METALS IN SEDIMENTS FROM THE SHELF-SLOPE INTERFACE OFF THE POTIGUAR BASIN OFFSHORE OIL EXPLORATION AREA, NE BRAZIL. Marine sediments collected in November 2009 and July 2011 at depths ranging from 150 m to 2,000 m in the Potiguar Basin, northeastern Brazil, were analyzed for their main sedimentological characteristics (contents of carbon, nitrogen and their stable isotopes) and metals (Al, Fe, Mn, As, Cr, Cu, Ni, Pb, V and Zn) concentrations and their spatial distribution. Sediments were relatively rich in organic matter (C-org: 0.21% to 0.56%) and metals concentrations increased with depth, suggesting an accumulation of fine and terrigenous sediments eroded and transported from the continental shelf to the slope region. Metals concentrations were higher than those observed in coarser shelf sediments, because of sorting of fine-grained sediments. Iron (Fe), Cr and Cu distribution, although presenting this general pattern, also suggests some changes along the transport. Fe and Cr, probably in discrete minerals, are less affected by accumulation in deeper sediments. The high enrichment in Cu, however, suggests additional sources directly to slope sediments, probably by biological productivity and deposition through the water column. The concentrations of all metals are lower or fall close to the lowest range of concentrations reported for slope sediments from other marine regions worldwide and no evidence of anthropogenic contribution was evident.
Keywords:
metals; geochemistry; offshore oil exploration; slope sediments
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