Current Articles
2026, Volume 44, Issue 4
Display Method:
2026,
44(4):
1215-1237.
doi: 10.14027/j.issn.1000-0550.2026.004
Abstract:
Objective The Late Ordovician to Early Silurian represents a critical transition in Earth's history， characterized by the Hirnantian glaciation and the end-Ordovician mass extinction event. However， significant uncertainties persist in the chronostratigraphic framework for this interval， limiting our understanding of the mechanisms driving biotic extinction and climatic evolution. This study aims to establish a high-resolution absolute astronomical time scale for the Late Ordovician-Early Silurian through the integration of cyclostratigraphy and isotopic geochronology， providing robust temporal constraints for major geological events. Methods Three sections （Shuanghe in Chang-ning， Sichuan； Anwen in Qijiang， Chongqing； and Wangjiawan in Yichang， Hubei） were selected as study sites. High-resolution elemental data （Si， Fe， Ca， Al， Rb/Sr， etc.） were analyzed using AnalySeries and Acycle software to identify Milankovitch cycle signals. Sedimentation rates were estimated using the COCO/eCOCO and TimeOpt methods to construct floating astronomical time scales. CA-ID-TIMS zircon U-Pb dating was conducted on volcanic ash beds to obtain absolute age anchors， enabling precise conversion from the depth domain to the time domain. Results （1） Stable sedimentary cycles corresponding to 405-kyr and ~100-kyr long and short eccentricity cycles were identified in the XRF elemental series. Floating astronomical time scales of 12.2 Myr， 10.3 Myr， and 2.75 Myr were established for the Shuanghe section， Anwen section， and Wangjiawan section， respectively. （2） Given the most complete geological record preserved in the Shuanghe section， the ages of the Ordovician/Silurian （O/S） boundary and the base of the Hirnantian stage， calibrated to 442.34 ± 0.22 Ma and 443.78 ± 0.22 Ma respectively through cyclostratigraphic analysis combined with U-Pb dating of volcanic ash beds （Shuanghe section： 438.47 ± 0.17 Ma）， can serve as a candidate for future international chronostratigraphic standards. （3） The duration of the Hirnantian stage is 1.44 Myr at the Shuanghe section， but only ~0.41 Myr at the Wangjiawan section， suggesting that a sedimentary hiatus may exist in the Wangjiawan section. （4） Paleoclimatic proxies and sea-level changes exhibited long-period fluctuations of 1.2 Myr and 2.4 Myr. Conclusions The high-precision astronomical time scale established in this study significantly improves the accuracy of the chronostratigraphic framework for the Late Ordovician-Early Silurian， revealing the rapid onset of the end-Ordovician mass extinction. Astronomical cycles played a significant role in driving climate-environmental evolution during this interval， providing key temporal constraints for understanding the triggering mechanisms of the end-Ordovician mass extinction.
Objective The Late Ordovician to Early Silurian represents a critical transition in Earth's history， characterized by the Hirnantian glaciation and the end-Ordovician mass extinction event. However， significant uncertainties persist in the chronostratigraphic framework for this interval， limiting our understanding of the mechanisms driving biotic extinction and climatic evolution. This study aims to establish a high-resolution absolute astronomical time scale for the Late Ordovician-Early Silurian through the integration of cyclostratigraphy and isotopic geochronology， providing robust temporal constraints for major geological events. Methods Three sections （Shuanghe in Chang-ning， Sichuan； Anwen in Qijiang， Chongqing； and Wangjiawan in Yichang， Hubei） were selected as study sites. High-resolution elemental data （Si， Fe， Ca， Al， Rb/Sr， etc.） were analyzed using AnalySeries and Acycle software to identify Milankovitch cycle signals. Sedimentation rates were estimated using the COCO/eCOCO and TimeOpt methods to construct floating astronomical time scales. CA-ID-TIMS zircon U-Pb dating was conducted on volcanic ash beds to obtain absolute age anchors， enabling precise conversion from the depth domain to the time domain. Results （1） Stable sedimentary cycles corresponding to 405-kyr and ~100-kyr long and short eccentricity cycles were identified in the XRF elemental series. Floating astronomical time scales of 12.2 Myr， 10.3 Myr， and 2.75 Myr were established for the Shuanghe section， Anwen section， and Wangjiawan section， respectively. （2） Given the most complete geological record preserved in the Shuanghe section， the ages of the Ordovician/Silurian （O/S） boundary and the base of the Hirnantian stage， calibrated to 442.34 ± 0.22 Ma and 443.78 ± 0.22 Ma respectively through cyclostratigraphic analysis combined with U-Pb dating of volcanic ash beds （Shuanghe section： 438.47 ± 0.17 Ma）， can serve as a candidate for future international chronostratigraphic standards. （3） The duration of the Hirnantian stage is 1.44 Myr at the Shuanghe section， but only ~0.41 Myr at the Wangjiawan section， suggesting that a sedimentary hiatus may exist in the Wangjiawan section. （4） Paleoclimatic proxies and sea-level changes exhibited long-period fluctuations of 1.2 Myr and 2.4 Myr. Conclusions The high-precision astronomical time scale established in this study significantly improves the accuracy of the chronostratigraphic framework for the Late Ordovician-Early Silurian， revealing the rapid onset of the end-Ordovician mass extinction. Astronomical cycles played a significant role in driving climate-environmental evolution during this interval， providing key temporal constraints for understanding the triggering mechanisms of the end-Ordovician mass extinction.
2026,
44(4):
1238-1272.
doi: 10.14027/j.issn.1000-0550.2024.135
Abstract:
Significance The study of the provenance of fine-grained sedimentary rocks is a crucial first step in the "source-to-sink" system theory of fine-grained sedimentary rocks. It is important for restoring the ancient sedimentary environment， understanding the formation mechanism of fine-grained sedimentary rocks， and predicting the distribution of unconventional oil and gas resources. Fine-grained sedimentary rocks are characterized by small particle size， complex composition， and difficulty in observation and research， with different material components corresponding to a variety of sources and origins. A review of the existing research results worldwide shows that currently there is a lack of systematic organization and summary of research outcomes regarding the provenance and origins of fine-grained sedimentary materials. Progress This paper synthesizes current research findings and categorizes the sources of fine-grained sedimentary rocks into three major types： terrigenous， endogenic， and volcanic-hydrothermal. It provides an in-depth summary and conclusion on the common sources and origins of fine-grained sediments， pointing out： （1） Clay minerals are of detrital weathering origin， diagenetic transformation from other minerals， transformation among clay minerals themselves， hydrolysis of submarine volcanic materials， and biologically mediated by extracellular polymeric substances； （2） Quartz mainly originates from the weathering of terrigenous materials， intra-basin biological activity， devitrification of volcanic ash materials， and authigenic formation； （3） Feldspar originates from the weathering of terrigenous detritus， input from volcanic-hydrothermal activity， and recent studies have also indicated that feldspar can be formed through microbial chemical processes； （4） Carbonate minerals are primarily endogenic， formed through chemical， bio-chemical， biological， and re-transport and deposition processes within the basin， and the input of terrigenous and volcanic-hydrothermal materials not only directly provides carbonate minerals for fine-grained sedimentary rocks but also promotes the formation of carbonate minerals within the basin； （5） Pyrite is mainly formed by the two ore-forming elements， iron and sulfur， through dissimilatory iron reduction and iron shuttling mechanisms， microbial reduction， and thermogenic reduction of sulfate within the basin； （6） Organic matter can be divided into terrigenous vitrinite， inertinite， and some liptinite， as well as endogenic liptinite， zooclastic organic debris， and secondary organic matter. [Conclusions and Perspectives] Future research on the provenance and origins of fine-grained sedimentary rocks will develop in a multidisciplinary and high-precision direction， and there is still an urgent need for a systematic approach suitable for the study of the provenance of fine-grained sedimentary rocks.This paper aims to clarify the provenance and origins of fine-grained sedimentary rocks， enhance the understanding of the sources and formation mechanisms of fine-grained sediments， and thus promote the development of fine-grained sedimentology theory. It provides a solid theoretical foundation and scientific basis for identifying the distribution characteristics of fine-grained sedimentary strata and predicting the distribution of unconventional oil and gas resources.
Significance The study of the provenance of fine-grained sedimentary rocks is a crucial first step in the "source-to-sink" system theory of fine-grained sedimentary rocks. It is important for restoring the ancient sedimentary environment， understanding the formation mechanism of fine-grained sedimentary rocks， and predicting the distribution of unconventional oil and gas resources. Fine-grained sedimentary rocks are characterized by small particle size， complex composition， and difficulty in observation and research， with different material components corresponding to a variety of sources and origins. A review of the existing research results worldwide shows that currently there is a lack of systematic organization and summary of research outcomes regarding the provenance and origins of fine-grained sedimentary materials. Progress This paper synthesizes current research findings and categorizes the sources of fine-grained sedimentary rocks into three major types： terrigenous， endogenic， and volcanic-hydrothermal. It provides an in-depth summary and conclusion on the common sources and origins of fine-grained sediments， pointing out： （1） Clay minerals are of detrital weathering origin， diagenetic transformation from other minerals， transformation among clay minerals themselves， hydrolysis of submarine volcanic materials， and biologically mediated by extracellular polymeric substances； （2） Quartz mainly originates from the weathering of terrigenous materials， intra-basin biological activity， devitrification of volcanic ash materials， and authigenic formation； （3） Feldspar originates from the weathering of terrigenous detritus， input from volcanic-hydrothermal activity， and recent studies have also indicated that feldspar can be formed through microbial chemical processes； （4） Carbonate minerals are primarily endogenic， formed through chemical， bio-chemical， biological， and re-transport and deposition processes within the basin， and the input of terrigenous and volcanic-hydrothermal materials not only directly provides carbonate minerals for fine-grained sedimentary rocks but also promotes the formation of carbonate minerals within the basin； （5） Pyrite is mainly formed by the two ore-forming elements， iron and sulfur， through dissimilatory iron reduction and iron shuttling mechanisms， microbial reduction， and thermogenic reduction of sulfate within the basin； （6） Organic matter can be divided into terrigenous vitrinite， inertinite， and some liptinite， as well as endogenic liptinite， zooclastic organic debris， and secondary organic matter. [Conclusions and Perspectives] Future research on the provenance and origins of fine-grained sedimentary rocks will develop in a multidisciplinary and high-precision direction， and there is still an urgent need for a systematic approach suitable for the study of the provenance of fine-grained sedimentary rocks.This paper aims to clarify the provenance and origins of fine-grained sedimentary rocks， enhance the understanding of the sources and formation mechanisms of fine-grained sediments， and thus promote the development of fine-grained sedimentology theory. It provides a solid theoretical foundation and scientific basis for identifying the distribution characteristics of fine-grained sedimentary strata and predicting the distribution of unconventional oil and gas resources.
