The geology of the continental shelf between Luderitz and Cape Town (Southwest Africa), with special reference to Tertiary strata

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Abstract
The geology and morphology of the continental shelf between Luderitz and Cape Town are described. The shelf is shown to be a thick sediment wedge constructed mainly during Cretaceous times, with a thin capping of Lower Tertiary, Upper Tertiary and Holocene sediments. Shallow-water sediments dominate the Upper Tertiary succession, and four main facies are identified which are controlled to a great extent by the Lower Tertiary ridge; a topographical high possibly representing secondary features related to basement structures at depth. ?Coniacian, ?Eocene, ?Miocene and ?Pliocene transgressions are recognized. Earliest Cretaceous sediments are probably Aptian or earlier. A progressive decrease in the sedimentation rate since Cretaceous times is postulated and present-day regional disparities in shelf depth are explained in the light of subsidence and sedimentation rates. The double shelf break has been in existence since at least Lower Tertiary times and has been periodically modified by erosion and sedimentation. Bottom currents have kept the outer shelf area sediment-free since ?Pliocene times. The distribution of organic-rich and authigenic mineral-rich sediments is mentioned.