Evidence of bottom current influence on the Neogene to Quaternary sedimentation along the northern Campos Slope, SW Atlantic Margin

Abstract

Abstract Geophysical and sedimentological data indicate that bottom currents have played a fundamental role in deposition along the Campos continental slope, especially during the Neogene and Quaternary. Sediment drifts are clearly observed in 2D and 3D seismic data. The external geometry and internal reflection pattern of these drifts suggest the predominant action of northward-flowing currents (Southern Ocean Current) along the middle and lower slope (650-1200 m). Upper Quaternary sediments within that zone are composed of highly bioturbated, silty to sandy mud, with rare lamination and no other primary structures. On the upper slope, below the southward flowing Brazil Current, sub-bottom profiles and side-scan sonar records indicate the development of several bedform styles. On the uppermost slope, between 200-300 m, longitudinal lineations and transverse bedforms (2D and 3D dunes) are observed. Sediments are siliciclastic to mixed silty to muddy sand, with rare primary traction structures preserved. Downslope, from 300 to 650 m, linear crested bedforms, a few metres high (2-7 m) are developed. In this zone, an alongslope similarity in the depositional style over more than 50 km suggests bottom current control on sedimentation. The deposits are composed of 1 m of silty muds overlying a decimetric layer of silty sand that grades downslope to a highly oxidized, bioturbated, fine-grained interval. The variability of sediment accumulation rate (2 to 30 cm ka _1 ) is related to high frequency temporal and local modifications