Upwelling Project: oceanographic and geochemical process in the boundary between Campos and Santos basins

Abstract

The Continental Shelf off Cabo Frio, RJ - Brazil is characterized by geomorphological and hydrodynamic peculiarities that contribute to the complexity of the sedimentary processes along this area of the platform. One of the groundbreaking findings in the “Projeto Ressurgência” (Upwelling Project) is the description of continental shelf mud deposition. The Upwelling Project aims to establish models of production, transformation, accumulation and transport of organic material in multiple timescales. An initial geophysical survey showed different features along the shelf, including beachrock, paleolagoons, stratified and chaotic eco characters, confirming the potential of this region as being a modern analogue of the ancient carbon rich depositional material. Geochemical processes in sediment-water interface showed essentially suboxic conditions, dominated by sulfate reduction reactions a few centimeters below the surface. Stable sulfur minerals, such as pyrite, were found showing differing degrees and types of crystallization. Geochronological models revealed two distinct sedimentation periods, the first directly influenced by sea level changes and the second driven by the oceanographic dynamic. In agreement with the regional sedimentation model, the paleoceanographic record describes two productivity phases, the current have begun at approximately 3.000 years cal BP. Coupled with the sedimentary record the oceanographic dynamic drivers the character of the shelf on accumulation and/or exportation of material to the continental slope, contributing with sediments to Campos and Santos basins.