沉积学报2023，Vol.41Issue(6)：1810-1829,20.DOI:10.14027/j.issn.1000-0550.2023.118
陆相黑色页岩沉积环境及有机质富集机制
Sedimentary Depositional Environment and Organic Matter Enrichment Mechanism of Lacustrine Black Shales:A case study of the Chang 7 member in the Ordos Basin
摘要
Abstract
[Objective]Analyses of elemental geochemistry and depositional environment reconstruction are an im-portant prerequisite for better understanding the mechanisms of organic matter enrichment in shale strata.In this study,a large number of recent research results on the paleoenvironment identification of offshore and continental shale in China were investigated.[Methods]Taking the black shale of five representative key exploration wells in dif-ferent facies zones(shallow lake,shore-shallow lake,and semi-deep lake-deep lake)from the Chang 7 member of the Yanchang Formation in the Ordos Basin as an example,its petrology,organic geochemistry,paleontology and el-ement geochemistry were systematically analyzed.On this basis,the sedimentary environment and organic matter en-richment mechanism of continental black shales were restored.[Results and Discussions]The study shows that dif-ferent black shale segments(Chang 73,Chang 72,and Chang 71)of the Chang 7 shale series in the Ordos Lake Basin have different geochemical characteristics and sedimentary environments:(1)Chang 73 shale is the most rich in or-ganic matter(the average total organic carbon(TOC)content is approximately 8.21%),and its abnormally high or-ganic matter shale is the thickest,followed by Chang 71 and Chang 72.(2)The characteristics of the main and trace elements show that the sedimentary period of the Chang 7 member in the lake basin had an island arc and active conti-nental margin tectonic background,dominated by a mixture of felsic and basic rocks,and containing a small amount of andesite island arc sources,but the intensity of terrigenous clastic input in Chang 73 is significantly lower than that of Chang 72 and Chang 71.(3)The higher CIAcorr and Cvalue indicated that the whole sedimentary period of the Chang 7 member was in a hot,rainy,and humid climate,and the highest temperature and humidity were found in Chang 73.(4)Sr/Ba and Rb/K2O values indicate that the Chang 73 was an overall freshwater environment with localized brine,whereas the Chang 72 and Chang 71 were relatively stable freshwater environments.[Conclusions]Based on the com-parative analysis of the high-precision geochemical characteristics of the upper and lower black shale of the typical volcanic ash layer of the Chang 7 member,combined with the exploration of the volcanic activity characteristics of dif-ferent periods of the Chang 7 member and the main controlling factors of organic matter enrichment,this comprehen-sive study suggests that the enrichment of organic matter in the Chang 7 black shale of the Ordos Basin,particularly the enrichment of unusually high organic matter scale,is closely related to volcanic activity(eruption)events:Volca-nic activity can lead to a series of chain effects,including the"explosive"growth of primary productivity in the"hys-teresis"period and the enhancement of water reducibility,which is conducive to the deposition of abnormally high or-ganic matter scale.关键词
鄂尔多斯盆地/长7段/页岩油/元素地球化学/异常高有机质Key words
Ordos Basin/Chang 7 member/shale oil/elemental geochemistry/extraordinarily high organic matter分类
天文与地球科学引用本文复制引用
刘翰林,李士祥,张岩,邹才能,邱振,尹帅,杨智,吴松涛,张国生,陈艳鹏,马锋..陆相黑色页岩沉积环境及有机质富集机制[J].沉积学报,2023,41(6):1810-1829,20.基金项目
国家自然科学基金项目(42222209) （42222209）
中石油勘探开发研究院项目(R2PED-2023-JS-1447,2021yjcq02)National Natural Science Foundation of China,No.42222209 （R2PED-2023-JS-1447,2021yjcq02）
China Petroleum Exploration and Development Research Institute Project,No.R2PED-2023-JS-1447,2021yjcq02 （）
