Shelf-edge trajectory and sediment dispersal in a lacustrine setting: A case study from Qinnan Depression, Bohai Bay Basin, China

Abstract

The Oligocene succession of Dongying Formation in Qinnan depression in Bohai Bay Basin has preserved well-imaged lacustrine prograding shelf-edge scale clinoforms, providing a good opportunity to study the relationship between shelf-edge trajectory, stratal stacking patterns and sediment dispersal, and to investigate the effect of controlling factors on sediment dispersal shelf-edge trajectories in a lacustrine setting. 3D seismic volumes were used for defining seismic units, bounding surfaces, shelf-edge trajectories and sediment dispersal. Four seismic units have been subdivided, and four types of shelf-edge trajectories and the associated stratal stacking patterns have been recognized. Greater volume of sandstone in deep-water area tends to develop in seismic units with descending shelf-edge trajectory angles and tends be linked to lower shelf-edge trajectory angles. Differential tectonic subsidence rates along the shelf and along-strike variation in sediment supply were prime factors controlling lateral variability in trajectory, progradation and sediment dispersal. The evolution of shelf-edge trajectory can be subdivided into three stages. Local climate might play a major role in controlling lake-margin evolution during the first two stages, when dry hot weather foster basin floor fan deposition and descending trajectories, and humid cold weather hindered the development of basin floor fan and forms ascending trajectories. While differential tectonic subsidence could have the dominate role during the third stage, when climate signal can hardly be recognized and lateral variability in trajectory angles and sediment supply is most obvious.