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High-resolution fluvial records of Holocene environmental changes in the Sahel: the Yame River at Ounjougou (Mali, West Africa)
Lespez L, Le Drezen Y, Garnier A, Rasse M, Eichhorn B, Ozainne S, Ballouche A, Neumann K, Huysecom E
Type of Publication:
Reviewed Journal Article
Quaternary Science Reviews, 2011, V30, N5-6, MAR, pp 737-756 DOI: http://dx.doi.org/10.1016/j.quascirev.2010.12.021.
The Yame river, in the Bandiagara Plateau, Dogon Country, Mali, is characterised by extensive alluvial sedimentary records, particularly in the 1 km long Ounjougou reach where Holocene floodplain pockets are inset in the Pleistocene formations. These alluvial records have been investigated via geomorphologic fieldwork and sedimentologic and micromorphologic analyses and are supported by 79 radiocarbon dates. The alluvial deposits of the valley floor correspond to a vertical accretion of 3-10 m. The reconstruction of fluvial style changes provides evidence of four main aggradation periods. From 11,500 to 8760 cal. BP, the alluvial architecture and grain-size parameters indicate a wandering river. This period included phases of pulsed high-energy floods and avulsion related to a northward shift of the summer monsoon to around 14 degrees N after 11,500 cal. BP. From 7800 to 5300 cal. BP, a swampy floodplain environment with standing water pools within a Sudanian savanna/woodland mosaic corresponds to the culmination of the Holocene humid period. From 3800 cal. BP onwards, rhythmic sedimentation attests to an increase in the duration and/or intensity of the dry season, giving a precise date for the local termination of the Holocene Optimum period. During the last two millennia and for the first time during the Holocene, the alluvial formations are progressively restricted whereas the colluvial deposits increase, indicating strong soil erosion and redeposition within the watershed related to an increase in human impact. Four major periods are characterised by incision (I1: ante 11,500, I2: 8760-7800; I3: 6790-6500 cal. BP; I4; 2400-1700 cal. BP) pointing to dramatic changes in fluvial style. They result from high-energy flood flows during dry spells and confirm the capacity of the floodplain pocket in the upstream reach of the Sahelian belt to record rapid Holocene climatic change.
2 Past Global Change
Paleontology , Hydrology , Geology , Plant Sciences , Geomorphology
late quaternary climate; last glacial maximum; late pleistocene; northeast nigeria; vegetation history; jikariya lake; mid holocene; chad basin; nw africa; pollen
fluvial archives; fluvial system; climatic change; human impact; holocene; sahel; africa
L Lespez, Univ Caen Basse Normandie, Geophen CNRS Umr Letg 6554, Bp 5186, F 14032 Caen, France ; Research Addresses: L ; Lespez, A ; Garnier: Univ Caen Basse Normandie, Geophen CNRS Umr Letg 6554, F 14032 Caen, France; Y ; Le Drezen: Univ Paris 01, CNRS, Prodig Umr 8586, F 75005 Paris, France; M ; Rasse: Univ Rouen, Ledra CNRS Umr Idees 6228, F 76821 Mont St Aignan, France; B ; Eichhorn, K ; Neumann: GoETHe Univ Frankfurt, Inst Archaeol Sci, D 60323 Frankfurt, Germany; S ; Ozainne, E ; Huysecom: Univ Geneva, Dept Anthropol, CH 1211 Geneva, Switzerland; A ; Ballouche: Univ Angers, Leesa Equam, Ufr Sci, F 49045 Angers, France ; Email: Laurent.firstname.lastname@example.org
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