Looking through the Orange Glass – A Novel Perspective on Key Seismic Features and Their Influence on Hydrocarbon Potential within the Orange Basin, South Africa

Abstract

This work evaluates the hydrocarbon potential of the Orange Basin offshore South Africa by considering key seismic features such as basement, Gravity Slide Systems (GSS), Mass Transport Complexes/Deposits (MTCs/MTDs), contourites, mixed depositional systems, and seafloor morphology. Further, by integrating an updated structural domains classification, we revise the chronostratigraphy of the basin. Two gravity slide systems within the northern and southern parts of the basin are mapped in their entirety and named the Orange-Senqu and Bergoli Deepwater Fold and Thrust Belts (DWFTBs), respectively. In addition to uplift, gravitational collapse, and differential sediment loading, sediment failure is likely also triggered by fluid expulsion from the basement and gas hydrate dissociation. MTCs comprise 70–90% of the Cretaceous succession from the slope seaward. We propose the name ‘crestal deformation surface’(creds) for the top of an MTC. Contourite and mixed depositional systems are described for the first time in the basin. The Sandhaai prospect is a new turbidite-contourite fan play type. Venus and Graff-type analogues, and ‘intra MTC’ plays are also recorded within the basin. Finally, we document a segmented continental slope. Segmentation is attributed to sediment mass failure and deposition, and large-scale erosion driven by bottom currents, giving the slope a graded-to-stepped appearance.