Quaternary Science Reviews 22 (2003) 1059–1065 The timing of climbing dune formation in southwestern Niger: ﬂuvio-aeolian interactions and the r # ole of sand supply Helen M. Rendell a, *, Mich " ele L. Clarke b , Andrew Warren c , Adrian Chappell d a Department of Geography, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK b School of Geography, University of Nottingham, University Park, Nottingham, NG7 2RD, UK c Department of Geography, University College London, 26 Bedford Way, London WC1H 0AP, UK d School of Environment & Life Sciences, University of Salford, Salford, M5 4WT UK 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. r 2003 Elsevier Science Ltd. All rights reserved. 1. Introduction The Late Glacial and Holocene palaeoclimatic record of Africa inferred from the analysis of lake levels and lake cores, and supported by evidence from deep-sea cores from the continental margins, is characterised by the alternation of arid and humid phases reﬂecting changes in monsoon strength and penetration. This record is one of abrupt rather than gradual change (Street-Perrott and Perrott, 1990; Gasse, 2000), with the transition between humid and arid conditions occurring over time periods as short as several centuries (deMe- nocal et al., 2000). Actual records of environmental change from the Sahelian region of West Africa are sparse and mostly derived from the analysis of lake cores in Ghana, Nigeria, Chad and Mali (Talbot and Johannessen, 1992; Gasse, 2000), supplemented by data from deep-sea cores off the Mauritanian coast of West Africa (deMenocal et al, 2000) and the Niger delta (Pastouret et al., 1978; Zabel et al., 2001). This paper focuses on the record of sand dune development in southwestern Niger where the southern bank of the Niger River is ﬂanked by climbing dunes that partly cover a series of river terraces (Dubois et al., 1984; Bergoing and Gilliard, 1997). These dunes lie near the southern limit of Sahelian ﬁxed dunes (Talbot, 1984), in a climatically sensitive zone where the strength of Hadley Cell circulation determines seasonal move- ments of the Intertropical Convergence Zone (ITCZ), inﬂuencing the patterns of monsoonal rainfall, wind- speeds and dominant wind directions (Gasse, 2000). The interpretation of the palaeoclimatic signiﬁcance of dune building episodes is based on developing an under- standing of how the controlling factors of sand supply, windspeed and vegetation cover have interacted at local and regional levels. 2. Site description Karey Gorou village (N13  34 0 , E02  05 0 ) lies immedi- ately to the south of the Niger River and to the west of Niamey (Fig. 1). Climbing dunes can be clearly seen, banked up against a low ferricrete plateau that has been *Corresponding author. E-mail address: h.m.rendell@lboro.ac.uk (H.M. Rendell). 0277-3791/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0277-3791(03)00026-X