Lower–Middle Triassic conodont biostratigraphy of the Qingyan section, Guizhou Province, Southwest China

Abstract

The Middle Triassic Qingyan Formation at its type section, the Qingyan section of Guizhou, Southwest China, yields more than 300 species belonging to 17 fossil groups, which mark the radiation of benthic organisms following the end-Permian mass extinction. This study intends to establish a primary conodont biostratigraphical succession through the Lower and Middle Triassic sequence at Qingyan to provide a time framework for the understanding of the recovery and radiation process from the mass extinction. A total of 30 species in 8 conodont genera are stratigraphically significant and assigned to the Neospathodus dieneri, Neospathodus cristagalli, Neospathodus waageni, Neospathodus homeri, Chiosella timorensis, and Neogondolella cf. bulgarica Zones in ascending order. Most conodont zones correlate well with their counterparts recognized from elsewhere in China and even worldwide. The first appearance of Ns. waageni marks the Induan–Olenekian boundary, which is placed at the lower–middle part of the Luolou Formation, 121.47 m above the Permian–Triassic boundary. The Olenekian–Anisian (Early–Middle Triassic) boundary is here defined by the first occurrence of Chiosella timorensis at the base of the Qingyan Formation. Although no conodonts retrieved from the upper Qingyan Formation containing the extraordinarily diverse biota, i.e. the Qingyan Biota, stratigraphical correlation with the neighbouring conodont-bearing sections in Guizhou and the ammonoid zones suggest that the Qingyan Biota has an age of early late Anisian (early–Middle Triassic).