Multiple borehole samples are collected from the Baiyun Depression in deep-water area of the northern South China Sea(SCS)in an effort to reconstruct transgression processes during the Paleogene based on palynalgal an...Multiple borehole samples are collected from the Baiyun Depression in deep-water area of the northern South China Sea(SCS)in an effort to reconstruct transgression processes during the Paleogene based on palynalgal analysis.This study indicates that the Baiyun Depression generated a large group of palynopore assemblages and fluvial/lacustrine-related algae during the early and middle Eocene when the Wenchang Formation was deposited.The entire depression was dominated by fluvial and lacustrine facies before transgression.Its eastern and southeastern sags transitioned to shallow marine environment by generating a large abundance of marine dinoflagellates during the Enping deposition of the late Eocene.Meanwhile,the southern uplift zone simply yielded fluvial/lacustrine-related palynopores and algae,and was dominated by the fluvial and lacustrine environment during the early stage of the Enping Formation,prior to shifting into transitional setting in the later period.Northwestern sags remained extensive fluvial and delta facies without existence of marine dinoflagellates.It was until the depositional stage of the Zhuhai Formation(Oligocene)that the overall depression was strongly impacted from transgression process.Both eastern and southeastern sags were mainly under deep marine setting on a continental slope while northwestern and southern areas developed transitional facies.Although distribution and accumulation patterns varied greatly among sub-sags,the overall Baiyun Depression was characterized by widespread development of marine dinoflagellates.It should be noted that the northwestern sag also partly generated large-scale river delta deposits.Due to the eustatic rise and change of SCS spreading axis,the overall Baiyun Depression was mostly influenced by the deep marine environment on a continental slope during the early Miocene.Both northwestern sag and southern uplift zone were found plentiful marine dinoflagellates.In summary,transgression initiated from the eastern and southeastern Baiyun Depression before subsequently progressing into the farther west.Evolution of transgression process is also greatly consistent with the gradual westward expansion of the SCS.展开更多
The relationship between marine transgression and the distribution of lacustrine organic matter has restricted shale oil and gas exploration for decades.In this study,the research objective is to analyze the sedimenta...The relationship between marine transgression and the distribution of lacustrine organic matter has restricted shale oil and gas exploration for decades.In this study,the research objective is to analyze the sedimentary environment and evaluate its influence on organic matter in transgressive lacustrine shale.The study uses various analyses including total organic carbon(TOC),Rock-Eval pyrolysis,gas chromatography-mass spectrometry(GC-MS),trace element and isotope analysis.Finally,the study proposes an enrichment model for organic matter.The lacustrine shale of the second member of the Funing Formation(E_(1)f^(2))is divided into three sequences.The results indicate that the depositional environment of the organic matter during this period was an arid and humid,reduced,closed,rift lake basin.In the first sequence,high salinity resulted from increased evaporation,leading to low primary biological productivity.At this time,the lake basin belonged to a salinized closed lake basin.Intermittent transgressions began in the second sequence,with the deep lake area still being dominated by a reducing environment.The third sequence saw the environment evolve into a closed lake basin characterized by a warm and humid freshwater environment with high primary productivity.Marine transgressions introduce a substantial amount of marine plankton,nutrient elements,as well as more CO_(2) and CO_(3)^(2−)into the lake,leading to increased primary productivity.The sedimentary model for transgressive lacustrine source rocks proposed here serves as an example for similar transgressive lake basins.展开更多
The Late Cretaceous global transgression is one of the best documented episodes of continental submergence events.The extent of transgression of the Neotethys Ocean into the African continent is generally thought to b...The Late Cretaceous global transgression is one of the best documented episodes of continental submergence events.The extent of transgression of the Neotethys Ocean into the African continent is generally thought to be limited to north Africa.Here,we describe transgression traces in the Muglad Basin in central Africa that indicate a greater spatial extend of the Neotethys during the late Cretaceous.A series of molecular markers detected in the Upper Cretaceous Santonian-Maastrichtian sediments of the Muglad Basin are typical for marine depositional conditions and differ from those in the typical lacustrine sediments of the Lower Cretaceous Barremian-Aptian.Combining the geological-geochemical implications of these markers with the paleogeographic,paleontological and lithological records,we propose that the Muglad Basin received intermittent marine inundations during the Santonian-Maastrichtian stages(86.3-66.0 Ma)and these special molecular markers are therefore the products of seawater incursion.Consequently,this study proposes that the transgression extent of the Neotethys Ocean into the African continent southern extended to the central Africa during the Late Cretaceous.展开更多
