Evidences for a non-steady state and a reorganization of the fluvial network in the Ouarzazate basin (Morocco)

Since it became externally drained, the fluvial dynamics of the Ouarzazate foreland basin has been dominated by erosive processes due to a base level fall. The basin landscape is dominated by extensive Quaternary deposits aggraded by the transverse rivers draining the High Atlas Mountains. These deposits accumulated in valleys and pediments incised in the basin Tertiary infill, characterized mostly by fine-grained and soft sediments. Evidences of fluvial captures are abundant in recent times and throughout the Quaternary, in a scenario where there is more incision efficiency in the interfluves’ secondary streams (characterized by fine-grained or sediment-free pediments) than in the main transverse rivers (characterized by thick gravel deposits). Satellite imagery, elevation data and field observations demonstrate how minor streams increase their catchment areas by headward erosion, creating extensive pediments lying under the main rivers and producing captures of the main rivers. This study demonstrates the unsteady-state of the drainage network of the Ouarzazate basin and its recent reorganization, apparently uncoupled from tectonic or climatic processe