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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 | Copyright
Earth Surf. Dynam., 6, 121-140, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 05 Mar 2018

Research article | 05 Mar 2018

U–Th and 10Be constraints on sediment recycling in proglacial settings, Lago Buenos Aires, Patagonia

Antoine Cogez1, Frédéric Herman1, Éric Pelt2, Thierry Reuschlé3, Gilles Morvan2, Christopher M. Darvill4, Kevin P. Norton5, Marcus Christl6, Lena Märki1, and François Chabaux2 Antoine Cogez et al.
  • 1University of Lausanne, Institut des Dynamiques de la Surface Terrestre, Quartier Unil-Mouline, Bâtiment Geopolis, 1015 Lausanne, Switzerland
  • 2University of Strabourg, Laboratoire d'Hydrologie et de Géochimie de Strasbourg, Strasbourg, France
  • 3University of Strabourg, Institut de Physique du Globe de Strasbourg, Strasbourg, France
  • 4Geography Program and Natural Resources and Environmental Studies Institute, University of Northern British Columbia, 3333 University Way, Prince George, BC, V2N 4Z9, Canada
  • 5Victoria Univeristy of Wellington, School of Geography, Environment, and Earth Sciences, Wellington, New Zealand
  • 6Swiss Federal Institute of Zürich, Ion Beam Physics Laboratory, Zürich, Switzerland

Abstract. The estimation of sediment transfer times remains a challenge to our understanding of sediment budgets and the relationships between erosion and climate. Uranium (U) and thorium (Th) isotope disequilibria offer a means of more robustly constraining sediment transfer times. Here, we present new uranium and thorium disequilibrium data for a series of nested moraines around Lago Buenos Aires in Argentine Patagonia. The glacial chronology for the area is constrained using in situ cosmogenic 10Be analysis of glacial outwash. Sediment transfer times within the periglacial domain were estimated by comparing the deposition ages of moraines to the theoretical age of sediment production, i.e., the comminution age inferred from U disequilibrium data and recoil loss factor estimates. Our data show first that the classical comminution age approach must include weathering processes accounted for by measuring Th disequilibrium. Second, our combined data suggest that the pre-deposition history of the moraine sediments is not negligible, as evidenced by the large disequilibrium of the youngest moraines despite the equilibrium of the corresponding glacial flour. Monte Carlo simulations suggest that weathering was more intense before the deposition of the moraines and that the transfer time of the fine sediments to the moraines was on the order of 100–200kyr. Long transfer times could result from a combination of long sediment residence times in the proglacial lake (recurrence time of a glacial cycle) and the remobilization of sediments from moraines deposited during previous glacial cycles. 10Be data suggest that some glacial cycles are absent from the preserved moraine record (seemingly every second cycle), supporting a model of reworking moraines and/or fluctuations in the extent of glacial advances. The chronological pattern is consistent with the U–Th disequilibrium data and the 100–200kyr transfer time. This long transfer time raises the question of the proportion of freshly eroded sediments that escape (or not) the proglacial environments during glacial periods.

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Short summary
Sediments produced by glaciers are transported by rivers and wind toward the ocean. During their journey, these sediments are weathered, and we know that this has an impact on climate. One key factor is time, but the duration of this journey is largely unknown. We were able to measure the average time that sediment spends only in the glacial area. This time is 100–200 kyr, which is long and allows a lot of processes to act on sediments during their journey.
Sediments produced by glaciers are transported by rivers and wind toward the ocean. During their...