FACTORS CONTROLLING THE RECENT SEDIMENTATION IN THE UPPER CONTINENTAL SLOPE OF THE JACUÍPE BASIN (NE BRAZIL)

Abstract

This work is based on textural, mineralogical (XRD) and compositional data of 50 bottom sediments’ samples in the upper continental slope between 80-1000 m water depth of the Jacuípe Basin, northern region of Bahia State (Brazil). It intends to study the recent sedimentary coverture and infer possible conditioning factors influencing the recent sedimentation in this region. Despite the study area has been considered oligotrophic, pyrite that is supposed to be mostly the result of the initial diagenetic processes of organic matter degradation, occurs throughout the upper slope of the Jacuípe Basin. The organic matter flux is abundant enough to establish anoxic environments or microenvironments favorable to the formation and preservation of pyrite. The textural, mineralogical and compositional data allow us to define latitudinal and longitudinal variations of bottom sediments possibly influenced by changes in the geomorphology of the study area and hydrodynamic conditions. The supply of detrital sediments to the southern region seems to be scarce but relatively more abundant in the northern part, closer to the São Francisco River delta. The northern region is also more favorable to sediment deposition than the southern one, where erosional processes appear to be more common. This difference may also be ascribed to the process of formation of the Brazil Current, and its southward development. A significant compositional change of sediments was observed at about 435 m depth possibly due to the enhanced influence of the North Brazil Undercurrent.