UNEXPECTEDLY RAPID SEDIMENT EROSION IN ARENA VALLEY, ANTARCTICA

The Dry Valleys of Antarctica have proven to be a critical location for understanding past ice sheet dynamics, landscape stability and climate history. The geologic history is generally based on dating, mapping, stratigraphy of sediments, and in situ volcanic ashes. Existing cosmogenic-nuclide surface exposure ages from many parts of the Dry Valleys are in general younger than the age of surface deposits inferred from stratigraphic relations, presumably due to some combination of surface erosion or past ice cover, both of which would serve to reduce the apparent exposure age. Here we report both measurements of multiple cosmogenic nuclides from the exposed surface, which help to detect potential long periods of past ice cover, and measurements of the changes in nuclide concentration with depth below the surface of the deposit, which help to understand rates of soil mixing, soil transport, and soil erosion. Beryllium-10 and Aluminium-26 measurements from the surface of a landslide deposit that contains 11.3 Ma volcanic ash yield an apparent exposure age of only 0.4 Ma. However, measurements of the subsurface nuclide concentrations, show that the age of the ash does not conflict with the apparent exposure age when erosion of the deposit (ca. 2 m/Ma) since deposition is taken into account. This finding allows us to shed light on the apparent conflict between the stratigraphic evidence for great antiquity of the landscape and the relatively young apparent exposure ages for some surfaces, as well as to better understand rates of erosion, sediment transport, and landscape evolution.