HEAVY-METAL GEOCHEMISTRY OF SURFACE SEDIMENTS FROM THE SOUTHERN BLACK SEA SHELF AND UPPER SLOPE

Abstract

A wide variety of sediment types (mud to sandy gravel) was obtained at fourty-seven stations on the southern Black Sea shelf and upper slope and analyzed for their heavy-metal geochemistry. Distribution of grain size, carbonates, organic carbon and heavy metals show marked changes in the topography, biological activity and land geology of the region studied.Sediments constitued up to 39% CaCO3, mainly of biogenic origin from the shell remains of benthic organisms. Organic carbon contents of the sediments (0.13-3.09%) usually reflect the prevailing primary productivities in the Black Sea although significant terrigenous influences are also inferred.The heavy-metal concentrations largely indicate the influences from the geochemical weathering of terrigenous sources on land. In comparison with the average sedimentary rocks and other modern sediments from the adjacent regions, the concentrations of Cr, Ni, Cu, Zn and Pb are somehow higher in the surface sediments from the southern Black Sea. In particular, Cr, Ni and Cu are found in high abundances in the eastern parts of the study area. This is thought to reflect not only the well-mixed fine-grained nature of the sediments but also the possible contribution from metal-rich rocks (mafic and ultramafic sources) and associated economic mineral deposits in the catchment areas of rivers which drain this part of the coast. The presence of significant positive correlations between the concentrations of Cr and Ni, and Zn and Pb strongly suggest common sources and/or similar enrichment mechanisms for these metals. The relationships among the geochemical variables revealed