2026,
44(4):
1273-1297.
doi: 10.14027/j.issn.1000-0550.2025.017
Abstract:
Significance Sepiolite is a clay mineral with a unique fibrous crystal structure； it has a significant potential application in the geological field due to its high adsorptive capacity and thermal stability. Progress The genesis types for sepiolite include direct deposition， terrestrial transport sedimentation and diagenetic alteration. Direct deposition is influenced by chemical conditions such as element concentration and pH. Terrestrial transport sedimentation is closely related to the geological environment and climatic conditions. Diagenetic alteration of sepiolite is affected by the burial depth and the properties of the hydrothermal fluids. Sepiolite is generally formed in an alkaline reducing environment rich in Mg and Si， but with a low Al content. During the thermodynamic evolution process， it undergoes mineral phase transitions and is transformed into minerals such as talc or montmorillonite， which imply different depositional and diagenetic evolutionary paths. In terms of geological applications， sepiolite has an excellent adsorptive behavior， and thus it can efficiently enrich organic matter， providing a basis for the formation of hydrocarbon source rocks with significantly enhanced oil- and gas-generating potential and quality. The diagenetic fluids of the sepiolite layer help promote the transformation of high-energy beach limestone at the edge of a depression into a high-quality dolomite reservoir， thereby giving rise to either of two oil and gas accumulation models： self-generation and self-storage， or lower generation and greater storage. In addition， the thickness and distribution of sepiolite strata inverts undulating paleolandforms and is also an effective indicator of oil and gas reservoir regions， thus providing an important basis for oil and gas exploration. In terms of paleoenvironment， the formation process of sepiolite also records a range of information （e.g.， evaporation environment， water level changes， climate evolution and anoxic events） that can be used to reveal major geological events in the region. Conclusions and prospects Sepiolite has shown significant research value in oil and gas exploration， paleogeomorphic reconstruction and paleoenvironmental restoration. Future development trends of sepiolite will include its use in defining paleoenvironmental conditions， enhancing the analytical ability of seismic data on the thickness of sepiolite strata， and developing the exploration of oil and gas in sepiolite strata.
Significance Sepiolite is a clay mineral with a unique fibrous crystal structure； it has a significant potential application in the geological field due to its high adsorptive capacity and thermal stability. Progress The genesis types for sepiolite include direct deposition， terrestrial transport sedimentation and diagenetic alteration. Direct deposition is influenced by chemical conditions such as element concentration and pH. Terrestrial transport sedimentation is closely related to the geological environment and climatic conditions. Diagenetic alteration of sepiolite is affected by the burial depth and the properties of the hydrothermal fluids. Sepiolite is generally formed in an alkaline reducing environment rich in Mg and Si， but with a low Al content. During the thermodynamic evolution process， it undergoes mineral phase transitions and is transformed into minerals such as talc or montmorillonite， which imply different depositional and diagenetic evolutionary paths. In terms of geological applications， sepiolite has an excellent adsorptive behavior， and thus it can efficiently enrich organic matter， providing a basis for the formation of hydrocarbon source rocks with significantly enhanced oil- and gas-generating potential and quality. The diagenetic fluids of the sepiolite layer help promote the transformation of high-energy beach limestone at the edge of a depression into a high-quality dolomite reservoir， thereby giving rise to either of two oil and gas accumulation models： self-generation and self-storage， or lower generation and greater storage. In addition， the thickness and distribution of sepiolite strata inverts undulating paleolandforms and is also an effective indicator of oil and gas reservoir regions， thus providing an important basis for oil and gas exploration. In terms of paleoenvironment， the formation process of sepiolite also records a range of information （e.g.， evaporation environment， water level changes， climate evolution and anoxic events） that can be used to reveal major geological events in the region. Conclusions and prospects Sepiolite has shown significant research value in oil and gas exploration， paleogeomorphic reconstruction and paleoenvironmental restoration. Future development trends of sepiolite will include its use in defining paleoenvironmental conditions， enhancing the analytical ability of seismic data on the thickness of sepiolite strata， and developing the exploration of oil and gas in sepiolite strata.
2026,
44(4):
1298-1310.
doi: 10.14027/j.issn.1000-0550.2025.024
Abstract:
Significance Mires serve as the fundamental environment for coal deposition throughout geological history， offering invaluable insights into Earth’s history， palaeoclimate and environmental evolution， and they are also significant with regards to the global carbon cycle. Numerous geological scholars have conducted a wealth of research on mires. Understanding the research fronts and trends in mire-related studies within coal geology can guide future research. When writing research papers and using professional terminology， scholars may confuse or misuse terminology due to the diverse concepts and English expressions of mires， thus making it particularly crucial to clarify and accurately apply mire-related terminology. Progress Based on data from the Web of Science， common English terms related to “mire” were used as search keywords. A PRISMA flowchart was used to screen out 7479 relevant articles which focused investigations into the temporal evolution and international distribution of mire research in the field of geology. This was further examined using VOSviewer 1.6.20 to conduct keyword co-occurrence analysis on 726 research papers focused on mires in coal geology （selected from the 7479 screened articles）. Subsequently， by integrating English definitions of mire-related terms with studies on mires in coal geology， suggestions are offered for simplifying the application of mire-related terminology. Conclusions （1） From 1943 to 2023， a total of 123 nations and regions worldwide participated in mire research， with the year 2000 marking a significant turning point when mire studies gained momentum and became a subject for detailed discussion. Since then， the number of research publications on mires in geology has generally exhibited an upward trend， with scholars from leading research countries engaging in frequent exchanges and academic discussion. Usage frequencies of English mire-related terminology vary between countries， reflecting particular research emphases on different mire types. （2） By integrating meta-analysis， bibliometrics and visualization techniques， research on mires in the field of coal geology is systematically reviewed and summarized. Research themes linked to the topic include coal depositional environments and their evolution， palaeowildfire， atmospheric deposition， carbon accumulation， palaeoclimate and palaeoecology. （3） “Mire” should be considered as a general term for mire-related concepts. When there is a need to emphasize the spatial distribution of mires， “fen” is an appropriate term for low-lying mire， and “bog” should be used instead of “mire” for raised mires. When the ecological or vegetative characteristics of mires need to be highlighted in research， it is recommended to use the words “swamp” or “marsh”. [Prospects] The results offer valuable insights for understanding the deve-lopmental trajectory of international mire research， identifying research fronts of mires in coal geology， and standardizing the application of mire-related terminology in English. Future research on mires in the field of coal geology should actively and effectively utilize big data or machine learning techniques （e.g.， simulation modeling， database construction， statistical data analysis， and image recognition classification）. Additionally， a multidisciplinary approach integrating geochemical， organic petrological， coal petrological， and mineralogical methods should be systematically employed throughout the research process to ensure comprehensive insights.
Significance Mires serve as the fundamental environment for coal deposition throughout geological history， offering invaluable insights into Earth’s history， palaeoclimate and environmental evolution， and they are also significant with regards to the global carbon cycle. Numerous geological scholars have conducted a wealth of research on mires. Understanding the research fronts and trends in mire-related studies within coal geology can guide future research. When writing research papers and using professional terminology， scholars may confuse or misuse terminology due to the diverse concepts and English expressions of mires， thus making it particularly crucial to clarify and accurately apply mire-related terminology. Progress Based on data from the Web of Science， common English terms related to “mire” were used as search keywords. A PRISMA flowchart was used to screen out 7479 relevant articles which focused investigations into the temporal evolution and international distribution of mire research in the field of geology. This was further examined using VOSviewer 1.6.20 to conduct keyword co-occurrence analysis on 726 research papers focused on mires in coal geology （selected from the 7479 screened articles）. Subsequently， by integrating English definitions of mire-related terms with studies on mires in coal geology， suggestions are offered for simplifying the application of mire-related terminology. Conclusions （1） From 1943 to 2023， a total of 123 nations and regions worldwide participated in mire research， with the year 2000 marking a significant turning point when mire studies gained momentum and became a subject for detailed discussion. Since then， the number of research publications on mires in geology has generally exhibited an upward trend， with scholars from leading research countries engaging in frequent exchanges and academic discussion. Usage frequencies of English mire-related terminology vary between countries， reflecting particular research emphases on different mire types. （2） By integrating meta-analysis， bibliometrics and visualization techniques， research on mires in the field of coal geology is systematically reviewed and summarized. Research themes linked to the topic include coal depositional environments and their evolution， palaeowildfire， atmospheric deposition， carbon accumulation， palaeoclimate and palaeoecology. （3） “Mire” should be considered as a general term for mire-related concepts. When there is a need to emphasize the spatial distribution of mires， “fen” is an appropriate term for low-lying mire， and “bog” should be used instead of “mire” for raised mires. When the ecological or vegetative characteristics of mires need to be highlighted in research， it is recommended to use the words “swamp” or “marsh”. [Prospects] The results offer valuable insights for understanding the deve-lopmental trajectory of international mire research， identifying research fronts of mires in coal geology， and standardizing the application of mire-related terminology in English. Future research on mires in the field of coal geology should actively and effectively utilize big data or machine learning techniques （e.g.， simulation modeling， database construction， statistical data analysis， and image recognition classification）. Additionally， a multidisciplinary approach integrating geochemical， organic petrological， coal petrological， and mineralogical methods should be systematically employed throughout the research process to ensure comprehensive insights.
2026,
44(4):
1311-1332.
doi: 10.14027/j.issn.1000-0550.2025.012
Abstract:
Objective The uplift of the Tibetan Plateau is a direct expression of the Earth’s interior geodynamic processes caused by the impact of the collision of the India-Eurasia Plates. Investigating the uplift history is essential to clarify the deformation mechanisms of the continental lithosphere， and remains a central scientific issue in deciphering interactions of the Earth’s multiple spheres. Despite extensive studies， intense debate continues regarding the plateau uplift and expansion. The timing of the uplift in the northern Tibetan Plateau is pivotal for resolving these questions； the Eastern Kunlun Mountains are a crucial geomorphic boundary， since they form the southern margin of the northern plateau and were a critical conduit for the northward propagation of collision-related stresses. The Eastern Kunlun range is an ideal area for studying the uplift processes of the northern Tibetan Plateau， but the timing of their initial uplift remains highly debated. Methods A comprehensive low-temperature thermochronological analysis of the bedrock in the Eastern Kunlun Mountains was conducted to constrain the Cenozoic uplift history. It included integrating the results of 37 low-temperature studies in the region comprising 203 apatite fission track data points and 142 apatite （U-Th）/He data points. Sample selection criteria for low-temperature thermochronology were strictly followed during dataset compilation， and a series of rigorous data-screening strategies were established to minimise disturbances from experimental errors， sample characteristics and complex thermal histories to enhance the accuracy and reliability of the dataset. The analysis involved three steps： （1） the low-temperature thermochronological age distribution was visualised； （2） the relationship between mean track length and age was established； and （3） thermal history modelling results were compiled. Integrating these enabled a detailed， comprehensive low-temperature thermochronology framework to assess the uplift history of the Eastern Kunlun Mountains in the Cenozoic. [Results and Conclusions] Since the Upper Cretaceous， the surface rocks of the Eastern Kunlun Mountains have generally remained in a relatively stable or slowly cooling state within the apatite fission track partial annealing zone and the apatite （U-Th）/He partial retention zone. The Eastern Kunlun Mountains did not form a significant topographic barrier during the Paleogene， and the drainage systems of adjacent basins were likely interconnected. Although the possibility cannot be entirely excluded that sporadic highlands in local areas of the Eastern Kunlun Mountains provided sediment sources for adjacent basins， the data indicates that widespread uplift of the Eastern Kunlun Mountains did not begin to occur until about 20 Ma， when rapid uplift took place causing an estimated rock displacement not less than approximately 2 km relative to the surface， corresponding to the length of the rock column recording Early Miocene apatite （U-Th）/He （22-17 Ma） and apatite fission track （23-15 Ma） age components. This finding provides new evidence for understanding the timing of the paleo-Qaidam Basin disintegration， the paleo-elevation history of the northern Tibetan Plateau in the Early Miocene， and the uplift processes and dynamic mechanisms involved.
