Conodont biostratigraphy across the Permian-Triassic boundary at the Xinmin Section, Guizhou, South China

Abstract

A continuous sedimentation at the Xinmin Section, Anshun, Guihzou Province, with the Upper Permian Talung Formation dominated by bedded siliceous rocks, and the Lower Triassic Luolou Formation consisting mudstones and marls as well as siliceous mudstones at its basal part indicates that it represents a deeper-water basinal facies across the Permian-Triassic boundary. Based on a systematic conodont biostratigraphic work, nine conodont species belong to two genera have been identified in this study. It enable us to establish five conodont zones at this section, in ascending order, they are: Clarkina changxingensis Zone (beds 1-3-4-2), Clarkina yini Zone (beds 4-3-5-1-1), Clarkina meishanensis Zone (beds 5-1-2-5-2), Hindeodus changxingensis Zone (beds 5-3-1-5-3-2) and Hindeodusparvus Zone (beds 5-3-3-5-3-4), respectively. According to the first occurrence of Hindeodus parvus in bed 5-3-3, the Permian-Triassic boundary is placed at the base of bed 5-3-3. This conodont zonation of the Xinmin Section provides precise biostratigraphic framework for further investigations on the geological events across the Permian-Triassic boundary at this section. In addition, the new conodont data also reveals that several siliceous beds occurred at the basal Triassic. It provides an exception of Early Triassic Chert Gap.