湘西地区晚震旦世黑色岩系地层层序、沉积环境与成因

Sequence Stratigraphy and Depositional Enviroments of the Late Sinian-Early Cambrian Black Rock Series in Western Hunan and Its Origins

在对湖南大庸、新晃、沅陵、溆浦和黔阳等地上震旦统—早寒武世初期露头层序地层学的研究表明，湘西地区上震旦统内部存在３个与视海平面变化相对应的超层序，其上限大致可以留茶坡组顶部区域性成磷事件的出现为标志。黑色岩系的形成是海平面上升的结果，尽管该岩系具有色深、层薄和富含有机质的共同特点，但不同层位黑色岩系的岩石化学成分和微量元素组成不同，因此具有不同的沉积环境和形成机制。经研究，晚震旦世金家洞组第二段和寒武纪初期黑色岩系的形成与海底火山和深大断裂的热泉喷流作用有关；而金家洞组第四段和留茶坡组下部黑色岩系的形成则与盆地断陷、地壳拉张减薄并造成地幔流体上涌和地球排气作用有关；

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.