基金The National Natural Science Foundation of China under contract No.42076066。
文摘Multiple borehole samples are collected from the Baiyun Depression in deep-water area of the northern South China Sea(SCS)in an effort to reconstruct transgression processes during the Paleogene based on palynalgal analysis.This study indicates that the Baiyun Depression generated a large group of palynopore assemblages and fluvial/lacustrine-related algae during the early and middle Eocene when the Wenchang Formation was deposited.The entire depression was dominated by fluvial and lacustrine facies before transgression.Its eastern and southeastern sags transitioned to shallow marine environment by generating a large abundance of marine dinoflagellates during the Enping deposition of the late Eocene.Meanwhile,the southern uplift zone simply yielded fluvial/lacustrine-related palynopores and algae,and was dominated by the fluvial and lacustrine environment during the early stage of the Enping Formation,prior to shifting into transitional setting in the later period.Northwestern sags remained extensive fluvial and delta facies without existence of marine dinoflagellates.It was until the depositional stage of the Zhuhai Formation(Oligocene)that the overall depression was strongly impacted from transgression process.Both eastern and southeastern sags were mainly under deep marine setting on a continental slope while northwestern and southern areas developed transitional facies.Although distribution and accumulation patterns varied greatly among sub-sags,the overall Baiyun Depression was characterized by widespread development of marine dinoflagellates.It should be noted that the northwestern sag also partly generated large-scale river delta deposits.Due to the eustatic rise and change of SCS spreading axis,the overall Baiyun Depression was mostly influenced by the deep marine environment on a continental slope during the early Miocene.Both northwestern sag and southern uplift zone were found plentiful marine dinoflagellates.In summary,transgression initiated from the eastern and southeastern Baiyun Depression before subsequently progressing into the farther west.Evolution of transgression process is also greatly consistent with the gradual westward expansion of the SCS.
基金financially supported by the National Natural Science Foundation of China(Grant No.42072150)and we thank the sponsors of these projects.
文摘The relationship between marine transgression and the distribution of lacustrine organic matter has restricted shale oil and gas exploration for decades.In this study,the research objective is to analyze the sedimentary environment and evaluate its influence on organic matter in transgressive lacustrine shale.The study uses various analyses including total organic carbon(TOC),Rock-Eval pyrolysis,gas chromatography-mass spectrometry(GC-MS),trace element and isotope analysis.Finally,the study proposes an enrichment model for organic matter.The lacustrine shale of the second member of the Funing Formation(E_(1)f^(2))is divided into three sequences.The results indicate that the depositional environment of the organic matter during this period was an arid and humid,reduced,closed,rift lake basin.In the first sequence,high salinity resulted from increased evaporation,leading to low primary biological productivity.At this time,the lake basin belonged to a salinized closed lake basin.Intermittent transgressions began in the second sequence,with the deep lake area still being dominated by a reducing environment.The third sequence saw the environment evolve into a closed lake basin characterized by a warm and humid freshwater environment with high primary productivity.Marine transgressions introduce a substantial amount of marine plankton,nutrient elements,as well as more CO_(2) and CO_(3)^(2−)into the lake,leading to increased primary productivity.The sedimentary model for transgressive lacustrine source rocks proposed here serves as an example for similar transgressive lake basins.
基金supported by the National Natural Science Foundation of China(No.42202134)Science Foundation of China University of Petroleum,Beijing(No.2462023YJRC010)the postdoctoral fellowship by the Central Research and Development Fund of the University of Bremen.The authors would like to thank the editor and the two anonymous reviewers for their constructive comments and suggestions which significantly improved the quality of the manuscript.
文摘The Late Cretaceous global transgression is one of the best documented episodes of continental submergence events.The extent of transgression of the Neotethys Ocean into the African continent is generally thought to be limited to north Africa.Here,we describe transgression traces in the Muglad Basin in central Africa that indicate a greater spatial extend of the Neotethys during the late Cretaceous.A series of molecular markers detected in the Upper Cretaceous Santonian-Maastrichtian sediments of the Muglad Basin are typical for marine depositional conditions and differ from those in the typical lacustrine sediments of the Lower Cretaceous Barremian-Aptian.Combining the geological-geochemical implications of these markers with the paleogeographic,paleontological and lithological records,we propose that the Muglad Basin received intermittent marine inundations during the Santonian-Maastrichtian stages(86.3-66.0 Ma)and these special molecular markers are therefore the products of seawater incursion.Consequently,this study proposes that the transgression extent of the Neotethys Ocean into the African continent southern extended to the central Africa during the Late Cretaceous.
