Uppermost Katian (Ka4, Upper Ordovician) conodonts in South China: Biostratigraphy, biofacies, and paleobiogeography

Abstract

The conodont fauna from the Daduhe Formation in southwestern Sichuan and northeastern Yunnan, southwestern China, is analyzed and correlated with the uppermost Ordovician Amorphognathus ordovicicus conodont Biozone. This age assignment is further supported by the graptolites from the same sections, indicating a Ka4 Stage Slice, i.e., from the Dicellograptus complexus to Paraorthograptus pacificus graptolite biozones. Two common conodont species of the Upper Ordovician, Hamarodus brevirameus and Scabbardella altipes, are reported for the first time from the upper Katian in South China. The analysis of conodont biofacies indicates that the conodont fauna in the Daduhe Formation belongs to the cool-water Hamarodus brevirameus–Dapsilodus mutatus–Scabbardella altipes Biofacies. This discovery provides additional evidence for the cold tongue model during the Late Ordovician. The distribution of Yaoxianognathus yaoxianensis confirms the close biogeographical ties among South China, North China and Tarim. This distinctive species of eastern Gondwana might have originated in North China and dispersed to Tarim and South China.