The Ladinian-carnian Conodont Biostratigraphic Framwork And Sedimentary Environmental Evolution In Yunnan And Guizhou Provinces,South China

The Permian-Triassic mass extinction and the extreme lethally environment of Early Triassic retrained the prosperous of biotic and recovery of ecosystem.The ecosystem became normal condition during the Middle to Late Triassic and the biotic flourished during Middle Triassic and reached the peak of diversity in Late Triassic.So the co-evolution of ecological environment and organism during Middle to Late Triassic became the new hot research topic.Conodont is an effective tool for subdivision of biostratigraphy and reconstruction of paleotempreature of sea water.In this research,five studied sections are from different sedimentary environments,which are Caizitang section in Luoping city,Tianshuo section in Guanling city,Wolongang section in Guanling city,Bamaolin section in Guanling city and Yongyue section in Zhenfeng city.In order to understand the co-evolution of ecological environment and biotic changes during Middle to Late Triassic,relative high–resolution of conodont biostratigraphy,inorganic carbon isotope,oxygen isotope of conodont apatite and the size variation of pyrite framboids are all used in the investigation of these five sections.In ascending order,the lithostratigraphic units of the studied sections composed of Yangliujing,Zhuganpo and Wayao Formations.The Yangliujing Formation consists of thick-bedded,cyclic dolomitic limestone to calcitic dolostones,representing a shallow-marine facies.The Zhuganpo Formation is characterized by thin-middle beded nodular limestone,representing a deeper environment.The Wayao Formation consists of black shales,thin bedded marl and micrite,representing a basinal setting.1.In Yongyue section,six conodont zonations are identified from Anisian to Carnian,in ascending order,they are: Paragondolella foliata Zone,Quadralella polygnathiformis Zone,Quadralella tadpole Zone,Quadralella praelindae Zone,Quadralella auriformis Zone and Quadralella robusta Zone.In Caizitang section,four conodont zonation are recongnized from Ladinian to Carnian.In acending order,these are: Paragondolella foliata Zone,Quadralella polygnathiformis Zone,Quadralella auriformis Zone and Quadralella robusta Zone.In Tianshuo section,two conodont zonation are identified from the Ladinian to Carnian,in ascending order,these are: Quadralella polygnathiformis Zone and Quadralella robusta Zone.The Ladinian-Carnian boundary was tentative defined by the first appearance datum(FAD)of Quadralella polygnathiformis in the study sections.In Wolonggng section,the age attribution of the basal of this section should be Julian 1/Julian 2 judging from the condont fauna,sedimentary of black shales and correlated with above sections,the age of upper Wayao Formation may be extend to Tuvalian 2.2.The Carnian Humid Episode occurred at between the top of Zhuganpo Formation and basal of Wayao Formation in South China and correlated with the upper of Quadralella auriformis Zone-Quadralella robusta Zone.The Carnian Humid Episode associated with the cease of carbonate production,the deposition of black shales,a negative inorganic carbon isotope perturbation around 1.5‰-3‰,climate warming,biotic change and followed by the marine anxioc-euxinia in South China.Carnian Humid Episode may be directly associated with the eruption of Wrangellia large igneous province.3.In Caizitang and Yongyue sections,an abrupt negative inorganic carbon isotope shift around 2.5‰ occurred below the first appearance datum of Quadralella polygnathiformis.According to the character of sediment and sequence of conodont from South China,the age of this inorganic carbon isotope excursion may be belong to Early Ladinian(Fassanian).4.A relative high resolution of carbonate was sampled for pyrite framboid research in Wolonggang section.The mean size of pyrite framboids from carbonate ranged from 3.5-5.5 ?m indicting that the bottom of marine should be anoxic to euxinic environment.That may be the main reason why few conodont were obtained from the Wayao Formation.5.According to the FAD of Quadralella polygnathiformis respectively located at the lower part of Zhuganpo Formation in Yongyue and Caizitang sections and associated conodont fauna,the age of widely distributed ?Falang? Formation(Zhuganpo Formation)should belong to Ladinian to Carnian.6.The Wolonggang section recorded a thickness of 90 m continuous desposition ofcarbonate after the Carnian Humid Episode and later the carbonate unit was overlied by the siliciclastic oturbidites of Laishike Formation,these indicated that the age of demise of Yangtze carbonate platform is younger than the Carnian Humid Episode and they are not the same event.