ELSEVIER Sedimentary Geology 128 (1999) 179–199 Oligocene to Holocene sediment drifts and bottom currents on the slope of Gabon continental margin (west Africa) Consequences for sedimentation and southeast Atlantic upwelling Michel Se ´ranne L , Ce ´sar-Rostand Nze ´ Abeigne Institut des Sciences de la Terre de l’Eau et de l’Espace de Montpellier, UMR 5573, CNRS, Universite ´ Montpellier 2, Case 060, 34095 Montpellier cedex 05, France Received 10 June 1998; accepted 7 June 1999 Abstract Seismic reflection profiles on the slope of the south Gabon continental margin display furrows 2 km wide and some 200 m deep, that develop normal to the margin in 500–1500 m water depth. Furrows are characterised by an aggradation=progradation pattern which leads to margin-parallel, northwestward migration of their axes through time. These structures, previously interpreted as turbidity current channels, display the distinctive seismic image and internal organisation of sediment drifts, constructed by the activity of bottom currents. Sediment drifts were initiated above a major Oligocene unconformity, and they developed within a Oligocene to Present megasequence of general progradation of the margin, whilst they are markedly absent from the underlying Late Cretaceous–Eocene aggradation megasequence. The presence of upslope migrating sediment waves, and the northwest migration of the sediment drifts indicate deposition by bottom current flowing upslope, under the influence of the Coriolis force. Such landwards-directed bottom currents on the slope probably represent coastal upwelling, which has been active along the west Africa margin throughout the Neogene.  1999 Elsevier Science B.V. All rights reserved. Keywords: west Africa margin; southeast Atlantic; contourites; drifts; slope deposits; Oligocene; Neogene 1. Introduction Sedimentation on continental shelves has been the subject of intense studies for several decades. Sedimentary processes on continental margins are presently receiving increased attention since the dis- covery of large hydrocarbon reservoirs in the deep offshore South Atlantic, and was prompted by the progress of technology allowing deep-water indus- L Corresponding author. Tel.: C33-467-544-811; Fax: C33-467- 523-908; E-mail: seranne@dstu.univ-montp2.fr trial drilling. Knowledge of sediments and sedimen- tary processes in deep water (>200 m bathymetry) relies on facies analyses of sedimentary basins (e.g. Carminatti and Scarton, 1991; Mutti et al., 1992). Stratal relationships across the slope are critical in understanding the sedimentary processes involved. This is particularly true in areas where geometry is the only feature available for investigation. In spite of the variety of both sedimentary facies (Pickering et al., 1986) and processes involved in the deep-sea environment (Stow, 1994), a great deal of attention has been focused on turbidites. The current 0037-0738/99/$ – see front matter  1999 Elsevier Science B.V. All rights reserved. PII:S0037-0738(99)00069-X