Chapter 7.6 - Syndepositional fault constraints on sequence architecture and depositional systems in a multiple-rift lacustrine basin, the central Bohai Bay Basin

Abstract

The depositional systems and sequence stratigraphy are complicated by fault activity and this place emphasis on the characteristics of Paleogene strata in the Bohai Bay basin, eastern China. By using the seismic data, well logs combined with drilled cores, the sequence architecture, and evolution of depositions are investigated in the studied area. Second-order sequence boundaries are characterized by disconformity on seismic reflection as well as abrupt changes in well logs, while third-order sequences are identified with different packages. Fault activity can result in variations of thickness as well as depositional systems, in combined with the depocenter changes. At the early stage of rift, a series of lowstand braid delta as well as fan deltas developed adjacent to different boundary faults, and sublacustrine fan developed in the central deep basin. Following with the water transgression, delta depositions are characterized with progradation into the central and finally river delta developed at the late stage of the evolution. Rift evolution and climate both control the sediment accommodation for sediment supply, and then make contribution to the sequence geometries. Reservoirs with high quality are related with channel fill in deltas and sublacustrine fan. Fault activity can also provide the way for petroleum migration that could be sealed by fine-grained, prodelta mudstones.