The alluvial geology of the Lower Orange Rver and adjacent coastal deposits, south west Africa

Abstract

Six separate areas of raised river terraces of the Lower Orange River, South West Africa, have been mapped and investigated by drilling. The gravels are aggraded flashflood deposits formed under arid conditions, and in one area pits have been excavated to provide additional information. These river terraces can be divided into two groups of different age on petrological grounds. The transport of coarse gravels and the criteria for the recognition of river channel gravels are considered. The adjacent marine deposits, which form a raised beach complex on the coast, are described and the relationship between these marine and riverine deposits is examined. It is concluded that the marine deposits are considerably younger than the riverine deposits, which had previously been considered virtually contemporaneous. It is thought that the marine beaches range from Mid- to Late-Pleistocene, while the riverine deposits are possibly? Plio- Pleistocene to Early Pleistocene in age. Both the marine and riverine deposits lie unconformably on the rocks of the Precambrian Gariep Group. The succession of the latter within the area studied is briefly described.