The Study Of Paleo-oceanographical Environment In The Process Of Biological Recovery In Induan Of Yanlou,Huaxi,Guizhou

The end-Permian mass extinction is the largest and most far-reaching geological event in geologic history.And then the early Triassic is a highly unusual period in the history of the earth's surface,and it has a unique environment and ecosystem that leaves a distinctive geological record in the sediment.So the early Triassic is a key to study the ecosystem and the recovery process of marine environment after extinction.After the global sea retreat of late Permian,southern China is one of the few places in the world that is still covered by sea water.The relatively continuous carbonate deposits in the Yangtze plate and abundant fossils provide favorable conditions for recovery of ecological environment in erly Triassic.But in the past,the areas of the study are often selected in the deep water sections,and the shallow water areas have fewer studies.But more abundant life activities and the reoxygenation whithout affected by the depth of the water can be better to reflect the whole environment of the ocean.Based on the analysis of lithological,fossil composition,and elemental geochemistry follow opinions are be understanded.1.Geochemical characteristics of trace elements and rare earth elements of daye formation were analyzed in Yanlou,Huaxi.Relative to the PAAS,the enrichment of redox sensitive elements?U,V,Mo?and the ratios of U/Th,V/Th,Mo/Th were significantly improved.Some geochemical parameters redox sensitive elements such as V/?V+Ni?,V/Cr,Ni/Co,V/Sc and Mo_EF/U_EFF ratios indicate that the deposit of the first section of Daye formation was formed in hypoxia-lean oxygen environment,and the second segment of Daye formation in the lean oxygen-oxidizing environment.Rare earth element partition type is relatively flat.Hypoxia-lean oxygen environment was instructed by the characteristic parameters of rare earth elements??Ce and Ce/La?in early Triassic.Combined with the provenance analysis,the?Eu positive anomalies in bottom of Daye formation and the indicating Basalt-source fligur of?REE-?La/Yb?N showed that affected by volcanic hydrothermal process significantly caused by Siberian eruptions.Weaker influences of volcanism showed slightly positive anomaly in the top of Daye formation.The lean oxygen environment of early Triassic maybe associated with frequent volcanism.2.The transient negative drift at the bottom of the study section may be a continuation of the global negative drift of carbon isotopes near the T/P boundary,resulted from catastrophic geological events at the end of the Paleozoic,such as volcanic activity,transgression,and environmental degradation.The recoverying ecological system,abundant living organism and organic carbon were be showed by the positive?¹³C,ammonites and bivalves in the bottom marlstone.The positive?¹³C in the second section of Daye formation may be caused by the large-scale transgression,gradually improving environment,recovering biology,the increased primary biological productivity and organic carbon.Biomass growth,due to the preferential absorption of ¹22 c,will lead to the relative enrichment of ¹³c in sea water,and Marine carbonate delta ¹³c increased with the increase of the organic carbon reserves,which can be obtained through the section of fossil found in large Numbers in.It can be conclude that significantly negative carbon isotopic composition of the shell is due to the change of the environment after the action of the volcano,the rapidly increased temperature of the surface sea,the anoxic deep seawater is by further study on the shell microstructure of the analysis of the carbon oxygen isotopic.Lean oxygen-anoxic environment can be finded by the results of the geochemical characteristics?trace rare earth elements?in early Triassic.Combined lifestyle with the characteristic of shell,we find they may be living in shallow water whith weaker hydrodynamic conditions.The shell structure may be affected by the hypoxic-poor marine environment,which is so thinner and less stratified that can help to have a better respiration in this special environment.In combination with the outbreak and extinction time of Claraia,it belongs to the poor oxygen species.3.Based on analysis of the structure and way of life of bivalves,byssus sessile lifestyle was behaved by Claraia that belongs to lean-oxygen biology.Biological structures of bivalve fossils was divided into the prismatic shell and the complex interleaved laminated pearl layer,that mightly associated with hypoxia of the ocean environment.The The shallow water with weak hydrodynamic conditions should be the Claraia major living environment.