陆相黑色页岩沉积环境及有机质富集机制——以鄂尔多斯盆地长7段为例  

Sedimentary Depositional Environment and Organic Matter Enrichment Mechanism of Lacustrine Black Shales:A case study of the Chang 7 member in the Ordos Basin

作　　者：刘翰林 邹才能[1] 邱振[1] 尹帅 杨智[1] 吴松涛[1] 张国生[1] 陈艳鹏[1] 马锋[1] 李士祥[3] 张岩[3] LIU HanLin;ZOU CaiNeng;QIU Zhen;YIN Shuai;YANG Zhi;WU SongTao;ZHANG GuoSheng;CHEN YanPeng;MA Feng;LI ShiXiang;ZHANG Yan(PetroChina Research Institute of Petroleum Exploration&Development,Beijing 100083,China;School of Earth Science and Engineering,Xi’an Shiyou University,Xi’an 710065,China;Research Institute of Exploration and Development,Changqing Oilfield Company,PetroChina,Xi'an 710018,China)

机构地区：[1]中国石油勘探开发研究院,北京100083 [2]西安石油大学地球科学与工程学院,西安710065 [3]中国石油长庆油田分公司勘探开发研究院,西安710018

出　　处：《沉积学报》2023年第6期1810-1829,共20页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(42222209);中石油勘探开发研究院项目(R2PED-2023-JS-1447,2021yjcq02)。

摘　　要：【目的】元素地球化学特征分析与古环境恢复是深入认识页岩层系中有机质富集机制的重要前提。【方法】以鄂尔多斯盆地三叠系延长组7段沉积时期湖盆不同相带(浅湖、滨浅湖、半深湖—深湖)的黑色页岩为研究对象,开展了5口代表性钻井长7段页岩的岩石学、古生物学、有机地球化学、元素地球化学等分析,以此探讨陆相黑色页岩的沉积环境及其有机质富集机制。【结果】鄂尔多斯湖盆长7段页岩层系不同黑色页岩层段(长7_(3)、长7_(2)和长7_(1)亚段)具有差异地球化学特征与沉积环境:(1)长7_(3)页岩有机质最为富集(TOC平均含量约为8.21%),其异常高有机质页岩最厚,其次为长7_(1)和长7_(2);(2)主、微量元素特征显示湖盆长7段沉积时期总体上为岛弧及活动大陆边缘构造背景,以长英质与基性岩混合的物源为主,含少量安山岩岛弧物源,但长7_(3)时期陆源碎屑输入强度明显低于长7_(2)与长7_(1);(3)较高CIAcorr和Cvalue值表明长7段沉积时期整体处于高温多雨湿润气候,其中长7_(3)时期温度与湿度最高;(4)Sr/Ba和Rb/K_(2)O比值指示长7_(3)时期整体为淡水环境,并局部发生微咸化,而长7_(2)和长7_(1)表现为相对稳定的淡水环境。【结论】通过对长7段典型火山灰层上、下黑色页岩高精度地球化学特征对比分析,并结合长7不同时期火山活动特征与有机质富集主控因素探讨,认为鄂尔多斯盆地长7黑色页岩有机质富集,特别是异常高有机质规模富集,与火山活动(喷发)事件密切相关:火山活动能够引发一系列连锁效应,包括“迟滞”期初级生产力“爆发式”增长、水体还原性增强等,从而有利于异常高有机质规模沉积。[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 7_(3),Chang 7_(2),and Chang 7_(1))of the Chang 7 shale series in the Ordos Lake Basin have different geochemical characteristics and sedimentary environments:(1)Chang 7_(3) 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 7_(1) and Chang 7_(2).(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 7_(3) is significantly lower than that of Chang 7_(2) and Chang 7_(1).(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 7_(3).(4)Sr/Ba and Rb/K2O values indicate that the Chang 7_(3) was an overall freshwater environment with local

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 

分 类 号：P618.13[天文地球—矿床学]