PRODUCTION AND PRESERVATION OF SUBLIMATION TILL DETERMINED WITH 26AL AND 10BE, ONG VALLEY, ANTARCTICA

Ong Valley is an ice free valley in the Central Transantarctic Mountains that contains buried glacier ice, derived from past flow of the adjacent Argosy Glacier into the valley, covered by sublimation till and other glacial deposits. The present valley floor is covered with patterned ground and displays three distinct glacial deposits, two of which are currently underlain by stagnant glacier ice, that record repeated advance, stagnation, and retreat of the Argosy Glacier.

Here we describe measurements of cosmogenic ¹⁰Be and ²⁶Al in samples collected every ~10 cm in 1-meter-deep vertical transects through these three tills. In the younger two tills, these transects reach the surface of the buried ice. In general, cosmogenic-nuclide concentrations in these transects should reflect i) the age of the till, ii) the rate of formation of the till by sublimation of underlying ice, and iii) the rate of surface erosion of the till. Given a relatively young till unit, nuclide concentrations are primarily a function of till age. Over time, nuclide concentrations tend towards an equilibrium with erosion and sublimation rates; thus, nuclide concentrations in older tills primarily provide information about these rates and only weak constraints on till age.

¹⁰Be and ²⁶Al measurements in Ong Valley are consistent with a model in which tills are derived from sublimation of underlying ice. Nuclide concentrations in the two oldest tills are best explained by sublimation rates on the order of tens of meters per million years and surface erosion rates on the order of meters per million years. Nuclide concentrations provide only minimum limits on the emplacement age of the oldest tills of ~1 Mya. Nuclide concentrations in the youngest till are much lower and provide an estimate of the emplacement age of this till at ~8 kya.