Early Triassic Community Redox Conditions Remains Of Analysis On Upper Yangtze Area

The mass extinction event at the end of the Permian,leading to the complete collapse of the Paleozoic marine ecosystem.After slow environmental reconstruction and biological recovery in the early Triassic,it was not until the beginning of Middle Triassic that a new marine ecosystem with active benthic endangered species and carnivorous organisms developed gradually.As an important carrier of sedimentology and paleontology information,trace fossils are essential clues and evidences for understanding the process of geography.The lack of oxygen in the early Triassic Marine environment is considered to be the main cause of the extinction.However,the underlying mechanism for this mass extinction event is not clear,and most of the biostratigraphy records in the study area are not complete.Therefore,A lot of possible causes that scholars have given are found out.Among them,global hypoxia has become a research hotspot in sedimentary water environment.Therefore,the analysis of the redox conditions in ancient marine environment needs to be discussed in many aspects.In this paper,systematic investigation was made on the Daye Formation section of the Early Triassic Guiyanin the Upper Yangtze Area and the Yelang Formation section in the Guang'an area of Sichuan Province.The sedimentary environment in the Indian period,the fossil features in the relict community,Morphology and Particle Size of were analyzed in detail.Based on the characteristics of sedimentary environment and ichnocoenosis,the changes of marine redox environment and the effects of sediment water hypoxia on biotic resuscitation were discussed The particle size characteristics and distribution of strawberry pyrite microcrystal in Daye Formation section and Yelang Formation section in India period were analyzed by synthesis.,and according to the particle size and formation principle of strawberry-like pyrite,the redox conditions were analyzed.In this study,8 species of 7 fossils of trace fossils were collected in Daye Group:Planolites montanus;Planolites beverlegensis;Beaconichnus darwinum;Undichnai sp;Mammillichnis aggeris;Cosmorhaphei sp;Gordiamarina sp;Palaeophycus curvatus.Eight fossils of trace fossils collected in the Yelang Group:The composition of the relict community indicates that the early Triassic Indian fossils were relatively developed in the Upper Yangtze region,with the characteristics of individual miniaturization,shallow stratum distribution,and lower relic index as the basic characteristics,reflecting the hypoxicenvironment and the bottom of the ocean.Habitat ecosystem gradually recovers as the environment improves.A detailed analysis was made on the strawberry-like pyrite in the development stratum of the relict community.The particle size of the strawberry pyrite in the Daye Formation in the Huaxi area of Guiyang was mainly distributed in the interval of 4-10 ?m,and the maximum grain size was less than 18 ?m.The particle size of strawberry-like pyrite in the Yelang Formation section of the Xifeng area in the Fengyan area of Sichuan Province is mainly distributed in the interval of 4-10 ?m,and the maximum grain size is generally less than 18 ?m.Frequency histogram and frequency cumulative curve of the combined samples The major developmental strata of the relict communities in the Daye and Yelang Formations The depositional water environment is an anoxic environment.In the Upper Triassic of the Upper Yangtze in the Upper Yangtze region in the Indian period was an oxygen-deficient environment,which to some extent inhibited the recovery of early Triassic early life.However,the stable environment during this period also promoted the development of the oxygen-tolerant benthic organisms.