Tropical chemical weathering of a garnet rich micaschist in the rainforest zone of Cameroon

Abstract

Soils developed on garnet-rich micaschist in the Southern Cameroon plateau wereinvestigated. Morphologically, two weathering materials constituted the study profile,fine earth and nodules. Each material has a singular evolution from the coarse saproliteto the upper set of clayey and loose horizons. There is Al2O3 enrichment in the fineearth concomitantly to Fe2O3, Na2O and K2O enrichment in nodules in major element–Al2O3 variation diagrams. A–CN–K and A–CNK–FM diagrams show a progressivedepletion of Al in nodules concomitantly to an enrichment of this element in the fineearth. Three pedogenetic processes emerge from the evolution of weathering products.There is a ferruginization process whose importance increases from the coarsesaprolite to the upper set of clayey and loose horizons, giving rise to the formation ofdense nodules composed of hematite, goethite and gibbsite. This ferruginization occursconcomitantly with a desaluminization process, which causes Al2O3 depletion innodules. These nodules are formed by the process of induration where the hydratedamorphous hydroxide and oxides are dehydrated to their crystalline oxide form, due tocondensation. In addition, there is aluminization, which occurs in the fine earth, leadingto the development of a red clayey material composed of kaolinite and gibbsite.