Sediment flux distribution in the Southern Brazil Basin during the late Quaternary: the role of deep‐sea currents

Abstract

Detailed sedimentological and stratigraphic analyses were carried out on seven Kullenberg cores collected across the Brazilian continental margin during the French cruises Byblos and Apsara III, in order to highlight the factors controlling the sediment flux distribution in the Southern Brazil Basin during the late Quaternary. On the continental slope 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 width of the shelf and proximity of canyons. The material is characterized by high kaolinite contents, and originates from the coastal rivers draining the South American continent north of Rio de Janeiro. On the middle 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), because terrigenous input is trapped at shallower depths on the São Paulo Plateau. Pelagic settling is the dominant process. In the deep domains, below 4000 m depth, contouritic accumulations are developed on the path of the northwards moving Antarctic bottom water (AABW) currents. The deposits consist of fine‐grained silty‐clayey muds with very low carbonate contents. The sediment fluxes (1·45 g cm−2 10−3 yr) are higher than on the middle continental rise, as a consequence of fine‐grained terrigenous supply derived from higher latitudes (Argentine Basin and Southern Ocean), and transported in the basin through the Vema Channel by the AABW currents. This material is characterized by high smectite and chlorite contents. These data reveal large sediment flux variations which are linked to distinct depth‐related domains. Such a distribution is the consequence of the presence of two available sources of terrigenous sediments: (1) the Brazilian continental areas with a downslope material transport and a sediment distribution controlled by the morphology of the margin, and (2) the Argentine Basin with an alongslope material transport by deep‐sea currents which dominate the sedimentation in the abyssal domains.

Controls on the distribution of deep‐sea sediments

“…Preservation is further compounded by diagenesis [ De Wever et al ., ] and corrosion by bottom water currents [ Kamikuri et al ., ]. Another factor complicating the link between biosiliceous oozes and overlying surface productivity is the contribution from seasonally variable laterally transported material as observed in deep traps deployed in the Weddell and Scotia seas [ Abelmann , ] and redistribution of sediment by deep‐sea currents [e.g., Massé et al ., ].…”

Terrigenous Sediment Supply in the Polar to Temperate South Atlantic: Land-Ocean Links of Environmental Changes during the Late Quaternary

“…Accordingly, fluvial detrital input is reduced during arid glacial periods, causing a decline in kaolinite supply. Another effect in glacial periods that reduces kaolinite/chlorite ratios is the farther northward and increased vertical extension of chlorite-bearing southern-source deep and bottom water masses, which enhance chlorite advection in the area (Jones 1984;Masse et al 1996;) and is also indicated by higher concentrations of displaced Antarctic diatoms in sediments related to glacial periods (Jones and 10hnson 1984). On the time-slice maps, these modified processes are indicated by lower values and less pronounced vertical gradients ofkaolinitel chlorite ratios in the Vema Channel region for the last glacial situation (Fig.…”

“…At the continental margin off the Brazilian coast (GeoB 2110), higher MARTs appear during glacial periods and likely reflect a higher sediment input across the shelf edge, caused by low sea levels (Masse et al 1996;). …”

Climatic evolution of eastern South America during the last deglaciation: a paleoceanographic approach

“…Furthermore, geochemical measurements at the mid-continental slope of the Abrolhos Bank and the Doce River shelf Massé et al, 1996) registered high kaolinite contents, connected with the eastern and southeastern Brazilian rivers' mineralogical signature, supporting our provenance hypothesis. …”

“…River shelf Massé et al (1996) and registered high kaolinite contents, 84 connected with the eastern and southeastern Brazilian rivers' mineralogical signature. 85…”