Stratigraphic architecture and evolution of the continental slope system in offshore Hainan, northern South China Sea

Abstract

We investigate the evolution of the stratigraphic architecture of two siliciclastic northern South China Sea continental slope systems with distinct structural styles, including rift-transform and rift segments. Our results reveal that the stratigraphic patterns of the slope system in the Yinggehai basin are mainly characterized by progradational slope clinoforms, which result in a rapid shift of shelf edges seaward and southeastward due to a high rate of sediment supply. In contrast, in the eastern Qiongdongnan area, the slope margins show a vertical stacking pattern or a slight shift seaward, characterized by dense gravitational faults, rollover structures, and slump deposits. The associated stratigraphic architecture in slope clinoforms is chaotic. Reactivation of pre-existing strike-slip faults in the Yinggehai area and extensional faults in the Qiongdongnan area resulted in the formation of initial slope clinoforms during the Miocene post-rifting stage. Dextral movement of the northeast marginal fault (No. 1 fault) since the Early Pliocene resulted in the formation of a deep embayment and early slope clinoforms along the No. 1 fault in the Yinggehai basin. The formation of initial slope clinoforms is closely related to movement along the underlying basement fault in the eastern Qiongdongnan area. Although the development of the slope architecture is influenced by tectonic movement and eustasy, the primary control of the geometry of slope clinoforms is through the effects of sediment supply. Plentiful sediment supply leads to rapid progradational slope clinoforms at a large distance of progradation in the Yinggehai and adjacent areas between the two basins. Sediment-starved margins occur in the eastern Qiongdongnan area because of a very wide shelf and insufficient sediment supply.