鄂尔多斯盆地东缘山西组山23亚段泥页岩地球化学特征与沉积环境

鄂尔多斯盆地石炭系—二叠系海陆过渡相页岩气的研究主要集中在山西组山₂段泥页岩，山₂³亚段是山₂段泥页岩中有机质最为丰富的层段。对柳林县成家庄剖面进行实测并采集山₂³亚段泥页岩样品，并通过系统的有机碳含量、全岩矿物组成，主量、微量元素分析测试，对鄂尔多斯盆地东缘山西组山₂³亚段海陆过渡相泥页岩沉积期的古气候、水体环境、古生产力及与富有机质泥页岩发育关系进行了研究。结果表明：研究区山西组山₂³亚段泥页岩矿物组成中石英和黏土矿物占绝对优势，TOC平均值为2.04%，属于TOC较高的泥页岩；Sr、Sr/Ba、δ¹⁸O分析结果揭示山₂³亚段水体沉积环境经历了从下至上由咸水—半咸水—淡水的变化；Ce_anom、Ni/Co、V/（V+Ni）判别表明山₂³亚段主体为贫氧—缺氧的水体环境；CaO/Al₂O₃*MgO、CIA指数表明山₂³亚段沉积时期气温由下至上逐渐降低，风化程度减弱；V/Ni、Mn/Ti及δ¹³C揭示山₂³亚段沉积期水体深度自下而上呈先增大再逐渐减小趋势；P/Al和生物Ba在山₂³亚段变化趋势一致，表现为从下至上先增大再减小。山₂³亚段泥页岩有机质的富集主要受水体氧化还原条件与陆源碎屑输入的影响。

Geochemical characteristics and sedimentary environment of mudshale in Shan23 sub-member of Shanxi Formation， eastern margin of Ordos Basin

The study of Carboniferous-Permian marine continental transitional facies shale gas in Ordos Basin mainly focuses on the second member of Shanxi Formation， and Shan₂³ sub-member is the most abundant layer of organic matter in the second member of Shanxi Formation. Based on the observation and sampling analysis of Chengjiazhuang section in Liulin County， through the organic carbon content， whole rock mineral composition， combined with the analysis and test data of major and trace elements， the paleoclimate， water environment， paleoproductivity and their relationships with the development of organic-rich shale in Shan₂³ sub-member of Shanxi Formation in the eastern margin of Ordos Basin were studied. The results show that quartz and clay minerals are absolutely dominant in Shan₂³ shale， and the average TOC is 2.04%. The analytical results of Sr， Sr/Ba and δ¹⁸O content show that the sedimentary environment of Shan₂³ shale experienced the change from saline water to brackish water and then to freshwater from bottom to top. The discrimination of Ceanom， Ni/Co and V/（V+Ni） shows that Shan₂³ shale was deposited under an oxygen deficient anoxic reduction environment； CaO/Al₂O₃*MgO and CIA indexes show that the temperature gradually decreases from bottom to top and the weathering degree weakens during the deposition period； The contents of V/Ni， Mn/Ti and δ¹³C isotopes indicate that the depth of the sedimentary water in the Shan₂³ sub-member increases first and then gradually becomes shallow. The change trend of P/Al and biological Ba in Shan₂³ sub-member is consistent， which shows that it increases first and then decreases from bottom to top. The enrichment of organic matter in Shan₂³ sub-member is mainly affected by water redox conditions and terrestrial debris input.