Biotic Assemblages And Paleoenvironment Characteristics In The Early Cambrian Of Western Hubei, China

Sinian-Cambrian is an important period for the evolution of early life. What are the characteistis of lithostratigraphy,biostratigraphy and chemostratigraphy of Early Cambrian in Western Hubei?And what kinds of paleoevironment do they reflect? we study the petrology,paleontology and geochemistry of Xihaoping section,Dakengtang section and Zoumaling section,and get the following conclusion.Xihaoping Member mainly consist of sandy dolarenite, dolorudite and biodolomite in microcrystalline scale. It is conformably overlain by Shuijingtuo Formation. Shuijingtuo Formation is made up of black mudstone interbeded with carbonaceous. In Dakengtang section and Zoumaling section, Dengying Formation mainly contain siliceous dolomicrite. Shuijingtuo formation consist of mudstone and limestone interbedded. The contact relationship between Dengying Formation and Shuijingtuo Formation is parallel unconformity.And fossils of eodiscoids、brachiopoda and hyolithid are collect from Xihaoping Member and Shijingtuo Formation of Xihaoping section. The epoch of them belongs to Nangaoian. Fossils have’t been found in Dengying Formation of Dakengtang section and Zoumaling section. Tsunyidiscus,Redlichia(Redlichia)hupehensis,Metaredlichia cylindria,Botsfordia and Conotheca mammilata occur in Shuijingtuo formation. The epoch of them belongs to Nangaoian.The data of carbon and oxygen isotope of Xihaoping section and Dakengtang section show that there are a small degree negative drift and two small degree positive drift of δ13C. They relate to oceanic environmental characters at that time. δ13C from Dakengtang section is relatively stable,only a negative drift occurs at the top of Dengying Formation. The negative drift is compared with sections in Yichang,Jiangshan in Zhejiang and Xiaotan in yunnna.