川东地区二叠系吴家坪组页岩中黄铁矿形态及其对大洋缺氧事件的指示意义  

Pyrite morphology in shale of Permian Wujiaping Formation in eastern Sichuan Basin and its indicative significance to oceanic anoxic events

作　　者：温思宇 张兵 姚永君[4] 马恺[1,2] 王艳 杨凯 WEN Siyu;ZHANG Bing;YAO Yongjun;MA Kai;WANG Yan;YANG Kai(Institute of Sedimentary Geology,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;College of Geophysics,Chengdu University of Technology,Chengdu 610059,China;Chongqing Gas Mine,PetroChina Southwest Oil&Gas Field Company,Chongqing 400000,China)

机构地区：[1]成都理工大学沉积地质研究院,成都610059 [2]成都理工大学油气藏地质及开发工程国家重点实验室,成都610059 [3]成都理工大学地球物理学院,成都610059 [4]中国石油西南油气田公司重庆气矿,重庆400000

出　　处：《岩性油气藏》2023年第5期71-80,共10页Lithologic Reservoirs

基　　金：中国石油西南油气田分公司2020年科研计划项目“川东地区龙潭组页岩储层特征及有利区研究”(编号:20200304-16)资助。

摘　　要：通过川东地区二叠系吴家坪组页岩样品镜下薄片鉴定、X射线衍射分析、主微量元素测试等,对川东地区二叠系吴家坪组页岩中黄铁矿特征及缺氧事件进行了研究。研究结果表明:(1)川东地区吴家坪组页岩中矿物成分较为复杂,富含黏土矿物,黄铁矿发育,岩相主要划分为钙质硅质混合页岩、硅质页岩、黏土质页岩;(2)氧化-还原环境敏感参数U/Th,Ni/Co及V/Cr值指示研究区吴家坪组页岩的沉积环境整体为贫氧环境,并且在纵向上自下而上呈现由氧化环境向缺氧环境过渡的特征;(3)研究区页岩中草莓状黄铁矿的粒径为5.18~10.75μm,且在纵向上自下而上呈现逐渐变小的特征,这种粒径上的变化特征可视为其对二叠纪晚期大洋缺氧事件的响应;(4)由峨眉山玄武岩喷发所导致的缺氧事件涉及茅口组沉积晚期—吴家坪组沉积期—大隆/长兴组沉积期,自峨眉山玄武岩喷发开始,CO_(2)不断溶于水体,浮游生物大量增长,水中含氧量持续下降,至大隆/长兴组沉积时期川东地区水体已完全处于缺氧甚至硫化环境。Through microscopic thin section identification,X-ray diffraction analysis,major and trace elements test of shale samples from Permian Wujiaping Formation in eastern Sichuan Basin,the pyrite characteristics and anoxic events in shales of Permian Wujiaping Formation in eastern Sichuan Basin were studied.The results show that:(1)The shale mineral composition of Wujiaping Formation in eastern Sichuan Basin is relatively complex,rich in clay minerals,and pyrite is developed.The lithofacies are mainly divided into calcareous siliceous mixed shale,siliceous shale and clay shale.(2)The sensitive parameters of oxidation-reduction environment including U/Th,Ni/Co and V/Cr indicate that the sedimentary environment of Wujiaping Formation shale in the study area is generally suboxic environment,presenting the characteristics of transition from oxidation environment to anoxic environment from bottom to top vertically.(3)The grain size of framboidal pyrite in the study area is 5.18-10.75μm,and it gradually decreases from bottom to top.This change in grain size can be regarded as its response to the Late Permian oceanic anoxic event.(4)The anoxic event caused by the eruption of the Emeishan basalt involves the late stage of Maokou Formation,and the stage of Wujiaping Formation and Dalong/Changxing Formation.Since the eruption of the Emeishan basalt,CO_(2) has been continuously dissolved in the water,plankton has increased greatly,and the oxygen content in the water has continued to decline.By the stage of Dalong/Changxing Formation,the water in eastern Sichuan Basin has been completely in an anoxic or even sulfide environment.

关 键 词：页岩 黄铁矿形态 大洋缺氧事件 吴家坪组 二叠系 川东地区 

分 类 号：TE135[石油与天然气工程—油气勘探] P571[天文地球—矿物学]