The Deposit Characteristic Of Wudaoliang Group In Tongtianhe Basin Of Northern Tibet Early Miocene Period And The Relation With Tibetan Plateau Uplift

Early Miocene is the key period of Tibetan Plateau uplift.HXL is the largest nonmarine deposit basin in northern Tibet. Wudaoliang Group greatly distribute in this basin Early Miocene,which shows that large paleolake exist,the paleolake named Wudaoliang paleolake.The study of paleoenvironment evolution of the paleolake will provide more useful information for the relation of Plateau uplift and environment change. Wudaoliang Group in Tongtianhe Basin has been chosen in this paper.The samples has been collected by the numbers.The methods of sedimentology,petrology and geochemistry are used to study the deposit characteristic and paleoenvironment evolution of Wudaoliang Group.The results of petrology and sedimentology show that Wudaoliang Group in Tongtianhe Basin record the development of Wudaoliang paleolake,first is shallow lake environment to a long period saltlake environment ,in which exist a short period of shallow lake environment,and then the depth of the lake increased .After the lake level change shallow again, the depth of the lake increased continuouslyThe preserve condition of ostracod shell show that Wudaoliang Group in Tongtianhe Basin record Wudaoliang paleolake initially paleoproductivity is poor,and then together with the development of the lake, paleoproductivity of the lake rising .The geochemisty of Oxygen and Carbon isotopics of ostracod shell indicate that generally Wudaoliang paleolake is not a typical closed lake. The characteristic of Mg/Ca and Sr/Ca of ostracod shell geochemistry show that the salinity of Wudaoliang paleolake increased followed the development of the lake,at the meantime the temperature of the lake also increased.At the process the salinity and temperature of the lake change many times.Intergration the deposit characteristic of Wudaoliang Group reconstruct the paleosalinity and paleolake level of Wudaoliang paleolake,which reflect that during 23.8-21.8 Ma B.P. the evolution of climate in the area experience the course from west and west to dry ,at last to warm and west .The climate change should be the result of the tectonic reactive after the Tibetan Plateau uplift to denudation and planation. This work explores a new method to study the paleoenvironment in the hinter of the Tibetan Plateau further.