Dust and loessic alluvial deposits in Northwestern Namibia (Damaraland, Kaokoveld):: sedimentology and palaeoclimatic evidence based on luminescence data

In northwestern Namibia, silty deposits are widespread. The silts consist of two major components: locally produced weathering detritus and allochthonous dust blown in from the western Kalahari to the eastern margin of the Namib Desert. Sedimentological analysis and luminescence age estimations allow identification of distinct sedimentological and geomorphological processes associated with two different climatic periods. Between about 30 and 8 ka loessic alluvial deposits several metres in thickness accumulated in valleys and basins. The deposition was generated by weak slope wash and/or endoreic drainage of the ephemeral rivers. The dust input and the accumulation of silt in the valleys indicate semi-arid climatic conditions with weak summer rains and long dry seasons. Since about 9-8 ka. silt terraces caused by fluvial incision and erosion have been formed. These indicate more humid conditions than had occurred before. The change from a dry to a moister semi-arid climate at about 9-8 ka is confirmed by proxy data from drill cores off the Namibian coast and by dune studies in the south western Kalahari. (C) 2001 Published by Elsevier Science Ltd.