After an intensive phase of prospecting using vibracores, the inner-middle shelf west-north-west of the wave-dominated Orange Delta off southern Namibia is currently being mined for marine diamonds. The diamonds were deposited by surf-zone processes in gravels during Pleistocene low sea-level stands down to depths of about 130 m. As sea level rose to its present level during the postglacial transgression, between about 18 000 and 6 000 yr BP, water depth steadily increased in the study area and drowned the gravels. Initially, quartzose fine to very fine sand of the delta-front environment was deposited on top of the gravels. Finally, prodeltaic silts and clays of the seaward prograding-feather edge of the Holocene Orange Delta were deposited on the delta-front sands. However, the actively burrowing infauna of the region was able to bioturbate the prodeltaic silt and clay into the delta-front sand. As a result, representative vibracores reveal a typical fining-upward transgressive sequence with the upper 30 cm mainly consisting of muddy sand or sandy mud. Grain-size analysis of vibracored and grab-sampled unmined surface sediment and mined surface sediment has shown that unimodal size-distributions characterise the sand-fractions of unmined surface sediment and that polymodal size-distributions characterise those of the mined surface sediment. Conservation corridors are proposed both to preserve the original transgressive sequence and to provide refuges for the benthos to recolonise the substrate after mining.