Paper No. 7
Presentation Time: 3:00 PM


SEELY, Mary, Gobabeb Research and Training Centre, P.O. Box 20232, Windhoek, Namibia,

The bedrock, upon which the ancient and modern Namib Sand Sea rests, records several major phases of crustal evolution relating to the amalgamation and breakup of the Rodinia and Gondwana Supercontinents. The Namib-wide peneplain extending N-S along the 1500 km of coastal Namibia and inland over 100 km to 1000 m at the base of the Great Western Escarpment predates the development of the Namib Sand Sea. Fossils in fluvial-palustrine deposits suggest the pre-sand sea fluvial phase ended about 21Ma.

By the end of the Cretaceous, the Orange River was a major drainage system depositing vast amounts of sediment transported from eastern southern Africa onto a huge offshore wave-dominated delta representing the first stage of a three step conveyor system. Large amounts of marine sediment in the delta and on the continental shelf were exposed to long-shore drift (second step of the conveyor) and accompanying strong southerly winds (third step of the conveyor) which transported the sand back onshore. These aeolian sands consolidated onshore to form the Tsondab Sandstone Formation. More recently, from about 5 Ma the unconsolidated dune sands of the Sossus Sand Formation, accumulated.

This geological and geomorphological setting, ever buffeted by strong winds and shifting sand formations, provides a unique ecological habitat with at least sixteen different dune types. The clean sand allows relatively deep penetration of the atmosphere to several meters below the surface providing readily accessible habitat and thermal refuge to a variety of desert organisms. It also allows these organisms to rapidly swim rather than laboriously burrow through the loosely packed sand grains. Moreover, frequent on-shore wind-blown fogs provide moisture that also penetrates between the loose sand grains or precipitates on the sand grains for harvesting by various organisms. Recent observations of elements of the Sossus Sand Formation help elucidate the high level of endemicity of this unique habitat.