Seismic interpretation

During its evolution, the continental slope is frequently scoured by erosional events which may not always show up as unconformities on the seismic record. Pitfalls await the seismic interpreter, especially in the lower slope region where many of these unconformable reflec-tors merge and meet with the seemingly simple, conformably bedded horizons of the upper rise. In this setting, the acoustostratigraphy should be checked by drilling and refined by logging. Examples of pre- and post-Site 397 interpretation of profiles across the Cape Bo-jador continental margin are presented. They prove that slumps not clearly resolved with low-frequency airgun records mimic the con-tinuation of reflectors from the lower slope to the rise and cause er-roneous acoustostratigraphic identifications. Information about the undrilled section and the regional setting is discussed together with refraction seismic data. This results in a warning not to stratigraph-ically correlate layers with the same refraction velocities in the zone of facies change on the continental slope and upper rise.