Sequence architecture, depositional evolution and responses to tectonic subsidence and lacustrine fluctuation in lacustrine rift basin: A case study from Cenozoic Liaodong Bay, Bohai Bay Basin

Abstract

The sequence architecture and depositional evolution in Cenozoic Liaodong Bay, Bohai Bay Basin are formed mainly in response to rifting and lacustrine fluctuations which have been documented by integrated analysis of seismic reflections, well logs, lithology associations and core analysis. Four depositional-geomorphological systems are identified comprising fan delta systems, near-shore subaqueous fan systems, beach-bar systems and braided river delta systems. Three composite sequences (CS) are recognized including CS IV (S4), CS III (S3-3, S3-2, S3-1), and CS II (S2). The identification and description of sequence boundaries in different composite sequences vary from each other due to database. CS IV (S4) is difficult to identify across the whole area. CS III (S3-3, S3-2, S3-1) is bounded by regional unconformities along the slope or on the uplift and correlative conformities in the central depression. CS II (S2) is locally bounded by regional unconformities according to seismic resolution. The geomorphical processes and fault activities, during different stages of rifting, in addition to overlapping effects of lacustrine fluctuations, sediment supply and climate changes control composite sequences and depositional-geomorphological systems. Finally, fan delta systems and braided river delta systems are proposed to host petroleum reserves.