川西南下寒武统麦地坪组-筇竹寺组元素地球化学特征及其古环境意义——以JS1井为例  

Geochemical Characteristics and Paleoenvironmental Significance of Lower Cambrian Maidiping and Qiongzhusi Formations in Southwestern Sichuan Basin:A case study of well JS1

作　　者：陈威振 田景春[2] 林小兵[2] 梁庆韶 杨燕茹 王兴[2] CHEN WeiZhen;TIAN JingChun;LIN XiaoBing;LIANG QingShao;YANG YanRu;WANG Xing(College of Earth Science,Chengdu University of Technology,Chengdu 610059,China;State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Chengdu University of Technology,Chengdu 610059,China)

机构地区：[1]成都理工大学地球科学学院,成都610059 [2]成都理工大学油气藏地质及开发工程全国重点实验室,成都610059

出　　处：《沉积学报》2024年第5期1784-1798,共15页Acta Sedimentologica Sinica

基　　金：国家科技重大专项(2016ZX05007004-002);中国石化西南油气分公司项目(34450000-19-ZC0607-0017);成都理工大学沉积地质学科研创新团队项目(KYTD201703)。

摘　　要：【目的】埃迪卡拉纪—寒武纪作为地质历史上的一个关键转折时期,地球系统在构造演化、气候波动、海洋环境和生物群落演化等方面都发生了巨大转变。深入研究这一时期的沉积物来源、古水深、古盐度和氧化还原条件,具有重要意义。【方法】选取四川盆地西南地区JS1井麦地坪组和筇竹寺组样品,详细开展了有机碳(TOC)、主量元素、微量元素和稀土元素分析。【结果与结论】麦地坪组—筇竹寺组物质来源较为一致,母岩以沉积岩和花岗岩为主,物源区形成于大陆边缘环境。麦地坪组轻稀土相对重稀土富集((La/Yb)N=6.05),轻微右倾,δEu的平均值略小于1,指示正常海水沉积,水体较浅,受热液作用影响不明显。筇竹寺组轻重稀土分异明显((La/Yb)N=7.69),轻稀土富集,重稀土亏损,右倾明显,具有弱的δCe和δEu负异常,可能与间歇性热液活动有关。此外,不同钻井对比分析表明,麦地坪组沉积期水体以氧化环境为主,区域上表现为潮坪相—浅水陆棚相的沉积体系;筇竹寺组整体属于厌氧环境,其底部为还原环境,向上缺氧程度降低,区域上表现为浅水—深水陆棚相沉积体系。[Objective]The Ediacaran-Cambrian,as a key transition period in geological history,saw a dramatic transformation of the Earth system in terms of tectonic evolution,climate fluctuations,marine environment and biological community evolution.It is of great significance to study in depth the sediment sources,paleo-water depth,paleosalinity and redox conditions during this period.[Methods]Samples from the Maidiping Formation and the Qiongzhusi Formation of the well JS1 in the southwestern part of the Sichuan Basin were selected and analyzed in detail for total organic carbon(TOC),major elements,trace elements and rare earth elements(REE).[Results and Conclusions]The material sources of the Maidiping and Qiongzhusi Formations were found to be relatively consistent.The parent rock primarily consists of sedimentary rock and granite,and the material source area was created in the environment found at the continental margin.The Maidiping Formation contains more light rare earth elements(LREE)than heavy rare earth elements(HREE)((La/Yb)N=6.05),slightly to the right,and the averageδEu is slightly<1,indicating normal seawater deposition in a shallow water body that was not significantly affected by hydrothermal action.The Qiongzhusi Formation has obvious LREE differentiation((La/Yb)N=7.69),LREE enrichment,HREE depletion and an obvious right dip,with weak negativeδCe andδEu anomalies,possibly related to intermittent hydrothermal activity.In addition,comparative analyses for different wells have shown that the water body during the sedimentary period of the Maidiping Formation was in an oxidizing environment,and the sedimentary system in the region ranges from tidal-flat to shallow-shelf facies.The Qiongzhusi Formation as a whole belongs to an anaerobic environment,with a reducing environment its base and the degree of anoxia decreasing upwards.The regional development was a shallow-to deepwater shelf sedimentary system.

关 键 词：沉积环境 氧化还原指标 麦地坪组 筇竹寺组 下寒武统 四川盆地 

分 类 号：P512.2[天文地球—地质学]