Seismic geomorphology of the Safi Haute Mer exploration block, offshore Morocco’s Atlantic Margin

The lower continental slope of Morocco’s west coast consists of Triassic-age salt manifested in the form of diapirs, tongues, sheets, and canopies, and both extensional and compressional structures that result from salt movements. Salt diapirism and regional tectonics greatly influenced a broad spectrum of depositional processes along the margin. Mapping of a 1064-km² (411-mi²) seismic survey acquired in the Safi Haute Mer area reveals that Jurassic to Holocene salt mobilization has induced sedimentation that manifests itself in gravity slumps and slides and debris flows. An east-west–trending structural anticline located downdip of the salt-influenced region, was activated during the Atlas uplift (latest Cretaceous) and shaped much of the lower continental slope morphology from Tertiary time until present. The largest of the mass transport deposits (MTC) is a 500-m (1640-ft)-thick Cretaceous-age unit that spans an area of up to 20,000 km2 (7722 mi2). Seismic facies composing the MTC are (1) chaotic, mounded reflectors; (2) imbricated continuous to discontinuous folded reflector packages interpreted to represent internal syn-depositional thrusts; and (3) isolated, thick packages of continuous reflectors interpreted to represent transported megablocks (3.3 km2 [1.3 mi2]). The latter show well preserved internal stratigraphy. The MTCs originated from an upslope collapse of a narrow shelf during the earliest phases of the Alpine orogeny. Seismic geomorphologic analysis of the non-salt-deformed sections reveal numerous linear features that are interpreted as migrating Mesozoic-age deepmarine sediment waves. Three styles of sediment waves have been identified. These include: (1) type J1—small (less than 17 m thick) and poorly imaged, Jurassic in age, ridges that have wavelengths of up to 12 km and crest-to-crest separations of less than 1 km; (2) type K1—early Aptian constructional sediment waves (~110 m thick) that appear to show some orientation and size variations which suggest an influence on currents by salt-influenced seafloor topography, and (3) type K2—latest Albian and earliest post-Albian sediment waves exhibiting wave heights of 40 m and crest-to-crest separations of 1 km, that are continuous across the entire study area and show evidence of up-slope migration.