinity， shallow water environments. Conclusions The conclusion is that （1） the carbon， nitrogen， and phosphorus in the water body are derived from exogenous sources， such as from the land； （2） the development of terrestrial organisms controls the organic matter types of shale and coal； （3） the middle and upper Yangtze region， particularly the organic-rich shale of the Wufeng Formation- Longmaxi Formation in the Sichuan Basin， developed in a regressive environment， which is a shallow-water marine-continental transitional facies environment such as lagoons and relatively closed bays restricted by ancient continents and underwater low uplifts. It is located at the edge of the basin rather than the center of sedimentation and subsidence； the limestones of the Linxiang Baota Formation and Guanyinqiao member were developed in the open sea area with normal salinity after transgression and the bay with moderate salinity respectively； （4） Finally， the depth of the water body was established. The enrichment law of organic matter was described by a two-dimensional table of sealing； three main controlling factors of organic matter enrichment in marine shale were proposed： sealed， shallow， land， water body with good sealing， shallow water body （<40 m）， It is close to the land and has a rich supply of terrestrial organic matter.
Objective The depositional environmental conditions required for the enrichment of organic matter in black shale are not only related to shale oil and gas exploration， but also to other sedimentary minerals and geosciences. For example， bauxite， phosphate rock， manganese ore， and barite ore often coexist with black shale， and the development of black shale is an important environmental or ore prospecting symbol. It is also used as an important reference for paleoclimate， and even the most important evidence of ocean anoxic events is the development of black shale； the current carbon neutralization and carbon sequestration are also required to study carbon burial. Therefore， it is imporatnt to study the development of black shale and the enrichment mechanism of the contained organic matter. It is believed that organic-rich shale develops in deep-water environments， because the deeper the water body， the stronger the reducing environment， making it conducive to the preservation of organic matter. For example， deep-water continental shelves and deep-to-semi-deep lakes can develop high-quality source rocks. However， a large number of exploration practices have proven that these views may have problems and are contrary to modern ecology. Methods For this reason， this study took the Wufeng Formation-Longmaxi Formation shale in the Sichuan Basin as an example and fully combined the spatial distribution of primary productivity and the carbon fixation rate of different water bodies. Sedimentary facies and paleogeography， fossil development， salinity and other characteristics， and the distribution characteristics of shale and its organic matter in space and time were studied. Results The study found that the development of organic-rich shale requires three characteristics： shallow， continental， and sealed. （1） "Shallow" refers to the shallow water environment. The shallower the water body is， the higher the primary productivity and carbon fixation rate； shale is symbiotic with sapropelite， humic coal， evaporite rock， and other shallow water environments； it has cross-laminated， wavy shallow-water characteristic sedimentary structures， such as laminae and grain sequence texture. Judging from the characteristics of modern peat development， organic-rich peat developed only before or at the end of the transgression； the three major ice ages （regression） from the Proterozoic to the Early Paleozoic had a good correspondence with the enrichment of organic matter， confirming that more shallow swamps and lagoons are prone to appear in the regressive environment and are rich in organic matter； during transgression or high water body sedimentation， particularly in the period of maximum flooding， it is not conducive to the enrichment of organic matter， and the dense section is not rich in organic matter. （2） "Land" has two meanings： organic-rich shale is distributed near land and far from water， and the contribution of terrigenous organic matter. Shale oil and gas have the same pattern as coal seams， the horsetail pattern： the closer to the land， the richer the organic matter， which is consistent with the modern ocean primary productivity near the land and far water； the evolution and eruption age of the organic matter types of organic-rich shale and coal is consistent with that of land. The evolution process of organisms on land is consistent. From the Proterozoic to the Early Paleozoic， the lower organisms dominated the land， and the shale and coal were sapropelic. After the outbreak of higher plants on land， the organic matter type was mainly humic. （3） "Seal" means that the water body is well sealed. Closed lagoons and bays that are less affected by tidal currents and ocean currents are conducive to the enrichment of organic matter and most minerals， and this environment is a low-energy， stagnant， and strongly reducing environment. The more closed the water body is， the higher the carbon fixation rate， and most oil and gas shales are developed in restricted low-salinity， shallow water environments. Conclusions The conclusion is that （1） the carbon， nitrogen， and phosphorus in the water body are derived from exogenous sources， such as from the land； （2） the development of terrestrial organisms controls the organic matter types of shale and coal； （3） the middle and upper Yangtze region， particularly the organic-rich shale of the Wufeng Formation- Longmaxi Formation in the Sichuan Basin， developed in a regressive environment， which is a shallow-water marine-continental transitional facies environment such as lagoons and relatively closed bays restricted by ancient continents and underwater low uplifts. It is located at the edge of the basin rather than the center of sedimentation and subsidence； the limestones of the Linxiang Baota Formation and Guanyinqiao member were developed in the open sea area with normal salinity after transgression and the bay with moderate salinity respectively； （4） Finally， the depth of the water body was established. The enrichment law of organic matter was described by a two-dimensional table of sealing； three main controlling factors of organic matter enrichment in marine shale were proposed： sealed， shallow， land， water body with good sealing， shallow water body （<40 m）， It is close to the land and has a rich supply of terrestrial organic matter.
