Sedimentary Environment And Source Rock Characteristics Of Black Shale In The Lower Cambrian Qiongzhusi Formation,Eastern Yunnan

The black shale formation of the Lower Cambrian Qiongzhusi Formation in eastern Yunnan is stable,and it is one of the typical areas where the upper Yangtze black shale is developed.In this study,the typical black shale section of Cambrian Qiongzhusi Formation in eastern Yunnan was selected,including Shilong Village,Nazhang Town,Malong District,Qujing City,Shuhui Village,Deze Township,Zhanyi District,Qujing City,and Huize County,Qujing City.Six sections of Niejia Village in Buzhen,Zhujiaqing,Dahai Township,Huize County,Qujing City,Gulian Village Section in Xishan District,Kunming City,and Meishu Village Section in Jinning District,Kunming City were used for field profile measurement,observation,description and sample collection,and sedimentology was used.,Petrology and element geochemistry and other means,the high-resolution sedimentary environment of the black shale in the study area was analyzed,combined with organic geochemical test data,the distribution of favorable source rocks in eastern Yunnan was predicted.The black shale of the Lower Cambrian Qiongzhusi Formation in eastern Yunnan is dominated by black,grayish black,and gray.Sandstone;typical sedimentary structures developed include horizontal bedding,wave bedding and parallel bedding.Based on the analysis of the typical sedimentary facies signs above,two subfacies of shallow water shelf and deep water shelf were identified in the study area,including sandy shallow water shelf,sandy muddy shallow water shelf,muddy shallow water shelf and mud Four microfacies of quality deep water shelf.Based on the analysis of sedimentary microfacies in a single section and the comparative analysis of sedimentary microfacies in a continuous section,the distribution map of planar sedimentary microfacies in the study area was drawn.Based on the redox sensitive elements such as redox sensitive elements and their ratios,the characteristics of the paleo-ocean sedimentary environment were analyzed longitudinally.The results showed that the seawater during the black shale deposition period of the Qiongzhusi Formation experienced two sea-regression cycles Process;in this period,it was an anoxic-sulfurized sedimentary environment during two seaward advances,and the whole was in an anoxic-reducing state of seawater.The chemical weathering index(CIA)value is between 51.81-79.42,with an average of 70.47,indicating that the black shale of the Qiongzhusi Formation was moderately weathered during the deposition period and was in a warm and humid climate.The organic matter type of the black shale of the Qiongzhusi Formation is mainly type ?,with TOC content between 1.07-6.91%,with an average value of 2.05%,and 53.8% samples with TOC greater than 2%,which is a good-excellent hydrocarbon source on the whole In rocks,Ro ranges from 2.94 to 3.14%,with an average of 3.03%.The Ro distribution of most samples is above 3.0,and the source rock reaches the over-maturity stage.After comprehensive analysis,it is believed that favorable source rocks in the study area are distributed in the northeast of Kunming-Qujingxi-Huizen South.