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La Mékrou (Niger S.O.), une rivière jeune

Oumarou Amadou Idé, Mourad Betrouni and Ginette Aumassip
Journal of African Archaeology
Vol. 3, No. 2 (2005), pp. 277-282
Published by: Africa Magna Verlag
Stable URL: http://www.jstor.org/stable/43135380
Page Count: 6
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Abstract

Affluent de rive droite du Niger, la Mékrou a tracé son lit dans un épandage de dépôts argilo-sableux interrompus par de minces niveaux à cailloutis. Les uns traduisent une période d'inondation avec dépôt de matériel fin, les autres, une phase d'aridité ayant exondé les dépôts précédents. La rythmicité des phénomènes, leurs interférences climatiques et hydrologiques permettent de les rapporter au Pleistocène supérieur. Des installations humaines sont associées à chaque niveau de cailloutis, Paléolithique inférieur pour le niveau inférieur, Paléolithique moyen pour le niveau intermédiaire, Paléolithique récent, Néolithique, voire métallurgie du fer pour le niveau supérieur. L'absence de terrasses, l'existence d'un bourrelet sableux en bordure du lit traduisent une rivière jeune, ce que conforte l'aspect de son tracé à méandres anguleux et son changement brusque de direction ouvre à l'idée de capture. 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 fades change of sedimentation gives evidence for a repeated shilft in climate and hydrologie 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.

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