Distribution and sedimentary model of the Late Triassic strata in northern Qiangtang on the Qinghai-Xizang Plateau

The North Qiangtang Basin lies between the Lazhuglung-Jinshajiang suture zone and Shaunghu tectonic mélange zone.Five sedimentary facies belts/lithostratigraphic units have been distinguished for the Basin from north to south:Rola Kangri Group composed of sandy-muddy flysch-oceanic island and island arc volcanic rock-marble associations;Zangxiahe Formation dominated by grey deep-water flysch basin facies;Gyiza Group built up of dark deep-water fine-grained clastic basin facies; Juhuashan Formation consisting of open platform/ramp carbonate rocks,and Tumaingela Group filled by the deltaic coal-bearing clastic rock series. The North Qiangtang Basin once displayed the half-graben sedimentary framework of being gentle in the south and steeper in the north during the Late Triassic.The sediments in the basin pinch out southwards.The basin has double origins:the Rola Kangri thrust zone in the north and the Shuanghu mélange belt in the south. During the Late Triassic,the depocentre was located in the middle part of the basin,while the subsidence centre in the northern part of the basin,suggesting the sedimentary features of the basin as a foreland basin.