Geological event sequences of the Permian-Triassic transition recorded in the microfacies in Meishan section

The microfacies sequence in the key interval of Beds 24-29 of the Meishan section comprehensively recorded the geological events during the Permian-Triassic transition, including the anoxia, storm disturbance, hard-ground/firm-ground form, volcanic eruption, weathering input, and microbialite development. This investigation of event sequences on the microfacies provided synthetically some clues to clarifying the previously proposed mechanisms of the end-Permian extinction. The deposit succession in Bed 24 of the Changxing Formation was developed dominantly with organic-rich lamina, but interrupted intermittently by storm disturbances. It indicates characteristically a stagnated, stratified and anoxic ocean during the latest Permian. The latest Permian transgression occurred rapidly at the top of Bed 24d and was characterized by the hard-ground interface. Abundant clay mineral of illite indicates the occurrence of persistent weathering of continental volcanics and then buried in ocean throughout this key Permo-Triassic transitional interval. However, the "boundary ash clay" of Bed 25 yielding normal grading of hyaloclastite was the result of precipitation of volcanic dusts. The firm-ground substrate in Unit 27-2 was lithe and excavated intensively by trace fossil Glossifungites; it means also the occurrence of the earliest Triassic rapid transgression and coincides with the first appearance of conodont Hindeodus parvus. Dune-shaped microbialite in Unit 27-5 defines biostratigraphically that its development, especially in the carbonate platform of South China, should correspond to the earliest Triassic; and it also indicates the final episode of the end-Permian extinction event.