富有机质黑色页岩形成环境及背景的元素地球化学反演——以渝东北地区田坝剖面五峰组一龙马溪组页岩为例  

Element geochemistry inversion of the environment and background of organic-rich black shale formations:A case study of the Wufeng-Longmaxi black shale in the Tianba section in northeastern Chongqing

作　　者：熊小辉[1,2] 王剑[2] 余谦[2] 杨宇宁[2,3] 熊国庆[2] 牛丙超 郭秀梅[2,3] 邓奇[2] 

机构地区：[1]中国地质科学院 [2]国土资源部沉积盆地与油气资源重点实验室·成都地质矿产研究所 [3]成都理工大学研究生院

出　　处：《天然气工业》2015年第4期25-32,共8页Natural Gas Industry

基　　金：国家自然科学基金“华南新元古代楔状地层沉积充填序列及大地构造研究”(编号:41030315);渝东北页岩气地质潜力调查评价“扬子北缘新元古代花山群火山-沉积序列及其构造属性研究”(编号:41402103)

摘　　要：为深入研究渝东北地区奥陶纪—志留纪黑色页岩垂向上沉积环境的精细变化,指导区域页岩气的勘探及相关研究,对四川盆地渝东北地区田坝剖面上奥陶统五峰组下志留统龙马溪组黑色页岩进行了系统实测和连续采样,并开展了详细的元素地球化学研究。结果表明:①田坝剖面构造位置处于扬子北缘被动大陆边缘.主要接受陆源的细碎屑沉积.基本不受热水沉积作用的影响.但同时存在北边华北板块南缘活动陆缘大陆岛弧火山碎屑沉积的作用:②黑色页岩总体形成于水体缺氧、具有一定分层的硫化还厚环境.早期水体强烈还原,而在龙马溪晚期水体变浅,沿剖面向上.水体还厚性逐渐减弱:③生物生产率在龙马溪中期最高,该时期由于缺氧分层,水体有机质保存较多,其次为龙马溪晚期.但该时期由于水体变浅及溶氧量的增多使得更多的有机质被氧化分解.而五峰期及龙马溪早期尽管生物生产率不高.但由于水体较深,底层水体的缺氧使得大部分有机物得以保存。Systematic measuring, continuous sampling and detailed element geochemistry researches were conducted to study the delicate changes in the vertical sediment environment of Ordovician Wufeng and Silurian Longmaxi black shale formations in northeastern Chongqing and to provide guidance for the exploration and relevant researches of shale gas in the Sichuan Basin. The following re sults were obtained. （1） Situated on the passive continental margin at the northern edge of the Yangtze para-platform, the Tianba section structure predominantly accepted fine clastic deposits originated from the continent, and was basically not affected by hot water sedimentation. Besides, the structure contains volcanic clastic deposits of the continental island arc on the northern edge of North China Plate to its north. （2）Generally, black shale was formed in an environment with water poor in oxygen and with sulfurization reduction possessing certain layered properties. In early stages, water bodies experienced intensive reduction. In later stages of the Longmaxi Period, water turned shallower and the reduction capacity of water reduced gradually. （3）Biological productivity reached the peak in middle stage of the Longmaxi Period, which was characterized by layered structure and limited oxygen. Consequently, the water maintained abundant organic matters. Higher productivity was also observed in late stage of the Longmaxi Period. More organ- ic matters experienced oxidation and decomposition since water turned shallower and the content of dissolved oxygen increased. Though the Wufeng Period and early stages of the Longmaxi Period showed low biological productivity, the majority of organic mat ters were preserved in the water body at the bottom with oxygen deprived due to the significant depth.

关 键 词：四川盆地 渝东北 奥陶纪—志留纪 黑色页岩 元素地球化学 沉积环境 大地构造背景 

分 类 号：P618.13[天文地球—矿床学]