T160 Quantifying Geomorphic Processes and Rates of Landscape Evolution (Posters)

Monday, 23 October 2017
9:00 AM - 6:30 PM
Halls 4EF

AGE-EROSION CONSTRAINTS ON AN EARLY PLEISTOCENE PALEOSOL IN YUKON, CANADA, WITH PROFILES OF 10BE AND 26AL: EVIDENCE FOR A SIGNIFICANT LOESS COVER EFFECT ON COSMOGENIC NUCLIDE PRODUCTION RATES

Paper number: T160-5
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Wounded Moose paleosols developed on remnant deposits of Late Pliocene to Early Pleistocene [pre-Reid] Cordilleran Ice Sheet [CIS] glaciations in central Yukon, Canada. They are an important regional soil-geomorphic marker at the boundary between early CIS advances and the non-glaciated regions of Yukon and Alaska. Yet, at present, their age is poorly constrained between the Reid [0.2 Ma] and earliest [2.84 Ma] CIS advances. Here, we apply depth profiles of in situ-produced cosmogenic 26Al and 10Be to obtain a minimum exposure age [1.12 +0.44/-0.36 Ma, 2σ] and maximum surface erosion rate [1.1 +0.9/-0.5 m Myr-1] for this soil marker from a high-level glaciofluvial terrace near Dawson, Yukon. Our results show that this soil formed under exceptionally stable conditions [max erosion rate similar to polar bedrock erosion rates] and that it pre-dates the emergence of the 100 ka [eccentricity] climate cycle. Contrasting results from single- and joint-nuclide depth profile models reveals a significant discrepancy between calculated and effective 10Be and 26Al production rates [40-65% lower than expected values]. We interpret this difference as the result of intermittent loess cover [time-averaged depth between 60 and 110 cm] that significantly reduced apparent exposure ages obtained from the single–nuclide model. The observation of such a significant loess-cover effect on inferred cosmogenic nuclide production rates has implications for exposure dating in glacial and periglacial environments. A multi-nuclide sampling strategy is required to quantify this effect.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-304297

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