Recovery Of Terrestrial Ecosystems In The Ordos Basin Of China After The End-permian Mass Extinction

The end-Permian mass extinction(EPME,ca.252 Ma)was the largest biological and ecological crisis in the Phanerozoic Eon,and led to a major turn in marine and terrestrial ecosystems.The post-extinction recovery of marine ecosystems is thought to have been much delayed due to the harsh climate in the Early Triassic.Marine ecosystems are thought to have recovered substantially by the middle to late Anisian,8-10 million years after the EPME,and their restoration was still ongoing in the latest Triassic.The pattern of recovery of lacustrine ecosystems is still unclear due to Lower Triassic and lower Middle Triassic continental records are fluvially dominated successions with only local lacustrine deposits that were shallow,ephemeral,and evaporitic in character.The Triassic deposits in the Ordos Basin of China are clear in stratigraphic sequence,and contain abundant fossils,which can help to solve the problem of terrestrial ecosystem recovery after the EPME.This article relies on the four outcrops rich in organic-rich shales(Bawangzhuang outcrop,Mazhuang outcrop,and Yishicun outcrop)in the southern margin of the Ordos Basin.The methods of sedimentology,paleontology and geochemistry were used to reconstruct the Ordos paleo-lake ecosystem.The mid-Middle Triassic lacustrine organic-rich shales with abundant fossils and tuff interlayers in the Ordos Basin of China are herein dated to approximately 242 Ma,and assigned to Tongchuan Formation.The organic-rich sediments record the earliest known appearance,after the mass extinction,of a deep perennial lake that developed at least 5 m.y.earlier than the globally distributed lacustrine shales and mudstones dated as Late Triassic.The fossil assemblage in the organic-rich sediments is diverse and includes plants,notostracans,ostracods,insects,fishes,and fish coprolites,and thus documents a Mesozoic-type,trophically multi-levelled lacustrine ecosystem,supported by a generally oxic to dysoxic,highly productive lacustrine environment.The results reveal the earliest known Triassic complex lacustrine ecosystem after the EPME and suggest that Triassic lacustrine ecosystems took at most 10 million years to recover fully,which is consistent with termination of the 'coal gap' that signifies substantial restoration of peat-forming forests.