Composite Stratigraphic Study Of The Late Permian-The Middle Triassic Strata In The North Qiangtang, Mayer Kangri District, Tibet

The study area which is to the north to the south of MayerKangri Raggyorcaka, is located in the central hinterland of Qiangtang Basin in Qinghai-Tibet Plateau.The research objects are Raggyorcaka Formation, Kanglu Formation and Yingshuiquan Formation.In this paper, we get the following points through a large number of first hand field data and detailed indoor test.The carbon and oxygen isotope of limestone in the study area changed with correlation. It probably caused by metharmosis.The paleosalinity of Raggyorcaka Formation changed greatly, reflecting the environment changed from open sea to restricted sea to open sea. While, the paleosalinity of Yingshuiquan Formation which is stable sea face, changed more stable. The18O reduced slightly, reflecting the revamping of atmospheric water.The respond which is the carbon and oxygen isotope of limestone to different parts of the large folds in the study area, could reflect the strength of metharmosis.Grain size characteristics of sandstone shows that Kanglu Formation is delta front deposition. The depositional environment of the lower part is beach.The sedimentary facies in the study area can be divided into littoral facies, restricted platform facies, delta plain facies, delta front, front delta facies, platform margin shoal facies, open platform facies. There were four times transgression and regression in study area, from the Late Permian to Middle Triassic period.This paper supports the dissociation of Heitugou Formation from Raggyorcaka Formation and abandon Xishuanghu Formation.