Passive margin shale sedimentary palaeoenvironment and their controls over organic matter enrichment: a case study of the Lower Silurian Longmaxi Formation in northern Chongqing,Upper Yangtze
CHEN Hao1,2, SHEN Junjun1, TAN Guangchao3, WANG Yuman4, LI Shanshan3, YAN Jiakai3, ZHOU Lin5, LIU Jiyong5
1 Hubei Cooperative Innovation Center of Unconventional Oil and Gas of Yangtze University,Wuhan 430100,China; 2 School of Geosciences,Yangtze University,Wuhan 430100,China; 3 Hydrogeology and Engineering Geology Institute of Hubei Geological Bureau,Hubei Jingzhou 434020,China; 4 Research Institute of Petroleum Exploration and Development,PetroChina, Beijing 100083,China; 5 Exploration and Production Research Institute,Jianghan Oilfield Company,SINOPEC,Wuhan 430070,China
Abstract At present,there are relatively few studies on sedimentary palaeoenvironment evolution of passive margin. In particular,due to limited understanding of the changing patterns of upwelling current activity,the main controlling factors for organic matter enrichment remain unclear. On these grounds,we investigate passive margin shale sedimentary palaeoenvironments and their controls on organic matter enrichment,based on an integrated core/outcrop,mineral petrology,organic geochemistry and elemental analysis of the Lower Silurian Longmaxi Formation in northern Chongqing. The results show that organic enrichment in the study area is controlled by preservation conditions,terrigenous input and palaeoproductivity,but the main controlling factors vary in different periods. During the Rhuddanian(LM1-LM5 depositional period),the accumulation of organic matter was controlled jointly by preservation conditions,terrigenous input and palaeoproductivity,and the TOC content was the highest. In the early Aeronian(LM6 depositional period),the basin entered the flexural-migration period of enhanced tectonic activity,the barrier in the Yubei area opened,resulting in increased upwelling current activity,and the deteriorated preservation condition was the main cause of the decrease of TOC content. During the mid Aeronian(LM7 sedimentary period),the migration effect was enhanced,with the barrier further opened and the upwelling current reaching an activity peak,and the deteriorated preservation condition and sharply increased palaeoproductivity were the main reasons for little change in TOC content compared to the LM6 deposition period. During the late Aeronian(LM8 depositional period),the barrier opening migrated to the northwest,the TOC content decreased,and the main controlling factors of organic matter enrichment were the same as those of LM1-LM5. During the early Telychian(LM9 deposition period),the sea level dropped to the lowest,the oxygen-rich environment predominated,and the TOC content decreased to the lowest. The preservation conditions were the main factors controlling the enrichment of organic matter. Overall,the changes of controlling factors of organic matter enrichment in different periods in the study area are closely related to the varying sedimentary palaeoenvironments caused by tectonic activities and sea level changes.
Fund:Hubei Natural Resources Science and Technology Project(No. ZRZY2024KJ25)
Corresponding Authors:
SHEN Junjun,born in 1983,is an associate professor and Ph.D. He is mainly engaged in sedimentary reservoir and the investigation and evaluation of unconventional oil and gas resources. E-mail: shenhema@163.com.
About author: CHEN Hao,born in 1996,is a master degree candidate. He is mainly engaged in unconventional deposition and reservoir. E-mail: chen961223@foxmail.com.
Cite this article:
CHEN Hao,SHEN Junjun,TAN Guangchao et al. Passive margin shale sedimentary palaeoenvironment and their controls over organic matter enrichment: a case study of the Lower Silurian Longmaxi Formation in northern Chongqing,Upper Yangtze[J]. JOPC, 2024, 26(5): 1072-1089.
CHEN Hao,SHEN Junjun,TAN Guangchao et al. Passive margin shale sedimentary palaeoenvironment and their controls over organic matter enrichment: a case study of the Lower Silurian Longmaxi Formation in northern Chongqing,Upper Yangtze[J]. JOPC, 2024, 26(5): 1072-1089.
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