SEDIMENT FLUX DISTRIBUTION IN THE SOUTHERN BRAZIL BASIN DURING THE LATE QUATERNARY - THE ROLE OF DEEP-SEA CURRENTS

Detailed sedimentological and stratigraphic analyses were carried out on seven Kullenberg cores collected across the Brazilian continental m argin during the French cruises Byblos and Apsara III, in order to hig hlight the factors controlling the sediment flux distribution in the S outhern Brazil Basin during the late Quaternary. On the continental sl ope and upper continental rise above 3000 m depth, sediment fluxes are important and highly variable (4 . 2-14 . 2 g cm(-2) 10(-3) yr). The sediments show a pelagic or turbiditic character, depending on the wid th of the shelf and proximity of canyons. The material is characterize d by high kaolinite contents, and originates from the coastal rivers d raining the South American continent north of Rio de Janeiro. On the m iddle continental rise between 3000 and 4000 m depth, sediment fluxes are the lowest observed in the area (0 . 9 g cm(-2) 10(-3) yr), becaus e terrigenous input is trapped at shallower depths on the Sao Paulo Pl ateau. Pelagic settling is the dominant process. In the deep domains, below 4000 m depth, contouritic accumulations are developed on the pat h of the northwards moving Antarctic bottom water (AABW) currents. The deposits consist of fine-grained silty-clayey muds with very low carb onate contents. The sediment fluxes (1 . 45 g cm(-2) 10(-3) yr) are hi gher than on the middle continental rise, as a consequence of fine-gra ined terrigenous supply derived from higher latitudes (Argentine Basin and Southern Ocean), and transported in the basin through the Vema Ch annel by the AABW currents. This material is characterized by high sme ctite and chlorite contents. These data reveal large sediment flux var iations which are linked to distinct depth-related domains. Such a dis tribution is the consequence of the presence of two available sources of terrigenous sediments: (1) the Brazilian continental areas with a d ownslope material transport and a sediment distribution controlled by the morphology of the margin, and (2) the Argentine Basin with an alon gslope material transport by deep-sea currents which dominate the sedi mentation in the abyssal domains.