The age, extent, and origin of Quaternary uplift of the Atlantic coast of Morocco

Marine terraces, with elevations up to ~300 m above present-day sea-level, are known to occur along large parts of the Atlantic coast of Morocco. The uplift occurs over a distance of >100 km, which is of too long a wavelength to be explained solely by Quaternary fault activity, but which is instead of the appropriate length-scale to be generated either by lithospheric flexure or by support from thermally-driven upwelling in the mantle. We date beach and coastal dune sediments overlying the wave-cut platforms using optically-stimulated luminescence (OSL) in order to provide a rate of uplift. Our results show that a prominent and widespread terrace at ~60 m above present sea level is likely to represent the last interglacial at ~120 ka. Lower terraces, at 10 m and 25 m above present sea level, are likely to have formed at intermediate highstands at ~80 ka and ~100 ka when the sea-level was significantly lower than today. The age and elevation data indicate an average uplift rate that is much faster than previously thought. The wide spatial extent and rate of the coastal uplift are used to isolate the effects of lithospheric flexure and mantle upwelling, and to investigate the implications for the mechanical properties of the lithosphere.