Carbon-oxygen isotope and stratigraphic study of the Early Permian Angjie Formation in Xainza area, Tibet

The Permian Angjie Formation is deposited in Xainza area, Tibet. The upper part is composed of sandstone and mudstone, whereas the lower part is sandstone intercalated with limestone. The age of the Angjie Formation is considered to be from Artinskian to Kungurian. 24 carbonate samples were collected in accordance with the carbon and oxygen isotope analysis, and the dating results yielded the maximum value of 6.312‰, the minimum value of 4.032‰, and the average carbon isotope value of 5.794‰. The maximum value of oxygen isotope is -1.785‰, the minimum value is -7.476‰, and the average value is -4.494‰. The δ13C has a positive shift, which is obvious and slow. It might have been influenced by the glaciation of the northern margin of Gondwana in the middle-late Early Permian period and the large-scale terrestrial plant reproduction.