ORIGIN OF BERMUDA CLAY-RICH QUATERNARY PALEOSOLS AND THEIR PALEOCLIMATIC SIGNIFICANCE

Red clayey paleosols that are chiefly the product of aerosolic dust de position are interbedded in the Quaternary carbonate formations of the Bermuda oceanic island system. These paleosols provide a basis for re constructing Quaternary atmospheric circulation patterns in the northw estern Atlantic. Geochemical analyses were performed on representative paleosol samples to identify their parent dust source. Fine-grained f ractions were analyzed by energy-dispersive X ray fluorescence to dete rmine trace element (Zr, Y, La, Ti, and Nb) concentrations and to deri ve geochemical signatures based on immobile element ratios. These rati os were compared with geochemical signatures determined for three poss ible sources of airborne dust: (1) Great Plains loess, (2) Mississippi River Valley loess, and (3) Saharan dust. The Zr/Y and Zr/La ratios p rovided the dearest distinction between the hypothesized dust sources. The low ratios in the paleosol B horizons most closely resemble Sahar an dust in the <2-mu m size class fraction. Contributions from the two North American loessial source areas could. not be clearly detected. Thus Bermuda paleosols have a predominantly Saharan aerosolic dust sig nature. Saharan dust deposition on Bermuda during successive Quaternar y glacial periods is consistent with patterns of general circulation m odels, which indicate that during glacial maxima the northeast summer trade winds were stronger than at present and reached latitudes higher than 30 degrees N despite lower-than-present sea surface temperatures in the North Atlantic.