Morphological, physico-chemical and geochemical characterization of two weathering profiles developed on limestone from the Mintom Formation in the tropical humid zone of Cameroon. (July 2017)

• Record Type: Journal Article
• Authors: Engon, Thierry Constant; Abane, Monique Abessolo-Angue; Zo'o Zame, Philémon; Ekomane, Emile; Bekoa, Etienne; Mvogo, Kisito; Bitom, Dieudonné
• Is Part Of: Journal of African earth sciences. Volume 131(2017)
• Page Start: 198
• Page End: 212
• Publication Date: 2017-07
• Subjects: Geochemistry -- Mintom Formation -- Morphology -- Physico-chemical properties -- Weathering; Earth sciences -- Africa -- Periodicals; Earth sciences -- Middle East -- Periodicals; Geology -- Africa -- Periodicals; Geology -- Middle East -- Periodicals; Sciences de la terre -- Afrique -- Périodiques; Sciences de la terre -- Moyen-Orient -- Périodiques; Géologie -- Afrique -- Périodiques; Géologie -- Moyen-Orient -- Périodiques; Earth sciences; Geology; Africa; Middle East; Periodicals; Electronic journals; 556.05
• DOI: 10.1016/j.jafrearsci.2017.03.026
• Languages: English
• ISSNs: 1464-343X

Abstract

Abstract: The purpose of this work was to study the morphology, physico-chemistry and geochemistry of two weathering profiles developed on limestone using observations area, basic analysis, and X-ray Fluorescence. The results showed that these soils have three main sets from the bottom to the top: the alteritic set (isalteritic and alloteritic horizons), the glaebular set (exclusively on profile TCR) with a more or less hardened duricrust, and the loose set (loose clayey and humiferous horizons). The soils were acid, with moderate cation exchange capacity, low to moderate sum of bases (0.96–8.24 meq/100 g). The base saturation, organic carbon and C/N ratio (˂15) were low. The geochemical signatures of the bedrock along the whole profile are not preserved, with SiO2 (∼45.26 wt%) being the dominant oxide followed by Al2 O3 (∼13.37 wt%) and Fe2 O3 (∼09.36 wt%). Also, the Si/Al ratio is always higher than 1 (2.17–4.43). The other major oxides such as MgO, K2 O and Na2 O show negligible contents in the profiles, while CaO is well represented at the top of the isalteritic horizon reaching 14.25 wt%. Weathering indices show that CaO, MgO, Na2 O, and K2 O are rapidly lost during chemical weathering and the amount of these elements lost is proportional to the degree of weathering. Humid tropical soils show pedological evolution mainly dominated by the behaviour of silicon and aluminium, with an intensive release of carbonates during the early stage of weathering. However, contrary to soils in temperate climates, in which bisiallitisation is the predominant process, soils of the humid tropical zone, characterized by high evacuation of silica concomitantly to notable accumulations of aluminium, allitisation and monosiallitisation predominate. Highlights: The limestone soils of Mintom are thin and display three main sets. These soils are acid, with moderate cation exchange capacity and sum of bases. The base saturation, organic carbon and C/N ratio (˂15) were low. SiO2, Al2 O3 and Fe2 O3 are the dominant oxides. CaO, MgO, Na2 O and K2 O are rapidly lost during the early stage of weathering.