Geochemistry and sedimentology of shelf and upper slope sediments of the south-central Black Sea

摘要

Eighty-five surface samples from oxic, suboxic and anoxic sites of the south-central Black Sea shelf consist predominantly of clayey silts and silty clays, reflecting the moderate-to-high energy, wave-dominated hydrological regime. Grain size data and net sediment transport patterns suggest that the western part of this shelf is an area of east-directed active sediment transport. With the, exception of localized nearshore zones, the eastern shelf is by contrast an area of major sediment deposition. The sediment transport vectors are correlated with patterns of surface water circulation and storm-generated longshore currents. The sources of the shelf sediments are indicated by the total concentrations of 30 major, minor and trace elements in 59 surface samples. Factor analysis shows that 99.1 percent of the total variance can be explained by five factors. Factor 1 (As, Cu, Cr, Fe, Pb and Zn) reflects anthropogenic pollution by the Etibank copper mine. Factor 2 (mainly total organic carbon and S) is linked to anoxia/redox as saline conditions. Factor 3 (mainly Al, Si) represents aluminosilicates whereas Factor 4 (sand and silt abundance, total carbonate, Ca and Sr) represents the carbonate component. Factor 5 (Fe, Mn, P, Cr, Ni and V) tracks primary detrital delivery with strong overprints by redox-dependent, biogeochemical reactions within the anoxic sediments and the oxic/suboxic bottom waters. The combined data suggest that the sediments on the south-central Black Sea shelf were largely derived from the North Anatolian Mountains and supplied to the shoreline by a network of small rivers.