CALCAREOUS NANNOFOSSILS IN PLEISTOCENE SEDIMENT CORES FROM THE SOUTH AFRICAN CONTINENTAL SLOPE

Summary

The calcareous nannofossil content has been determined for six piston cores collected on the South African continental slope. Gephyrocapsids are dominant, making up 56% of the nannofossils. This group includes Gephyrocapsa ericsonii, G. doronicoides, G. oceanica, and G. caribbeanica, the last species being dominant. Cyclococcolithina leptopora is next in abundance, averaging 21%, followed by Emiliania huxleyi, which averages 11%. Species averaging between 1%and 5%are Coccolithus pelagicus, Cyclococcolithina macintyrei, Helicopontosphaera kamptneri, and Umbilicosphaera mirabilis. Trace amounts (<1%)of Ceratolithus cristatus, Helicopontosphaera wallichi, Rhabdosphaera claviger, Scapholithus fossilis, Syracosphaera pulchra, and Umbellosphaera tenuis are also present. All the cores, with the exception of PC-17, are in the Emiliania huxleyi biostratigraphic Zone (uppermost Pleistocene). Estimated ages of the bases of these cores range from 68 600 yrs B.P. to 150 000 yrs B.P. PC-17 grades downward from the E. huxleyi Zone into the Gephyrocapsa oceanica Zone. Estimated age of the base of PC—17 is 184 400 yrs B.P. Palaeoclimatic fluctuations have been investigated by determining, at regular core intervals, the relative abundance of ‘cold-water’ and ‘warm-water’ species, using both assemblage and single-species concepts. A marked ‘cold’ inflection is usually found in both the upper and lower part of each core. This inflection was also found in an earlier palaeoclimatic study of the same cores, using planktonic foraminifera. However, the positions of the foraminiferal and nannofossil climatic inflections do not correspond particularly well. The foraminiferal curve is more likely to be correct.