Fluvio-aeolian dynamics in the north-eastern Sahara: the relationship between fluvial/aeolian systems and ground-water concentration

This paper highlights the relationship between ground-water concentration and sand accumulations in the eastern Sahara by presenting a synoptic view of the surface geomorphology. It illustrates that the sand of the Sahara mainly originated from fluvial processes, and was deposited in inland lacustrine depressions by palaeo-rivers and streams. This is implied by the spatial organization of palaeo-channels that were revealed by radar images from space, the localization of major sand seas in topographic depressions, and by geoarchaeologial evidence. The fluvially-deposited sand was subsequently reshaped by aeolian activity into dunes and sheets during periods of drier climates. Aeolian processes are discussed, taking into account the wind currents and sand drifts, the sediment balance, and the initiation of aeolian deposits, including sand seas, using the concept of a regional aeolian action system (RAAS).