Shallow Mantle Convection Beneath West Africa, Solid Sedimentary Flux to the Mauritanian Basin and Continental Uplift Histories from Drainage Inversion

A complete history of post-rift solid sedimentary flux to the Mauritanian basin on the West African margin is calculated using well and seismic data. Seven Mesozoic to Recent isopachs are depth-converted using check-shot data. Compaction parameters at each well are calculated by minimizing misfit between observed and theoretical time-depth values by varying initial porosity and compaction wavelength. First and last occurrences of planktonic foraminifera, calcareous nannofossils and palynofossils are used to constrain age of stratigraphy. Solid sedimentary flux decreases steadily from 0.41_-0.18^+0.21 during the Cretaceous to 0.25_-0.17^+0.21 in the Paleocene and 0.16_-0.11^+0.18 x10³ km³Ma^-1 in the Eocene-Oligocene. Late Cretaceous subsidence due to salt tectonics is followed by tectonic quiescence until the Neogene.

We integrate seismic, well, gravity, magmatic and tomographic information to show that 0.4-0.8 km of rapid water-loaded subsidence occurs due to the initiation of shallow mantle convection and the of establishment of a 1/300 E-W bathymetrtic gradient between Cape Verde and the Mauritanian margin during the Neogene. Solid sedimentary flux increases significantly to 0.20_-0.10^+0.20 in the center of the basin during the Miocene and accelerates to 1.9_-1.4^+2.0 x10³ km³Ma^-1 across the basin during the last 5 Ma.

This history of sedimentary flux and facies change in the Mauritanian basin is similar to those observed at other African deltas. To investigate the sources of sedimentary flux, a continental database of 14700 longitudinal river profiles were inverted using a calibrated stream-power model to calculate a history of continental uplift. Our results are consistent with the notion that from 30 Ma to Recent, solid sedimentary flux to Africa's major deltas increased and induced a change from carbonate to clastic deposition. We suggest Neogene clastic flux to the Mauritanian margin was generated by denudation of the uplifting Atlas and Fouta-Djallon topographic swells from 25 Ma, which appears to have accelerated during the last 5 Ma. An increase in clastic sedimentary flux and concomitant change from carbonate to clastic offshore sedimentation is recorded at all major African deltas, which we suggest was generated by increased Neogene uplift rates at many of Africa's domal swells.