Marine REDOX Conditions In South China After The End Permian Mass Extinction

At the Permian-Triassic Boundary,organisms suffered a great disaster due to multiple geological disasters.The results show that the extinction rate at species level is as high as96%,indicating that the extinction event at the Turn of Permian-Triassic is undoubtedly a major setback in the history of the evolution of earth organisms in the Phanerozoic.The ecological environment in South China has changed rapidly after the mass extinction.Over the years,there have been different approaches to restoring the Marine REDOX environment of the Early Triassic,ranging from the idea that the shallow water environment was anoxic to the idea that there was life in the shallow water at that time,and it seems that there was oxygen.Therefore,based on the question of whether the sea is anoxic after the extinction,this paper focuses on the Cili high elevation profile(shallow water)and Sangzhirencun Ping profile(deep water)in south China,and carries out research on their REDOX conditions.The purpose of this study is to explore the REDOX conditions of the Early Triassic by comprehensive use of strawberry pyrite and sedimentary microfacies analysis,clarify the previous controversies,and provide new evidence for the causes of the early Triassic recovery after extinction.The results show that :(1)the daye formation of lower Triassic in cili high profile is composed of microbiolites,micritic limestones,oolitic limestones and wormlike limestones,which contain foramite fossils and kidney-shaped microbiolites.Combined with the grain size of strawberry pyrite,it is found that the carbonate platform facies in Cili area was relatively oxidized to oxygen poor.(2)The Permian Dalong Formation in Sangzhiren Village Section is composed of gray-black medium-thick argillaceous limestone and siliceous limestone,which contains forams fossils;Triassic Daye Formation is mainly composed of thin limestone and yellowish green clay rock.Moreover,a large number of strawberry pyrite is distributed in the Section of Songzhiren Village.Combining with the size distribution of strawberry pyrite,it can be clearly analyzed that the section of Songzhiren Village is in an oxygen-poor or even anoxic environment.(3)Based on the results of the two profiles,it is concluded that there were more microbial species in the shallow water area of South China after the mass extinction at the end of Permian under relatively aerobic conditions.The deep water area is in an anaerobic or even sulfide environment,and the quantity of strawberry pyrite is large and the particle size distribution is wide.