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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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Volume 6, issue 1
Earth Surf. Dynam., 6, 217-237, 2018
https://doi.org/10.5194/esurf-6-217-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Earth Surf. Dynam., 6, 217-237, 2018
https://doi.org/10.5194/esurf-6-217-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 21 Mar 2018

Research article | 21 Mar 2018

Colluvial deposits as a possible weathering reservoir in uplifting mountains

Sébastien Carretier1, Yves Goddéris1, Javier Martinez2, Martin Reich2,3, and Pierre Martinod1,2 Sébastien Carretier et al.
  • 1GET, Université de Toulouse, IRD, CNRS, UPS, (Toulouse), France
  • 2Department of Geology, FCFM, University of Chile, Santiago, Chile
  • 3Andean Geothermal Center of Excellence (CEGA), FCFM, University of Chile, Santiago, Chile

Abstract. The role of mountain uplift in the evolution of the global climate over geological times is controversial. At the heart of this debate is the capacity of rapid denudation to drive silicate weathering, which consumes CO2. Here we present the results of a 3-D model that couples erosion and weathering during mountain uplift, in which, for the first time, the weathered material is traced during its stochastic transport from the hillslopes to the mountain outlet. To explore the response of weathering fluxes to progressively cooler and drier climatic conditions, we run model simulations accounting for a decrease in temperature with or without modifications in the rainfall pattern based on a simple orographic model. At this stage, the model does not simulate the deep water circulation, the precipitation of secondary minerals, variations in the pH, below-ground pCO2, and the chemical affinity of the water in contact with minerals. Consequently, the predicted silicate weathering fluxes probably represent a maximum, although the predicted silicate weathering rates are within the range of silicate and total weathering rates estimated from field data. In all cases, the erosion rate increases during mountain uplift, which thins the regolith and produces a hump in the weathering rate evolution. This model thus predicts that the weathering outflux reaches a peak and then falls, consistent with predictions of previous 1-D models. By tracking the pathways of particles, the model can also consider how lateral river erosion drives mass wasting and the temporary storage of colluvial deposits on the valley sides. This reservoir is comprised of fresh material that has a residence time ranging from several years up to several thousand years. During this period, the weathering of colluvium appears to sustain the mountain weathering flux. The relative weathering contribution of colluvium depends on the area covered by regolith on the hillslopes. For mountains sparsely covered by regolith during cold periods, colluvium produces most of the simulated weathering flux for a large range of erosion parameters and precipitation rate patterns. In addition to other reservoirs such as deep fractured bedrock, colluvial deposits may help to maintain a substantial and constant weathering flux in rapidly uplifting mountains during cooling periods.

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The role of mountain uplift and associated silicate weathering in the global climate over geological times is controversial. Previous soil column models suggest that weathering falls at a high denudation rate. We present the results of a 3-D model that couples erosion and weathering, a CO2 consumer during mountain uplift. Our model suggests that the weathering of temporarily stocked colluvium may contribute significantly to the mountain weathering outflux at high denudation rates.
The role of mountain uplift and associated silicate weathering in the global climate over...
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