Sedimentation and tectonic evolution of the north Xorkol basin in the Altyn Tagh Range

The north Xorkol basin is located in the central segment of the Altyn Tagh(Altun)Range.Its formation and evolution is closely related to the strike-slip movement of the Altyn Tagh fault.Mainly on the basis of our geological mapping in2001and a study of the sedimentary facies and environment ,the conglomerate bed of the early Quaternary Qigequan Formation is distinguished and the Cenozoic sedimenta-ry strata in this basin are divided into two sequences:the lower sequence consists of the Oligocene Lower Ganchaigou For mation,Miocene Upper Ganchaigou Formation and Lower Youshashan Formation and the sedimentary facies changes gradually from the alluvial and diluvial fan facies at the base upward to the down-faulted lake basin facies in the middle and then again to the alluvial and diluvial fan facies at the top,forming a complete sequence of generation-development-extinction of a down-faulted lake basin;the upper sequence is the Early Quaternary Qigequan sequence,consisting mainly of alluvial and diluvial fan deposits.A model of multi-stage tectonic evolution has been constructed in combination the process of de-position and filling of the basin and an analysis of tectonic deformation and then the dynamic relation be-tween the formation and evolution of the basin and the strike-slip process of the Cenozoic Altyn Tagh fault is discussed.