Newly discovered Wuchiapingian to Olenekian conodonts from the Longgar area, southern Lhasa Terrane and their palaeobiogeographical implications

Biostratigraphical, geochemical and palaeomagnetic studies have demonstrated that the Lhasa Terrane occupied a low-latitude southern hemisphere region during Late Permian to Early Triassic time. However, the palaeogeographical relationship of the South Qiangtang and the Lhasa terranes remains a topic of debate. The principal dispute focusses are on whether the Bangong-Nujiang Suture Zone (BNSZ) separating the terranes was an ocean during the Late Permian to Early Triassic. Resolution of this problem requires the recognition and investigation of Permian - Triassic boundary (PTB) deposits and fossils of the Lhasa Terrane, especially proximal to the E-W trending Longgar-Gongbujiangda Fault, a region that has heretofore been considered devoid of these deposits. Our investigation of the Longgar area reveals that carbonate deposits correlated with the Middle Permian Xiala Formation are similar to PTB rocks described from elsewhere. We recovered conodont faunas spanning the Wuchiapingian and Changhsingian stages of the Permian and the Early Triassic Olenekian stage. Our results demonstrate that the studied carbonate succession ranges from the Upper Permian to the Upper Triassic (perhaps to the Lower Jurassic). The documented conodont succession demonstrates that PTB strata accumulated in the Longgar area. Thus, Late Permian and Early Triassic conodonts described from the Lhasa Terrane suggest a connection with the South Qiangtang Terrane. The BNSZ during this period of time was part of a carbonate platform that connected the Lhasa Terrane and the South Qiangtang Terrane.