Hunting for Africa’s New Transform Play Trends

Karyna Rodriguez¹* and Neil Hodgson¹ demonstrate how the Brulpadda-1 discovery in the Southern Outeniqua Basin, offshore South Africa, will lead to exploration for similar passive margins with obliquely cutting fault-ridge systems on the fragmented Gondwanna margins, all in latest issue of First Break Magazine.

The abyssal plains of Africa’s passive margins have been inaccessible to drilling until recently, and traps for true basin floor fans little explored. Turbidite flows reaching the basin floor through confined slope channels can begin to lose energy and deposit coarser clastic components, although if the basin floor continues to gently slope down in an offshore or lateral direction then turbidite flows can continue for long distances. However, younger, hotter and more buoyant oceanic crust generally lies offshore from older, colder oceanic crust riding deeper on the mantle. This creates an up-dip-to-offshore (UDTO) geometry to the basin floor. UDTO basins, can therefore present opportunities for basin floor turbidite flows to onlap and form stratigraphic trapping geometries towards the offshore on oceanic crust. Yet such plays are often in water deeper than 3 km (i.e. the Early Cretaceous basin floor play under the Raya-1 well offshore Uruguay), unless the crust is supported by mantle convection (Yakaar-1 offshore Senegal).

However, another UDTO trapping geometry is created when transform faults cut obliquely across passive margins. An example of this is the Agulhas-Falklands Ridge running perpendicular to the South African coast. This is the strike-slip or transform fault that allowed the Malvinas/Falklands Plateau to separate from Africa during the break-up of Gondwana. Here, the north side of the ridge comprises the wrenched Jurassic syn-rift graben that separated, accommodating the opening of the Atlantic, while the south side of the ridge is formed from oceanic crust that formed at a spreading centre to the NE.

This transform fault zone has provided a positive basin floor ridge since the Jurassic period against which turbidites supplied from the north have been directly onlapping, creating huge, later-ally continuous stratigraphic traps (Figure 1). Located at the basin floor, yet still on continental crust, these plays can be accessed in 1-2 km of water providing a new class of drilling target.


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Hunting for Africa’s New Transform Play Trends