Petrological Characterization of Pelites from the Mintom Basin and Their Weathering Mantle

Abstract

The aim of the present study is to characterize a weathering mantle developed on pelitic rock in the tropical forest region precisely in Mintom (South East Cameroun). This characterization include morphology, physico-chemical and mineralogic analyses. The region is characterize by a hot and wet climate consisting of four seasons of inequal length and intensity. The average temperature is about 24°C and the mean rainfall is about 1633mm/years. The rocks in the area consist of limestone, dolomites and pelites. Fieldwork consist of landscape analysis, geologic prospection and soil profile description. Mineralogical and physico-chemical was carried out on various samples in the laboratory. Morphological results show that the studied profile has a general brownish yellow aspect, with a thickness of about 6m and a silty-clayey texture. Five horizons can be distinguished from top to bottom: a humiferous horizon, a loose yellow set, a yellow horizon bearing quartz fragments and large indurated blocks, a saprolite consisting of a fine and coarse saprolite possessing some pelite relics of variable sizes and a deep red colour just like that of the parent rock. The parent rock is a massive pelite with a reddish colour when wet and a violet colour when dry. It has a powdery feel. Analytically, the soils have an acidic pH (4,0 to 4,2), a high organic matter content (4,8%), a C/N ratio of about 6,76, a cationic exchange capacity of 7,64meq/100g with a saturation rate S/T of about 7. Particle size distribution shows that the silty fraction is dominant (59%), followed by the clayey fraction (30%). The main minerals are kaolinite, quartz, smectites, calcites, dolomites, goethite and hematite.