Old landscapes, pre-weathered materials, and pedogenesis in tropical Africa: How can the time factor of soil formation be assessed in these regions?
2015
Da Costa, Pauline Y.D. | Nguetnkam, Jean-Pierre | Mvoubou, Castane M. | Togbé, Kodjo A. | Ettien, Jean-Baptiste | Yao-Kouame, Albert
The present paper is an overview of tropical West Africa soils with the aim to compile soil characteristics and identify research gaps in respect to rates of soil forming processes. Compilation of morphological, mineralogical and chemical data on soil development has distinguished several types of soils. The major soils identified and described include ferrallitic soils, ferruginous tropical soils, vertisols, semi-arid tropical soils, and hydromorphic soils. Their formation and their evolution depend on climate and paleoclimate actions, parent materials, vegetation, and geomorphology. Most of these soils have been mapped using FAO, CPS classification, and Worldwide Reference Base (WRB).Some aspects of the pedogenesis process are also discussed. Three new methods of investigation used by researchers: Potassium–argon, gold mineralogy, and cosmogenic beryllium-10 allow dating chemical and weathering processes and also led to a quantification of geochemical and mechanical processes in this area. The modern climate has an impact on soils. All these types of soils are experiencing secondary pedogenic processes such as rejuvenation, and especially reworking to some extent by water or wind erosion, giving rise to younger soils. Rapid disturbance through reworking leads to induration and armouring.Soil dating data in this area are very scarce. Some approaches (e.g. mass balance, relative chronology, chronostratigraphic, archaeological, luminescence, paleobiological, radiocarbon, OSL, and termite activity) have been implemented to assess the time factors of soil formation. Finally, this work highlights some gaps about soil research, particularly the need to define soil parameters which can be related to soil age.
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