The southern continental margin of Africa as a sheared margin in its post-shear stage represents an excellent example for studying tectonic processes and resulting structures along sheared margins. It developed during the early Cretaceous break-up of Gondwana when the African and South American plates separated from each other during a shear motion along the right-lateral Agulhas-Falkland transform. Today the remnant structure of this old transform - the Agulhas-Falkland Fracture Zone (AFFZ) presents one of the largest fracture zones on Earth stretching from the Falkland plateau to the southern African margin. We collected seismic refraction and reflection data along a 400 km long transect across the South African continental margin from the Agulhas Bank to the Agulhas Passage. Our velocity-depth model images the structure of the continent-ocean transition zone at the AFFZ. We find evidence for a sub-vertical reactivation of the AFFZ and discuss uplift due to a buoyant structure in the mid-lower mantle. Analysis of the velocity-depth structure beneath the Southern Outeniqua Basin and the Diaz Marginal Ridge (DMR) reveals a structure which is interpreted as a metasedimentary basin and termed Pre-Outheniqua Basin. Compressive phases during the continent-ocean shear stage of the continental margin may have pushed material from this basin upwards forming the DMR.