The timing of climbing dune formation in southwestern Niger: fluvio-aeolian interactions and the rôle of sand supply

Abstract

Contemporary gully erosion has exposed sections in a climbing dune which is banked up against ferricrete terraces along the southern bank of the Niger River in southwestern Niger. The main sand transport direction in this area is from northeast to southwest, and the immediate source of the dune sand is the Niger River. Dune stratigraphy contains evidence of episodic, fluvially controlled accretion, separated by two palaeosols. Channel fills and stone stringers suggest occasional alluvial and colluvial reworking. Infra-red stimulated luminescence dating of the aeolian sands shows that dune development occurred episodically during the African Humid Period (15–5 ka), probably in response to an increase in sediment supply from the Niger River. Soil development occurred during the relatively short-lived period of enhanced aridity associated with the Younger Dryas, driven by weakening of the southwesterly monsoon circulation. Climate-driven dune accretion and further soil development occurred during the Holocene period.