The continental lithospheric tectonics and geodynamics in the Tethyan domain are conspicuous by the frontiers of modern earth sciences.The tectonic units of the continental lithosphere are mainly composed of the orogenic belt systems and associated basin systems.This paper focuses on the orogeny related sedimentary basin analysis so as to acquire further information about the tectonic evolution of the Tethys. The Qiangtang Basin in northern Xizang 5000 m above sea level,is located in the eastern Tethyan,covering an area from latitudes 32°00′—35°30′ N and 86°00′—92°30′ E.It is now bounded by the Lazhuglung Jinshajiang suture zone on the north,and the Bangong Nujiang suture zone on the south.Four second order tectonic units have been distinguished,i.e.Goulushankecuo rise （GR）,North Qiangtang depression （NQD）,central rise （CR） and South Qiangtang depression （SQD）from north to south. The Upper Triassic Xiaochaka Formation,which is represented by terrigenous clastic rocks,carbonate rocks and mixed sediments,is confined to the uplifted zones （GR and CR）,displaying notable changes in sedimentary facies from north to south.During the Late Triassic,the arc basin sedimentary systems were well developed in the formation including,from north to south,the Upper Triassic strata represented by the Batang Group which may be assigned to the island arc facies consisting of the island arc volcanic formations and sandstone slate flysch formations;the Upper Triassic strata represented by the Goulushankecuo Group which may be assigned to the back arc turbidite basin facies made up of the grey sandy and muddy flysch formations with the depositional rates of about 0.14～0.24 mm/a,and palaeocurrent orientation of SW （about 220°265°）or SE （130°160°）;the Upper Triassic strata represented by the Gyiza Group which may be assigned to the back arc basin facies consisting of grey fine grained clastic rocks interbedded with thin carbonate rock formations;the Upper Triassic strata represented by the Juhua Formation which may be assigned to the ramp facies consisting of the carbonate rock formations;the Upper Triassic strata represented by the Tumengela Group which may be assigned to the littoral swamp facies or the coal bearing delta swamp facies consisting of the terrigenous clastic rock formations with a palaeocurrent orientation of NW and depositional rates of 0.11～0.19 mm/a,and the Upper Triassic strata represented by the Xiaochaka Group which may be assigned to the inner/outer shelf facies consisting of the dominant clastic rock formations and subordinate carbonate rock formations. The Lower Jurassic island arc volcanic rock formations,tuffaceous turbidite formations or terrigenous fine grained turbidite formations are widespread in the Nadigangri Formation （North Qiangtang depression） or the Quse Formation （South Qiangtang depression）,which disconformably and unconformably underlie the Upper Triassic strata and represent a sequence of deep water flysch sediments during the early stage of the foreland basin. The Middle and Upper Jurassic Yanshiping Group disconformably overlies the Lower Jurassic strata,and exhibits the structural unconformable contact with the overlying Lower Cretaceous strata.The individual formations in the group are conformable,and assembled by the gypsum bearing terrigenous clastic rock formations and carbonate rock formations representing the marine molasse sediments during the late stage of the foreland basin. The Lower Cretaceous Abushan Formation is built up of the terrigenous clastic rock formations representing the continental molasse sediments during the late stage of the foreland basin. The Middle and Late Jurassic marine molasse sediments are accentuated in the Qiangtang foreland basin.The basement of the basin has the features of being steep in the south and gentle in the north.The sediments are derived from two sources.Longitudinally,the sedimentary sequences are deepening and fining upward in the early stage,while shallowing and coarsening upward in the late stage.