Objective The uplift of the Tibetan Plateau is a direct expression of the Earth’s interior geodynamic processes caused by the impact of the collision of the India-Eurasia Plates. Investigating the uplift history is essential to clarify the deformation mechanisms of the continental lithosphere， and remains a central scientific issue in deciphering interactions of the Earth’s multiple spheres. Despite extensive studies， intense debate continues regarding the plateau uplift and expansion. The timing of the uplift in the northern Tibetan Plateau is pivotal for resolving these questions； the Eastern Kunlun Mountains are a crucial geomorphic boundary， since they form the southern margin of the northern plateau and were a critical conduit for the northward propagation of collision-related stresses. The Eastern Kunlun range is an ideal area for studying the uplift processes of the northern Tibetan Plateau， but the timing of their initial uplift remains highly debated. Methods A comprehensive low-temperature thermochronological analysis of the bedrock in the Eastern Kunlun Mountains was conducted to constrain the Cenozoic uplift history. It included integrating the results of 37 low-temperature studies in the region comprising 203 apatite fission track data points and 142 apatite （U-Th）/He data points. Sample selection criteria for low-temperature thermochronology were strictly followed during dataset compilation， and a series of rigorous data-screening strategies were established to minimise disturbances from experimental errors， sample characteristics and complex thermal histories to enhance the accuracy and reliability of the dataset. The analysis involved three steps： （1） the low-temperature thermochronological age distribution was visualised； （2） the relationship between mean track length and age was established； and （3） thermal history modelling results were compiled. Integrating these enabled a detailed， comprehensive low-temperature thermochronology framework to assess the uplift history of the Eastern Kunlun Mountains in the Cenozoic. [Results and Conclusions] Since the Upper Cretaceous， the surface rocks of the Eastern Kunlun Mountains have generally remained in a relatively stable or slowly cooling state within the apatite fission track partial annealing zone and the apatite （U-Th）/He partial retention zone. The Eastern Kunlun Mountains did not form a significant topographic barrier during the Paleogene， and the drainage systems of adjacent basins were likely interconnected. Although the possibility cannot be entirely excluded that sporadic highlands in local areas of the Eastern Kunlun Mountains provided sediment sources for adjacent basins， the data indicates that widespread uplift of the Eastern Kunlun Mountains did not begin to occur until about 20 Ma， when rapid uplift took place causing an estimated rock displacement not less than approximately 2 km relative to the surface， corresponding to the length of the rock column recording Early Miocene apatite （U-Th）/He （22-17 Ma） and apatite fission track （23-15 Ma） age components. This finding provides new evidence for understanding the timing of the paleo-Qaidam Basin disintegration， the paleo-elevation history of the northern Tibetan Plateau in the Early Miocene， and the uplift processes and dynamic mechanisms involved.
2026,
44(4):
1333-1352.
doi: 10.14027/j.issn.1000-0550.2025.013
Abstract:
Objective Neoproterozoin “Snowball Earth” （Cryogenian） glaciations is a long-standing hot topic in sedimentology. In South China， well-preserved sedimentary records during Cryogenian Period have been found in many places in the Yangtze Block. However， there are relatively few reports on deposits of this time in Kangdian Rift Basin on western margin of the Yangtze Block， and in the rift basin between northern margin of the Yangtze Block and southern margin of the Qingling Orogen. Methods This study focuses on the Cryogenian glacial deposits in the Gangchang-Yuanba section， Hanzhong area， northern margin of the Yangtze Block. Based on the field observations and measurements， zircons were selected from the bottom tuff layer and upper sandstones for U-Pb dating analysis using laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS）. Detailed features of the sedimentary rocks and their regional correlation are also discussed. Results Two sets of tillites were identified for the first time within the Neoproterozoic glacial sedimentary rocks in this region， both from a continental glacier. Several layers of sandstone and siltstone are presented between and above the tillite sets. Zircons from the bottom tuff yielded the earliest mean concordant age of （719 ± 11） Ma， indicating the beginning of glaciation in this region. Considering their lithological succession and sedimentary structures， these Cryogenian deposits are thought to have been formed during Sturtian glaciation， corresponding respectively to the Chang’an and Gucheng glaciation periods. The timing of this glaciation event， and the sedimentary associations， are consistent with contemporaneous sediments in the adjacent Zhenba and Chengkou areas， and also show similarities to Sturtian sediments widely distributed in other parts of South China.
Objective Neoproterozoin “Snowball Earth” （Cryogenian） glaciations is a long-standing hot topic in sedimentology. In South China， well-preserved sedimentary records during Cryogenian Period have been found in many places in the Yangtze Block. However， there are relatively few reports on deposits of this time in Kangdian Rift Basin on western margin of the Yangtze Block， and in the rift basin between northern margin of the Yangtze Block and southern margin of the Qingling Orogen. Methods This study focuses on the Cryogenian glacial deposits in the Gangchang-Yuanba section， Hanzhong area， northern margin of the Yangtze Block. Based on the field observations and measurements， zircons were selected from the bottom tuff layer and upper sandstones for U-Pb dating analysis using laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS）. Detailed features of the sedimentary rocks and their regional correlation are also discussed. Results Two sets of tillites were identified for the first time within the Neoproterozoic glacial sedimentary rocks in this region， both from a continental glacier. Several layers of sandstone and siltstone are presented between and above the tillite sets. Zircons from the bottom tuff yielded the earliest mean concordant age of （719 ± 11） Ma， indicating the beginning of glaciation in this region. Considering their lithological succession and sedimentary structures， these Cryogenian deposits are thought to have been formed during Sturtian glaciation， corresponding respectively to the Chang’an and Gucheng glaciation periods. The timing of this glaciation event， and the sedimentary associations， are consistent with contemporaneous sediments in the adjacent Zhenba and Chengkou areas， and also show similarities to Sturtian sediments widely distributed in other parts of South China.
2026,
44(4):
1353-1368.
doi: 10.14027/j.issn.1000-0550.2025.006
Abstract:
Objective The western Hunan region hosts extensive Neoproterozoic marine sedimentary manganese deposits. Manganese （Mn） is a typical redox-sensitive metallic element whose enrichment in sediments is strongly correlated with the redox condition of the bottom water in the basin. A detailed study of the sedimentary redox conditions of such deposits helps to explain their metallogenic mechanisms and the constraints on their marine cycling during the mineralization period， and also provides theoretical support for the assessment of regional mineralization potential. Methods This study involved mineralogical， geochemical and inorganic carbon isotope analyses of 16 manganese ore samples of various grades from the Nanhua System Datangpo Formation in the Minle area， western Hunan. Results Mineralogical and carbon isotope analyses revealed that high-grade （MnO>20%） and medium-grade （10%<MnO<20%） manganese ores consist of predominantly subhedral granular microcrystalline rhodochrosite （grain size <5 μm） and are relatively enriched in light carbon isotope （δ13C=-10.4‰~-8.3‰； n=10）. Conversely， low-grade （MnO<10%） manganese ores contain larger- grained （>20 μm） subhedral platy rhodochrosite enriched in heavier carbon isotope （δ13C=-7.4‰~-5.3‰； n=6）. Pyrite morphology and element geochemical proxies （Mo， V， Ni concentrations and Ni/Co， V/Cr ratios） indicate that the high-grade manganese ores were deposited in oxic conditions， the medium-grade ore in suboxic conditions， and the low-grade ore in anoxic conditions. Additionally， high-grade ores exhibit geochemical characteristics indicating hydrothermal deposition （e.g.， high Eu* values and high Fe/Ti ratios）. Conclusions These findings suggest that， in the Minle area of western Hunan， the rhodochrosite in the medium- to high-grade manganese ores was formed as a result of the reaction between Mn oxides with organic matter during diagenesis， whereas in the low-grade manganese ores the rhodochrosite was probably precipitated from Mn2+ and CO3 2 -
Objective The western Hunan region hosts extensive Neoproterozoic marine sedimentary manganese deposits. Manganese （Mn） is a typical redox-sensitive metallic element whose enrichment in sediments is strongly correlated with the redox condition of the bottom water in the basin. A detailed study of the sedimentary redox conditions of such deposits helps to explain their metallogenic mechanisms and the constraints on their marine cycling during the mineralization period， and also provides theoretical support for the assessment of regional mineralization potential. Methods This study involved mineralogical， geochemical and inorganic carbon isotope analyses of 16 manganese ore samples of various grades from the Nanhua System Datangpo Formation in the Minle area， western Hunan. Results Mineralogical and carbon isotope analyses revealed that high-grade （MnO>20%） and medium-grade （10%<MnO<20%） manganese ores consist of predominantly subhedral granular microcrystalline rhodochrosite （grain size <5 μm） and are relatively enriched in light carbon isotope （δ13C=-10.4‰~-8.3‰； n=10）. Conversely， low-grade （MnO<10%） manganese ores contain larger- grained （>20 μm） subhedral platy rhodochrosite enriched in heavier carbon isotope （δ13C=-7.4‰~-5.3‰； n=6）. Pyrite morphology and element geochemical proxies （Mo， V， Ni concentrations and Ni/Co， V/Cr ratios） indicate that the high-grade manganese ores were deposited in oxic conditions， the medium-grade ore in suboxic conditions， and the low-grade ore in anoxic conditions. Additionally， high-grade ores exhibit geochemical characteristics indicating hydrothermal deposition （e.g.， high Eu* values and high Fe/Ti ratios）. Conclusions These findings suggest that， in the Minle area of western Hunan， the rhodochrosite in the medium- to high-grade manganese ores was formed as a result of the reaction between Mn oxides with organic matter during diagenesis， whereas in the low-grade manganese ores the rhodochrosite was probably precipitated from Mn2+ and CO
2026,
44(4):
1369-1383.
doi: 10.14027/j.issn.1000-0550.2025.001
Abstract:
Objective The Luojiawopeng Formation is a set of purplish red sand and gravel accumulation strata in the Lower Pleistocene Series in the southeastern margin of Songnen plain. The clay mineral analysis of this formation is conducive to understanding the paleoclimate characteristics in this region and defining its stratigraphic age. Methods Whole rock geochemistry， X-ray diffraction （XRD）， Scanning electron microscopy （SEM）， and High-resolution transmission electron microscopy （HRTEM） analysis of clay minerals in Luojiawopeng Formation were conducted to reveal their composition and transformation characteristics of clay minerals. Comparisons were performed on clay mineral composition between the red clays in the Chinese Loess Plateau and Luojiawopeng Formation. Results The clay mineral composition of Luojiawopeng Formation is dominated by kaolinite （content of 57%⁃73%）， followed by illite （ranging from 25% to 41%）， and the content of biotite /vermiculite mixed layer minerals is the least （average 1%）. Kaolinite shows pseudo hexagonal morphology， and its high degree of euhedral crystallinity indicates its authigenic origin， as does its high illite crystallinity （average 0.55） and illite chemical index （average 0.50）. These results， combined with the high clay to quartz ratio， indicate intense weathering characteristics. The transformation process of clay minerals is illite → kaolinite and biotite → biotite /vermiculite mixed layer minerals → kaolinite， which is consistent with the significant kaolinization trend of constant element 4Si-M+-R2+ ternary diagram. combined with the high chemical index of alteration（CIA） and hematite-to-goethite ratio of the formation， this process indicates that these minerals formed in a humid and hot environment with increasingly strong weathering. Conclusions Thus， the Luojiawopeng Formation was likely formed in a humid and hot climate， rather than through moraine accumulation as previously reported， and the stratigraphic chronology of the formation may be in the humid and hot period when the East Asian summer monsoon prevailed before the Early Pleistocene.