2025, 43(2): 734-749.
doi: 10.14027/j.issn.1000-0550.2023.037
Abstract:
Objective It is important to clarify the response relationship between the evolution of sedimentary environment and the lithofacies and the enrichment characteristics of organic matter. Methods Conducting analyses such as microsection and major/trace element testing， combined with geological data of the study area， typical lithofacies types and their paleosedimentary environments were analyzed， and the differential enrichment mechanism of typical fine-grained sedimentary organic matter under the influence of different paleosedimentary environments was explained. Results The study shows that the lithofacies types of fine-grained sedimentary rocks in member 1 of the Qingshankou Formation in Changling Sag can be divided into medium organic matter massive mixed， high organic matter laminar / layered felsic， and low organic matter massive clayey shale facies according to the lower， middle and upper parts. The vertical evolution of paleoclimate， terrigenous input， paleoproductivity， paleosalinity， and redox environment of the target horizon has distinct stages， which jointly affect the vertical distribution of lithofacies types and the enrichment mechanism of organic matter. Among them， the lower organic matter is the enrichment mechanism of middle paleoproductivity， medium preservation conditions， and strong flocculation sedimentation； the middle organic matter is the enrichment mechanism of high paleoproductivity， high preservation conditions， and weak flocculation deposition； and the upper organic matter is the enrichment mechanism of low paleoproductivity， high preservation conditions， and strong flocculation deposition. Conclusions The establishment of the differential enrichment mechanism of organic matter in the fine-grained sedimentary rock of the First member of the Qingling Formation provides a new idea for the formation mechanism of organic rich shale， as well as a geological basis for unconventional oil and gas exploration of the Qing 1 member in Changling Sag.
Objective It is important to clarify the response relationship between the evolution of sedimentary environment and the lithofacies and the enrichment characteristics of organic matter. Methods Conducting analyses such as microsection and major/trace element testing， combined with geological data of the study area， typical lithofacies types and their paleosedimentary environments were analyzed， and the differential enrichment mechanism of typical fine-grained sedimentary organic matter under the influence of different paleosedimentary environments was explained. Results The study shows that the lithofacies types of fine-grained sedimentary rocks in member 1 of the Qingshankou Formation in Changling Sag can be divided into medium organic matter massive mixed， high organic matter laminar / layered felsic， and low organic matter massive clayey shale facies according to the lower， middle and upper parts. The vertical evolution of paleoclimate， terrigenous input， paleoproductivity， paleosalinity， and redox environment of the target horizon has distinct stages， which jointly affect the vertical distribution of lithofacies types and the enrichment mechanism of organic matter. Among them， the lower organic matter is the enrichment mechanism of middle paleoproductivity， medium preservation conditions， and strong flocculation sedimentation； the middle organic matter is the enrichment mechanism of high paleoproductivity， high preservation conditions， and weak flocculation deposition； and the upper organic matter is the enrichment mechanism of low paleoproductivity， high preservation conditions， and strong flocculation deposition. Conclusions The establishment of the differential enrichment mechanism of organic matter in the fine-grained sedimentary rock of the First member of the Qingling Formation provides a new idea for the formation mechanism of organic rich shale， as well as a geological basis for unconventional oil and gas exploration of the Qing 1 member in Changling Sag.
2025, 43(2): 750-768.
doi: 10.14027/j.issn.1000-0550.2023.016
Abstract:
Objective The lacustrine fine-grained sedimentary rocks in Dongying Sag have great prospects for unconventional oil and gas resources. However， owing to the 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 the organic matter enrichment model is unclear， limiting the progress of unconventional oil and gas exploration. Cyclostratigraphy can divide high-frequency sequences and conduct a fine stratigraphic correlation， and can also explore the process of fine-grained rock deposition driven by astronomical cycles， which is an important means to establish the organic matter enrichment model and predict the sweet spot of shale oil. Methods Taking well LY1 in Dongying Sag， Bohai Bay Basin， as an example， the cyclostratigraphy of lacustrine fine-grained sedimentary rocks in the lower Es3（Es3 l 4 u 3 l 4 u 3 l 4 u 4 u 3 l 3 l
Objective The lacustrine fine-grained sedimentary rocks in Dongying Sag have great prospects for unconventional oil and gas resources. However， owing to the 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 the organic matter enrichment model is unclear， limiting the progress of unconventional oil and gas exploration. Cyclostratigraphy can divide high-frequency sequences and conduct a fine stratigraphic correlation， and can also explore the process of fine-grained rock deposition driven by astronomical cycles， which is an important means to establish the organic matter enrichment model and predict the sweet spot of shale oil. Methods Taking well LY1 in Dongying Sag， Bohai Bay Basin， as an example， the cyclostratigraphy of lacustrine fine-grained sedimentary rocks in the lower Es3（Es
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Sponsor: Committee of Sedimentology, Chinese Society for Mineralogy, Petrology and Geochemistry
Commission on Sedimentary Geology, Geological Society of China
Northwest Institute of Eco-Environment and Resources, CAS
Editor-in-chief: Wang Chengshan
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