Current Issue
2025 Vol. 43, No. 2
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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
Abstract:
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
