Middle Permian foraminifers from the Zhabuye and Xiadong areas in the central Lhasa Block and their paleobiogeographic implications

Abstract

Two new Middle Permian foraminifer faunas are described from the Xiala Formation in the Zhabuye and Xiadong sections in the central Lhasa Block. The presence of some significant taxa in paleobiogeography such as Shanita, Lysites biconcavus, Hemigordiopsis subglobosa, indicates that the Lhasa Block was in the Cimmerian Province in paleobiogeography during the Middle Permian. Furthermore, the Nankinella-Chusenella fusuline assemblage that occurs in the upper part of the Xiala Formation in the Xiadong section resembles contemporaneous fusuline faunas from the Xainza and Bashor areas in the Lhasa Block and the northern part of the Tengchong Block. The endemism of the Nankinella-Chusenella assemblage in the Lhasa and Tengchong blocks indicates that these two blocks were isolated from both the South Qiangtang Block and the northern Gondwanan margin during the Middle Permian. It further suggests that both the Bangong-Nujiang Ocean and the Neotethys Ocean would have opened before the Middle Permian. A new species Chusenella tsochenensis sp.nov. was described.