Dynamic subsidence, continental uplift and sedimentary deposition to West Africa’s passive margin

Abstract

The relationship between offshore subsidence, continental uplift and sedimentary deposition to passive margins is poorly understood. A history of dynamic subsidence, continental uplift and sedimentary deposition to West Africa’s passive margin was synthesised to produce a framework for predicting patterns of sedimentary flux to the Mauritanian basin. Stratigraphy was mapped using seismic/well data and Cretaceous–Recent sedimentary flux was calculated. Clastic sedimentary flux to the centre of the basin increased significantly during Neogene times and accelerated across the basin at ~ 5 Ma. The origins of the Mauritanian basin were explored by backstripping wells from the study area to calculate subsidence histories. Seismic, well, gravity, magmatic and tomographic information was used to show that < 0:8 km of rapid Neogene– Recent subsidence occurred due to the initiation of shallow mantle convection. Neogene–Recent mantle draw-down caused the creation of accommodation within the Mauritanian basin that was subsequently filled by clastic sediments delivered by rivers draining West Africa’s passive margin. The causes of increased Neogene–Recent sedimentary flux were explored by inverting 14700 African longitudinal river profiles using a calibrated stream–power model to calculate a history of continental uplift and to predict the pattern of sedimentary flux to the Mauritanian basin. Results are consistent with independent stratigraphic observations which indicate that from ~ 30 Ma–Recent, sedimentary flux to Africa’s major deltas increased and induced a change from dominantly carbonate to clastic deposition. This pattern of sedimentary flux is consistent with calculations of offshore sedimentary volumes made using seismic and well data. I suggest Neogene clastic flux to the Mauritanian margin was generated by denudation of the uplifting Fouta-Djallon topographic swell and Mauritinides fold-belt, which appears to have accelerated during the last ~ 5 Ma. Results suggest that mantle-driven convective continental uplift exerts an important control on the sedimentary budget to Africa’s passive margins.