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Contourite origin for shelf and upper slope sand sheet, offshore Antarctica



A widespread (3200 km2), thick (10 cm to > 100 cm) sand deposit exists on the continental shelf and upper slope offshore of the Pennell Coast, Antarctica. The sand body occurs at water depths between 200 and 1200 m. The mean grain size of the sand varies from 3·3 phi to 1·2 phi, and the composition is dominantly volcanic. The only source for this volcanic material is Cape Adare, a volcanic headland. Sands are transported up to 70 km from Cape Adare by a westward-flowing circumpolar boundary current that impinges on the upper slope and shelf. Radiocarbon dates from the sand and from the glacial unit beneath it indicate that the deposit formed within the past 9000 years. The occurrence of this sand sheet demonstrates the ability of contour currents to assemble extensive sand bodies on the shelf and upper slope and the relatively rapid rate at which these deposits may form.