Spatial variation of soil weathering processes in the tropical high reliefs of Cameroon (Central Africa)

Abstract

The objective of the present work was to characterize the morphological, geochemical and mineralogical features of soil with regard to weathering processes as a function of topography and spatial variation of climate in tropical high reliefs of Cameroon. Field investigations permit to select three study sites Mbalam, Meleta and Secande respectively in the humid tropical zone, pseudotropical mountainous zone and in the tropical dry climate. Macroscopically, the studied soils are thick in Mbalam, medium thick in Meleta and relatively less thick in Secande. Globally, saprolite, a loose loamy clayey horizon and humiferous horizon were observed from the bottom to the top of the profiles. These profiles differ by their thickness, the differentiation of the saprolite horizons and the presence of humiferous horizons. They are characterized microscopically by in situ replacement of primary minerals by kaolinite/halloysite, gibbsite and iron oxides. Theses minerals are associated to anatase in Mbalam and to montmorilonite and calcite in Secande. Geochemical processes involving in the spatial differentiation of soils are monosiallitisation and allitisation in the humid tropical zone, monosiallitisation and high allitisation in the pseudotropical mountainous zone with Al2O3 content reaching 41% in the saprolite, and monosiallitisation associated to bisiallitisation in the tropical dry climate of Cameroon. The development of these geochemical processes is conditioned by topography, elevation, rainfall and temperature, which appear as the main factors responsible of the spatial variation of soil weathering processes in the tropical high reliefs of Cameroon.

Keywords

• spatial variation
• weathering processes
• soil
• tropical high reliefs
• cameroon.