川南马边地区五峰—龙马溪组页岩地球化学特征及有机质富集机理  

Shale geochemical characteristics and enrichment mechanism of organic matter of Wufeng-Longmaxi formation in the Mabian area of southeast Sichuan basin

作　　者：何利[1,2] 宋春彦[1,2] 刘建清[1,2] He Li;Song Chunyan;Liu Jianqing(Chengdu Geological Survey Center of China Geological Survey,Chengdu,Sichuan 610081,China;Key Laboratory for Sedimentary Basin and Oil and Gas Resources,Ministry of Land and Resources,Chengdu,Sichuan 610081,China)

机构地区：[1]中国地质调查局成都地质调查中心,四川成都610081 [2]国土资源部沉积盆地与油气资源重点实验室,四川成都610081

出　　处：《东北石油大学学报》2018年第4期52-65,126,共15页Journal of Northeast Petroleum University

基　　金：国家自然科学基金项目(41502112)

摘　　要：通过野外地质调查资料、X线衍射及主、微量元素测试分析,研究川南马边地区五峰—龙马溪组页岩的矿物学、地球化学特征及富有机质页岩的形成机理。结果表明:五峰—龙马溪组富有机质页岩段SiO_2质量分数随有机碳质量分数的减少而减少,Al_2O_3、TiO_2、Fe_2O_3和K_2O的质量分数随有机碳质量分数减少而逐渐增加,Ba、U、Nd和Sm等微量元素具有显著正异常,而Th、Nb、Sr、P和Ti表现为相对亏损;贫有机质页岩段SiO_2、Al_2O_3、TiO_2、Fe_2O_3、K_2O和MgO的质量分数较稳定,其微量元素与富有机质页岩段的相似,但元素波动小;所有页岩的轻稀土较富集,δCe亏损,δEu富集。五峰—龙马溪组自下而上由还原环境缓慢过渡到氧化环境,同时由深水陆棚缓慢过渡到浅水陆棚环境;生物钡总体向上逐渐减少,古生产力逐渐降低;有机质富集且受古生产力和氧化还原环境的控制。该研究结果为研究川南马边地区海相页岩气勘探提供参考。Based on outcrop geologic survey data and laboratory test results,such as ray diffraction,major element and trace element analyses,the authors investigated the mineralogical and geochemical characteristics and analyzed the organic matter enrichment mechanism of the shales from the upper Ordovician Wufeng formation and the lower Silurian Longmaxi formation in the Mabian area of southeast Sichuan basin.The results indicate that the SiO2 contents reduce with the decrease of organic carbon content,but the content of Al2O3,TiO2,Fe2O3 and K2O increase with the rising of organic carbon content.The contents of MnO,CaO,P2O5,MgO and Na2O vary in a large scope.Some trace elements,such as Ba,U,Nd and Sm,show remarkable positive anomalies.Other trace elements,such as Th,Nb,Sr,P and Ti,are obviously depleted.Rare earth elements of organic-rich shales have similar characteristics with those of organic-poor shales,LREE are rich but HREE are depleted.δEu is rich for all samples,butδCe is depleted.From buttom to top,the organic contents increase gradually,the depositional environment translate into shallow shelf from deep shelf,the redox condition translate into oxidation from anoxic environment,and the paleoproductivity increase gradually indicated by the changing of Ba contents.So,organic matter richness is controlled by depositional environment,redox condition and paleoproductivity.The results provide a reference for the marine shale-gas exploration in the Mabian area of the southeast Sichuan basin.

关 键 词：五峰-龙马溪组 地球化学特征 黑色页岩 有机质富集 微量元素 氧化还原环境 马边地区 

分 类 号：TE122.1[石油与天然气工程—油气勘探]