Evolution of the Edea‐Eseka geomorphic units: A 'natural laboratory' of a prototype active rifting cross‐cutting the Southern Cameroon (West African) passive margin

Abstract

The SW Cameroonian passive margin, a part of the Cameroon Low-Plateau, presents several topographic levels cross-cut by the Sanaga Fault (SF), Benue Triple Junction and Cameroon Volcanic Line (CVL), three pre-and syn-rift tectonic features that are still active. This study carried out on the Edea-Eseka Region (EER) a portion of this margin (3 30 0 -4 N, 10 -10 55 0 E) aims to constrain the relationships between these features and the development of the morphology. Geomorphic indices, combined with field observations and supported by literature data show that the interactive activity of these structures constitutes the main force that controls the EER morphology. From West to East, EER consists of three morphotectonic units: the Coastal, Intermediate and Upper units. The Coastal unit built on the Douala-Kribi/Campo Basin (<65 Ma) and assigned to the Aptian South Atlantic rifting, exhibits low reliefs deeply incised. The Intermediate and Upper units are developed on the Nyong and Oubanguide crystallophyllian complexes during the Eburnean/Trans-Amazonian (2,400-1,750 Ma) and Pan-African (650-540 Ma) orogenies, respectively. The Intermediate unit with moderate reliefs registers a strong differential erosion, whilst the Upper unit records high-reliefs. Geomorphic indices, tectonic and recent seismic data reveal that the EER has been rejuvenated, experienced uplifts and tiltings synchronously with the main active phases of these features. The timing and magnitude of these activities vary from one unit to another. The morphotectonic model is consistent to the crucial tectonic phases: emplacement of SF (Palaeozoic), the breakup of Gondwana and erection of CVL (Cretaceous).