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. The impact of glaciers on the Quaternary evolution of mountainouslandscapes remains controversial. Although in situ or bedrocklow-temperature thermochronology offers insights on past rock exhumation andlandscape erosion, the method also suffers from potential biases due to thedifficulty of sampling bedrock buried under glaciers. Detritalthermochronology attempts to overcome this issue by sampling sediments ate.g. the catchment outlet, a component of which may originate from beneaththe ice. However, detrital age distributions not only reflect the catchmentexhumation, but also spatially variable patterns and rates of surfaceerosion and sediment transport. In this study, we use a new version of aglacial landscape evolution model, iSOSIA, to address the effect of erosionand sediment transport by ice on the form of synthetic detrital agedistributions. Sediments are tracked as Lagrangian particles formed bybedrock erosion, and their transport is restricted to ice or hillslopeprocesses, neglecting subglacial hydrology, until they are deposited. Webase our model on the Tiedemann Glacier (British Columbia, Canada), whichhas simple morphological characteristics, such as a linear form and noconnectivity to large tributary glaciers. Synthetic detrital agedistributions are generated by specifying an erosion history, then samplingsediment particles at the frontal moraine of the modelled glacier. Results show that sediment sources, reflecting different processes such asglacier and hillslope erosion, can have distinct bedrock age distributionsignatures, and estimating such distributions should help to identifypredominant sources in the sampling site. However, discrepancies between the detrital and bedrock age distributions occur due to (i) the selective storage of a large proportion of sediments in small tributary glaciers and in lateral moraines, (ii) the large range of particle transport times due to varying transport lengths and strong variability of glacier ice velocity, (iii) the heterogeneous pattern of erosion, and (iv) the advectivenature of glacier sediment transport along ice streamlines. This last factor leads to a poor lateral mixing of particle detrital signatures inside the frontal moraine, and then local sampling of the frontal moraine is likely toreflect local sources upstream. Therefore, sampling randomly across themoraine is preferred for a more representative view of the catchment agedistribution. Finally, systematic comparisons between synthetic ( U - Th ) / He and fission track detrital ages, with different bedrock age-elevationprofiles and different relative age uncertainties, show that the nature ofthe age-elevation relationship and age uncertainties largely control theability to track sediment sources in the detrital record. However, depending on the erosion pattern spatially, qualitative first-order information may still be extracted from a thermochronological system with high uncertainties ( >30  %). Overall, our results demonstrate that detrital age distributions in glaciated catchments are strongly impacted not only by erosion and exhumation but also by sediment transport processes and their spatial variability. However, when combined with bedrock age distributions, detrital thermochronology offers a novel means to constrain the transport pattern and time of sediment particles.

earth surface dynamics

Modelling the effects of ice transport and sediment sources on the form of detrital thermochronological age probability distributions from glacial settings