Abstract

Since Paleozoic time, the development of sedimentary basins on the continental margin of southern Africa has been controlled by the structures formed during the breakup of Gondwanaland. In Mozambique, the earliest rift (∼180 m.y. B.P.), between East and West Gondwana, produced a north-south–trending series of large horsts and grabens which were buried beneath detritus from the Limpopo and Zambezi river systems. Oceanward sediment dispersion was controlled by the Mozambique Ridge. This stage of continental breakup coincided with the establishment of marine conditions in the older, epicontinental basins which lay over the present-day Agulhas Bank and off the Transkei and Natal coasts (Outeniqua, St. Johns, and Durban basins).

When West Gondwana broke up (125 to 130 m.y. B.P.), a large sediment wedge (Orange Basin) was initiated on the west coast of southern Africa by discharge from the Orange River and associated rivers onto a downfaulted, tensional-formed margin. At the same time, a large transform fault (Agulhas fracture zone) truncated the Outeniqua to Durban Basins as the Falkland Plateau separated from south and east Africa. These movements resulted in the formation of new ocean basins and the enlargement of older adjacent ones.

Subsequent major sea-level movements are attributable to epeirogenic/eustatic events which are possibly related to variations in world-wide ocean-ridge spreading rates. Most variations in sediment accumulation rates are related to the distribution of marginal traps rather than differences in detrital discharge rates from the major river systems.

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