A new foraminiferal fauna from the Tangra Yumco area, central Lhasa Block, Tibet and its palaeobiogeographic implications

Abstract

A foraminiferal fauna, consisting of 8 species of fusulines and 24 species of smaller foraminifers, is reported from the middle part of the Xiala Formation in the Tangra Yumco section in central Lhasa Block. The dominance of fusuline Nankinella-Chusenella assemblage and smaller foraminifera Hemigordiopsis indicates a Capitanian (late Guadalupian) age. Quantitative methods including Cluster analysis (CA) and Non-metric Multidimensional Scaling (NMDS) are employed to explore the palaeobiogeographic relationship among the Lhasa, South Qiangtang, Baoshan and Tengchong blocks as well as the localities within these blocks, based on a compilation of Guadalupian fusulines from the four blocks. Results of CA and NMDS for the Guadalupian fusulines from twelve localities show that different localities in the Lhasa Block have a close palaeobiogeographic relationship, indicating a unified environment for the whole Lhasa Block during the Guadalupian. Results of CA and NMDS from four blocks show that the Lhasa and Tengchong blocks have a closer relationship in palaeobiogeographic characteristics, whereas the South Qiangtang and Baoshan blocks are relatively closer. All these results indicate that the Mesotethys Ocean might have opened to a considerable width, forming a palaeogeographic barrier to allow for the discrepancy of palaeobiogeographic characteristics between the Lhasa-Tengchong and the South Qiangtang-Baoshan blocks.