TRACKING NON-EROSIVE, ALPINE GLACIAL EXPANSION IN THE DRY VALLEYS, ANTARCTICA WITH IN SITU-PRODUCED 14C AND 10BE

Desert pavements are ubiquitous throughout high elevation, inland locations in the McMurdo Dry Valleys, Victoria Land, Antarctica. The preservation of desert pavements underlying moraine boulders near Mt. Olympus, Wright Valley (~60 km inland, 1360 masl) indicates little to no post-formational reworking and thus overriding glacial ice temperature remained below the pressure melting point and protected, rather than obliterated, desert pavement topography. To date the formation of Mt. Olympus desert pavements, a suite of 41 surficial and shallowly buried desert pavement samples (sandstone and quartzite pebbles) and four overlying boulder samples were collected from two successive glacial moraines for in situ–produced carbon-14 (¹⁴C) and beryllium-10 (¹⁰Be) exposure dating. The ¹⁴C-¹⁰Be pair is chosen because of its ability to track glacial advance and retreat throughout the Holocene and late Pleistocene. Desert pavements were sampled directly below overlying boulders and on the surface adjacent to the boulders to discern the time between desert pavement formation and boulder deposition.

Assuming an erosion rate of 1 m/Myr, [¹⁰Be] measurements made on two boulders on the outer moraine indicate maximum exposure ages of ~32.2 ± 3.0 ky and ~43.4 ± 4.0 ky. Inner moraine boulders register maximum exposure ages of ~10.3 ± 0.9 ky and ~42.0 ± 3.9 ky; the age of the latter of the two boulders may reflect the previous ice front advance. At a single location on the inner moraine, desert pavement pebbles collected from beneath a boulder (max exposure age ≈ 32.2 ky) do not statistically differ from those collected adjacent to the boulder. Preliminary [¹⁰Be] measurements of all pebbles (n=15) range 1.76 ± 0.369 to 3.71 ± 0.049 x 10⁷ atoms/g and indicate a maximum exposure age range of ~225-308 ky. Desert pavement pebbles yield an average erosion rate of 2.06 m/Myr, an order of magnitude lower than boulder erosion rates which range from a maximum of 46.27 m/Myr on the inner moraine to a minimum of 11.53 m/Myr on the outer moraine. The ¹⁴C-¹⁰Be paired results will be treated with Goehring et al.'s (2013) Bayesian isochron technique to better constrain desert pavement age formation and decipher the time between desert pavement formation and boulder deposition, which ¹⁰Be cannot do alone.