Minor Metal Contents of Recent Organic-rich Sediments off South West Africa

Abstract

BRONGERSMA-SAUNDERS has recently proposed^1,2 that the extreme metal enrichment of many bituminous shales is brought about by the supply of metals by plankton in areas of oceanic upwelling. This model has been applied^1,2 to the well known Permian Kupferschiefer of northern Germany, where the concentrations of Cu, Pb and Zn are exceptionally high³. A modern environment of organic-rich sedimentation with metal enrichment is supposedly found on the continental shelf off South West Africa², especially the region in and around Walvis Bay. The area lies beneath the Benguela Current, a site of intensive upwelling⁴ and very high primary organic production⁵. Information on the bottom sediments accumulating here is meagre, although they are known to be organic and sulphide-rich^6–8.