The Orange River, southern Africa; an extreme example of a wave-dominated sediment dispersal system in the South Atlantic Ocean

• Published in: Journal of the Geological Society Vol. 164; no. 2; pp. 341 - 351
• Main Authors: Bluck, B. J, Ward, J. D, Cartwright, J, Swart, Roger
• Format: Journal Article
• Language: English
• Published: London Geological Society of London 01.03.2007; The Geological Society of London; Geological Society; Geological Society Publishing House
• Subjects: Africa; Atlantic Ocean; Brackish; Buntfeldschuh Namibia; Cenozoic; clastic sediments; climate change; continental shelf; Cretaceous; Crystalline rocks; currents; deltas; dunes; Earth sciences; Earth, ocean, space; Eocene; Exact sciences and technology; Freshwater; Geology; grain size; gravel; Igneous and metamorphic rocks petrology, volcanic processes, magmas; last glacial maximum; littoral drift; Marine; marine transport; Mesozoic; Namib Desert; Namibia; Ocean currents; ocean waves; Orange River; Paleogene; reworking; River basins; Rivers; sand; sea-level changes; sediment supply; Sediment transport; sediments; Sossus Sand; South Atlantic; Southern Africa; Stratigraphy; Tertiary; Tsondab Sandstone; uplifts; Upper Cretaceous; wind transport; South Atlantic; Orange River; Southern Africa; South Africa, Orange R; AS, South Atlantic; ocean currents; onshore; waves; Mesozoic; Paleogene; continental shelf; shorelines; Tertiary; Atlantic Ocean; Africa; Eocene; climate; transport; Cretaceous; gravel; sand; dunes; winds; uplifts; sand seas; Cenozoic; Phanerozoic; mud
• ISSN: 0016-7649; 2041-479X
• DOI: 10.1144/0016-76492005-189

Sediments delivered to the South Atlantic Ocean by the Orange River are fractionated and dispersed northwards and westwards by a vigorous longshore drift system and a number of ocean currents. Gravels are accreted to the coastline for a distance >300 km north from the Orange River mouth. Sands are transported alongshore for >700 km but are, in places along this transport path, returned onshore by coastal winds to form the main Namib Sand Sea and other smaller dune fields. Mud is more widely dispersed westwards, northwards and southwards, probably by slow-moving, ocean-scale currents into basins on the shelf and onto the continental shelf edge. This dispersal system, operating since at least Eocene times, is believed to have originated during a time when there was a Late Cretaceous-Early Cenozoic uplift of southern Africa, which resulted in: (1) intensification of the existing southerly wind system; (2) incision of the Orange River, which, coupled with a shift in climate, resulted in a coarsening of its sediment load delivered to the coast; (3) a broad, weakly subsiding or mildly uplifting inner continental shelf with little accommodation space for the sediment load of the incising Orange River.