湘西北下寒武统黑色岩系元素地球化学特征及地质意义  

Geological significance of the elemental geochemistry of lower Cambrian black shales from northwestern Hunan

作　　者：黄俨然[1,2] 肖正辉 余烨 焦鹏[3] HUANG Yan-ran;XIAO Zheng-hui;YU Ye;JIAO Peng(Key Laboratory of Shale Gas Resource Utilization of Hunan Province,Hunan University of Science and Technology,Xiangtan 411201,China;School of Resource,Environment and Safety Engineering,Hunan University of Science and Technology,Xiangtan 411201,China;School of Geosciences and Info-Physics Engineering,Central South University,Changsha 410083,China)

机构地区：[1]湖南科技大学页岩气资源利用湖南省重点实验室,湖南湘潭411201 [2]湖南科技大学资源环境与安全工程学院,湖南湘潭411201 [3]中南大学地球科学与信息物理学院,湖南长沙410083

出　　处：《地球化学》2020年第5期516-527,共12页Geochimica

基　　金：国家自然科学基金(41603046);湖南省自然科学基金(2019JJ50178)。

摘　　要：湘西北地区下寒武统牛蹄塘组广泛发育了一套黑色岩系,其具有有机质丰度高、多元素富集、生物化石发育和强还原环境下形成等特点。本次研究以研究区内花页1(HY1)井为研究对象,进行了总有机碳、X射线衍射、薄片、主元素和微量元素等方面的分析。研究表明,HY1井黑色岩系主要包括石英、方解石、斜长石、黄铁矿和黏土矿物,是各种细粒碎屑物质的沉积混合。HY1井远离当时的热水活动及沉积中心,受热水沉积作用影响有限,主要为正常海相沉积形成的黑色岩系,但部分微量元素的含量可能会受热水沉积物质的影响。HY1井牛蹄塘组属被动大陆边缘的构造环境,但其元素特征与下伏地层相似,元素地球化学指标反映的是其物源物质的构造环境特征,而不是沉积当时的构造环境。元素Al、Ti主要来自于陆源碎屑,陆源物质对黑色岩系的物质来源贡献较小,但对稀土元素含量的影响显著。HY1井有机质富集与高的古生产力、还原性沉积环境及沉积速率较慢等因素密切相关。A series of black shales are widely developed in the early Cambrian Niutitang Formation in northwestern Hunan.These black shales feature abundant organic matter,multiple enriched elements,a large amount of organism,and were formed in strongly reductive sedimentary environment.We analyzed the total organic matter(TOC),X-ray diffraction(XRD),section,and major and trace elements of well HY1 in our study area.Our research shows that the black shales in HY1 were formed mainly from a mixture of fine-grained fragments of quartz,calcite,plagioclase,pyrite,and clay minerals.HY1 was far from the hydrothermal and sedimentary center at that time;therefore,hydrothermal sedimentary conditions had a limited effect on it.The black shales were formed mainly in a normal marine sedimentary environment;however,the content of certain trace elements might have been affected by hydrothermal sedimentary conditions.The black shales of HY1 mainly are normal marine sediments but not hydrothermal sediments;however,the characteristics of the elements present in the former are similar to those in the underlying stratum.Element-geochemical indexes of HY1 revealed the structural and environmental characteristics of its provenance,not the structural environment in which it was deposited.The Al and Ti present are mainly contributions from terrigenous grains,which make a limited contribution to the provenance of the black shales but have clear effects on the content of rare elements therein.The enrichment of organic matter in HY1 is closely related to the high paleo-productivity during sedimentation,reductive sedimentary environment,and slow deposition rate.

关 键 词：黑色岩系 花页1井 热水活动 有机质富集 湘西北 

分 类 号：P595[天文地球—地球化学]