DISCOVERIES OF PERMIAN FUSULINE FAUNAS FROM THE SHUANGHU AREA, CENTRAL TIBET AND ITS IMPLICATIONS FOR THE CLIMATIC CHANGE AND TECTONIC EVOLUTION OF THE QIANGTANG BLOCK

Recent geology, paleontology and geochemistry studies in the Qinghai-Tibet Plateau highly support that the Longmuco-Shanghu Suture that divides the Qamdo Block and Qiangtang Block is the Paleo-tethys suture. However, the tectonic evolution of the Qiangtang Block remains controversial.

The Permian strata in the Qiangtang Block comprise Zhanjin,Qudi and Lugu formations. Zhanjin Formation is dominated by widespread diamictites containing glacio-marine deposits. The Qudi Formation consists of sandstone and shale of typical flysh deposits. In the upper part of the Qudi Formation, the limestone interlayers can be discovered in which comprise fusulines such as Pseudofusulina, Schwagerina and Chalaroschwagerina. These schwagerinid fusulines overall indicate an Early Permian Artinskian time. The first occurrence of fusuline fauna indicates that the climate has ameliorated because the glacio-marine deposits were replaced by carbonate deposition with fusuline faunas. Also, there is a lot of basalt debris or breccias in the limestones. The concurrentness of the basalt and the limestones implies that the volcanism is active in Artinskian. The flysh deposits and active volcanism may imply that the Qiangtang Block began to drift in the Artinskian. This is also supported by the paleomagnetic data (Li et al., 2004)

The Qudi Formation is overlain by massive basalt which covers more than 100 kilometers. Above the basalt, the strata are composed of reddish limestones named Lugu Formation. According to the geochemistry studies, the basalt is typically island-arc type (Zhai Qingguo, personal communication). Thus, the limestones above the basalt are highly probable the seamount type carbonates. The fusulines in the Lugu Formation comprise Parafusulina, Pseudodoliolina, Maklaya and Nankinella indicating an age of Late Kungurian.

Thus, it is tentatively proposed that the fusulines such as Pseudofusulina and Chalaroschwagerina in the Qudi Formation represents the climate amelioration in the Qiangtang Block in Artinskian as well as provides the time for the beginning of drifting for the Qiangtang Block. After the departure of the Qiangtang Block, the basalt erupted to form the massive island on which form the limestone Lugu Formation containing the fusulines Pseudodoliolina, Maklaya and Parafusulina.