湘西牛蹄塘组黑色岩系的地球化学特征及其油气地质意义  

Geochemistry,paleontology and sedimentary environment significance of Niutitang Formation in Western Hunan Province of China

作　　者：李苗春[1] 姚素平[1] 丁海[1] 吴浩[1] 汤中一[1] 胡凯[1] 

机构地区：[1]南京大学地球科学与工程学院,江苏南京210093

出　　处：《煤炭学报》2013年第5期857-863,共7页Journal of China Coal Society

基　　金：国家重点基础研究发展计划(973)资助项目(2012CB214703);国家自然科学基金资助项目(40638042;40973051)

摘　　要：通过湘西三岔地区牛蹄塘组黑色岩系的地球化学和有机岩石学的综合研究,讨论了湘西牛蹄塘组沉积时期氧化还原条件变化特征及其油气地质意义。结果表明：①V/（V＋Ni）比值为0.42~0.92,平均0.71;V/Cr比值为0.53~44.50,平均5.34;Ni/Co比值为1.92~23.30,平均7.80;U/Th比值为0.16~15.73,平均4.98;δU比值为0.64~1.99,平均1.50。δCe呈负异常。微量元素在剖面中的分布特征反映牛蹄塘组沉积早期在海侵引起的大范围缺氧还原条件下发生了短暂充氧事件,使得海水的氧化还原条件不断变化。牛蹄塘组沉积早期主要为缺氧还原环境,中期受充氧事件的影响,多表现为贫氧环境,后期随着海平面下降,多为氧化环境。②牛蹄塘组黑色岩系烃源岩的成烃生物母质主要为浮游藻类、底栖宏观藻类、浮游动物、底栖海绵等,有机质类型有I型和II型之分;I型分布区间广,主要分布在还原环境中,而II型主要出现于含氧环境中。③黑色岩系TOC含量平均达6.04%,120 m以下的岩石中均〉2%,而110 m以上多小于2%,表明牛蹄塘组还原环境下沉积的页岩生烃潜力较大。Through comprehensive study on the geochemistry and organic petrology of Niutitang Formation in Sancha,the authors discussed the redox conditions change during Niutitang Formation sedimentary period and its petroleum geologic significance.The study results are as follows：① The trace element redox index V/（V＋Ni） ratio is 0.42-0.92,and its average is 0.71;V/Cr value is 0.53-44.50,and its average is 5.34;Ni/Co value is 1.92-23.30,and its average is 7.80;U/Th value is 0.16-15.73,and its average is 4.98;δU value is 0.64-1.99,and its average is 1.50;and the Ce is negative anomaly.The distribution characteristics of redox index in the section reflect that the short oxygenated events such as ocean current upwelling occurred in early Niutitang sedimentary period which is on over reduction condition as a result of transgression,making the sea redox conditions cycle fluctuation.The effects of the aerobic event is lean oxygen environment in the medium term and more for oxidation environment in later term with the sea level＇s drop.② Fungi,planktonic algae,benthic macro algae,zooplankton and benthic sponge comprise the hydrocarbon generation organisms.As a result,organic matters are divided into Type I and II,and the former distribution range is wider than that of the latter which is mainly found in aerobic environment.③ The organic matter abundance is much high,with TOC content average of 6.04%,which in rocks below 120 m are all more than 2% while those over 110 m are less than 2%.Therefore,the shales deposited in reducing environment are thought to have more shale gas potential.

关 键 词：牛蹄塘组 黑色岩系 地球化学 有机岩石学 沉积环境 生烃潜力 

分 类 号：P618.13[天文地球—矿床学]