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U-Th and <sup>10</sup>Be constraints on sediment recycling in proglacial settings, Lago Buenos Aires, Patagonia
Darvill, Christopher M.
Norton, Kevin P.
- Other Publication
Rights / licenseIn Copyright - Non-Commercial Use Permitted
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 5 Patagonia, as well as a refined glacial chronology for the area using in situ cosmogenic 10Be analysis from corresponding 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 10 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 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 100-200 ka. Long transfer times could result from a combination of long sediment residence times in the proglacial lake (recurrence time of a glacial cyle) and the remobilization of 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 5 the 100-200 ka 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 Show more
Journal / seriesEarth Surface Dynamics Discussions
Organisational unit08619 - Labor für Ionenstrahlphysik (LIP)
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