The discovery and significance of the Upper Triassic Jiangrang Formation in the Daggyai Lake area, Xizang

The Upper Triassic Jiangrang Formation newly discovered in the Daggyai Lake area, Coqen, Xizang is built up of a succession of sedimentary formation composed of mixed marine clastic rocks and carbonate rocks. Lithologically, these rocks include bedded quartzose conglomerates, dark grey thin-bedded to massive bioclastic micritic limestones, sand-bearing silty micritic limestones, quartz-bearing gravelly bioclastic limestones and sandy limestones intercalated with calcareous fine-grained sandstones, in which there occur the Carnian-Norian (Late Triassic) organic fossils such as the corals Distichophyllia sp., Volzeia sp., Montlivaltia sp. and M. cf. xainzaensis, the sponges Hartmanina sp., and the bivalves Xenocardita ? sp.. The Jiangrang Formation displays an angular unconformable contact with the Lower Permian Angjie Formation. The discovery of the Jiangrang Formation will improve the Triassic stratigraphic systems in western Gangdise, and may provide the new evidence for the better understanding of the Indosinian movements in western Gangdise and the evolution of the PalaeoTethys.