Morphotectonic of Regolith Landsurfaces in Cameroon (Central Africa): Weighting the Evidences of Late Cretaceous Uplift and Climatic Deep Weathering and Stripping
Résumé
In the last few decades, a range of regolith-related issues highlighted their usefulness on assessing landform dynamics for better understanding and quantifying earth surface processes. A model for the evolution of weathered landsurfaces in Cameroon is developed using available data on their morphology and petrogeochemical patterns, tectonic evidences, geophysical anomalies and sedimentological data. On deformed orogens, the model demonstrates the pivotal role of uplift, consequent volcanic cover and rheology-dependent gravitational collapses in inducing large scale compartmentalization. In areas of tectonic quiescence, it enhances a well known predominance of deep weathering and striping resulting in morphogenetic sequences similar to that of climate-dependent dynamics on the West African craton. These schemes in accordance with regional correlations allow assuming four regolith landsurfaces recognizable with their actual relicts and their specific petrogeochemical patterns. These are the high glacis, the widespread Intermediate ferricrete, the African bauxitic surface, and the modern bauxites developed on Neogene volcanics across the so-called Cameroon Volcanic Line. These findings provide a unique geomorphic record resulting in interplay between late Cretaceous epeirogeny, heterogeneity of uplifted basement, and climate variability. It stands as an input in understanding the dynamics of the complex geomorphic system of the African tropical belt, and specifically in Central Africa where no tectonic input were considered in old issues. It is also a basis for assessing denudation rates and their comparison with weathering-limited steady cratonic denudation of West Africa, and to investigate Cenozoic drainage rearrangement and stabilization as a consequence of uplift.