上扬子地区下寒武统牛蹄塘组富有机质页岩岩相及沉积环境分析——以贵州温水村剖面为例

Analysis of lithofacies and sedimentary environment of shale deposited in shelf facies:A case study of the Wenshuicun section in Guizhou Province,South China

贵州温水村剖面发育有一套完整的下寒武统牛蹄塘组富有机质黑色页岩,为厘清下寒武统牛蹄塘组页岩岩相类型,明确不同岩相形成环境特征,通过采集25块该剖面页岩样品,进行岩石薄片观察、X射线衍射(全岩)分析、总有机碳含量(TOC)测定及主微量和稀土元素分析,划分出温水村剖面下寒武统页岩的岩相类型,并明确了该层位页岩的沉积环境和有机质富集特征,建立了沉积模式。根据TOC值、沉积构造和矿物组成,同时考虑岩石脆性特征,共划分出9类页岩岩相:①富有机质块状强脆性硅质细粒岩;②富有机质纹层状强脆性硅质页岩;③高有机质块状强脆性硅质细粒岩;④高有机质纹层状强脆性硅质页岩;⑤高有机质块状中等脆性硅/黏土混合质细粒岩;⑥中有机质块状强脆性硅质细粒岩;⑦中有机质纹层状强脆性硅质页岩;⑧低有机质块状强脆性硅质细粒岩;⑨低有机质纹层状中脆性硅/黏土混合质页岩。其中,前5类页岩相形成于深水缺氧、暖湿型气候和以低温热水沉积作用为主的环境,初级生产力和古盐度较高,有机质富集受控于古氧化还原条件、古生产力、古盐度、古水深、暖湿型气候和热液活动,而其他岩相有机质富集则不受热液活动影响,沉积环境初级生产力和古盐度有所下降;建立了一个受氧化还原条件、古生产力、古盐度、热液活动及暖湿型气候影响的深水陆棚相沉积模式。

A complete set of organic matter-rich black shale in the Lower Cambrian Niutitang Formation is developed in the Wenshuicun section of Guizhou Province,South China.In order to clarify the lithofacies types of shale in Lower Cambrian Niutitang Formation and clarify the formation environmental characteristics of different lithofacies,25 shale samples from this section were collected for thin section observation,X-ray diffraction(whole rock)analysis,total organic carbon content(TOC)determination,and major,trace and rare earth element analysis.The lithofacies types of the Lower Cambrian shale in the Wenshuicun section are divided,and the sedimentary model and organic matter enrichment characteristics of the shale in this layer are defined:①Organicrich massive strongly brittle siliceous fine-grained rock;②Highly brittle organic laminated siliceous shale;③High-organic massive strongly brittle siliceous fine-grained rock;④Highly organic laminated strongly brittle siliceous shale;⑤High-organic massive medium-brittle silica/clay mixed fine-grained rock;⑥Medium organic massive strongly brittle siliceous fine-grained rock;⑦Medium organic laminated strong brittle siliceous shale;⑧Low-organic massive strongly brittle siliceous fine-grained rock;⑨Low-organic laminated medium-brittle silica/clay mixed shale.According to TOC value,sedimentary structure and mineral composition,and considering the brittle characteristics of rocks,nine types of shale facies are divided.Among them,the first five types of shale facies were formed in deep-water anoxic,warm and humid climate and environment dominated by low-temperature hydrothermal sedimentation,with high primary productivity and paleo-salinity.The enrichment of organic matter was controlled by paleo-oxidation-reduction conditions,paleo-productivity,paleo-salinity,paleo-water depth,warm and humid climate and hydrothermal activities,while the enrichment of other lithofacies organic matter was not affected by hydrothermal activities,and the primary productivity and paleo-salinity of sedimentary environment decreased.A sedimentary model of deep-water shelf facies is established,which is affected by redox conditions,paleo-productivity,paleo-salinity,hydrothermal activities and warm and humid climate.