A right bank tributary of the Niger River, the Mekrou, has formed a strongly incised river bed within clayey to sandy alluvium, locally interrupted by thin layers of gravel and coarser deposits. The alluvia give evidence to different climatic conditions: finer material was accumulated during flooding within a humid period, whereas the arid times seem to be reflected by coarser sediments. The cyclic facies change of sedimentation gives evidence for a repeated shilft in climate and hydrologic conditions, assuming that the alluvia originate in the upper Pleistocene. Some human artefacts are associated to the different gravel layers (subjacent bed = Palaeolithic, intermediate bed = middle Palaeolithic, overlying bed = ‘recent’ Palaeolithic, Neolithic, and iron Metallurgy). The absence of terraces, the occurrence of sandy sediments on the border of the river bed indicates to active morphodynamic processes; some angularly shaped meanders give evidence for a rapid change of drainage and leads to the hypothesis of a modified flow-off by the river’s recent capture.