MAGNETIC-PROPERTIES AND ORIGIN OF UPPER QUATERNARY SEDIMENTS IN THE SOMALI BASIN, INDIAN-OCEAN

The magnetic concentrations and magnetic fluxes of marine sediments fr om the Somali Basin show positive correlations with insolation, using oxygen isotopes for calibration. Investigations of the rock magnetic p roperties indicate an increase in the magnetite/hematite ratio during warmer episodes and the presence of additional fine grains of magnetit e. The magnetic susceptibility profiles of several other cores suggest that the same characteristics prevail over a large area within the ba sin. These features are opposite to the variations observed to the nor th of this area (DeMenocal et al., 1991) where eolian deposition is do minant. Magnetic measurements performed on the coarse and fine fractio ns of the sediment show that the magnetic signal is carried by the fin er fraction. Analyses of the principal components of clay mineralogy s how that river transported sediments are geographically very limited a nd confirm that there is no indication of significant eolian depositio n. It is most likely that the Antarctic bottom currents were responsib le for the transport of the magnetic particles and thus for the correl ation between the magnetic and climatic records.