Uplift histories and sedimentary flux at passive margins: Examples from Africa

It is generally accepted that topographic swells in Africa have grown in response to changing patterns of sub-crust support. Drainage patterns, magmatism, uplifted terraces and sediment efflux at its margins indicate that sub-crust and probably sub-plate support has varied during the last 30 million years. We measure the Cenozoic sedimentary flux to the northwest African passive margin using a dense grid of 2D and 3D reflection data and 43 wells. lsopachs of six Eocene-Recent horizons have been mapped and tied to well data. Depth converted and decompacted isopachs indicate that solid sedimentary flux has varied during Cenozoic times. We compare our measurements to flux predicted by inverting a dense onshore drainage network centered on the Senegal River. Calculated Neogene uplift is consistent with removal of deltaic top-sets observed in the reflection data on West Africa's continental shelf. We tentatively suggest that Cenozoic dynamic support has controlled the delivery of sediment to the western seaboard of North Africa.