Discovery of the Bivalvia-Qiyangia Assemblage in the Northern Qiangtang Area and Its Stratigraphic Significances LI Qian, LU Gang, ZHANG Nen, XU Hua, TANG Zhaoxia and WEI Xiaoyan (Guangxi Institute of Regional Geological Survey, Guilin, Guangxi 541003; No. 271 Team of Geological Survey, Guangxi Bureau of Geological Exploration, Guilin, Guangxi 541100) A set of Early Jurassic freshwater Bivalvia assemblage, Qiyangia assemblage, was discovered recently from the "Qoima Co Formation" in the Duxue Mountain area in the Qiangtang Basin, northern Tibet. The "Qoima Co Formation" overlies