Controls on the Geometry and Internal Architecture of Submarine Fan Elements, Tanqua Depocentre, Karoo Basin, South Africa: Insights from Process-Based Modeling

Groenenberg, Remco M.¹, David M. Hodgson², Stefan M. Luthi³ (1) Delft University of Technology, 2628RX, Delft, Netherlands (2) University of Liverpool, Liverpool, United Kingdom (3) Delft University of Technology, 2628 RX Delft, Netherlands

The spatial distribution of grain sizes in deepwater reservoirs is of primary importance in assessing production potential. Grain size segregation in deep-water deposits is primarily caused by changes in the hydrodynamic behavior of turbidity currents, which in turn is controlled by flow density, initial sediment composition, and basin-floor relief.

This study aims to investigate the influence of turbidity current process (magnitude, density), sediment composition (grain size range) and basin-floor relief on the architecture and connectivity of basin floor fan elements in the Tanqua Depocentre, SW Karoo Basin, South Africa. For this purpose, a process-based model has been developed which simulates turbidity current flow, erosion, and deposition based on principles of fluid dynamics that can deal with arbitrary basin-floor topography and accommodates various grain sizes. It unifies conservation of fluid mass, sediment mass and momentum in the form of the depth-averaged shallow water approximation in combination with the Boussinesq approximation for density-driven flow in three dimensions. Sediment transport is modeled by an advection-diffusion type equation. Exchange of sediment with the bed is largely based on existing models for entrainment and deposition. Input for the model consists of parameters defining the initial basin-floor topography and parameters related to the composition of the flows (size range, density, magnitude and frequency of the flows).

The model is compared and calibrated with high-resolution outcrop and borehole data. Results show how the internal architecture and connectivity of the basin floor fans have been influenced by initial flow composition (density, magnitude), sediment composition, and basin-floor topography.