Initiation and Progradation of Clinoforms in a Sequence Stratigraphic Framework: The Expression of Parasequences in a Lower Slope to Shelf Edge Succession, Permian Karoo Basin, South Africa

Wild, Richard J.¹, Stephen S. Flint², David M. Hodgson³ (1) Chevron ETC, Houston, TX (2) University of Liverpool, Liverpool, United Kingdom (3) The University of Liverpool, Liverpool, United Kingdom

The Permian Ecca Group of the Karoo Basin, South Africa preserves an exceptionally well-exposed siliciclastic basin floor to shelf edge succession of which the Kookfontein Formation represents the lower slope to shelf edge portion of the basin-fill. Three sequences, identified by pronounced basinward shifts in facies, and 13 upward shallowing successions are recognized in the Kookfontein Formation and interpreted to represent the distal expression of shallow marine parasequences. These parasequences display clinoform geometries that are interpreted to represent the deposits of a lower slope to shelf succession that reflect decreasing depositional gradient and volume of sediment bypassed to the deeper basin through time. This suggests a direct linkage between the gradient, slope length and the dominant sedimentary process operating on the slope, and the initiation of clinoform advancement. Sediment was transferred to the slope via overextension of shelf edge deltas during the falling stage and lowstands of relative sea level. The rapid progradation of the delta front onto, and over, the shelf edge resulted in the failure and readjustment of local slope gradients, thereby promoting subsequent progradation of the margin. The continued progradation of the basin margin resulted in a change in the dominant shoreline regime from predominantly fluvial-dominated/tide- and/or wave-influenced to wave-dominated/tide-influenced. This detailed knowledge of spatial and temporal variations in facies and architecture is key to our understanding of submarine slope depositional systems. Moreover, this approach allows us to evaluate the relative volumes of sediment accreted to the slope or bypassed to the deeper basin and greatly improves reservoir prediction and characterization.