Study On The Sedimentary Facies Of Permian-Triassic Boundary Section In Lichuan, Western Hubei

The biggest extinction in Phanerozoic occurred at the end of Permian all over the world. The significant geological mutation completely changed the ecological system and, in the mean time, largely transformed the environment system. The special sedimentary structural called "Anachronistic Facies" started to widely show in normal neritic environment in early Triassic, which provides a useful evidence for exploring the reason of extinction.A large amount of previous studies on this catastrophic event have been down and many hypotheses have been raised, including widely accepted theories such as the volcano eruption, oxygen deplete, global warming and sea-level change. However, there is no consistent conclusion so far.In this article, Permian-Triassic strata in Lichuan was investigated. Through field observation and measurement, sample collection and indoor microscope observation, the categories were analysed and the changes in Permian-Triassic environment rebuilt. Based on reviewing existing literatures and clearing mainstream theories of the reasons of contemporary extinction, the real causes of extinction in Permian-Triassic are reviewed here and the results are as following:Two sections (Ruiping, Xiajiacao) in Lichuan area include6microfacies categories (foraminiferamicrocrystalline limestone, calcareous algal layered rock microbes, algae-foraminifera bioclastic limestone, calcareous dendritic microbiolite flowers porphyritic rock structure microorganisms calcareous, pyritic micrite and carbonate turbidites) Microfcies of transition in Sanxia area may plus to another3microfacies and the show features of worsening environment (deterioration or crisis) deterioration (crisis).Volcanic events are considered to be the main reasons for environmental degradation by the author in early Triassic. Based on geochemical data analysis of Meishan section and Emeei section, intracontinental volcanic activities remains the fundamental reason of extinction. The composition of Triassic tuffaceous mudstone from the west margin of Yangtze Platform to the lower Yangtze region is very similar to that of the basalts of Emei Mountain according to the geochemical properties. And the volcanic material of tuffaceous mudstone of Emei Mountain contains the composition derived from mantle wedge (or Lower crust).