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 Ostracoda were studied from the continental shelf off the Orange River, SW Africa. 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 off the Orange River at that time experienced sub-tropical conditions, with water temperatures >20°C. In contrast, there were barriers to faunal exchange with areas farther north along the west African shelf (SC for Gabon=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 frontal turbulence was established in the southern Benguela region. It is postulated that these phenomena isolated the Orange shelf ostracod faunas from further influence by the east coast Agulhas Current. A comparison of the Orange shelf ostracods with those from adjacent SE Atlantic deep-water regimes, indicates no simultaneous faunal changes in response to major Neogene palaeo-oceanographic events.