Early Permian conodonts from the Xainza area, central Lhasa Block, Tibet, and their palaeobiogeographical and palaeoclimatic implications

Abstract

The Tibetan Plateau, the highest plateau in the world, is relatively difficult to access. Therefore, the stratigraphy and fossils in this area are poorly known, although they are very important for interpreting the palaeogeographical evolution of different tectonic blocks. Here we report the new discovery of an abundant conodont fauna from the lowest part of the Xiala Formation in the central part of the Lhasa Block, Tibet. This conodont fauna includes three genera and four species (Mesogondolella idahoensis, M. siciliensis, Vjalovognathus nicolli Yuan, Shen & Henderson sp. nov. and Hindeodus sp.). The conodont fauna indicates that the lowest part of the Xiala Formation is late Kungurian in age based on the presence of abundant Mesogondolella idahoensis and the denticle characters of Vjalovognathus nicolli sp. nov. The presence of the conodont genus Vjalovognathus, the associated small solitary corals and the absence of any fusulinids clearly suggest a cool-water condition in the lower part of the Xiala Formation. Thus, the Xiala Formation in the central Lhasa Block can be restricted to an age from late Kungurian to Wuchiapingian. This is in contrast to the warm-water faunas consisting of abundant fusulinids, compound and large solitary corals, and warm-water conodonts in the upper part of the Xiala Formation from late Guadalupian to Wuchiapingian in age. This dramatic faunal change suggests that either the palaeoclimate had greatly changed from a cold condition to a warm condition after the late Kungurian in the peri-Gondwanan region, or the palaeogeographical position of the Lhasa Block had drifted northward into the warm-water regime from the late Kungurian to Guadalupian. The new family Vjalovognathidae Shen, Yuan & Henderson fam. nov. and the new species Vjalovognathus nicolli Yuan, Shen & Henderson sp. nov. are proposed, based on abundant specimens from central Tibet.http://zoobank.org/urn:lsid:zoobank.org:pub:35EFEF79-315E-4CCE-A72E-5BE27CFAFBF5