Present day dune systems of the Plain of Souss contain sands from two sources, littoral (marine) and continental (derived from wadis). In addition there is a third source, some sands being inherited from fossil dune systems, sometimes of considerable antiquity (Moghrebian = Plio-Pleistocene). Since the end of the Pleistocene «Upper Soltanian»), the existence of three successive fossil systems demonstrates the stability of the phenomenon, linked, on the one hand, to marine sources continuing from the last transgression, and, on the other, to fluvial sources active during the Upper Pleistocene and the Middle Holocene. These fluvial deposits are followed by drier aeolian periods in the «Late Soltanian» and the Upper Holocene.
