Abstract: Geochemistry of Recent Continental-Margin Sediments Off Northwest Africa Between Canary and Cape Verde Islands

M. Schoettle

During cruise 25 of the German research vessel Meteor along the continental margin of northwest Africa, surface and core sediment samples were taken on three traverses from the coast to the deep sea. As part of this study 35 samples of the uppermost surface layer on different profiles were investigated for grain-size distribution, mineralogy, heavy metals (Fe, Mn, Co, Cr, Cu, Ni, Pb, Zn), organic carbon, and phosphate.

The northern part of the area of investigation is influenced by the Sahara Desert, whereas the southern part is dominated by the Senegal River. The terrigenous input in the northern part is small and consists mainly of wind-blown quartz, whereas in the southern part off Senegal more clay minerals are admixed with the carbonate constituents.

Generally two different zones of distribution were found: (1) the northern part with high carbonate, high phosphate, and high amounts of Mn, Co, Cu, Ni, Pb, and Zn; and (2) the southern part with lesser amounts of carbonate and phosphate, but higher amounts of Fe and Cr. Here the metals are associated mainly with the clay fraction and can be traced to the Senegal River.

Correlation analyses show a strong dependency of metals to either carbonate or clay minerals, organic carbon, and phosphate. Phosphate is correlated with carbonate and appears as an overgrowth on carbonate grains. Trace-element patterns show for all metals lithogene and nonlithogene components. Organic-carbon distribution is dominated by marine upwelling and shows enrichment on the continental slope.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC