The shallow-water delta deposits from the 3rd and 4th members of the Quantou Formation in the Wangfu depression, Songliao Basin: Sedimentary characteristics and associated model

The shallow-water delta deposits are of widespread occurrence in the 3rd and 4th members of the Quantou Formation in the Wangfu depression, Songliao Basin. Different from the classical deltas, the shallow-water delta deposits in the study area have the features of constructive delta deposits, developed subaqueous distributary channel, vertically interrupted normal rhythems, widespread purplish red mudstones with highly bioturbated structures, highly hydrodynamic shallow-water sedimentary structures, and indistinct three-layer structures of the Gilbert-type deltas. Two sedimentary subfacies are discriminated, including the delta plain and delta front subfacies, and seven sedimentary microfacies are recognized, including the subaqueous distributary channel, subaqueous crevasse splay, interdistributary bay, distributary channel, crevasse splay, natural levee and floodplain microfacies. Because of near the hydrocarbon-generating depression, the overlying Qingshankou Formation dark mudstones and shales may serve as the excellent cap rocks. The subaqueous distributary channel and distributary channel sandstones reservoirs are believed to be favourable hydrocarbon reservoirs.