Permian-Triassic Continental Weathering And Climates Reconstructed In North China From Chemical Weathering Indices

The largest biotic extinction event of the entire Phanerozoic occurred at the Permian-Triassic(P-Tr)boundary,during which ~90% of marine invertebrate species and ~70% of vertebrate terrestrial species died out.Numerous studies have proposed that the marine and terrestrial ecological systems were severely affected by various environmental factors,and global warming has been supposed as one of the main cause of Permian-Triassic(P-Tr)mass extinction.Previous studies from conodont O isotope,Sr isotope and weathering indexes also indicated that there was a distinct temperature rise of the seawater during the P-Tr transition.Although a strong temperature rise in tropical sea-surface temperatures during the latest Permian has been documented,coeval climate changes in terrestrial sections are less well-known.The climatic change of the Permian-Triassic is still one of the important issues to be solved,which is also the core of this research.Here,we synthesized multiple weathering indexes of terrestrial section in North China(Shichuanhe section and Yima section),including CIA,CIW,PIA,WIP and log(Al/Ca),to reconstruct the terrestrial environment condition and climate changes during the P-Tr transition.And we made use of additional geochemical proxies to evaluate the potential effects of provenance,sedimentary recycling,post-depositional diagenesis on the study units.Besides,we have made quantitative estimates of temperature changes in terrestrial environments during the end-Permian crisis.At Shichuanhe section,CIA increase from 70.5 to 75.3 before the end Permian plant extinction(EPPE),upon the EPPE,the CIA is relatively stable at a higher standard until the top of Sunjiagou Formation.At Yima section,CIA increase from 62.6 to 78.7 before the EPPE,upon the EPPE,the change of CIA is similar to Shichuanhe section.The result implies that an obvious warming event occurred at the end Permian and lasted into the Early Triassic.Furthermore,the temperature curve was established in this study based on a published CIA-temperature relationship.Estimation of atmospheric temperatures from the CIA data indicate rapid rises at Shichuanhe(from ~14.9 °C to 23.1 °C)and Yima(from 9.3 °C to 18.4 °C)during the end-Permian crisis.The finding in this study coincides with the previous evidence from the marine sections,which supports the hypothesis that a sharp temperature rise caused the extinction of terrestrial organisms during the end-Permian crisis.