Geoquímica de sedimentos da plataforma continental do Estado do Ceará - Brasil

Abstract

The object of this work is to systematize information about geochemistry of sediments found in the Ceará State continental shelf, contributing to the knowledge about the distribution of trace elements within the continental shelf of northeastern Brazil. The study area is located between 1° N and 5° S latitudes, as well as between 30° and 40° W longitudes. We analyzed samples of sediments, collected at eight stations, during the years of 1997 (summer), 1998 (autumn) and 2000 (spring), resulting in 19 samples. In reference to the sedimentary cover, we found the following types: quartz sands, carbonate sands, fragments of shells, calcareous algae Halimeda and Lithothanmium. The fragments of shells have the highest total concentration of metals, while in algae Lithothanmium, there is the highest level of carbonate. A strong correlation between iron, manganese, zinc and lead can be observed in all the samples properly examined. In the above aforesaid samples, the average ratio between iron and manganese was about 1:25, and it was also found that a significant correlation between the concentrations of chromium and carbonate in the samples, showed up carbonate contents, which are higher than 20%. Samples of quartz sand, shells and fragments of Halimeda, were identified with similar results, concerning the distribution of iron, manganese, zinc and chromium.