Early Triassic conodonts from the Liangshan area, Hanzhong, Shaanxi, South China

Abstract

The Liangshan area in Hanzhong city, Shaanxi Province, China, is in the northwestern part of the Yangtze Platform. Strata across the Permian–Triassic boundary (PTB) are continuous, well developed, and fossiliferous, providing an ideal place for biostratigraphic study. However, there is a dearth of reliable conodont biostratigraphic data from PTB sequences in the Liangshan area. In this study, conodonts are examined at the Zhangkouzi and Chencun sections in the Liangshan area. Three conodont species are documented from the Zhangkouzi section, Hindeodus parvus, H. sosioensis, and H. postparvus, and six conodont species are documented from the Chencun section, Pachycladina multidentata, Pa. costatus, Pa. magnus, Pa. bidentata, Foliella formosa, and Neospathodus concavus. Based on the stratigraphic distribution of conodonts, the Zhangkouzi section is Changhsingian–Griesbachian (early Induan) in age, and the Chencun section is Smithian (early Olenekian) in age. Our data suggest that the genus Foliella evolved from the genus Pachycladina, that F. gardenae evolved from F. formosa, and that the latter evolved from Pa. multidentata. The multi-element apparatus of Pachycladina is reconstructed with 15 elements.