Abstract

Sedimentation over large areas of a marginal plateau, the northernmost Natal Valley (NNV), is influenced by the tropical/sub-tropical Agulhas Current. Through mobilization of detritus and concentration of sedimentation into localized depo-centres, current action provides a mechanism for hiatus development both in on-shelf and off-shelf areas. Post-Gondwana break-up sedimentary basin in-fill is interrupted by several regional hiatuses. These correlate with coastal regressions, global sea-level low-stands, proposed phases of invigorated oceanic circulation and with global phases of slow deep-sea sedimentation. An assessment of these mechanisms indicates detritus supply related to sea-level changes cannot explain correlation of on-shelf and off-shelf hiatuses. Current action may have been a contributory factor in development of a Cenomanian/Turonian hiatus and facies change and a Cretaceous/Tertiary boundary hiatus.

An Early Oligocene hiatus clearly marks a change in the Agulhas Current regime. Current-moulded features, asymmetric sediment distributions and re-working attest to enhanced current action. Establishment of a cold bottom layer in the ocean at this time stimulated Indian Ocean surface/near-surface circulation. New circulation patterns were established after a Miocene/Pliocene boundary hiatus. Since then the main flow-paths have been fairly stable, although local depo-centre shifts late in the Pliocene–Recent sequence suggest eastward movement of a counter-current and cyclonic eddy off Maputo.

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