The regionally correlated and dated regolith-paleolandform sequence of Sub-Saharan West Africa offers a unique opportunity to constrain continental-scale regolith dynamics as the key part of the sediment routing system. In this study, a regolith mapping protocol is developed and applied at the scale of Southwestern Burkina Faso. Mapping combines field survey and remote sensing data to reconstruct the topography of the last pediplain that formed over West Africa in the Early and Mid-Miocene (24-11Ma). The nature and preservation pattern of the pediplain are controlled by the spatial variation of bedrock lithology and are partitioned among large drainage basins. Quantification of pediplain dissection and drainage growth allows definition of a cratonic background denudation rate of 2m/My and a minimum characteristic timescale of 20Ma for shield resurfacing. These results may be used to simulate minimum export fluxes of drainage basins of constrained size over geological timescales. Background cratonic denudation results in a clastic export flux of ~4t/km2/year, which is limited by low denudation efficiency of slope processes and correlatively high regolith storage capacity of tropical shields. These salient characteristics of shields' surface dynamics would tend to smooth the riverine export fluxes of shields through geological time.
Bibliographical noteFunding Information:
This work was funded by WAXI , the CNRS and the ANR TopoAfrica ( ANR-08-BLAN-572 0247–02 ). The manuscript benefited from the comments of R. Teeuw and an anonymous referee as well as from editorial suggestions by A. Plater. We thank M. Jessell, D. Rouby, L. Baratoux and D. Huyghe for discussions and support and A. Fofana for participation in the fieldwork. We acknowledge AMIRA International and the industry sponsors, including AusAid and the ARC Linkage Project LP110100667, for their support of the WAXI project (P934A) as well as the Geological Surveys/Departments of Mines in West Africa as sponsors in kind of WAXI.
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- Landform evolution processes
- Sediment routing system
- Source to sink