Conodont biostratigraphy across the Permian–Triassic boundary at Chaotian, in Northern Sichuan, China

Abstract

Detailed conodont biostratigraphy of the Permian–Triassic boundary (PTB) interval was analyzed at the fossiliferous Chaotian section in northern Sichuan, China. The PTB interval at Chaotian is composed of the uppermost Permian mudstone/limestone of the Dalong Formation and the lowermost Triassic marl/limestone of the Feixianguan Formation both representing deep basinal facies. The PTB interval is enriched in ammonoids and conodonts, and is divided into 6 conodont zones including 1) Clarkina changxingensis changxingensis– C. subcarinata Assemblage Zone, 2) C. postwangi– C. sp. B Assemblage Zone, 3) C. taylorae– C. zhejiangensis– C. changxingensis yini Assemblage Zone, 4) barren intra-zone, 5) Hindeodus parvus Zone, and 6) Isarcicella Zone in ascending order. The first four zones correspond to the Changhsingian, whereas the latter two to the Lower Induan (Griesbachian). The first occurrence (FO) of H. parvus in the lowermost Feixianguan Formation is regarded as the conodont biostratigraphic boundary. From the uppermost Dalong Formation, various taxa of the genus Clarkina occurred abundantly, and suddenly disappeared at the top of the Dalong Formation, therefore, the top of the Dalong Formation is interpreted as a horizon of the eventostratigraphic boundary. On the basis of conodont zones, the Chaotian section is correlated with the Shangsi and Meishan (GSSP of the PTB) sections in South China, and the Zal section in Iran.