Paleoenviriomental interpretation based on variations of the color of foraminifera carapaces, Flamengo bay, Ubatuba, São Paulo

Abstract

Two cores obtained respectively from Saco da Ribeira and Saco do Perequê-Mirim, both located within Flamengo Bay, northern coast of São Paulo, Brazil, have been studied. At former site many pyrite- filled foraminifera carapaces were observed. At the other site, there occur carapaces filled with pyrite, as well as carapaces impregnated with limonite and iron monosulfide, the latter showing a close relationship between limonite and iron monosulfide impregnated carapaces with strongly bioturbated levels. These observations reveal more reducing conditions in the Saco da Ribeira than in the Saco do Perequê-Mirim. By quantifying the number of carapaces impregnated with hydroxide/oxide vs. those filled by ferrous sulfide, it was possible to estimate some differences in redox potenciais at these two sites.