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Modern and palaeo-oceanographic environments under Benguela upwelling cells off southern Namibia

1996; Elsevier BV; Volume: 123; Issue: 1-4 Linguagem: Inglês

10.1016/0031-0182(96)00116-2

1872-616X

R.V. Dingle, J. M. Bremner, Jacques Giraudeau, Dieter Bühmann,

Geological formations and processes

Averaged benthic physical and chemical, and key microfaunal (Ostracoda) parameters of the bottom waters and substrate allow a ranking of the intensity of upwelling in the modern cells off southwestern Africa (B1–B6): —B1 Namib cell (temperature, salinity, dissolved oxygen, total organic matter: 10.3°C, 34.94‰, 1.2 ml/l, 6.2%): Palmoconcha walvisbaiensis, Cytherella namibensis, Garciaella knysnaensis robusta and Neocaudites lordi. —B2 Walvis cell (11.0°C, 35.00‰, 1.0 ml/l, 9.2%): Palmoconcha walvisbaiensis, Cytherella namibensis, Garciaella knysnaensis robusta, Buntonia rogersi, Neocaudites lordi and Ruggieria cytheropteroides (leeward side only). —B3 Luderitz cell (9.1°C, 34.77‰, 1.8 ml/l, 6.3%): Palmoconcha walvisbaiensis, Cytherella namibensis, Incongruellina venusta, Kuiperiana angulata, and Ruggieria cytheropteroides (leeward side only). —B4 Namaqua cell (10.0°C, 34.82‰, 2.4 ml/l, 3.1%): Pseudokeijella lepralioides and Ruggieria cytheropteroides. —B5 Columbine cell (8.3°C, 34.70‰, 3.1 ml/l, 3.9%): Ruggieria cytheropteroides, Pseudokeijella lepralioides, Poseidonamicus panopsus and Ambostracon (A.) flabellicostata. —B6 Peninsula cell (8.9°C, 34.63‰, 3.6 ml/l, 1.9%): Pseudokeijella lepralioides, Ambostracon (A.) keeleri, Cytherella dromedaria, Neocytherideis boomeri, Xestoleberis africana, Neocaudites osseus, Coquimba birchi and Urocythereis arcana. Pleistocene palaeo-upwelling characteristics of the shelf north-west of Luderitz are investigated by analysing the ostracod faunas, sediment textures and mineralogy of three large-volume gravity cores. Q-mode factor analyses using previously published transfer functions allow predictions for benthic environmental parameters. During the Late Pleistocene the area experienced less-intense upwelling and lower primary productivity than at present, in an environment equated with a modified Peninsula cell (B6): B7 cell (9.6°C, 34.73‰, 3.2 ml/l, 3.9%), Neocaudites lordi, Ambostracon (A.) keeleri, Bairdoppilata simplex, Paracypris lacrimata, Parakrithella simpsoni, Xestoleberis hartmanni, Ruggieria cytheropteroides and Pseudokeijella lepralioides. In Middle and Early Pleistocene/Late Pliocene times, the core sites lay closer inshore, adjacent to evaporite (halite) and authigenic (phosphorite)-rich lagoons, with a high-intensity upwelling Walvis-like cell (B1) to the north-west, and a low-intensity upwelling cell (B7) to the south.