Sedimentary record of Late Neoproterozoic rifting in the NW Tarim Basin, China

Upper Neoproterozoic sediments which have been exhumed in the NW Tarim Basin, China, comprise a 600–900 m thick non-marine to marine synrift succession that reveals an early phase of extension. This study presents new data from two measured and interpreted stratigraphic sections near Aksu and Wushi. The synrift succession unconformably overlies high-grade metamorphic basement and consists of the non-marine Sugaitebulake Fm and the marine Qegebulake Fm. The Sugaitebulake Fm is characterised by a basal (alluvial fan) conglomerate that passes upwards into fluvial and lacustrine facies sandstones and siltstones. The stratigraphic position of the basal unconformity and the thickness of the basal conglomerate is locally variable, which reflects the formation of small, isolated depocentres during the onset of extension, in addition to a pre-existing topography. The Sugaitebulake Fm also contains a series of concordant, extrusive basalts which record episodic volcanism, and together with the fluvial and lacustrine facies indicate the development of the rift system and the growth, interaction and linkage of extensional faults. The conformable Qegebulake Fm is characterised by foreshore to intertidal facies dolomites that contain abundant stromatolites, representing a basin-wide marine transgression and the rift climax stage. This synrift sequence is shown to correlate with a similar succession in NW Australia, and corresponds to at least partial separation of the Tarim Block from East Gondwana during the latest Neoproterozoic to Early Palaeozoic.