Depositional system of the Neogene shallow water delta in Bohai Sea area

The sedimentary facies of Neogene in Bohai Sea area used to be considered as fluvial facies over a long time.Results of exploration in recent two years indicate that shallow lake is widely developed in the Neogene in Bozhong Sag and Huanghekou Sag in Bohai Sea area,in which a kind of excellent reservoir is also found—shallow water deltaic sand bodies.It is proved that the shallow lake exists in the Neogene in Bohai Sea area by the evidence of paleontological assemblages,characteristics of mudstone,litho-electric relationship,sand percentage,sand grain size,sedimentary structure.Shallow water delta is developed in the river mouth around the shallow lake which can be identified with sedimentary sequence and types of sedimentary facies.Being different from the classical Gilbert delta,shallow water delta is with thinner mouth bar and broadly spread sheet sands,and displays that the facies sequence is discontinuous in vertical direction,and the matrix sand bodies are distributary channel sand bodies.The type of the shallow water delta is fluvial-dominated delta.