Paleoenvironmental Reconstruction and Organic Matter Enrichment of Middle Permian Black Shale:Insights From the Gufeng Formation,Enshi Area,Western Hubei
A series of black rocks dominated by basin facies developed in the Middle Permian Gufeng Formation in the Enshi area,Western Hubei Province.This formation was recently identified for shale gas development and exploration;however,little is known about the sedimentary paleoenvironment and the mechanisms of orga-nic matter enrichment in the black rock series.In this study,we focus primarily on two sections of the Gufeng Formation,Tianfengping and Yutangba,located in the Enshi area,Western Hubei.Our aim is to elucidate the paleoenvironment during the sedimentary phase of the Gufeng Formation shale and to identify the key factors governing organic matter accumulation in this area.A comprehensive suite of analytical techniques was used in this study,including petrography,mineralogy,total organic carbon(TOC)quantification,and elemental geo-chemistry.The results reveal that the Gufeng Formation shale predominantly consists of siliceous shale facies,with a notable TOC content ranging from 5.8％to 41.6％.Quartz(81.5％on average)and clay minerals(12.6％on average)constitute the bulk of the mineral assemblages,with minor contributions from feldspar,pyrite,and carbonate minerals.The Chemical Alteration Index(CIA)suggests that the sedimentary environ-ment of the Gufeng Formation shale was primarily characterized by hot and humid climate.The V/(V+Ni)and U/Th ratios indicate anoxic to sulfidic conditions in the bottom waters.The biogenic silicon(Sibio),Cu/Al,Ni/Al values indicate higher primary productivity during the depositional phase.The weak correlation be-tween TOC and U/Th,Al,Ti/Al suggests that bottom water anoxic sulfidic conditions and terrigenous detrital input have a limited influence on organic matter enrichment in black shales of the Gufeng Formation.Converse-ly,the positive correlation with Ni/Al suggests the primary productivity is a pivotal factor driving organic matter enrichment.The sedimentary environment of the Gufeng Formation shale is characterized by deep-water anoxia,a hot and humid climate,and high primary productivity.We therefore established a depositional environmental model for deep-water intraplatform basins,constrained by redox conditions,paleo-productivity,and a hot-humid paleoclimate.
Enshi area of Western HubeiGufeng Formation of the Middle Permianblack shalelithofaciessedimentary environmentorganic matter enrichment
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维普
