Sedimentary characteristics of the fan delta deposits from the Upper Triassic Bagong Formation in the Dongqu area, northern Qiangtang depression

The Upper Triassic Bagong Formation in the Dongqu area, northern Qiangtang depression is made up of a succession of clastic deposits with two coarsening-upward depositional-filling sequences. According to the stacking patterns, rock associations and fabrics, sedimentary structures, and flow regimes, these clastic deposits belong to the fan delta deposits which may be subdivided into the proximal fan, mid-fan and distal fan subfacies. Sedimentary structures are common, including the basal scour structures, graded beddings, parallel beddings and crossbeddings generated by the gravity flows and tractional flows. The study of the fan delta deposits may assist in the understanding of palaeotectonic settings, sedimentary environments, and oil and gas accumulation in the study area.