Objective The Luojiawopeng Formation is a set of purplish red sand and gravel accumulation strata in the Lower Pleistocene Series in the southeastern margin of Songnen plain. The clay mineral analysis of this formation is conducive to understanding the paleoclimate characteristics in this region and defining its stratigraphic age. Methods Whole rock geochemistry， X-ray diffraction （XRD）， Scanning electron microscopy （SEM）， and High-resolution transmission electron microscopy （HRTEM） analysis of clay minerals in Luojiawopeng Formation were conducted to reveal their composition and transformation characteristics of clay minerals. Comparisons were performed on clay mineral composition between the red clays in the Chinese Loess Plateau and Luojiawopeng Formation. Results The clay mineral composition of Luojiawopeng Formation is dominated by kaolinite （content of 57%⁃73%）， followed by illite （ranging from 25% to 41%）， and the content of biotite /vermiculite mixed layer minerals is the least （average 1%）. Kaolinite shows pseudo hexagonal morphology， and its high degree of euhedral crystallinity indicates its authigenic origin， as does its high illite crystallinity （average 0.55） and illite chemical index （average 0.50）. These results， combined with the high clay to quartz ratio， indicate intense weathering characteristics. The transformation process of clay minerals is illite → kaolinite and biotite → biotite /vermiculite mixed layer minerals → kaolinite， which is consistent with the significant kaolinization trend of constant element 4Si-M+-R2+ ternary diagram. combined with the high chemical index of alteration（CIA） and hematite-to-goethite ratio of the formation， this process indicates that these minerals formed in a humid and hot environment with increasingly strong weathering. Conclusions Thus， the Luojiawopeng Formation was likely formed in a humid and hot climate， rather than through moraine accumulation as previously reported， and the stratigraphic chronology of the formation may be in the humid and hot period when the East Asian summer monsoon prevailed before the Early Pleistocene.
2026,
44(4):
1384-1396.
doi: 10.14027/j.issn.1000-0550.2025.007
Abstract:
Objective Xinying Bay， Hainan province， has retained a relatively complete sedimentary record of marine stratigraphy since the Pleistocene. Owing to its closure and stability， it serves as a good window to reflect the paleoenvironmental changes since the Pleistocene in the northern South China Sea. Methods Based on the analysis of whole rock major elements and Sr-Nd isotopes， the source of sediment material and the evolution of paleoclimate in this area since the Pleistocene were reconstructed， and the driving mechanism was discussed. Results The borehole has three sections from bottom to top. The bottom section， U1， has a relatively low εNd（0） value and a relatively high 86Sr/87Sr value. The middle section， U2， has relatively high ratios of Al/Ti， K/Ti， Fe/Ti， and Mg/Ti. The results of provenance analysis show that the sediments of the borehole come from the intermediate source area， and the U1 section contains more older sedimentary materials， and the Sr-Nd isotope ratio is similar to that of the Red river sediments， whereas U2 and U3 are similar to the Cretaceous-Permian feldspar granite in Hainan Island. The paleo-environmental analysis shows that this region has experienced changes from dry cold to warm wet， and then to dry cold since the Pleistocene. Conclusions The sedimentary period of section U1 corresponds to the coldest period， MIS16， in the Northern Hemisphere， which combined with previous chronological studies， the dry and cold climate， and relatively low sea level， enable the clastic sediments of the Indochina continent to be transported to Xinying Bay. Then， the East Asian summer monsoon strengthened， and the climate changed from cold and dry to warm and humid. As a result， the source area of U2 was dominated by granitic rocks in Hainan Island because the sea level increased. U3 has undergone regional tectonic uplift， and the sedimentary source area is dominated by granite in the island.
Objective Xinying Bay， Hainan province， has retained a relatively complete sedimentary record of marine stratigraphy since the Pleistocene. Owing to its closure and stability， it serves as a good window to reflect the paleoenvironmental changes since the Pleistocene in the northern South China Sea. Methods Based on the analysis of whole rock major elements and Sr-Nd isotopes， the source of sediment material and the evolution of paleoclimate in this area since the Pleistocene were reconstructed， and the driving mechanism was discussed. Results The borehole has three sections from bottom to top. The bottom section， U1， has a relatively low εNd（0） value and a relatively high 86Sr/87Sr value. The middle section， U2， has relatively high ratios of Al/Ti， K/Ti， Fe/Ti， and Mg/Ti. The results of provenance analysis show that the sediments of the borehole come from the intermediate source area， and the U1 section contains more older sedimentary materials， and the Sr-Nd isotope ratio is similar to that of the Red river sediments， whereas U2 and U3 are similar to the Cretaceous-Permian feldspar granite in Hainan Island. The paleo-environmental analysis shows that this region has experienced changes from dry cold to warm wet， and then to dry cold since the Pleistocene. Conclusions The sedimentary period of section U1 corresponds to the coldest period， MIS16， in the Northern Hemisphere， which combined with previous chronological studies， the dry and cold climate， and relatively low sea level， enable the clastic sediments of the Indochina continent to be transported to Xinying Bay. Then， the East Asian summer monsoon strengthened， and the climate changed from cold and dry to warm and humid. As a result， the source area of U2 was dominated by granitic rocks in Hainan Island because the sea level increased. U3 has undergone regional tectonic uplift， and the sedimentary source area is dominated by granite in the island.
2026,
44(4):
1397-1406.
doi: 10.14027/j.issn.1000-0550.2025.002
Abstract:
Objective Trace elements in modern and ancient dunes from the southern Mu Us Desert record environmental information related to weathering， transportation， and deposition. Analysis of this information facilitates a better understanding of sediment provenance and climatic evolution in the region. Methods Samples of modern and ancient dunes in the southern Mu Us Desert were collected， and the content characteristics and correlations of 14 trace elements including phosphorus （P）， lead （Pb）， and rubidium （Rb） were analyzed to explore the differences in trace element contents and spatial distribution characteristics among different types of dunes. Results （1） The trace elements in modern and ancient dunes are mainly barium （Ba）， strontium （Sr）， and phosphorus （P）， whereas the contents of arsenic （As）， niobium （Nb）， and copper （Cu） are relatively low. Their distribution patterns show certain regional characteristics. （2） The trace element contents in fixed dunes are significantly higher than those in mobile dunes owing to the nature of the dunes and vegetation coverage； however， the trace element contents in ancient dunes are higher than those in modern dunes， owing to the influence of sedimentary history， climate change， and special geomorphic positions. （3） The values of Sr/Cu， Rb/Sr， and Sr/Ba in modern and ancient dunes are comparable， indicating that they were formed in similar sedimentary environments. Conclusion There are certain similarities and differences in the trace element contents of modern and ancient dunes and different types of dunes. The changes in trace element contents in ancient dunes can provide clues to the sources of modern dunes to a certain extent. The ratios of trace elements in modern and ancient dunes have certain implications for climate and environmental conditions.
Objective Trace elements in modern and ancient dunes from the southern Mu Us Desert record environmental information related to weathering， transportation， and deposition. Analysis of this information facilitates a better understanding of sediment provenance and climatic evolution in the region. Methods Samples of modern and ancient dunes in the southern Mu Us Desert were collected， and the content characteristics and correlations of 14 trace elements including phosphorus （P）， lead （Pb）， and rubidium （Rb） were analyzed to explore the differences in trace element contents and spatial distribution characteristics among different types of dunes. Results （1） The trace elements in modern and ancient dunes are mainly barium （Ba）， strontium （Sr）， and phosphorus （P）， whereas the contents of arsenic （As）， niobium （Nb）， and copper （Cu） are relatively low. Their distribution patterns show certain regional characteristics. （2） The trace element contents in fixed dunes are significantly higher than those in mobile dunes owing to the nature of the dunes and vegetation coverage； however， the trace element contents in ancient dunes are higher than those in modern dunes， owing to the influence of sedimentary history， climate change， and special geomorphic positions. （3） The values of Sr/Cu， Rb/Sr， and Sr/Ba in modern and ancient dunes are comparable， indicating that they were formed in similar sedimentary environments. Conclusion There are certain similarities and differences in the trace element contents of modern and ancient dunes and different types of dunes. The changes in trace element contents in ancient dunes can provide clues to the sources of modern dunes to a certain extent. The ratios of trace elements in modern and ancient dunes have certain implications for climate and environmental conditions.
2026,
44(4):
1407-1425.
doi: 10.14027/j.issn.1000-0550.2025.043
Abstract:
Objective Shallow-water deltas are widely observed in petroliferous basins and can form large-scale hydrocarbon reservoirs. Based on the relative proportions of mud and sand in their deposits， they can be classified into three types—sand-rich， sand-mud， and mud-rich deltas—whose geomorphological expression， depositional characteristics， sedimentary architecture， and sediment heterogeneity differ substantially. At present， systematic research on these three types of shallow-water deltas remains limited， which has severely constrained the efficient exploration and development of oil and gas resources. Methods This study employed sedimentary numerical simulation technology to reproduce the depositional evolution processes of the three types of deltas. Their sedimentary architecture and grain size models were reconstructed from the simulated depositional interfaces and grain size data. Subsequently， from a detailed analysis of the evolutionary processes， sedimentary architectural models for shallow-water deltas were established and the characteristics of sedimentary heterogeneity within this model framework were elucidated. [Results and Conclusions ] （1） The sediment supply ratio is a crucial influencing factor in deltaic depositional evolution， as it determines the sedimentation rate and erosion resistance of channel margins. On this basis， the evolution and ultimately the resultant architecture and heterogeneity are determined. （2） As the sand-to-mud ratio decreases， distributary channels exhibit reduced quantity， hierarchical complexity and areal proportion， as well as increased sinuosity， greater stability， diminished lateral migration capacity， and a transition from lateral migration-dominated filling to abandonment-dominated filling. （3） Sand-dominated deltas typically exhibit lobate or triangular shapes， with extensively developed distributary channels forming multistage， radial patterns. They frequently display lateral migration characteristics. Sand-mud deltas manifest as multi-fingered， branching forms with fewer distributary channels that are primarily controlled by trunk distributary channels with multi-directional bifurcations at their termini， creating multiple laterally amalgamated finger-like bar assemblages. Mud-rich deltas possess few distributary channels， being characterized by the development of narrow， sinuous， belt-like trunk distributary channels lacking lateral accretion features. These channels are predominantly infilled with muddy sediments following avulsion and abandonment. （4） Sand-rich deltas show near-continuous sand distribution with downstream fining. Coarsest grains occur in trunk channels， with finer grains in mouth bars， yielding weak planar heterogeneity but strong vertical heterogeneity due to multi-stage lateral/progradational fine-grained interbeds. Sand-mud deltas exhibit broad-banded sand bodies with coarse-grained reservoirs in trunk channels and mouth bars， weak planar heterogeneity， and strong vertical heterogeneity from muddy interbeds. Mud-rich deltas display strong planar heterogeneity， with reservoirs being restricted to mouth-bar cores that are laterally isolated by muddy channels， with weak vertical heterogeneity resulting from multi-stage muddy interbeds.
