摘要
Through the analyses of core,cast thin sections and well logging data,we found the Upper Xiaganchaigou Formation in Maxian region of Qaidam Basin is mainly a set of terrigenous clastics,including conglomeratic sandstones,sandstones,siltstones and mudstones,and it develops planar-trough cross bedding.The clastic rock has coarse grain,medium compositional maturity and textural maturity,and the grain-probability curve represents three-stage or two-stage.The authors consider it to be the product of tractive current under fairly strong hydrodynamic condition.Its sedimentary environment belongs to braided delta.According to the characteristics of hydrodynamic conditions,core and log facies,the authors identified 2subfacies and 5microfacies,which include braided delta distributary channel,braided delta interdistributary channel,braided delta subaqueous distributary channel,braided delta subaqueous interdistributary channel,and mouth bar.The Upper Xiaganchaigou Formation experienced a transgression-regression evolution,and the distribution of sedimentary facies is slightly different in each period.The braided delta distributary channel and braided delta subaqueous distributary channel widely distributed in the study area and its sandbody with great thickness has a broad exploration prospects.