Sequence Stratigraphy of the Lower 2nd Member of the Shahejie Formation, W Oilfield, Bohai Bay Basin, China

Analysis of the 2nd member of the Shahejie Formation of the W Oilfield of China, has revealed that the study area, previously interpreted as a shallow water delta system, actually mainly originated in a subaerial setting with... [ view full abstract ]

Analysis of the 2nd member of the Shahejie Formation of the W Oilfield of China, has revealed that the study area, previously interpreted as a shallow water delta system, actually mainly originated in a subaerial setting with a distributive pattern. Distributive fluvial complex depositional systems have been recognized. The regional correlation of the lithofacies within the different depositional systems has led to a high-resolution-stratigraphic framework of 2 long-term base level cycles, 6 middle-term base level cycles and more than 58 short-term base level cycles. Sequence boundary SB1 marks the top of the target interval and is characterized by thick and continuous mudstone overlying sand-rich channel sediments. Sequence boundary SB2 marks the bottom of the target interval and is characterized by stably distributed shales between sand-rich sediments. The base-level fluctuation has a strong tectonic component consistent with the regional tectonic setting; during the active subsidence stage, base level rising semi-cycles were recorded in the strata, and during the relatively stable stage, base level falling semi-cycles were recorded.