Sedimentary facies in the Neogene Upper Ganchaigou Formation on the northern margin of the Qaidam Basin,Qinghai

The examination of the sedimentary facies is based on the field outcrops,core observation and well logs for the Neogene Upper Ganchaigou Formation on the northern margin of the Qaidam Basin,Qinghai.The Upper Ganchaigou Formation is built up of the alluvial fan,fan delta,braided stream,braided delta,lacustrine facies and grain flow deposits.Two depositional systems have been recognized,including the fan delta-lacustrine depositional system in the Eboliang-Lenghu-Qianxi zone,and alluvial fan-braided stream-braided delta-lacustrine depositional system in the Mahai-Nanbaxian zone.The results of research in the western part of the northern margin of the Qaidam Basin may provide reliable geological information for further petroleum exploration.