Late Quaternary pelagic sedimentation on the southern Calabrian Ridge and western Mediterranean Ridge, eastern Mediterranean

Cores from plateaus, lying some 150–200 m above the basin floors in areas of strong vertical relief visited during the Cobblestone Project, consist entirely of pelagic marls with sapropels and tephras as minor lithologies. All the plateau cores were correlated by means of isochronous lithologies and biostratigraphically calibrated. A core from Area 3 (No. 29) and two cores from Area 4 (No. 45 and 6) were selected as reference sections and studied quantitatively in terms of grain sizes, carbonate content and microfossil content. Faunal curves based on selected species of planktonic foraminifers correlate between the three cores, which extend back in time to approximately 185 000 yr for Area 4 and to 430 000 yr for Area 3. Winnowing resulted in a reduced sedimentation rate in Area 3, in unusually high percentages of the coarser sediment fraction and in extended hiatuses at the top of the cores. The highest temperature in surficial waters as indicated by the foraminiferal faunas is recorded in all three references sections at the base of an interval correlative with isotopic stage 5e (∼ 125 000 yr B.P.), within sapropel S-5. Clay mineralogy indicates basically uniform conditions in the two areas, with the exception that smectite is more abundant in the Calabrian Ridge, which is closer to its source area (Sicily, Sicily Channel). Carbonates include calcite, magnesian calcite and some dolomite. Sapropels, sedimentary expression of stagnation, represent up to 25% of the sedimentary column in an interval encompassing isotopic stage 5 through 7. The average organic carbon content in analysed sapropels is 3.1%, versus 0.29% in normal pelagic sediments. Sapropels S-6 and S-8 are consistently accompanied by a foraminiferal fauna that is indicative of low-salinity cool surficial waters, whereas sapropels S-1, S-5 and S-7 occur in coincidence with the warmest peaks of the climatic faunal curve. Average sedimentation rate is 3.2 cm/1000 yr for Core 29; 5.5 cm/1000 yr for Core 45. Sedimentation rates calculated for basin cores are five to ten times higher. Sedimentation rates of sapropels and tephras are independent from regional sedimentation rates. Hiatuses in plateau cores correlate with debris flows in base-of-slope cores, both occurring during times of enhanced bottom circulation and submarine erosion related to low stands of sea level in cold periods.