Detrital composition of Upper Carboniferous sandstone in northern Tarim basin and its implications for provenance and tectonic attributes

Since the late Paleozoic,the south Tianshan Mountain has gone through a series of collision and micro-plate collage events,which have had obvious reflection in the sedimentation and tectonic evolution of northern Tarim basin.The analysis of depositional provenance is an important method for understanding basin evolution and interpreting tectonic background,and is also the first prerequisite for confirming the evolution of the basin.The variation in the composition of depositional provenances reflects the relationship between the uplift of basin margin orogen and the basin subsidence.With the improvement of modern analytical techniques,the provenance analytical methods have increased in number,become gradually perfected in quality and complemented each other.Based on Dickinson's provenance analytical method,the authors studied and analyzed sandstone detrital composition and source rocks of Upper Carboniferous sandstone along different geological sections in northern Tarim basin.The results show that the major types of the Upper Carboniferous sandstone are quartz sandstone and lithic quartz sandstone,with low compositional maturity,and the average Q/(F+L)in Cedaya,Dashankou hydropower station and Bayinbuluke geological section are respectively 1.80,3.11,3.32.The detrital composition is mainly quartz and subordinately feldspar and some rock debris,with minor organic matrix or biotite.According to the study of sandstone detrital compositions,sandstone of Upper Carboniferous Ayilihe Formation in northern Tarim basin is composed averagely of 70.7% quartz(53%~86%),7.1% feldspar(5%~17%),and 22.5% rock debris(20%~30%).Metamorphic debris and sedimentary debris are mainly existent in this area,while in Cedaya,volcanic debris possesses 42%.On the basis of Dickinson's triangular plot and the characteristics of rock debris,the Upper Carboniferous provenance in northern Tarim basin is characterized by the recycled orogen type,and the primary attribute is the suture zone for subduction and collision orogeny,with minor arc orogenic attributes.In combination with the late Carboniferous lithofacies-paleogeography of northern Tarim,it is held that the source of the northern Tarim basin might have been derived from the ancient Tianshan orogenic belt in the north.