Pedo-sedimentary constituents as paleoenvironmental proxies in the Sudano-Sahelian belt during the Late Quaternary (southwestern Chad Basin)

QUATERNARY SCIENCE REVIEWS

卷:191

Article

Diaz, Nathalie^1,2  Dietrich, Fabienne¹  Sebag, David^1,3,4  King, Georgina E.^1,5,6  Valla, Pierre G.^1,5,6  Durand, Alain³  Garcin, Yannick⁷  de Saulie, Geoffroy⁸  Deschamps, Pierre⁹  Herman, Frederic¹  Verrecchia, Eric P.¹ 

[1] Univ Lausanne, Fac Geosci & Environm, Inst Earth Surface Dynam, Geopolis, CH-1015 Lausanne, Switzerland

[2] Royal Holloway Univ London, Dept Geog, Egham TW20 0EX, Surrey, England

[3] Normandie Univ, UNIROUEN, UNICAEN, CNRS,M2C, F-76000 Rouen, France

[4] Univ Montpellier, HSM, IRD, CNRS, Montpellier, France

[5] Univ Bern, Inst Geol Sci, Bern, Switzerland

[6] Univ Bern, Oeschger Ctr Climate Change, Bern, Switzerland

[7] Univ Potsdam, Inst Earth & Environm Sci, D-14476 Potsdam, Germany

[8] IRD, UMR PALOC, F-75005 Paris, France

[9] Aix Marseille Univ, CNRS, IRD, CEREGE, F-13284 Marseille, France

关键词: Pedogenic carbonate nodules;    Vertisol genesis;    Soil water balance;    Optical methods;    Radiogenic isotopes;    Quaternary;    Monsoon;    Western Africa;   

DOI  :  10.1016/j.quascirev.2018.05.022

来源: Elsevier

【 摘 要 】

Climate and environmental changes since the Last Glacial Maximum in the tropical zone of West Africa are usually inferred from marine and continental records. In this study, the potential of carbonate pedo-sedimentary geosystems, i.e. Vertisol relics, to record paleoenvironmental changes in the southwestern part of Chad Basin are investigated. A multi-dating approach was applied on different pedogenic organo-mineral constituents. Optically stimulated luminescence (OSL) dating was performed on the soil K-rich feldspars and was combined with radiocarbon dating on both the inorganic (C-14(inorg)) and organic carbon (C-14(org)) soil fractions. Three main pedo-sedimentary processes were assessed over the last 20 ka BP: 1) the soil parent material deposition, from 18 ka to 12 ka BP (OSL), 2) the soil organic matter integration, from 11 cal ka to 8 cal ka BP (C-14(org)), and 3) the pedogenic carbonate nodule precipitation, from 7 cal ka to 5 cal ka BP (C-14(inorg)). These processes correlate well with the Chad Basin stratigraphy and West African records and are shown to be related to significant changes in the soil water balance responding to the evolution of continental hydrology during the Late Quaternary. The last phase affecting the Vertisol relics is the increase of erosion, which is hypothesized to be due to a decrease of the vegetation cover triggered by (i) the onset of drier conditions, possibly strengthened by (ii) anthropogenic pressure. Archaeological data from Far North Cameroon and northern Nigeria, as well as sedimentation times in Lake Tilla (northeastern Nigeria), were used to test these relationships. The increase of erosion is suggested to possibly occur between c. 3 cal ka and 1 cal ka BP. Finally, satellite images revealed similar geosystems all along the Sudano-Sahelian belt, and initial C-14(inorg) ages of the samples collected in four sites gave similar ages to those reported in this study. Consequently, the carbonate pedo-sedimentary geosystems are valuable continental paleoenvironmental archives and soil water balance proxies of the semiarid tropics of West Africa. (C) 2018 Elsevier Ltd. All rights reserved.

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