Palaeogene sedimentary evolution in the Xitieshan-Changshanliang region,northern Qaidam Basin

Sedimentary facies in the Palaeogene Lulehe Formation in the Xitieshan section consist,from the base upwards,of the braided stream,braided delta,littoral-shallow lake,pluvial fan facies,dislaying an overall progradation-regradation-progradation depositional cycle.The palaeocurrents are oriented to NNW,and the sediments are derived from the Xitie Mountains in the southeastern part.Sedimentary facies in the Palaeogene Ganchaigou Formation in the Changshanliang section are assembled,from the base upwards,by the braided delta and littoral-shallow lake,constituting three progradation-regradation depositional cycles.The palaeocurrents are oriented to SSE,and the sediments are derived from the South Qilian Mountains in the northern part.