A set of Late Permian-Early Triassic quartzose sandstone was found in the Xijin Ulan area, Qinghai Province during the Hoh Xil comprehensive scientific expedition in 1990. Together with the basal conglomerate, it overlies unconformably the Early Carboniferous-Early Permian ophiolitic melange. The quartzose sandstone, has been proven to be beach-subfaacies sandstone. The tectonic setting of the provenance of the quartzose sandstone is craton interior landmass. The depositional environment of the sandstone is craton margin. It indicates that paleotethyan ocean fundamentally closed at the end of Early Permian-the beginning of Late Permian. During Late Permian-Early Triassic Xijin Ulan and its adjacent areas were relatively stable.
Bian Qiantao,Sha Jingeng,Zheng Xiangshen. THE LATE PERMIAN-EARLY TRIASSIC BEACH-SUBFACIES QUARTZOSE SANDSTONE IN THE XIJIN ULAN AREA. AND ITS TECTONIC SIGNIFICANCE[J]. Chinese Journal of Geology, 1993, (4): 327-335.