Conodont and ammonoid biostratigraphies around the Permian-Triassic boundary from the Jianzishan of South China

Conodonts and ammonoids have played significant roles in the Permian-Triassic timescale. In order to uncover the nature of the Permian-Triassic mass extinction and subsequent recovery, we studied conodont and ammonoid biostratigraphies around the Permian-Triassic boundary from Jianzishan of Hubei, South China. A total of four conodont zones and two ammonoid beds are recognized. In ascending order, the conodont zones are Late Changhsingian Clarkina changxingensis Zone, Clarkina yini Zone and Griesbachian Hindeodus parvus Zone, Hindeodus postparvus Zone; the ammonoid beds are Late Griesbachian Ophiceras beds and Early Dienerian Ussuridiscus varaha beds. At Jianzishan, Ophiceras beds are stratigraphically younger than Hindeodus parvus Zone, but it is likely to be the same level with Hindeodus postparvus Zone. The Lower Dienerian in Bed 8 in this section is characterized by ammonoid Ussuridiscus varaha beds, which is associated with many Late Griesbachian conodonts including Hindeodus postparvus, Hindeodus praeparvus, Hindeodus typicalis, Hindeodus pisai, Hindeodus latidentatus, Hindeodus parvus, Hindeodus anterodentatus and Isarcicella turgida, indicating these conodont species could pass through the Griesbachian-Dienerian boundary and occurred in the Early Dienerian oceans.