四川盆地东北部地区陡山沱组黑色页岩古海洋环境与有机质富集机制  

Paleomarine environment and organic matter enrichment mechanism of Doushantuo black shale in the northeastern Sichuan Basin

作　　者：王剑 肖洒 杜秋定 周刚[4] 王铜山[5] 李秋芬[5] 付修根 韦恒叶 和源 沈利军 WANG Jian;XIAO Sa;DU Qiuding;ZHOU Gang;WANG Tongshan;LI Qiufen;FU Xiugen;WEI Hengye;HE Yuan;SHEN Lijun(School of Geoscience and Technology,Southwest Petroleum University,Chengdu,Sichuan 610500,China;Qiangtang Institute of Sedimentary Basin,Southwest Petroleum University,Chengdu,Sichuan 610500,China;State Key Laboratory of Oil&Gas Reservoir Geology and Exploitation//Southwest Petroleum University,Chengdu,Sichuan 610050,China;Exploration and Development Research Institute,PetroChina Southwest Oil&Gasfield Company,Chengdu,Sichuan 610041,China;PetroChina Research Institute of Petroleum Exploration&Development,Beijing 100083,China)

机构地区：[1]西南石油大学地球科学与技术学院 [2]西南石油大学羌塘盆地研究院 [3]“油气藏地质与开发工程”国家重点实验室·西南石油大学 [4]中国石油西南油气田公司勘探开发研究院 [5]中国石油勘探开发研究院

出　　处：《天然气工业》2023年第4期76-92,共17页Natural Gas Industry

基　　金：中国石油—西南石油大学创新联合体科技合作项目(编号:2020CX010000);国家自然科学基金项目名称(编号:41972121、41762003);四川省科技厅重点研发项目(编号:2022YFS0466、2022YFS0451)。

摘　　要：四川盆地下震旦统陡山沱组页岩不仅是重要的烃源岩层系也是页岩气勘探的潜力层位,目前对其黑色页岩古海洋环境演化与异常富有机质形成的响应关系还不清楚,因此制约了盆地烃源岩整体评价与资源勘探部署。为此,基于四川盆地东北部地区(以下简称川东北地区)城口区块陡山沱组二段(以下简称陡二段)黑色页岩沉积相与沉积微相研究、环境特征矿物(草莓状黄铁矿)粒径与形态统计分析结果,以黑色页岩有机地球化学分析及古海洋环境关键元素地球化学指标研究为依据,重建了该区陡二段黑色页岩形成的古海洋环境模式,探讨了古海洋环境演化与有机质富集响应的关系。研究结果表明:①陡二段黑色页岩整体为斜坡—盆地相沉积环境,可划分为灰色粉砂质泥岩或泥质粉砂岩、灰色浊积泥岩—粉砂岩、灰黑色块状含钙粉砂质泥岩、黑色薄层富有机质泥岩、灰黑色薄层钙质泥岩5个沉积微相,异常富集有机质层段主要发育于后面2个微相;②环境特征矿物(草莓状黄铁矿)粒径与形态统计分析、U与Mo富集系数(UEF、MoEF)分析共同揭示陡二段早期古海洋为缺氧沉积环境,晚期逐渐过度贫氧环境;③陡二段古生产力水平整体为低—中等水平,期间有间歇性高生产力沉积期;④陡二段沉积晚期与早期相比,陆源碎屑输入量明显增加,其中下部异常富集有机质层泥岩及钙质泥岩TOC介于1.89%~7.26%,均值为4.09%。结论认为,该区氧化还原条件与TOC具有良好的协变关系,是有机质富集主要控制因素;间歇性高生产力是钙质泥岩相异常富集有机质的原因,而较多的陆源碎屑输入通量会在一定程度上削弱有机质的富集。The shale in the Lower Sinian Doushantuo Formation in the Sichuan Basin is an important source rock and also a potential horizon for shale gas exploration.The responses of the formation of abnormally rich organic matters to the paleomarine environment evolution in the black shale in the Doushantuo Formation remain unclear,which restricts the overall evaluation of source rocks and the planning of resource exploration in the basin.In this study,the black shale in the second member of the Doushantuo Formation(Dou 2 Member)in the Chengkou block,northeastern Sichuan Basin,was investigated for sedimentary facies and microfacies,and analyzed statistically for particle size and morphology of environmental characteristic minerals(pyrite framboids).Combined with the organic geochemical analysis and other geochemical indexes of key elements which can help to better understand the paleomarine environment,the paleomarine environment model for the black shale in the Dou 2 Member was reconstructed,and the responses of organic matter enrichment to the paleomarine environment evolvement were discussed.The results are obtained in four aspects.First,the black shale in the Dou 2 Member records a sedimentary environment of slope–basin facies.It can be divided into five microfacies,i.e.grey silty mudstones or muddy siltstones,grey turbidite mudstones–siltstones,grey black massive calciumbearing silty mudstones,black thin-bedded organic-rich mudstones,and grey black thin-bedded calcareous mudstones.Horizons with abnormally rich Oms are mainly found in black thin-bedded organic-rich mudstones and grey black thin-bedded calcareous mudstones.Second,the statistical analysis of particle size and morphology of environmental characteristic minerals(pyrite framboids)and the analysis of redox-sensitive geochemical proxies(UEF and MoEF)reflect that the paleomarine environment of the Dou 2 Member was an anoxic environment in the early stage and gradually transformed into a hypoxic environment in the late stage.Third,the Dou 2 Member reveals a

关 键 词：四川盆地 下震旦统陡山沱组 黑色页岩 沉积微相 古海洋环境 有机质富集 响应关系 草莓状黄铁矿 

分 类 号：P618.13[天文地球—矿床学]