Palaeo-oceanographical implications of Early-Middle Miocene subtropical ostracod faunas from the continental shelf of the SE Atlantic Ocean

Early (Aquitanian and Burdigalian) and Middle (Langhian) Miocene marine Ost racoda were studied from the continental shelf off the Orange River, SW Afr ica. Eighty-one species belonging to 44 genera were recognised. Comparison with contemporary East African faunas indicate strong similarities (Simpson coefficient of generic affinity, SC = 38%). This suggests that the shelf o ff the Orange River at that time experienced sub-tropical conditions, with water temperatures > 20 degreesC. In contrast, there were barriers to fauna l exchange with areas farther north along the west African shelf (SC for Ga bon = 24%). Previously published ODP data suggest that by Late Miocene time , significant upwelling of cool water had begun over the northern Benguela region of the Walvis Ridge Abutment, and by Late Pliocene time intense fron tal turbulence was established in the southern Benguela region. It is postu lated that these phenomena isolated the Orange shelf ostracod faunas from f urther influence by the east coast Agulhas Current. A comparison of the Ora nge shelf ostracods with those from adjacent SE Atlantic deep-water regimes , indicates no simultaneous faunal changes in response to major Neogene pal aco-oceanographic events. (C) 2001 Elsevier Science B.V. All rights reserve d.