Sedimentary Ecology Analysis Of Middle-Carnosian Mudstone In Northwest Sichuan:Paleontological Response Of Humid Climate Events

The mid-Carnian(Late Triassic)Extreme Carnian Climate Event,one of significant global climatic events after the geological event in the end of late Permian,was identified in Guizhou,Yunnan province and Hanwang town,Mianzhu city in northwestern Sichuan.Sedimentary sequences in Carnian of Qingyangou reveals the lithological change from carbonate rocks to clastic rocks,oolitic limestone,bioclastic limestone,sponge reef limestone,tuff,black shale and siltstone appeared from the bottom to the top.Sedimentary sequences in Carnian of Qingyangou and Guanyinya reveals the lithological change from carbonate rocks to clastic rocks,oolitic limestone,bioclastic limestone,sponge reef limestone,tuff,black shale and siltstone appeared from the bottom to the top.Sedimentary sequences in Carnian of Ma'antang formation reveal the lithological turnover,which are oolitic limestone-bioclast limestone-sponge reef limestone with black shale-black shale-argillaceous siltstoneformation from bottom to top in Hanwang and Jushui section in Northwestern Sichuan.And the sets of black sandstone interlayers show a very significant multi-curtain wet period.Based on the field investigation and the observation of the section of Hanwang Qingyan section and Anxian Jushui section,this paper includes fossil sampling,analysis of its sedimentary evolution and process,and focuses on the response of paleontology in humid climate events.Abundant fossil fragments,such as fish teeth,sponge spicules,crinoid ossicles,corals,foraminifera,broken shells of bivalves,brachiopods,ostracods and gastropods occur in the(sandy)carbonate rocks of the three studied sections,though most ofthem are not well enough preserved for an exact determination.Most of the fossils are well preserved and are mainly produced from silty shale,muddy siltstone to slag limestone.In the carbonatite rock production crisis above a few meters of silty mudstone,collected a wealth of ammonoid and bivalve marine fossils,identified as Discotropites Thisbites Halobia Parahalobia etc.,it represent the typical animal fossils of the central Carnian(Tuvalian 1 and 2).It is associated with plant fossils,and large deposits in the formation may be associated with a large inputs of terrestrial and freshwater.The coexistence of thin shell and thick shell double shell fossils shows that the paleo-water depth changes greatly in the study area.By means of the analysis of the key paleontology in the Hanwang Mianzhu and Anxian Jushui areas in the northwest Sichuan province,and the comparison of the Guanling biota,the paleontological responses in the humid climate events of the Carnian period were discussed about the time,processes and impacts of climate events were discussed,and the impact of humid climate palaeontology was compared with the geophysical events of the same period in the world,and a series of complex and varied changes in the late Triassic Carnian period were discussed.The complex evolution of the earth system presents a new perspective and direction.