Denudation rates on cratonic landscapes: Comparison between suspended and dissolved fluxes, and 10Be analysis in the Nyong and Sanaga River basins, South Cameroon

Vincent Regard (1, 2, 3, 4, 5, 6) , Sébastien Carretier (1, 2, 3, 4, 5, 6) , Jean-Loup Boeglin (1, 2, 3, 4, 5, 6) , Jules-Rémy Ndam (7) , Jean-Guy Dzana (7) , Jean-Pierre Bedimo Bedimo (8) , Jean Riotte (1, 9, 2, 3, 4, 5, 6) , Jean-Jacques Braun (1, 8, 2, 3, 4, 5, 6)

1 GET - Géosciences Environnement Toulouse
2 IRD - Institut de Recherche pour le Développement
3 CNRS - Centre National de la Recherche Scientifique
4 UT3 - Université Toulouse III - Paul Sabatier
5 PRES Université de Toulouse
6 UT - Université de Toulouse
7 UY1 - Université de Yaoundé I
8 Centre de Recherche Hydrologique
9 Indo-French Cell for Water Sciences

South Cameroon is located in a tropical and tectonically quiescent region, with landscapes characterized by thick highly weathered regolith, indicative of the long term predominance of chemical weathering over erosion. Currently this region undergoes huge changes due to accelerated mutations related to a growing population and economical developments with associated needs and increasing pressures on land and natural resources. We analysed two of the main South Cameroon rivers: the Nyong River and Sanaga River. The Sanaga catchment undergoes a contrasted tropical climate from sub-humid mountainous and humid climate and is impacted by deforestation, agriculture, damming, mining and urbanization, especially in the Mbam sub-basin, draining the highly populated volcanic highlands. By contrast, the Nyong catchment, only under humid tropical climate, is preserved from anthropogenic disturbance with low population except in the region of Yaoundé (Méfou sub-basin). Moreover the Nyong basin is dam-free and less impacted by agriculture and logging. We explore both denudation temporal variability and the ratio between chemical and physical denudation through two catchment-averaged erosion and denudation datasets. The first one consists of an 11-year long gauging dataset, while the second one comes from cosmogenic radionuclides (CRN, here 10Be) from sand sampled in the river mainstreams (time scale of tens to hundreds of thousands of years). Modern fluxes estimated from gauging data range from 5 to 100 m/Ma (10 to 200 t/km2/yr); our calculations indicate that the usual relative contribution of chemical vs physical denudation is 60% and 40%, respectively, of the total denudation. 10Be denudation rates and sediment fluxes range from 4.8 to 40.3 m/Ma or 13 to 109 t/km2/yr, respectively, after correction for quartz enrichment. These fluxes are slightly less than the modern fluxes observed in Cameroon and other stable tropical areas. The highest 10Be-derived fluxes and the highest physical vs. chemical denudation ratios are attributed to anthropogenic impact.

Mots clés: Denudation rate; weathering; cosmogenic nuclides; Cameroon; craton

Domaines: Géomorphologie; Géochimie; Hydrologie

Vincent Regard, Sébastien Carretier, Jean-Loup Boeglin, Jules-Rémy Ndam, Jean-Guy Dzana, et al.. Denudation rates on cratonic landscapes: Comparison between suspended and dissolved fluxes, and 10Be analysis in the Nyong and Sanaga River basins, South Cameroon. 2016. ⟨hal-01286896⟩