Objective Shallow-water deltas are widely observed in petroliferous basins and can form large-scale hydrocarbon reservoirs. Based on the relative proportions of mud and sand in their deposits， they can be classified into three types—sand-rich， sand-mud， and mud-rich deltas—whose geomorphological expression， depositional characteristics， sedimentary architecture， and sediment heterogeneity differ substantially. At present， systematic research on these three types of shallow-water deltas remains limited， which has severely constrained the efficient exploration and development of oil and gas resources. Methods This study employed sedimentary numerical simulation technology to reproduce the depositional evolution processes of the three types of deltas. Their sedimentary architecture and grain size models were reconstructed from the simulated depositional interfaces and grain size data. Subsequently， from a detailed analysis of the evolutionary processes， sedimentary architectural models for shallow-water deltas were established and the characteristics of sedimentary heterogeneity within this model framework were elucidated. [Results and Conclusions ] （1） The sediment supply ratio is a crucial influencing factor in deltaic depositional evolution， as it determines the sedimentation rate and erosion resistance of channel margins. On this basis， the evolution and ultimately the resultant architecture and heterogeneity are determined. （2） As the sand-to-mud ratio decreases， distributary channels exhibit reduced quantity， hierarchical complexity and areal proportion， as well as increased sinuosity， greater stability， diminished lateral migration capacity， and a transition from lateral migration-dominated filling to abandonment-dominated filling. （3） Sand-dominated deltas typically exhibit lobate or triangular shapes， with extensively developed distributary channels forming multistage， radial patterns. They frequently display lateral migration characteristics. Sand-mud deltas manifest as multi-fingered， branching forms with fewer distributary channels that are primarily controlled by trunk distributary channels with multi-directional bifurcations at their termini， creating multiple laterally amalgamated finger-like bar assemblages. Mud-rich deltas possess few distributary channels， being characterized by the development of narrow， sinuous， belt-like trunk distributary channels lacking lateral accretion features. These channels are predominantly infilled with muddy sediments following avulsion and abandonment. （4） Sand-rich deltas show near-continuous sand distribution with downstream fining. Coarsest grains occur in trunk channels， with finer grains in mouth bars， yielding weak planar heterogeneity but strong vertical heterogeneity due to multi-stage lateral/progradational fine-grained interbeds. Sand-mud deltas exhibit broad-banded sand bodies with coarse-grained reservoirs in trunk channels and mouth bars， weak planar heterogeneity， and strong vertical heterogeneity from muddy interbeds. Mud-rich deltas display strong planar heterogeneity， with reservoirs being restricted to mouth-bar cores that are laterally isolated by muddy channels， with weak vertical heterogeneity resulting from multi-stage muddy interbeds.
2026,
44(4):
1426-1441.
doi: 10.14027/j.issn.1000-0550.2025.011
Abstract:
Objective The discharge rate regulates the sedimentary evolution and morphological scale of a braided river. In this study， the influence of discharge rate on the formation of braided channels， bars and internal sedimentary architecture is systematically analyzed for the first time. Methods Five groups of three-dimensional sedimentary numerical simulation experiments with different flow rates were carried out using Delft3D software to explore the evolution， morphological patterns and scale differences of braided channels and bars formed as a result of various flow rates. The models reproduce the internal architectural patterns of a range of bars developed in braided rivers with different flow rates and summarize the sedimentary characteristics and evolution of sandy braided rivers. Results （1） The rate of discharge is positively correlated with the sedimentary evolution of braided rivers. Low-discharge braided rivers exhibit limited evolution， in which bars mainly tend to migrate vertically and are less dissected by channels. By contrast， high-discharge braided rivers undergo intensive evolution， characterized by lateral migration and frequent dynamic equilibrium processes involving compound bars and dissection. （2） The discharge rate influences the plane pattern and channel depth of braided channels. As discharge increases， the braided channel becomes wider and deeper， resulting in a reduced overall number of channels but more highly developed chutes of the channel bars. Lower-discharge braided channels are shallower and primarily consist of numerous narrow， relatively fixed interwoven river networks. （3） Discharge further governs the co-evolution of channels and bars. Greater discharge enhances bar complexity， promoting the development of large complex compound bars and side bars with intricate internal stacking relationships and more frequent chutes. （4） Despite strong spatial heterogeneity in the internal architecture of channel bars in sandy braided rivers， consistent patterns emerge： all bars develop downstream accretions （DA） in the core， vertical accretions （VA） layered above， and lateral accretions （LA） deposited at the sides. A key distinction lies in the increased proportion of LA at higher discharge conditions. （5） Discharge correlates positively with accretion size but inversely with aspect ratio and flakiness ratio. Median aspect ratios of bars are 3.5 in low-discharge systems versus 4.5 in high-discharge systems. Conclusions The study proposes a positive correlation between discharge and the scale of channel bars and accretions in sandy braided rivers. This clarifies flow-controlled sedimentary characteristics and scale variations， providing a basis for analyzing complex subsurface reservoir architectures.
Objective The discharge rate regulates the sedimentary evolution and morphological scale of a braided river. In this study， the influence of discharge rate on the formation of braided channels， bars and internal sedimentary architecture is systematically analyzed for the first time. Methods Five groups of three-dimensional sedimentary numerical simulation experiments with different flow rates were carried out using Delft3D software to explore the evolution， morphological patterns and scale differences of braided channels and bars formed as a result of various flow rates. The models reproduce the internal architectural patterns of a range of bars developed in braided rivers with different flow rates and summarize the sedimentary characteristics and evolution of sandy braided rivers. Results （1） The rate of discharge is positively correlated with the sedimentary evolution of braided rivers. Low-discharge braided rivers exhibit limited evolution， in which bars mainly tend to migrate vertically and are less dissected by channels. By contrast， high-discharge braided rivers undergo intensive evolution， characterized by lateral migration and frequent dynamic equilibrium processes involving compound bars and dissection. （2） The discharge rate influences the plane pattern and channel depth of braided channels. As discharge increases， the braided channel becomes wider and deeper， resulting in a reduced overall number of channels but more highly developed chutes of the channel bars. Lower-discharge braided channels are shallower and primarily consist of numerous narrow， relatively fixed interwoven river networks. （3） Discharge further governs the co-evolution of channels and bars. Greater discharge enhances bar complexity， promoting the development of large complex compound bars and side bars with intricate internal stacking relationships and more frequent chutes. （4） Despite strong spatial heterogeneity in the internal architecture of channel bars in sandy braided rivers， consistent patterns emerge： all bars develop downstream accretions （DA） in the core， vertical accretions （VA） layered above， and lateral accretions （LA） deposited at the sides. A key distinction lies in the increased proportion of LA at higher discharge conditions. （5） Discharge correlates positively with accretion size but inversely with aspect ratio and flakiness ratio. Median aspect ratios of bars are 3.5 in low-discharge systems versus 4.5 in high-discharge systems. Conclusions The study proposes a positive correlation between discharge and the scale of channel bars and accretions in sandy braided rivers. This clarifies flow-controlled sedimentary characteristics and scale variations， providing a basis for analyzing complex subsurface reservoir architectures.
2026,
44(4):
1442-1457.
doi: 10.14027/j.issn.1000-0550.2025.003
Abstract:
Objective The distribution patterns of favorable sand bodies in deltaic sedimentary systems serve as the theoretical foundation for oil and gas exploration. Traditional lobe classification and microfacies analysis methods have limitations in revealing the evolution mechanisms of the channel-lobe system， thus restricting the development of studies on lobe morphology and sand body connectivity. Methods Using the Cretaceous delta of the eastern depression of the Doseo Basin as a model， a flume experiment with a movable base was conducted. By capturing Hi-Res time-series images and sand body morphology data， and applying a new lobe classification method， an effective regional sedimentary model was established. Results （1） A consistent overlapping relationship exists between channels and lobes， where the migration， evolution， or disappearance of channels leads to the formation of new lobes. （2） Within the channel-lobe system， three main evolution mechanisms are driven by hydrodynamic strength： erosion of existing lobes， formation of lobes dominated by sandy deposition， and formation of mud layers dominated by fine-grained deposition. （3） The characteristics of channels determine the type of lobe development， whereas lobe morphology is influenced by factors such as sedimentary slope， tectonic activity， base level， and sediment source conditions. （4） The connectivity of sand bodies is affected by the constituent units of lobes， their contact relationships， lobe properties， and the types of lobe complexes. Later channel evolution can improve sand body connectivity to a certain extent. （5） The eastern depression of the Doseo Basin exhibits two sedimentary models： deep-water and shallow-water delta systems. In the deep-water delta model， the channel evolution area is larger， and connectivity improvements are more pronounced. In contrast， the shallow-water delta model features larger lobe deposition areas and wider planar distribution of lobes. Conclusions The new lobe classification method and the channel-lobe system evolution mechanism are applicable to the study of sand body connectivity and sedimentary models in the study area， and they are expected to be widely used in future delta sedimentary simulation research.
Objective The distribution patterns of favorable sand bodies in deltaic sedimentary systems serve as the theoretical foundation for oil and gas exploration. Traditional lobe classification and microfacies analysis methods have limitations in revealing the evolution mechanisms of the channel-lobe system， thus restricting the development of studies on lobe morphology and sand body connectivity. Methods Using the Cretaceous delta of the eastern depression of the Doseo Basin as a model， a flume experiment with a movable base was conducted. By capturing Hi-Res time-series images and sand body morphology data， and applying a new lobe classification method， an effective regional sedimentary model was established. Results （1） A consistent overlapping relationship exists between channels and lobes， where the migration， evolution， or disappearance of channels leads to the formation of new lobes. （2） Within the channel-lobe system， three main evolution mechanisms are driven by hydrodynamic strength： erosion of existing lobes， formation of lobes dominated by sandy deposition， and formation of mud layers dominated by fine-grained deposition. （3） The characteristics of channels determine the type of lobe development， whereas lobe morphology is influenced by factors such as sedimentary slope， tectonic activity， base level， and sediment source conditions. （4） The connectivity of sand bodies is affected by the constituent units of lobes， their contact relationships， lobe properties， and the types of lobe complexes. Later channel evolution can improve sand body connectivity to a certain extent. （5） The eastern depression of the Doseo Basin exhibits two sedimentary models： deep-water and shallow-water delta systems. In the deep-water delta model， the channel evolution area is larger， and connectivity improvements are more pronounced. In contrast， the shallow-water delta model features larger lobe deposition areas and wider planar distribution of lobes. Conclusions The new lobe classification method and the channel-lobe system evolution mechanism are applicable to the study of sand body connectivity and sedimentary models in the study area， and they are expected to be widely used in future delta sedimentary simulation research.
