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

• The Ogooué River catchment is denuding at a low rate (38 t/km 2 /a, 15 m/Ma) • There is substantial chemical denudation: > 30 % of the total denudation. • Batéké Px not producing solutes because constituted by already weathered material. • The southern part of the catchment is denuding twice as fast as the northern part. • Landscape seems close to equilibrium: chemical proportional to physical denudation. We measured the long-term physical denudation of the Ogooué River catchment using 10 Be 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/km 2 /a, 15 m/Ma), slightly higher than in Equatorial West Africa (from Senegal to Angola, 26 t/km 2 /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/km 2 /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/km 2 /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”.

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Journal
Gondwana Research
Published
2024-11-08
DOI
https://doi.org/10.1016/j.gr.2024.10.013
Citations
2
Primary Topic
Soil erosion and sediment transport
Type
article
Field-Weighted Citation Impact
0.67

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article

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

Yoann Dénèle, Auguste Paulin Mbonda, Michel Séranne, Julien Charreau et al.
2 citations
Gondwana Research
Soil erosion and sediment transport
0.67
article

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

Yoann Dénèle, Auguste Paulin Mbonda, Michel Séranne, Julien Charreau, Jean‐Sébastien Moquet, Vincent Regard, Jérôme Gaillardet, Sandrine Choy, Sakaros Bogning, Sébastien Carretier, Pierre‐Henri Blard, Delphine Rouby, Julien Bouchez, Jean‐Jacques Braun, Emmanuel Mambela, Marie Claire Paiz
article en
2 citations

Abstract

• The Ogooué River catchment is denuding at a low rate (38 t/km 2 /a, 15 m/Ma) • There is substantial chemical denudation: > 30 % of the total denudation. • Batéké Px not producing solutes because constituted by already weathered material. • The southern part of the catchment is denuding twice as fast as the northern part. • Landscape seems close to equilibrium: chemical proportional to physical denudation. We measured the long-term physical denudation of the Ogooué River catchment using 10 Be 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/km 2 /a, 15 m/Ma), slightly higher than in Equatorial West Africa (from Senegal to Angola, 26 t/km 2 /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/km 2 /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/km 2 /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”.

Gondwana ResearchVol. 138
Université d'Orléans (FR), The Nature Conservancy (US), Centre National de la Recherche Scientifique (FR), Université Libre de Bruxelles (BE), Université de Yaoundé I (CM), Université Toulouse III - Paul Sabatier (FR), Institut de physique du globe de Paris (FR), University of Douala (CM), Université Fédérale de Toulouse Midi-Pyrénées (FR), Université de Montpellier (FR), Université Paris Cité (FR), Centre de Recherches Pétrographiques et Géochimiques (FR), Géosciences Montpellier (FR), Institut de Recherches Géologiques et Minières (CM), Observatoire Midi-Pyrénées (FR), National Agency for National Parks (GA), Institut National des Sciences de l'Univers (FR), Bureau de Recherches Géologiques et Minières (FR), Géosciences Environnement Toulouse (FR), Institut de Recherche pour le Développement (FR), Institut des Sciences de la Terre d'Orléans (FR), Université de Lorraine (FR)
Institut de Recherche pour le Développement, Strong, Agence Nationale de la Recherche, Centre International de Recherches Médicales de Franceville, Centre National de la Recherche Scientifique, Bureau de Recherches Géologiques et Minières, Agence Nationale Des Parcs Nationaux
Climate action
Openalex Percentile: Top 26%
Soil erosion and sediment transport
0.67
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