Stabilization of large drainage basins over geological timescales : Cenozoic West Africa, hot spot swell growth and the Niger River

Abstract : Reconstructing the evolving geometry of large river catchments over geological timescales is crucial to constraining yields to sedimentary basins. In the case of Africa, it should further help deciphering the response of large cratonic sediment routing systems to Cenozoic growth of the basin-and-swell topography of the continent. Mapping of dated and regionally correlated lateritic paleolandscape remnants complemented by onshore sedimentological archives allows the reconstruction of two physiographic configurations of West Africa in the Paleogene. Those reconstructions show that the geometry of the drainage stabilized by the Late Early Oligocene (29 Ma) and probably by the end of the Eocene (34 Ma), allowing to effectively link the inland morphoclimatic record to offshore sedimentation since that time, particularly in the case of the Niger catchment – delta system. Mid-Eocene paleogeography reveals the antiquity of the Senegambia catchment back to at least 45 Ma and suggests that a marginal upwarp forming a continental divide preexisted Early Oligocene connection of the Niger and Volta catchments to the Equatorial Atlantic Ocean. Such a drainage rearrangement was primarily enhanced by the topographic growth of the Hoggar hot spot swell and caused a major stratigraphic turnover along the Equatorial margin of West Africa.