Sedimentary system and environment research on the Triassic strata in northwest Junggar Basin

Sedimentary microfacies research has great significance in reconstructing the palaeoenvironment and predicting the benefi-cial facies belt.Combining outcrop, core, logging and seismic data together, it is considered that the northwest Junggar Basin devel-oped the combination of alluvial fan-fan delta, fluid-delta and lacustrine systems in Triassic period.The alluvial fan-fan delta system developed the braided stream channel and the sand (glutenite) floodplain microfacies and some other geological bodies, the fluid-del-ta system, containing sand and glutenite braided rivers, consisted of such geological bodies as the channel, the bar, the floodplain and the flood lucastrine microfacies, and the lacustrine system mainly developed the shore-shallow lacustrine mud microfacies.Further-more, according to the analysis of pollen and δ¹³C, δ¹⁸O, it is suggested that the Upper Karamay belongs to the Middle Triassic peri-od.Northwest Junggar Basin was in continental crust environment, and its climate gradually changed from the dry hot subtropical zone into wet warm temperate zone which was suitable for plants growth from Early to Late Triassic.