2026,
44(4):
1458-1470.
doi: 10.14027/j.issn.1000-0550.2026.028
Abstract:
Objective The Permian Jiamuhe Formation in the Zhongguai area of the Junggar Basin contains a suite of proximal coarse clastic deposits developed during the tectonic transition from rifting to depression. However， the depositional system type， depositional model， and formation mechanism of thick conglomerates remain poorly constrained， thereby limiting hydrocarbon exploration of conglomeratic reservoirs in the region. This study aims to clarify the depositional system type of the coarse clastic succession in the Jiamuhe Formation， reveal the controlling factors governing the development of thick conglomerates， establish a depositional model， and discuss its exploration significance. Methods Based on analyses of heavy mineral assemblages， paleogeomorphologic reconstruction， and seismic profile interpretation， combined with results from tectonic evolution and fault characterization， extensive core-based lithofacies analyses were conducted. On the basis of sedimentary microfacies identification and classification， the depositional system was summarized， the geological controls on thick conglomerate formation in the Jiamuhe Formation were clarified， and a depositional model was established. Results Three subfacies—fan delta plain， fan delta front， and pro-fan delta—and nine sedimentary microfacies were identified in the Jiamuhe Formation of the Zhongguai area， indicating an overall progradational fan delta depositional system controlled by multiple syndepositional fault terraces. The depositional development was jointly governed by four major factors： （1） during the rift⁃depression transitional stage， elevated topography， abundant sediment supply， and high topographic potential energy provided sufficient coarse clastic input； （2） under arid to semi-arid climatic conditions， frequent short-duration intense precipitation triggered high-energy transport processes including flood flows， debris flows， and clastic flows； （3） continuous syndepositional fault activity generated large accommodation space， promoting sustained aggradation of thick conglomerates； and （4） the development of multi-stage fault terraces controlled the continuous progradation of subaqueous fan bodies， resulting in basin-filling conglomerate distribution. Based on these characteristics， a fault-terrace-controlled fan delta depositional model was established. Conclusions The fault-terrace-controlled fan delta represents a distinctive fan delta depositional system developed under a rift-depression transitional tectonic setting， controlled by multiple syndepositional fault terraces and characterized by sustained proximal supply of high-energy coarse clastic sediments. It exhibits continuous progradation and aggradation， the combined action of multiple high-energy transport mechanisms， and the superposition of thick， mud-poor conglomerates. This model challenges the traditional perception that “proximal source areas necessarily correspond to poor reservoirs” and provides a depositional analogue for hydrocarbon exploration of deep to ultra-deep conglomeratic reservoirs in basin depressions and slope zones， fault transition belts， and concealed fault-terrace zones in other basins.
Objective The Permian Jiamuhe Formation in the Zhongguai area of the Junggar Basin contains a suite of proximal coarse clastic deposits developed during the tectonic transition from rifting to depression. However， the depositional system type， depositional model， and formation mechanism of thick conglomerates remain poorly constrained， thereby limiting hydrocarbon exploration of conglomeratic reservoirs in the region. This study aims to clarify the depositional system type of the coarse clastic succession in the Jiamuhe Formation， reveal the controlling factors governing the development of thick conglomerates， establish a depositional model， and discuss its exploration significance. Methods Based on analyses of heavy mineral assemblages， paleogeomorphologic reconstruction， and seismic profile interpretation， combined with results from tectonic evolution and fault characterization， extensive core-based lithofacies analyses were conducted. On the basis of sedimentary microfacies identification and classification， the depositional system was summarized， the geological controls on thick conglomerate formation in the Jiamuhe Formation were clarified， and a depositional model was established. Results Three subfacies—fan delta plain， fan delta front， and pro-fan delta—and nine sedimentary microfacies were identified in the Jiamuhe Formation of the Zhongguai area， indicating an overall progradational fan delta depositional system controlled by multiple syndepositional fault terraces. The depositional development was jointly governed by four major factors： （1） during the rift⁃depression transitional stage， elevated topography， abundant sediment supply， and high topographic potential energy provided sufficient coarse clastic input； （2） under arid to semi-arid climatic conditions， frequent short-duration intense precipitation triggered high-energy transport processes including flood flows， debris flows， and clastic flows； （3） continuous syndepositional fault activity generated large accommodation space， promoting sustained aggradation of thick conglomerates； and （4） the development of multi-stage fault terraces controlled the continuous progradation of subaqueous fan bodies， resulting in basin-filling conglomerate distribution. Based on these characteristics， a fault-terrace-controlled fan delta depositional model was established. Conclusions The fault-terrace-controlled fan delta represents a distinctive fan delta depositional system developed under a rift-depression transitional tectonic setting， controlled by multiple syndepositional fault terraces and characterized by sustained proximal supply of high-energy coarse clastic sediments. It exhibits continuous progradation and aggradation， the combined action of multiple high-energy transport mechanisms， and the superposition of thick， mud-poor conglomerates. This model challenges the traditional perception that “proximal source areas necessarily correspond to poor reservoirs” and provides a depositional analogue for hydrocarbon exploration of deep to ultra-deep conglomeratic reservoirs in basin depressions and slope zones， fault transition belts， and concealed fault-terrace zones in other basins.
2026,
44(4):
1471-1494.
doi: 10.14027/j.issn.1000-0550.2024.130
Abstract:
Objective The Upper Paleozoic Yanghugou Formation-Taiyuan Formation in the northwestern margin of the Ordos Basin is a good prospect for oil and gas exploration. The strata are completely developed and continuous， with large thickness changes and various types of sedimentary facies. Defining the distribution characteristics of sand bodies and clarifying the law of sedimentary evolution directly affect the selection of preferred exploration zones for oil and gas. Methods This study takes the Yanghugou Formation to Taiyuan Formation in the northwestern margin of Ordos Basin as the target horizon. Based on previous studies， through typical field profile measurement， drilling core observation， paleocurrent direction analysis， logging data， and test data analysis， the sedimentary environment， facies type characteristics， evolution， and model of the study area were evaluated. [Results and Conclusions] There are 19 lithofacies types and three sedimentary systems in the study area， including four sedimentary facies types， and 13 sedimentary microfacies are further divided. The Yanghugou Formation-Taiyuan Formation in the study area is supplied by the two provenance systems of the Alxa ancient land in the northwest of the basin and the Yinshan ancient land in the northeast. The Dickinson triangle plot reveals that the tectonic background of the provenance area is dominated by the recycled orogenic belt. The characteristics of heavy mineral assemblages are clear. The northwestern margin of the basin has a clear affinity with the Alashan Group （Ar3-Pt1）， Archean Jining Group （Ar3）， and the Wulashan Group （Ar1-2）. The ZTR index shows that the unstable minerals gradually decrease from north to south； analysis of the paleocurrent direction also reflects the material sources from northwest to southeast and from northeast to southwest. Based on the above provenance analysis， paleo-sedimentary environment evolution and sedimentary facies type characteristics， it is clear that the main body of the Yanghugou Formation-Taiyuan Formation in the study area is the coexistence stage of sea and land. During the sedimentary deposition of the Yanghugou Formation， under the background of the revival of Helan aulacogen and the backlog of north-south tectonics， the sea water enters rapidly. The whole study area is controlled by the delta-clastic coastal sedimentary system. The northern source supply is sufficient， resulting in the development of tidal-controlled delta deposits in the north. Affected by tides and waves， tidal flat-barrier island-desalination of lagoons-shelf sedimentary microfacies are developed in the south. During the deposition of the Taiyuan Formation， the crust continued to sink and seawater invaded. During this period， the basin became the most widely distributed period of the sea area. The sedimentary environment was similar to that of the Yanghugou Formation. The overall performance was the coexistence of tidal-controlled delta， tidal flat， desalination of lagoons-barrier island sedimentary environment， and the erosion range in the northern region was relatively reduced， the source supply continued to increase， and the tidal-controlled delta range extended wider to the south.
Objective The Upper Paleozoic Yanghugou Formation-Taiyuan Formation in the northwestern margin of the Ordos Basin is a good prospect for oil and gas exploration. The strata are completely developed and continuous， with large thickness changes and various types of sedimentary facies. Defining the distribution characteristics of sand bodies and clarifying the law of sedimentary evolution directly affect the selection of preferred exploration zones for oil and gas. Methods This study takes the Yanghugou Formation to Taiyuan Formation in the northwestern margin of Ordos Basin as the target horizon. Based on previous studies， through typical field profile measurement， drilling core observation， paleocurrent direction analysis， logging data， and test data analysis， the sedimentary environment， facies type characteristics， evolution， and model of the study area were evaluated. [Results and Conclusions] There are 19 lithofacies types and three sedimentary systems in the study area， including four sedimentary facies types， and 13 sedimentary microfacies are further divided. The Yanghugou Formation-Taiyuan Formation in the study area is supplied by the two provenance systems of the Alxa ancient land in the northwest of the basin and the Yinshan ancient land in the northeast. The Dickinson triangle plot reveals that the tectonic background of the provenance area is dominated by the recycled orogenic belt. The characteristics of heavy mineral assemblages are clear. The northwestern margin of the basin has a clear affinity with the Alashan Group （Ar3-Pt1）， Archean Jining Group （Ar3）， and the Wulashan Group （Ar1-2）. The ZTR index shows that the unstable minerals gradually decrease from north to south； analysis of the paleocurrent direction also reflects the material sources from northwest to southeast and from northeast to southwest. Based on the above provenance analysis， paleo-sedimentary environment evolution and sedimentary facies type characteristics， it is clear that the main body of the Yanghugou Formation-Taiyuan Formation in the study area is the coexistence stage of sea and land. During the sedimentary deposition of the Yanghugou Formation， under the background of the revival of Helan aulacogen and the backlog of north-south tectonics， the sea water enters rapidly. The whole study area is controlled by the delta-clastic coastal sedimentary system. The northern source supply is sufficient， resulting in the development of tidal-controlled delta deposits in the north. Affected by tides and waves， tidal flat-barrier island-desalination of lagoons-shelf sedimentary microfacies are developed in the south. During the deposition of the Taiyuan Formation， the crust continued to sink and seawater invaded. During this period， the basin became the most widely distributed period of the sea area. The sedimentary environment was similar to that of the Yanghugou Formation. The overall performance was the coexistence of tidal-controlled delta， tidal flat， desalination of lagoons-barrier island sedimentary environment， and the erosion range in the northern region was relatively reduced， the source supply continued to increase， and the tidal-controlled delta range extended wider to the south.
