康滇古陆西侧志留系龙马溪组红-黑转换特征——以宁蒗大槽子剖面为例  

Red-black transitional characteristics of the Silurian Longmaxi Formation in the west of the Kangdian Ancient Land:taking Dacaozi outcrop of Ninglang as an example

作　　者：王正和[1] 张海全[1] 程锦翔[1] 邓敏[1] WANG Zhenghe;ZHANG Haiquan;CHENG Jinxiang;DENG Min(Chengdu Center of China Geological Survey,No.2 North 3rd section,Yihuan Road,Jinniu District,Chengdu,Sichuan 610083,China)

机构地区：[1]中国地质调查局成都地质调查中心,610083

出　　处：《海相油气地质》2020年第2期97-107,共11页Marine Origin Petroleum Geology

基　　金：中国地质调查局地质调查项目“四川盆地下古生界页岩气基础地质调查”(编号:DD20160176)资助。

摘　　要：中上扬子区康滇古陆以东的志留系龙马溪组无“红层”发育,但在康滇古陆西侧的盐源-丽江地区,龙马溪组底部却发育有“红层”(为厚约2m的紫红色硅质泥页岩)。为了明确该套“红层”的成因及地质意义,以盐源-丽江地区的宁蒗大槽子剖面为例,从岩性、岩相及岩石地球化学等方面,对龙马溪组下部“红层”到上部“黑层”的红-黑转换特征进行了研究。结果表明:①龙马溪组下部“红层”中含Fe^3+,且无有机碳存在,推测这是“红层”致红的原因;②“红层”与“黑层”中稀土元素特征相似,但微量元素特征差异较大,尤其是“红层”中Co的含量均值高出“黑层”9倍以上,而“黑层”中Mo的含量均值高出“红层”9倍以上;③龙马溪组下部“红层”至上部“黑层”,整体上是从相对富氧的氧化沉积环境转变为相对缺氧的还原沉积环境,也是沉积水体逐渐由浅变深的过程,这是红-黑转换的主控因素;④龙马溪组从下部“红层”转换至上部“黑层”,其间构造背景均为活动大陆边缘环境,不同于康滇古陆以东的稳定大陆边缘背景。The Silurian Longmaxi Formation to the east of the Kangdian Ancient Land in the Middle and Upper Yangtze Region has no red beds,but in the Yanyuan-Lijiang area to the west of the Kangdian Ancient Land,there are red beds(about 2 m thick purple red siliceous shale)at the bottom of the Longmaxi Formation.In order to make clear the genesis and geological significance of the red beds,this paper studies the red-black transitional characteristics from the red beds in the bottom of Longmaxi Formation to the black beds in the upper part of Longmaxi Formation,from the aspects of lithology,lithofacies and petrochemistry,taking the Dacaozi outcrop of Ninglang in Yanyuan-Lijiang area as an example.The results show that:(1)the“red bed”contains Fe3+and there is no organic carbon in it,which may be the primary reason for its red color;(2)the characteristics of rare earth elements in“red layer”and“black layer”are similar,but the characteristics of trace elements are quite different,especially the mean value of Co content in“red layer”is more than 9 times higher than that in“black layer”,and the mean value of Mo in the“black bed”is more than 9 times higher than that of the“red bed”;(3)from the“red layer”in the bottom of Longmaxi Formation to the“black layer”in the upper part of Longmaxi Formation,it is a process from relatively oxygen rich sedimentary environment to relatively anoxic sedimentary environment,and it is also a process that the sedimentary water gradually changes from shallow to deep,which is the main controlling factor of the red-black transition;(4)the tectonic setting from the lower“red bed”to the upper“black bed”is always in the active continental margin,which is different from the stable continental margin to the east of Kangdian Ancient Land.

关 键 词：红层 沉积转换 龙马溪组 志留纪 康滇古陆西侧 

分 类 号：TE121.3[石油与天然气工程—油气勘探]