Abstract:

The anastomosed deltaic deposits at the bottom of the Pliocene in Youshashan,Chaidam Basin are controlled mainly by the macro axis of a lake basin.The contents of sandstone and conglomerate is about 30%.The lower maturity of composition and texture of the sandstone and conglomerate reflect quick deposition and near provenance.The vertical sequences of irregularly alternate normal and reversal cycles are related to intermittent expanding and shrinking of the lake water level.The anastomosed deltaic plain subfacies developed well,consisting of braided channel sandbodies,interchannel proluvials,dams and splays.Deltaic front subfacies is not big,river mouth bars are small,deltaic front sheet sands distribute widely.According to the above mentioned characters,four sedimentary models such as low water,the early stage and the mid late stage of flood and flush sedimentary models could be established.