Sequence Stratigraphy and Depositional Enviroments of the Late Sinian-Early Cambrian Black Rock Series in Western Hunan and Its Origins
湘西地区晚震旦世黑色岩系地层层序、沉积环境与成因

The study of outcrop sequence stratigraphy of the Late Sinian and earliest Cambrian sections located in Dayong,Xinhuang,Yuanling,Xupu and Qianyang indicates that the Upper Sinian of western Hunan Province can be divided into three different supersequences corresponding with the relative changes of sea levels,and the basal boundary of the Cambrian can be marked by the occurrence of the regional phosphogenic event at the top of the Liuchapo Formation.The formation of the black rock series in this period is the result of the sea_level rise.Because the black rock series occurring in different horizons have different chemical compsitions and contents of trace elements and REE,they formed in different depositional environments and by different mechanisms though all of them are dark_colored,thin_bedded and organic_rich.The origin of the black rock series of Member 2 of the Late Simian Jinjiadong Faormation and the lower part of the Lower Combrian Xiaoyanxi(or Niutitang)Formation may be related to hot spring_emanations of deep faults and submarine volcanism,whereas the origin of the block rock series of Member 4 of the Jinjiadong Formation and the lower part of the Liuchapo Formation may be related to upwelling of mantle fluids and degassing of the earth due to the downwarping of the basin and crustal extension and thinning.The black rock series in the middle and upper parts of the Liuchapo Formation,is the product of hydrothermal deposition of a deep_water basin.