Tectonic controls on geomorphological dynamics and sediment dispersal in source-to-sink systems in the Qingdong Sag, Bohai Bay Basin

Abstract

Well-log and three-dimensional (3D) seismic data are used to investigate the tectonic controls during the depositional periods of the Kongdian and Shahejie formations from Ek–Es 4 L to Es 4 U–Es 3 L–M on strata distribution, depositional systems and sediment dispersal in the Qingdong Sag, Bohai Bay Basin, East China, from a source-to-sink perspective. This tectonic transition is characterised by the Tanlu Fault switching from sinistral to dextral strike-slip as the fault system changed from a dominant NW–WNW trend during the Ek–Es 4 L period to a dominant WNW–EW trend during the Es 4 U and Es 3 L–M periods. These changes subsequently controlled the framework and areal extent of sediment dispersal in the inner-basin source-to-sink systems and resulted in a change in trend of inner-basin secondary structural belts, from primarily being NW-trending during the Ek–Es 4 L period to E–W-trending during the Es 4 U and Es 3 L–M periods. The tectonic transition also resulted in the western and southern source-to-sink systems expanding with time and controlled the flow path and sediment redistribution within each source-to-sink system with migration of the subsidence centre of the Qingdong Sag and even the region. The significant changes in the basin structure controlled the source area, flow path, sediment transport distance and direction, and have a significant impact on the interpretation of depositional environments and reservoirs in rift basins with a multi-phase evolution history. KEY POINTS The Qingdong Sag, Bohai Bay Basin, experienced a tectonic transition during sediment deposition in the Eocene. The tectonic transition resulted in changes to the fault system and basin geomorphology. Fault movement and changes in basin geomorphology affected source-to-sink systems.