The geomorphology of the Southwest Guinea Margin: tectonic, volcanic, mass movement and bottom current influences

Abstract

Slope morphology controls were examined in two topographically different areas on the southern transform margin of the Guinea Plateau (Sectors G1 and G2). Tectonic control is manifested by steep, faulted slopes in both study areas, and by basement warping in Sector G1 and magmatic emplacements in Sector G2. Sediment deposition and the formation of bedforms such as sediment waves on the margin are influenced by topographically intensified bottom currents within the intermediate-deep water mass, the North Atlantic Deep Water (NADW), as well as in the shallower Equatorial Surface Water (ESW)/ Antarctic Intermediate Water (AAIW) at the uppermost slope/plateau-edge level. Thus, unconsolidated sediments are eroded from steep slopes (the upper and lower slopes, canyon walls and the slopes of the volcanic cones) and concentrated into slope-parallel depocentres in Sector G1, and ponded in moats between the volcanic cones in Sector G2. Surficial sediment waves, which are apparently oriented at an angle to the slope, range from 0.5 to 2 km in wavelength and up to 100 m in height. Mass movement of the sediment cover is significant on the lower slopes of both sectors and is the result of slope steepness and instability caused by the continuing tectonic activity.