PALEOCEANOGRAPHIC AND PALEOCLIMATIC HISTORY OF THE SOMALI BASIN DURING THE PLIOCENE-PLEISTOCENE - MULTIVARIATE ANALYSES OF BENTHIC FORAMINIFERA FROM DSDP-SITE-241 (LEG-25)

This study quantitatively examines benthic foraminifera (>125 mu m) fr om 40 Pliocene-Pleistocene samples from Deep Sea Drilling Project (DSD P) Site 241, Somali Basin, R-mode factor and Q-mode cluster analyses o f the 26 highest ranked species define five significant factor assembl ages and five clusters reflecting different environmental characterist ics in the Plio-Pleistocene sequence, Assemblage 1, consisting of Buli mina marginata, Nonionella japonicum, Cassidulina carinata, and Uviger ina proboscidea, reflects high flux of organic matter from high surfac e productivity and dominates Custer II, Eggerella bradyi, Melonis pomp ilioides, and Oridorsalis umbonatus constitute Assemblage 2, which is inferred to reflect intermediate flux of relatively degraded organic m atter (Cluster IV), Assemblage 3, characterized by Cibicides wuellerst orfi and Epistominella exigua, coincides with Cluster I, This assembla ge indicates increased oxygenation and strongly pulsed food supply, As semblage 4, marked by Loxostomum karrerianum (=Bolivina karrerianum), Trifarina angulosa and Bolivina spathulata, corresponds to Cluster LU and suggests an oxygen-deficient. organic carbon-rich environment. The principal species of Assemblage 5 is Nuttallides umbonifera, with Ast rononion umbilicatulum and Epistominella exigua as secondary species, This assemblage, which corresponds to Cluster V, suggests low food, hi gh oxygen and increased bottom water corrosiveness, Mean test diameter s of the planktic foraminifer Orbulina universa were used to interpret sea-surface temperature history at Site 241, Based on earlier observa tions that a positive correlation exists between the mean test diamete r of O, universa and surface water temperature, several intervals of c ool and warm sea-surface temperatures have been interpreted in the Ple istocene. The Pliocene surface water temperatures were less variable t han those of the Pleistocene, indicating increased monsoonal activity in the younger interval.