Biota and Organic Matter in the Late Sinian and EarlyCambrian Black Rock Series of West Hunan andIts Significance for Metallization

Abstract: A great amount of black rock series has been found in the Upper Sinian Members 2 and 4 of the Jinjiadong Formation, middle-upper Liuchapo Formation and the Lower Cambrian Xiaoyanxi Formation in West Hunan, which is associated with periodic sea-level changes. By the studies of relationships between the distribution and development of the biota and the abundance of Au, Ag, U, V, Ni, Mo and Cu in the Upper Sinian and Early Cambrian black rock series in Cili, Dayong, Yuanling, Xupu and Qianyang of West Hunan, central China, it has been revealed that the enrichment of Ag, V, and Mo is related with the development of multi-cell plants and vendotaenides, and that of Cu and Ni is related to flourishing of bacteria and shelly fossils. The black rock series in the study area contains abundant organic matter, among which the siliceous shale contains the highest TOC, amounting to 4.51–13.4%. All the values of the equivalent vitrinite reflectance (medium values) determinated with the IR-spectroscopic method in the area are over 2.65%, indicating that the organic evolution was at an overmature stage. Due to the effect of enhancement of organic maturation by hydrothermal fluids, the Upper Sinian and Lower Cambrian had a reverse organic maturity profile in most areas of West Hunan. The enrichment of Ag, V, Ni, Mo and U is a result of organic absorption, and that of Au might be attributed to the migration by hydrothermal fluids.

湘西震旦—寒武纪黑色岩系的有机岩石学特征及其形成条件

湘西上震旦统、下寒武统黑色岩系主要由富碳硅质页岩、石煤、硅质页岩、硅质岩、磷块岩和重晶石岩等组成。有机质属于腐泥型， 无形态组分是黑色岩系的主要显微组分类型， 微粒体、细粒状体呈密集状组成岩石的基质。有形态组分总体含量较低， 多为藻类体， 零星分布于基质中， 表明一方面有机质受热演化程度较高， 另一方面表明有机质来源于浅水台地边缘。湘西黑色岩系中有机质主要来源于藻、菌类生物， 台缘斜坡带是有机质聚集的有利场所， 缺氧环境 （事件） 主要起因于藻类的大量发育与有机质降解的耗氧过程， 为有机质得以保存、转化提供了必要条件。

贵州—湖南黑色岩系的有机碳和有机硫特征及成因意义

黑色岩系是多种元素的富集体,其中常产出许多大型超大型矿床,越来越受到国内外地学界的重视。然而,关于黑色岩系的成因一直是有争议的问题。对贵州—湖南地区下寒武统黑色岩系有机碳和有机硫的研究,表明黑色岩系的有机碳和有机硫含量较高,因而本文认为黑色岩系形成于低能、缺氧还原的浅水台地边缘环境。

湘西地区晚震旦世—早寒武世黑色岩系的生物和有机质及其成矿作用

根据湘西地区晚震旦世—早寒武世黑色岩系的分布、生物群类型与分布及其与金属元素富集的关系 ,提出黑色岩系中的Ag -V ,Mo和Ni-P的富集成矿分别与浮游菌藻、多细胞植物和介壳化石的分布发育关系密切。黑色岩系分散有机质红外光谱研究表明 ,区内晚震旦世—早寒武世地层黑色岩系的有机质演化处于过成熟阶段 ,且垂向分布存在明显倒置的特点。探讨了黑色岩系地层分散有机质成熟度倒置的原因以及有机质及其演化与金属元素富集成矿的关系。