Paper No. 3
Presentation Time: 8:30 AM
OUT OF AFRICA: PALEOCLIMATIC AND PALEOBIOGEOGRAPHIC IMPLICATIONS OF A PLEISTOCENE ASSEMBLAGE FROM ANGOLA, TROPICAL WEST AFRICA
SESSA, Jocelyn A.1, CALLAPEZ, Pedro M.
2, DINIS, Pedro A.
2 and HENDY, Austin J.W.
3, (1)Division of Paleontology, American Museum of Natural History, Central Park West at 79th St, New York, NY 10024, (2)Departamento de Ciências da Terra, Universidade de Coimbra, Lg. Marquês de Pombal, Coimbra, 3001-272, Portugal, (3)Florida Museum of Natural History, P.O. Box 117800, University of Florida, Gainesville, FL 32611, jsessa@amnh.org
Raised marine terraces are the products of tectonic processes and of sea level fluctuations caused by the climatic transitions that drive the waxing and waning of ice-sheets. Because of their sensitivity to temperature and salinity, molluscs found within these coastal remnants are often used to deduce mean and seasonal climatic and oceanographic parameters. Perhaps the best examples of molluscs as indicators of past conditions result from work on the thermophilous "Senegalese fauna", which is a subset of the hyperdiverse fauna that today inhabits the West African coast. Dramatic incursions of this fauna during Pleistocene interglacials are well documented throughout Mediterranean Africa and Europe, and the thermal tolerances of these species have been used to provide precise temperature estimates for many localities. While much is known about the Quaternary history of these "warm guests" outside of West Africa, there are essentially no known Plio-Pleistocene mollusc faunas between Morocco and South Africa, resulting in an information gap than spans 6,000 km.
We analyzed the fossil assemblages and sedimentology of two Middle Pleistocene marine terrace deposits in Baía das Pipas, southwest Angola. Bulk sampling and strategic collecting revealed 46 gastropod and 29 bivalve species, along with scleractinian corals, encrusting bryozoans, polychaete tubes, barnacles, and echinoids. The fauna is characteristic of intertidal and nearshore rocky substrates and sandy soft-bottom habitats. Sedimentological analysis is consistent with faunal data and indicates an upper shoreface environment along a gravel coast. The assemblage is dominated by extant tropical West African molluscs, including several key indicator species from the Senegalese fauna. As along the modern Namibe Desert coast, the influence of the cool-water Benguela Current is apparent in the paleofauna by the occurrence of a few temperate species that today range from southern Angola to South Africa. The distribution and thermal tolerances of extant species identified in the Pipas fauna indicate that this region experienced similar climatic and oceanographic conditions as that of the present during this Pleistocene interstadial. Surface water temperature varied seasonally between ~20 and 28 ºC and resulted from upwelling in this tropical setting.
