Triassic marine biogeography constrains the palaeogeographic reconstruction of Tibet and adjacent areas

Palaeobiogeographic studies can provide valuable constraints on palaeogeographic reconstructions. The Triassic marine bivalves from Tibet and adjacent areas, including the tectonic units of Qamdu, Qiangtang, Lhasa, Himalaya, North China, Songpan Ganzi, South China, Simao, and Indochina, and from three relevant and representative Triassic biogeographic regions, i.e. the western Tethys, Japan, and New Zealand, are rigorously analysed at the generic level. Analyses of diversity changes of the six clades and of the total bivalve fauna against latitude in the studied areas reveal that the diversity is highest along the northern margin, and gradually declines southward to the southern margin of the Tethyan Ocean during the Triassic. A dynamic Triassic palaeobiogeographic pattern is presented applying cluster analysis, and analysis of taxonomic diversity gradients and endemism to four time intervals, i.e. the Early Triassic Epoch, the Anisian, Carnian, and the Norian–Rhaetian. Three provinces, i.e. the North-Eastern Tethyan (NE), South-Eastern Tethyan (SE), and the Himalayan (HI) province, are recognised from the Early Triassic to the Carnian. The HI joined the SE and a new province, the Arctic-Pacific (AP) formed in the Norian–Rhaetian in the study area. The dynamic palaeobiogeographic pattern is used in the palaeogeographic reconstruction of the study area, such as position and timing of collision processes of the Palaeo-Tethys and Meso-Tethys during the Triassic.