Glacial erosion and sediment dispersion from detrital cosmogenic nuclide analyses of till

Abstract

Field evidence based on sedimentology, geomorphology, and sediment provenance, supported by thermo-mechanical ice sheet model simulations, are used to classify the thermal regime of paleo-ice cover in northern central Baffin and evaluate the spatial and temporal variability of those conditions. A new means to identify paleo-glacier polythermal conditions from the measurement of terrestrial in situ cosmogenic nuclides (TCN) in till was developed to test the assertion that glacial erosion and till production are partially controlled by the thermal regime at the base of a glacier. Concentrations of cosmogenic 10Be and 26Al in 19 till samples from north central Baffin Island reflect the spatial pattern of areas classified as warm-based or cold-based (end member) systems. An ice sheet simulation of bed conditions produces the same pattern. The 26Al/ 10Be ratio is also used to confirm the long cold-based ice burial histories of surfaces that have not been significantly eroded. The data suggest that till and regolith near the current terminus of the Oliver Glacier preserve a record of >3 Ma of continuous glacial cover. In three localities resembling intermediate cases (i.e., where field observations yield conflicting interpretations of basal thermal regime), the TCN concentrations and 26Al/ 10Be reveal that the surface experienced a combination of cold-based ice burial and glacial erosion. When coupled with a high-resolution ice sheet model, the 10Be concentrations in till provide a more robust means of establishing the temporal and spatial variability in glacial erosion, and can be an important new tool for mineral exploration in glaciated terrain.