Sedimentary Environment Evolution During The Permo-Triassic Transition In Shanxi Province

A severe environmental change occurred worldwide during the Permian-Triassic?P/T?transition followed by a mass extinction.Some similar drastic environmental changes and biological depression also occurred around the P/T boundary in China.There is a great potential to for progress in northwestern and southern China because of the natural continuous emergence of the Dicynodon Sinkiangensis and Lystrosaurus,and the continuous evolution of ancient plants and negative drift of C-O isotopes within this area.Shanxi,as one of the most representative regions with extensive continuous continental P/T strata in North China,consists of four Formations?Fm.?from late Late Permian bottom up to the top,including the Sunjiagou Fm.?P₃s?,Liujiagou Fm.Heshanggou Fm.and Ermaying Fm.where a first breakthrough in reptile research was made,discovered in middle Triassic.We conducted a specialized research,dominated by traditional sedimentology methods,combining qualitative and quantitative geochemistry data and C-O isotope geochemistry in northern and central China.The new research area included the newest fossil spot,where we explored the co-evolution of continental paleo-sedimentary environment and paleo-ecological environment during the P/T transition period.The study focused on sedimentary facies of the P/T transition zone in the northern and central parts of northern Shanxi province,including the newly discovered Late Permian landmark reptiles-Pareiasaurus flocked fossil burial,This paper summarizes the synergetic laws of sedimentary paleo-environment and paleo-ecology in the transitional stage of P/T in Shanxi Province,using some research methods such as constant and trace element geochemistry research methods,as well as C-O isotope geochemical qualitative and quantitative analysis.The study shows that during the P/T transition,the sedimentary facies within the study area mainly consisted of meandering river facies-widespread braided river sand bars-lacustrine-meandering river systems respectively.The paleo-ecology underwent a period of depression after an extinction in Sunjiagou Fm.,which transitioned into a terrible depression in Liujiagou Fm.,the ecological environment in Heshanggou Fm.gradually recovered from the bottom up and flourished on the upper side.During the T₂e period,the ancient ecological environment recovered completely and the biological diversity broadened.T₂e was very warm and humid for a paleo-climate while the others were in much more arid..The average temperature of four Formations within the study area was about 15.7?and all were in a terrestrial fresh water environment.The newly discovered Pareiasaurus fossils flocked burial was found in the middle part of P₃s,where the sedimentary facies mainly consists of overbank lakes deposits of meandering river system,its petrographic facies is composed of dark purple reddish silty mudstone and muddy gravel,significant negative anomalies in geochemistry indicate that a sudden biological extinction event may have occurred at the that time.Low temperatures in the region may have been one of the main factors leading to the gradual decline of paleontology.Mass extinctions occurred both at the end of Permian era and around the PTB.Its sedimentary environment evolution shows a global consistency,while the complex terrestrial environment reflects diversity at the same time.The sedimentary environment in Shanxi shows apparent differences from the northwest and southwest of China,while remaining consistent with many other international classical terrestrial P/T sections including Karoo Basin of South Africa,Siberian platform in Russia and many other international classic sections where the geological background is in retrogression sequence.This paper fills the gap of geochemistry in the transitional period of P/T in Shanxi,which reflects a harsh environment under an oxidative drought climate.