Jurassic rocks, bivalves, and depositional environments of the source area of the Yangtze River, Qinghai Province, western China

Jurassic rocks are abundantly developed in the source area of the Yangtze River, South Qinghai, with the greatest thickness of 6311 m, including five stratigraphic units: Qoimaco Formation, Buqu Formation, Xiali Formation, Suowa Formation, and Xueshan Formation. Based on sufficient fossils of bivalves, ammonites, and brachiopods, the major part of these formations is ascribed to the Middle Jurassic Bathonian to Callovian. No diagnostic fossils have been found from the Lower Qoimaco Formation or Upper Xueshan Formation, which could possibly contain in part Bajocian and Oxfordian taxa respectively.