Middle Permian fusulines from the Thitsipin Formation of Shan State, Myanmar and their palaeobiogeographical and palaeogeographical implications

Abstract

AbstractFusuline faunas including 29 species belonging to 19 genera/subgenera are described from the Thitsipin Formation in eight sections/localities on the Shan Plateau in eastern Myanmar. These fusulines broadly indicate a Midian (middle Permian, Guadalupian) age. The lower diversity and the presence of some genera, such as Monodiexodina and Eopolydiexodina, suggest that the Sibumasu Block belonged to the palaeobiogeographic Cimmerian Province during the Midian. Furthermore, quantitative cluster analysis of middle Permian fusulines from the Shan Plateau and adjacent Cimmerian blocks suggests close faunal affinities between the Sibumasu Block and the Baoshan Block in western Yunnan. More importantly, the widespread occurrence of fusulines Eopolydiexodina afghanensis and Jinzhangia shengi on the Shan Plateau is similar to that of contemporaneous fusuline faunas from the Baoshan Block and the South Qiangtang Block but different to that of the Tengchong and Lhasa Blocks, which are dominated by the characteristic Nankinella–Chusenella assemblage. This faunal discrepancy provides strong evidence that the Bangong–Nujiang suture passes through the Gaoligong Orogen in western Yunnan rather than through the Myitkyina ophiolites in northern Myanmar. Additionally, palaeobiogeographical analysis of these fusuline faunas from the Lhasa, Tengchong, South Qiangtang, Baoshan and Sibumasu Blocks implies that the Bangong–Nujiang Ocean might have been present before the Midian.