EGU General Assembly 2021
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Delayed sedimentary grains

Sebastien Carretier1, Laure Guerit2, Rebekah Harries3, Vincent Regard1, Pierre Maffre4, Stéphane Bonnet1, Sandrine Choy1, and Marcelo Farías5
Sebastien Carretier et al.
  • 1GET, Université de Toulouse, IRD, UPS, CNRS, Toulouse, France (
  • 2Géosciences Rennes, University of Rennes, CNRS, UMR 6118, France
  • 3Research Center for Integrated Disaster Risk Management (CIGIDEN), PUC, Santiago, Chile
  • 4Department of Earth and Planetary Science, University of California, Berkeley, United States of America
  • 5Departamento de Geología, Universidad de Chile, Santiago, Chile

River sediment grains are transported and stored episodically in different reservoirs (terraces, alluvial fans, foreland basin, etc.). The residence time of sediment grains in each reservoir has important implications for the paleo-environmental interpretation established from these grains, and their stratigraphic record, as well as for soil contamination, when these grains come from contaminated sources. The recycling of old sediments, via erosion of an old reservoir (e.g. foreland basin erosion), is a known problem. What is less well recognised is that the recycling of a minority of very old grains can strongly bias the average residence time of a grain population deposited in a stratum. In this case, the time-dependent paleo-environmental properties of a population of grains, such as the degree of weathering, or the concentration of cosmogenic isotopes, can then be biased. Several lines of evidence for this phenomenon, inherent to fluvial transport processes, have emerged, though reconstructing the residence time distribution of a grain population over long times (>>ka) remains a challenge. Using a landscape evolution model coupled with grain transport, we show that at the scale of a piedmont, grains can remain several hundred ka before being evacuated. At the scale of a river in Northern Chile, we used the concentration of 10Be in individual pebbles to show that some pebbles remain stored for several tens of ka before being evacuated to the river outlet. In addition, the distribution of residence times can also provide information on the nature of the diffusive processes that control the fluxes of exported sediment. These results suggest that the characterisation of grain-by-grain properties in a grain population can not only help to avoid possible interpretation biases but also provide constraints for models of long-term fluvial sediment outfluxes.  

How to cite: Carretier, S., Guerit, L., Harries, R., Regard, V., Maffre, P., Bonnet, S., Choy, S., and Farías, M.: Delayed sedimentary grains, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5200,, 2021.


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