2026,
44(4):
1495-1506.
doi: 10.14027/j.issn.1000-0550.2025.028
Abstract:
Objective The Wuotuo village in Zongdi town， Ziyun county， southern Guizhou province， developed an Early Permian coral reef that is exposed with a thickness of approximately 45 m and lateral exposure of nearly 100 m. The reef displays a positive relief. It is of great importance to the study of the construction of shallow marine organisms and the paleoenvironment. Methods The coral reef in this area was systematically studied from the perspectives of paleontology and sedimentary petrology. Results The fusulinids collected from the reef indicated an Early Asselian age. The primary reef-building organism was identified as the fasciculate colonial coral Fomichevella， whereas biotic compositions of the coral reef included foraminifers， brachiopods， gastropods， and calcareous algae. The coral reef in Wotuo village and its underlying and overlying strata contained a broad variety of microfacies types， including bioclastic wackestone-packstone， coral bafflestone， bioclastic packstone， bioclastic grainstone， phylloid algae-cement framestone， fasciculate coral framestone， bioclastic wackestone， and foraminifer-fusulinid grainstone. Conclusions During the Early Permian， glacial-interglacial cycles were the primary factors influencing the variations in palaeoocean temperature and global sea levels. The vertical microfacies succession in this study provides a record of relative sea-level change. The decline of Late Paleozoic glaciation， which resulted in global warming and a relative rise in sea level， played a pivotal role in the development and flourishing of the coral reefs in southern Guizhou province.
Objective The Wuotuo village in Zongdi town， Ziyun county， southern Guizhou province， developed an Early Permian coral reef that is exposed with a thickness of approximately 45 m and lateral exposure of nearly 100 m. The reef displays a positive relief. It is of great importance to the study of the construction of shallow marine organisms and the paleoenvironment. Methods The coral reef in this area was systematically studied from the perspectives of paleontology and sedimentary petrology. Results The fusulinids collected from the reef indicated an Early Asselian age. The primary reef-building organism was identified as the fasciculate colonial coral Fomichevella， whereas biotic compositions of the coral reef included foraminifers， brachiopods， gastropods， and calcareous algae. The coral reef in Wotuo village and its underlying and overlying strata contained a broad variety of microfacies types， including bioclastic wackestone-packstone， coral bafflestone， bioclastic packstone， bioclastic grainstone， phylloid algae-cement framestone， fasciculate coral framestone， bioclastic wackestone， and foraminifer-fusulinid grainstone. Conclusions During the Early Permian， glacial-interglacial cycles were the primary factors influencing the variations in palaeoocean temperature and global sea levels. The vertical microfacies succession in this study provides a record of relative sea-level change. The decline of Late Paleozoic glaciation， which resulted in global warming and a relative rise in sea level， played a pivotal role in the development and flourishing of the coral reefs in southern Guizhou province.
2026,
44(4):
1507-1522.
doi: 10.14027/j.issn.1000-0550.2024.134
Abstract:
Objective The Taiyuan Formation of Permian System in Ordos Basin has the characteristics of large thickness， wide distribution， and rich types of oil and gas resources， which indicates a substantial potential for exploration. At present， the study of this formation is mainly concentrated in the eastern part of the basin， while the exploration and study of Taiyuan Formation in the western part of the basin need to be further discussed due to the complex and variable tectonic pattern and sedimentary evolution. Methods The detrital material source， tectonic setting and paleogeographic evolution of Taiyuan Formation in western Ordos Basin are systematically studied by means of outcrop observation， drilling sample collection， detrital zircon U-Pb dating and paleo-flow analysis. Results The sediments in the northeastern part of the study area （Group A） are mainly from the Yinshan Orogenic Belt under the collision-compressional tectonic background， with strong provenances. The delta plain， delta front， tidal sand ridge and tidal sand bar are successively developed in the middle of the basin. The sediments in the northwest （Group B） are derived from the Alxa Block under the collisional compression and convergent orogenic tectonic background， and the delta plain， delta front and lagoon-tidal flat develop successively towards the middle of the basin. The sediments in the southern （Group D） area came from the North Qilian and North Qinling tectonic belts under the extension-subduction-collision tectonic environment of the Paleo-Tethyan Ocean. The central paleo-uplift of the Taiyuan Period was slow， the provenance-supply was weak， and the mainly developed barrier island-barrierisland-lagoon-tidal flat deposits. Conclusions The northern part of the study area is characterized by high uplift and strong provenance supply in the context of collision and convergence orogenic structures， and large tide-delta complex system， while the southern part is characterized by weak provenance supply in the context of tensile extension structures， and is dominated by tidal flat and lagoon. This study not only deepens the understanding of the sedimentary system and provenance supply mechanism in the western Ordos Basin， but also provides a new perspective and reference for the reconstruction of the tectono-sedimentary evolution process and paleogeographic pattern in the western Ordos Basin.
Objective The Taiyuan Formation of Permian System in Ordos Basin has the characteristics of large thickness， wide distribution， and rich types of oil and gas resources， which indicates a substantial potential for exploration. At present， the study of this formation is mainly concentrated in the eastern part of the basin， while the exploration and study of Taiyuan Formation in the western part of the basin need to be further discussed due to the complex and variable tectonic pattern and sedimentary evolution. Methods The detrital material source， tectonic setting and paleogeographic evolution of Taiyuan Formation in western Ordos Basin are systematically studied by means of outcrop observation， drilling sample collection， detrital zircon U-Pb dating and paleo-flow analysis. Results The sediments in the northeastern part of the study area （Group A） are mainly from the Yinshan Orogenic Belt under the collision-compressional tectonic background， with strong provenances. The delta plain， delta front， tidal sand ridge and tidal sand bar are successively developed in the middle of the basin. The sediments in the northwest （Group B） are derived from the Alxa Block under the collisional compression and convergent orogenic tectonic background， and the delta plain， delta front and lagoon-tidal flat develop successively towards the middle of the basin. The sediments in the southern （Group D） area came from the North Qilian and North Qinling tectonic belts under the extension-subduction-collision tectonic environment of the Paleo-Tethyan Ocean. The central paleo-uplift of the Taiyuan Period was slow， the provenance-supply was weak， and the mainly developed barrier island-barrierisland-lagoon-tidal flat deposits. Conclusions The northern part of the study area is characterized by high uplift and strong provenance supply in the context of collision and convergence orogenic structures， and large tide-delta complex system， while the southern part is characterized by weak provenance supply in the context of tensile extension structures， and is dominated by tidal flat and lagoon. This study not only deepens the understanding of the sedimentary system and provenance supply mechanism in the western Ordos Basin， but also provides a new perspective and reference for the reconstruction of the tectono-sedimentary evolution process and paleogeographic pattern in the western Ordos Basin.
2026,
44(4):
1523-1534.
doi: 10.14027/j.issn.1000-0550.2025.010
Abstract:
Objective The Second member of the Middle Permian Lucaogou Formation is the main exploration target for lacustrine carbonate shale oil in the Santanghu Basin， Xinjiang province， China. Clarifying its paleoenvironment and organic matter enrichment mechanism provides scientific evidence in support of shale oil exploration and development in the study area. Methods Tests for total organic carbon content， major and trace elements and carbon-oxygen isotopic composition of primary carbonate rocks were conducted on shale samples collected from the well Luye 1 in the Second member of the Lucaogou Formation in the in the Malang Sag， Santanghu Basin. These deciphered the paleoenvironment and associated organic matter enrichment mechanism of the shale sequence， hence helping to gain a better understanding of the effects of paleoproductivity， paleoclimate， paleosalinity and paleoredox conditions on the organic matter enrichment and the key elements. Results Shale oil sweet spots are present in the middle and upper parts of this shale sequence. The tests indicated a closed lacustrine setting. The lowest part of the middle sweet spot was deposited in an arid， saline and reduced deep-water environment with low paleoproductivity， whereas its upper section has high paleoproductivity and was deposited in a semi-arid， brackish and weakly reducing deep-water environment. The upper sweet spot was deposited in an arid， saline and weakly reduced semi-deep water setting with medium paleoproductivity. Conclusions The organic matter enrichment mechanisms vary between the different shale sections. The influencing elements were the redox conditions and paleoproductivity in the lowest part of the middle sweet spot， paleoclimatic conditions and paleoproductivity for the upper part of the middle sweet spot， and paleoproductivity in the upper sweet spot. This study will assist in shale oil exploration and development in the Second member of the Lucaogou Formation in the Santanghu Basin.
Objective The Second member of the Middle Permian Lucaogou Formation is the main exploration target for lacustrine carbonate shale oil in the Santanghu Basin， Xinjiang province， China. Clarifying its paleoenvironment and organic matter enrichment mechanism provides scientific evidence in support of shale oil exploration and development in the study area. Methods Tests for total organic carbon content， major and trace elements and carbon-oxygen isotopic composition of primary carbonate rocks were conducted on shale samples collected from the well Luye 1 in the Second member of the Lucaogou Formation in the in the Malang Sag， Santanghu Basin. These deciphered the paleoenvironment and associated organic matter enrichment mechanism of the shale sequence， hence helping to gain a better understanding of the effects of paleoproductivity， paleoclimate， paleosalinity and paleoredox conditions on the organic matter enrichment and the key elements. Results Shale oil sweet spots are present in the middle and upper parts of this shale sequence. The tests indicated a closed lacustrine setting. The lowest part of the middle sweet spot was deposited in an arid， saline and reduced deep-water environment with low paleoproductivity， whereas its upper section has high paleoproductivity and was deposited in a semi-arid， brackish and weakly reducing deep-water environment. The upper sweet spot was deposited in an arid， saline and weakly reduced semi-deep water setting with medium paleoproductivity. Conclusions The organic matter enrichment mechanisms vary between the different shale sections. The influencing elements were the redox conditions and paleoproductivity in the lowest part of the middle sweet spot， paleoclimatic conditions and paleoproductivity for the upper part of the middle sweet spot， and paleoproductivity in the upper sweet spot. This study will assist in shale oil exploration and development in the Second member of the Lucaogou Formation in the Santanghu Basin.
2026,
44(4):
1535-1551.
doi: 10.14027/j.issn.1000-0550.2025.004
Abstract:
Objective The shale gas of the Cambrian Qiongzhusi Formation in the Sichuan Basin has good prospects for exploration and development， and a knowledge of its sedimentary environment is necessary to evaluate these resources. Methods The focus of this study was the Chengjiaba section shale series in the Qiongzhusi Formation. A detailed field geological survey and whole rock X-ray diffraction and geochemical analyses were carried out. The elements and ratio parameters in the study area were optimized to determine the sedimentary paleoenvironment of the organic-rich shale. Results （1） The First and Second members of the Qiongzhusi Formation are mainly gray-black or black mudstone and silty mudstone， with siliceous rock and siliceous shale facies. The horizontal bedding indicates a deep-water shelf paleoenvironment. （2） The shale TOC（Total Organic Carbon） is relatively high in the Qiongzhusi Formation， ranging from 0.22% to 4.34% （average 2.68%）. （3） The geochemistry of the elements indicates a warm and humid paleoclimate during the deposition of the black shale. The water body was anoxic and highly retained. Conclusions The formation of organic-rich shale in the Qiongzhusi Formation is controlled by multiple factors. Organic matter enrichment in the First member of the Qiongzhusi Formation conforms to the preservation mode， primarily controlled by redox conditions and sedimentation rate. In contrast， the organic matter enrichment in the Second member of the Qiongzhusi Formation follows the comprehensive model， synergistically controlled by paleoclimate， paleoproductivity， sedimentation rate， and redox conditions.
