摘要
The Middle Permian Chihsian Formation in Sangzhi area in western Hunan Province shows remarkable cyclicity, where organic matter cycles also occurred. The study of origin of organic matter accumulation in the Chihsian Formation helps understand the role of sea level fluctuation on the formation of organic-carbon-rich sediments. Using a cycle as the study interval, based on the study of pyrite morphology and geochemical parameters, such as TOC, δ34S, DOP and trace elements, we find out that the variation of ocean surface water primary productivity parameters, such as Ba, Ni, Cu and Zn, are consistent with TOC contents, suggesting organic matter accumulation was controlled by primary productivity. The redox condition in bottom water is related to primary productivity. The ultimate origin for the organic matter accumulation should be the high-frequency sea level fluctuation. Rapid sea level rising brought rich nutrients, flourishing surface water biologic productivity. The decomposition of organic matter from dead body demanded more oxygen concentration, resulting in dysoxic-anoxic environment in bottom water.