Post-orogenic transients and relict landforms of the Bafoussam – Mamfe region (West-Cameroon Highland margin)

The Bafoussam-Mamfe Region (BMR) belongs to the Western Cameroon Highland margin, an amalgam of transient landscape that evolved from the interactions between tectonics, lithology and climate forcings. This area is tectonically active and shows differential tectonic uplift, contrasting relief, variations in erosion rates, in river incision, and in channel gradient. In order to appraise the BMR tectono-geomorphic evolution, it is essential to understand relationships between internal and external processes and their geomorphic expression at a river basin scale. For this purpose, we use drainage texture (Dt), stream frequency (Fs), drainage density (Dd), asymmetry factor (AF), the transverse topographic symmetry factor (TTSF), the mean of mountain front sinuosity per unit (Smf), concavity factor (Cf), hypsometry integral (HI) and stream-length gradient index (SL-index) based on 30 m Digital Elevation Models (DEM) and field survey. The results reveal considerable variations in geology, relief, topography and geomorphic indices values differentiated into three geomorphic units; the Mamfe unit developed on the Mamfe Cretaceous basin, the Nguti and Bafoussam high plateau units build up on the Precambrian granito-gneissic basement overlaid by a volcanic cover. The stepped (longitudinal and normalized) river profiles and complex hypsometric curves show the lithostructural control of the hydrographic network. Dt (from ~1.21 to ~4.59), Fs (from ~0.26 to ~1.91), Dd (from ~0.66 to ~1.71) geomorphic indice values indicate a part of lithologic control on this morphology while the AF (from ~1.16 to ~24.91), TTSF (from ~0.20 to ~0.71), Smf (U2 = 1.11 and U3 = 1.19), Cf (from ~-20.91 to ~78.93), HI (from ~0.12 to ~0.52) and SL-index designate the active tectonics as the main factor that had controlled the morphology of this same area. Above results pinpoint the combined post-Pan-African to Recent tectonic features, lithologic heterogeneities and the differential erosion processes as main factors that have controlled the BMR landscape. These results highlight how the Central African surface and the West African passive margin evolved since Proterozoic time.