LATE PERMIAN TO MIOCENE BIVALVE ASSEMBLAGES FROM HOHXIL, QINGHAI-XIZANG PLATEAU, CHINA

Nine fossil bivalve assemblages have been recognized in the Hohxil des ert area of western Qinghai, China: Wuchiapingian Netschajewia jiangsu ensis assemblage, Smithian - Spathian Bakevellia costata - Leptochondr ia virgalensis - Entolium microtis assemblage, Carnian Halobia austria ca - Halobia yunnanensis - Halobia convexa assemblage, Norian Halobia yandongensis - Halobia aff. dilatata assemblage, Carnian-Norian Trigon odus carniolicus - Unionites? rhomboidalis assemblage, Bathonian Kimme ridgian Radulopecten pamirensis - Protocardia stricklandi assemblage, Late Jurassic Pseudolimea - Opis assemblage, Early Cretaceous Eokorean aia qinghaiensis assemblage, and Miocene Sphaerium nitidum assemblage. The marine bivalves, except for the cosmopolitan Halobia, are Tethyan and characterised mainly the northern margin of the Tethys. Non-marin e taxa are restricted Asian forms. These assemblages are very signific ant in studying the biostratigraphy, paleobiogeography and tectonic hi story of the Qinghai - Xizang Plateau. In the Early Cretaceous marine connections were broken and the area has experienced since then only t errestrial conditions.