The Evolution Of The Late Permian Reef System In Eastern Sichuan

Late Permian ecological crisis is the largest biological crisis in Phanerozoic. The process and cause of the crisis has always been controversial. Previous studies that reefs (especially skeletal reef) greatly influenced by climate change. Through the study of the evolution of reef paleoecosystems, then discussing the response and feedback of Biological mass extinction event, and the correlation between biological reef system evolution and paleoenvironment changes.The paper based on field outcrop section data, combined with microsection and paleontology. Skeletal reef is prosperous in early-middle Changhsingian, then disappearing in Clarkina yini zone, and replaced by microbial reef systems. This microbialite is formed by massive or porphyritic thrombolite, intertwined by cyanobacteria and block mass a few Tubiphytes,which is different from the microbialite above of the extinction, and its top is located about few distance below the extinction. The evolution of reef paleoecosystems of Wantanhe section can be divide into three stage before the extinction. The paleoecosystem remain normal in the first stage, and then it began to deteriorate in the second stage, the skeletal reef paleoecosystem being broken down, and the narrow eligibility epigenetic multicellular organisms gradually disappear. In the third stage, the skeletal reef paleoecosystem is replaced by microbial reef paleoecosystem, but the paleoenvironment have not been improved. And then, those eurytopic bioclasts begin to disappear. The deposits contain only calcarenite from the microbial mound to the beginning of the H. parvus zone. The biological-environmental evolution of Wantanhe section show multiple stage, indicating the instable and long lasting change of paleoenvironment in Late Permian.According to the carbon and oxygen isotopes, microelement characteristics, the paleoenvironment begin to be worsen in late Changhsingian, with prolonged and multi-phase nature. Based on the analysis of paleo oxygenation facies and paleo Sea Surface Temperature, it show theanoxia and temperature increment in Late Permian. Therefore, the combined ofvolcanism, oceanic anoxic and greenhouse effect maybe the reason to the massextinction.