Magnetic properties and origin of Upper Quaternary sediments in the Somali Basin, Indian Ocean

Abstract

The magnetic concentrations and magnetic fluxes of marine sediments from the Somali Basin show positive correlations with insolation, using oxygen isotopes for calibration. Investigations of the rock magnetic properties indicate an increase in the magnetite/hematite ratio during warmer episodes and the presence of additional fine grains of magnetite. The magnetic susceptibility profiles of several other cores suggest that the same characteristics prevail over a large area within the basin. These features are opposite to the variations observed to the north of this area (DeMenocal et al., 1991) where eolian deposition is dominant. Magnetic measurements performed on the coarse and fine fractions of the sediment show that the magnetic signal is carried by the finer fraction. Analyses of the principal components of clay mineralogy show that river transported sediments are geographically very limited and confirm that there is no indication of significant eolian deposition. It is most likely that the Antarctic bottom currents were responsible for the transport of the magnetic particles and thus for the correlation between the magnetic and climatic records.