The Late Carboniferous conodont Neognathodus fauna in Xainza, Tibet, China, and its significance

The conodont Neognathodus fauna is found in the middle and upper parts of the Yunzhug Formation in Xainza County, northern Tibet. Three assemblage zones are distinguished; they are in ascending order the Neognathodus cf. symmetricus-N, cf. asymmetricus Assemblage Zone, N; medadultimus-N, medexultimus-N, roundyi Assemblage Zone and Rhachistognathus sp. A-Neognathodus ultimus sp. nov. Assemblage Zone. The above-mentioned Neognathodus fauna suggests that the strata in question are Late Carboniferous middle Bashkirian to late Moscovian in age. The correlation of the fauna with those in the Russian platform, North America and South China shows that the fauna is characterized by low diversity and low abundance, suggesting that the eco-environment at that time was not quite favorable for the growth of conodonts, possibly because this area was located near the medium-high latitudes of the southern hemisphere then, where the temperature of the seawater was slightly cold.