Deep exploration blocks of the Gulf of Guinea off West Africa were investigated. Survey data include swath bathymetry, deep towed high-resolution sub-bottom profiles, side-scan sonar images and Kiillenberg core analysis. A slide was identified on seismic profiles. It is interpreted as a translational mass movement with a distinct failure surface at 25 m depth below the seafloor. Triggering factors were quantitatively investigated to explain the failure. However, rigorous assessment of the failure processes would require in-situ measurements as well as theoretical and experimental developments on the mechanical behavior of sediments in fluid-laden environments.
Since the first recognition of pockmarks in the early 70s (King and MacLean, 1970), evidence of seepage features has frequently been reported in several marine environments. The North Sea, the Norwegian Sea or the Gulf of Mexico have often been quoted for the frequent occurrence of such features (Anderson and Bryant, 1990; Evans et al., 1996; Hovland and Judd, 1988), usually identified through patches on side scan sonar images or acoustic turbidity on seismic records (in case of gas seepage). The presence of gas or gas hydrates in or around failed sediments has often been observed on continental slopes (Field and Jennings, 1987; Papatheodorou and Ferentinos, 1997), also in relation with seismic activity (Hampton et al., 1978; Kastens, 1984; Lee et al., 1993; Lee and Edwards, 1986). In this context of gas laden sediments, the opening of deep water exploration blocks in the Gulf of Guinea, off West Africa, initiated a scientific and industrial partnership between Ifremer and Elf Aquitaine Production to characterize morphological features and sedimentary processes of deep African waters (over 200 m water depth). Both sedimentological and geotechnical approaches aimed at identifying instability failures and tentatively understanding recent or active sedimentary dynamics in relation with the presence of fluid migration features.
