Study on Sedimentary Facies of Xiaganchaigou Formation in Nanbaxian Area of Northern Qaidam Basin

By researching the date of core and drilling and well logging,it was considered that the sedimentary facies,such as delta and lake facies were developed in Xiaganchaigou Formation of Nanbaxian Area.The two facies could be subdivided into distributary channel,natural barrier,inter-distributary bay,crevasse splay,underwater distributary channel,underwater inter-distibutary area,channel mouth bar,distal bar-sand sheet,delta front,predelta and shore shallow lake.Sedimentary evolution of the formation was separated into two stages.One was the lower segment(E 1 3),the other was the upper segment(E 2 3).In E 1 3 the area mainly developed shore shallow lake and distal bar-sand sheet.Sand body was at low development degree.In E 2 3,water became shallow,provenance was moved forward from northeast to south-west.Sand body is abnormally developed,delta and shore shallow lake deposit is multistage superposition.The delta front facies is especially well developed.