Magnetic and microfaunal characterization of late Quaternary sediments from the Western Mediterranean: inferences about sapropel formation and paleoceanographic implications

Late Quaternary samples collected in the Wesern Mediterranean Sea at Ocean Drilling Program Leg 161 Sites 974 (TyrrhenianSea), 975 (Balearic Basin), and 976 (Alboran Sea) were analyzed for paleoceanographic and paleoclimatic purposes by means of quantitative analysis of planktonic foraminifer and rock-magnetic measurements. The chronostratigraphic framework is based on the comparison between the paleoclimatic curve and oxygen-isotope profiles available for Sites 975 and 976. By combining the organic carbon content, the magnetic properties, and especially the microfaunal assemblages, it has been possible to identify at Site 976 the presence of intervals corresponding to the deposition of sapropels S1-S5 in the eastern Mediterranean sea. Magnetic parameters show that reductive diagenesis occurs during several time intervals at this site, suggesting that suboxic to anoxic conditions characterize the basin. Sulfur/organic carbon relationships appear in agreement with this observation. In the Balearic basin (Site 975), the record extends back to oxigen-isotope stage 8. The paleomagnetic record at Site 975 shows the presence of the Blake event, which occurred between the oxygen-isotope substages 5d-5e, as observed in eastern Mediterranean cores by Tucholka et al (1987).