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Contrasting physical erosion rates in cratonic catchments: The Ogooué and Mbei rivers, Western Central Africa

Published Article

Africa

Publication date: November 24, 2024

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Using in situ 10Be, this study quantifies long‑term physical denudation across the Ogooué River catchment, averaging 38 t/km²/yr over 25–200 kyr. Denudation varies widely (10–60 t/km²/yr), with the southern basin eroding nearly twice as fast as the north, consistent with uplift from the African superswell. Chemical weathering contributes over 30% of total denudation, and long‑term patterns align with modern solute‑flux studies. Results show that erosion dynamics have remained stable for ~100 kyr, offering new insight into landscape evolution in Central Africa.

Subject Tags

  • Rivers
  • Soils

Abstract

We measured the long-term physical denudation of the Ogooué River catchment using 10Be produced in situ by cosmic rays. These measurements are averaged over 25–200 ka (average 40 ka), depending on the physical denudation rate. The denudation rate of the Ogooué River catchment is slow (38 t/km2/a, 15 m/Ma), slightly higher than in Equatorial West Africa (from Senegal to Angola, 26 t/km2/a, 10 m/Ma). Physical denudation and chemical weathering fall within the same order of magnitude. Thus, although low, there is substantial chemical weathering compared to physical denudation, that likely contributes over 30% of the total denudation.

Denudation rates are spatially variable (from 10 to 60 t/km2/a) within the large Ogooué River catchment. Over the long term, physical denudation and chemical weathering roughly match, except in the Batéké Plateaux area, because the plateaus are made up of already weathered detrital material and therefore their modern flux of solutes is very low (∼9.5 t/km2/a). The spatial distribution is similar to the one described in the work of Moquet et al. (2021) on the basis of solute fluxes, i.e. the southern part of the catchment is denuding twice as fast as the northern part. We show here that the whole picture did not vary much since 100 ka, as shown by both methods which give consistent results. Faster denudation in the southern part of the catchment may be related to more uplift than in the northern part caused by the southern African “superswell.”

Citation

Regard, V., Carretier, S., Moquet, J. S., Choy, S., Blard, P. H., Bogning, S., ... & Denèle, Y. (2025). Contrasting physical erosion rates in cratonic catchments: the Ogooué and Mbei rivers, Western Central Africa. Gondwana Research, 138, 192-209. https://doi.org/10.1016/j.gr.2024.10.013

TNC Authors