Role of continental break-up, mantle plume development and fault reactivation in the evolution of the Gamtoos Basin, South Africa

Abstract

In response to the break-up of Gondwana the Gamtoos Basin rifted in the Oxfordian/Kimmeridgian with reactivation of Cape Fold Belt thrusts as extensional structures. Rifting was rapid with an initial divergent syn-rift sequence passing into a parallel passive infill sequence as rifting waned. Dextral movement on the Agulhas–Falkland Fracture Zone during the Valanginian resulted in reactivation of Oxfordian/Kimmeridgian structures with extensional, compressional and strike-slip senses of movement. Post-rift thermal subsidence phase of basin evolution began during latest Valanginian times with passive infill and onlap of the topography created during the Valanginian. Subsequently the basin began to be uplifted due to the westward migration of the Falkland Plateau and Natal Valley spreading centre past the basin resulting in a non-depositional hiatus and local channelling before erosion during the Cenomanian. Following renewed subsidence the basin experienced uplift during the Palaeocene and Eocene the cause of which remains problematic but is contemporaneous with igneous intrusion in southern Africa.