Objective The shale gas of the Cambrian Qiongzhusi Formation in the Sichuan Basin has good prospects for exploration and development， and a knowledge of its sedimentary environment is necessary to evaluate these resources. Methods The focus of this study was the Chengjiaba section shale series in the Qiongzhusi Formation. A detailed field geological survey and whole rock X-ray diffraction and geochemical analyses were carried out. The elements and ratio parameters in the study area were optimized to determine the sedimentary paleoenvironment of the organic-rich shale. Results （1） The First and Second members of the Qiongzhusi Formation are mainly gray-black or black mudstone and silty mudstone， with siliceous rock and siliceous shale facies. The horizontal bedding indicates a deep-water shelf paleoenvironment. （2） The shale TOC（Total Organic Carbon） is relatively high in the Qiongzhusi Formation， ranging from 0.22% to 4.34% （average 2.68%）. （3） The geochemistry of the elements indicates a warm and humid paleoclimate during the deposition of the black shale. The water body was anoxic and highly retained. Conclusions The formation of organic-rich shale in the Qiongzhusi Formation is controlled by multiple factors. Organic matter enrichment in the First member of the Qiongzhusi Formation conforms to the preservation mode， primarily controlled by redox conditions and sedimentation rate. In contrast， the organic matter enrichment in the Second member of the Qiongzhusi Formation follows the comprehensive model， synergistically controlled by paleoclimate， paleoproductivity， sedimentation rate， and redox conditions.
2026,
44(4):
1552-1569.
doi: 10.14027/j.issn.1000-0550.2024.103
Abstract:
Objective The Wufeng Formation-Longmaxi Formation black rock series in eastern Sichuan and western Hubei is a focus for marine shale gas exploration in South China. These show great differences in sedimentary characteristics， which record major geological events during the Ordovician–Silurian transition. Further knowledge of these differences is of benefit to exploration for shale gas in western Hubei， and helps to understand global paleo-climate and sea-level changes during that time. Methods The sedimentary properties， main influencing factors and sedimentary processes of the black rock series in the Wufeng Formation and Longmaxi Formation were studied in detail by petrological， sedimentological and geochemical analysis. Results The sedimentary attributes of the Wufeng Formation are similar in both study areas， but in the Longmaxi Formation they differ significantly. In eastern Si-chuan， the large thickness of the Longmaxi black shale with completed graptolite zones and thick silty shale in the Rhuddanian-Aeronian transition is overlain by thick， organic-rich shale. Three long-term sedimentary cycles are recognized in the Longmaxi black rock series， but in western Hubei the Longmaxi black shale is very thin and only two long-term sedimentary cycles are identified. Neither silty shale nor Coronograptus cyphus and Demirastrites triangulatus graptolite zones are present in the Rhuddanian-Aeronian transition， but thin lime-bearing dolomitic mudstone covered by thin organic-rich shale are developed. Additionally， the Longmaxi black shale contains less quartz in eastern Sichuan than in western Hubei. Conclusions In this study， tectonic paleogeomorphology and paleoclimate changes are considered to be the main factors influencing the different evolutionary histories of the Wufeng Formation⁃Longmaxi Formation black rock series in the two study areas. During the Upper Ordovician， eastern Sichuan and western Hubei both subsided as a result of the Cathaysia Block⁃Yangtze Block collision. The paleogeomorphology and sedimentary environments in eastern Sichuan and western Hubei are not significantly different， but continuous tectonic compression beginning in the Early Silurian caused non-uniform subsidence. Continuing subsidence in eastern Sichuan and gradual uplift in western Hubei led to significantly different thicknesses of the Rhuddanian black shale in the two regions. Global sea-level fall during the Rhuddanian⁃Aeronian transition related to intensified glaciation further exacerbated the sedimentary differences in the two study areas， resulting in a sedimentary gap in western Hubei and abundant sandy deposits with low TOC in eastern Sichuan. Subsequent significant sea-level rise following global climatic warming promoted the development of black shale in both areas， although thicker in eastern Sichuan than in western Hubei. However， gradually intensifying tectonic compression and gradual sea-level fall， along with sufficient terrigenous sediment supply， sustained a sedimentary environment in both regions that led to the termination of development of the Longmaxi black shale in the two study areas.
Objective The Wufeng Formation-Longmaxi Formation black rock series in eastern Sichuan and western Hubei is a focus for marine shale gas exploration in South China. These show great differences in sedimentary characteristics， which record major geological events during the Ordovician–Silurian transition. Further knowledge of these differences is of benefit to exploration for shale gas in western Hubei， and helps to understand global paleo-climate and sea-level changes during that time. Methods The sedimentary properties， main influencing factors and sedimentary processes of the black rock series in the Wufeng Formation and Longmaxi Formation were studied in detail by petrological， sedimentological and geochemical analysis. Results The sedimentary attributes of the Wufeng Formation are similar in both study areas， but in the Longmaxi Formation they differ significantly. In eastern Si-chuan， the large thickness of the Longmaxi black shale with completed graptolite zones and thick silty shale in the Rhuddanian-Aeronian transition is overlain by thick， organic-rich shale. Three long-term sedimentary cycles are recognized in the Longmaxi black rock series， but in western Hubei the Longmaxi black shale is very thin and only two long-term sedimentary cycles are identified. Neither silty shale nor Coronograptus cyphus and Demirastrites triangulatus graptolite zones are present in the Rhuddanian-Aeronian transition， but thin lime-bearing dolomitic mudstone covered by thin organic-rich shale are developed. Additionally， the Longmaxi black shale contains less quartz in eastern Sichuan than in western Hubei. Conclusions In this study， tectonic paleogeomorphology and paleoclimate changes are considered to be the main factors influencing the different evolutionary histories of the Wufeng Formation⁃Longmaxi Formation black rock series in the two study areas. During the Upper Ordovician， eastern Sichuan and western Hubei both subsided as a result of the Cathaysia Block⁃Yangtze Block collision. The paleogeomorphology and sedimentary environments in eastern Sichuan and western Hubei are not significantly different， but continuous tectonic compression beginning in the Early Silurian caused non-uniform subsidence. Continuing subsidence in eastern Sichuan and gradual uplift in western Hubei led to significantly different thicknesses of the Rhuddanian black shale in the two regions. Global sea-level fall during the Rhuddanian⁃Aeronian transition related to intensified glaciation further exacerbated the sedimentary differences in the two study areas， resulting in a sedimentary gap in western Hubei and abundant sandy deposits with low TOC in eastern Sichuan. Subsequent significant sea-level rise following global climatic warming promoted the development of black shale in both areas， although thicker in eastern Sichuan than in western Hubei. However， gradually intensifying tectonic compression and gradual sea-level fall， along with sufficient terrigenous sediment supply， sustained a sedimentary environment in both regions that led to the termination of development of the Longmaxi black shale in the two study areas.
2026,
44(4):
1570-1587.
doi: 10.14027/j.issn.1000-0550.2024.115
Abstract:
Objective To identify the next exploration direction， the main controlling factors and exploration potential of different types of shale oil enrichment in the Chang 7 member of the Ordos Basin are discussed. Methods In this study， the formation conditions and exploration potential of shale oil such as petrology， geochemical characteristics and reservoir capacity of the Chang 7 member shale were comprehensively studied using organic geochemistry， whole rock X-ray diffraction （XRD）， field emission scanning electron microscopy， and rock pyrolysis experiments. Results （1） The Chang 73 sub-member shale has high organic matter abundance， the best type， the highest maturity， and the greatest hydrocarbon generation potential. （2） The Chang 7 member shale is dominated by inorganic pores and fractures， with the largest proportion of micropores， and the shale reservoir capacity is stronger than that of mudstone. （3） The enrichment of shale oil in the Chang 7 member is controlled by five factors ： high-quality source rock， lithologic combination， fracture， mobility， and fracability. The distribution of high-quality source rocks controls the distribution range of shale oil， the lithology combination controls the hydrocarbon expulsion efficiency and the enrichment type of shale oil. The hydrocarbon expulsion efficiency of the source-reservoir interbedded type is the highest， which is conducive to the enrichment of sand bodies； the hydrocarbon expulsion efficiency of the thick source-thin reservoir type is the lowest， which is conducive to the in-situ retention and enrichment of shale oil. The two-sidedness of fractures controls the enrichment degree of shale oil. The development of fractures is conducive to the enrichment of sandstone interlayer shale oil， and the underdevelopment of fractures is conducive to the retention and enrichment of pure shale-type shale oil. The mobility and fracability of crude oil control the high yield of shale， and the mobility and brittleness index of shale crude oil are better than those of mudstone. Conclusions The Chang 73 sub-member in the Jiyuan area is a favorable exploration block for pure shale-type shale oil. The Zhengning and northern Shaanxi areas are favorable exploration blocks for sandstone-intercalated shale oil in the Chang 71 and Chang 72 sub-members. The Huachi area in Longdong is a favorable area for the exploration of both sandstone-intercalated and pure shale-type shale oil.
Objective To identify the next exploration direction， the main controlling factors and exploration potential of different types of shale oil enrichment in the Chang 7 member of the Ordos Basin are discussed. Methods In this study， the formation conditions and exploration potential of shale oil such as petrology， geochemical characteristics and reservoir capacity of the Chang 7 member shale were comprehensively studied using organic geochemistry， whole rock X-ray diffraction （XRD）， field emission scanning electron microscopy， and rock pyrolysis experiments. Results （1） The Chang 73 sub-member shale has high organic matter abundance， the best type， the highest maturity， and the greatest hydrocarbon generation potential. （2） The Chang 7 member shale is dominated by inorganic pores and fractures， with the largest proportion of micropores， and the shale reservoir capacity is stronger than that of mudstone. （3） The enrichment of shale oil in the Chang 7 member is controlled by five factors ： high-quality source rock， lithologic combination， fracture， mobility， and fracability. The distribution of high-quality source rocks controls the distribution range of shale oil， the lithology combination controls the hydrocarbon expulsion efficiency and the enrichment type of shale oil. The hydrocarbon expulsion efficiency of the source-reservoir interbedded type is the highest， which is conducive to the enrichment of sand bodies； the hydrocarbon expulsion efficiency of the thick source-thin reservoir type is the lowest， which is conducive to the in-situ retention and enrichment of shale oil. The two-sidedness of fractures controls the enrichment degree of shale oil. The development of fractures is conducive to the enrichment of sandstone interlayer shale oil， and the underdevelopment of fractures is conducive to the retention and enrichment of pure shale-type shale oil. The mobility and fracability of crude oil control the high yield of shale， and the mobility and brittleness index of shale crude oil are better than those of mudstone. Conclusions The Chang 73 sub-member in the Jiyuan area is a favorable exploration block for pure shale-type shale oil. The Zhengning and northern Shaanxi areas are favorable exploration blocks for sandstone-intercalated shale oil in the Chang 71 and Chang 72 sub-members. The Huachi area in Longdong is a favorable area for the exploration of both sandstone-intercalated and pure shale-type shale oil.
