--> Regional uplift and basement deformation recorded by the Quaternary submarine terraces offshore Safi (Morocco margin).

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Regional uplift and basement deformation recorded by the Quaternary submarine terraces offshore Safi (Morocco margin).

Abstract

During the Mirror cruise (2010), geophysical data were acquired on the North-West of Africa margin, offshore Safi (Morocco), by IFREMER (French Institute for Sea) and 3 universities (University of Brest, University of Lisbon and German BGR). Reflection and wide-angle seismic profiles together with multi-beam echo sounder data and chirp sub-bottom profiles have been acquired in this portion of the margin.

The analysis of multibeam bathymetry, high-resolution sub-bottom and seismic data on the continental slope of offshore Safi reveal the existence of several discrete morphologies such as salt domes, faults, several channels and canyons. These canyons reflect the importance of sediment fluxes in this area. The seafloor is affected by numerous faults and deformation with a large wave-length (bulge), from 300m to 3000m of water depths and these. These structures seem be located in the West African Coast Magnetic Anomaly (WACMA).

On the offshore Safi (North Aggadir canyon), four terraces have been mapped around 3000 m of water depth. These terraces correspond to paleo-Canyon archives and show the migration of a canyon from south-west to north-east. This migration is associated with a tectonic uplift of the basement. The morphogenesis of these terraces seems to be influenced by uplift and basement deformation. In fact, the seismic profiles and bathymetric map shows the existence of deformation materialized by convex seabed morphology and basement bulge (deformation with a large wave-length). If we trust this hypothesis that this shift terraces canyons is purely tectonic origin and the uplit made throughout the quaternary period. Average uplift rates is 0.30 mm/yr for a quaternary period and the uplift rate tends to slow down landward.

This bulge may correspond to the marine extension of the High Atlas mountains. We called this bulge the Atlantic Atlas and suggest that the timing of the terraces morphogenesis is contemporaneous with the recent uplift of the Atlas Atlantic.