Ronald S. Sletten1, Daniel H. Mann2, William C. McIntosh3, Nelia W. Dunbar3, Mike Prentice4, Warren Dickinson5, and John O. Stone1. (1) Earth & Space Sciences, University of Washington, Johnson Room 70, Seattle, WA 98195-1310, (2) University of Alaska Fairbanks, Fairbanks, AK 99707, (3) Department of Earth and Environmental Sciences, New Mexico Tech, 801 Leroy Pl, Socorro, NM 87801, (4) Indiana Geological Survey, Bloomington, IN 47405, (5) Antarctic Research Center, Victoria University, Wellington, New Zealand
Debate continues whether Antarctica has been in a stable deep freeze since the Miocene or experienced major fluctuations in climate and glacier extent through the Pliocene. Volcanic ashes are key chronostratigraphic markers in the Dry Valleys, and there is now evidence that some of them have been reworked from older deposits. This evidence comes from three sources. First, we found blocks of glacially-transported ash in Beacon Valley. After disintegrating, these erratics leave localized deposits of relatively pure volcanic ash much older than the surfaces they overlie. Second, most surface-age estimates older than 2 Ma in the Dry Valleys are based on the eruption (Ar-Ar) ages of these reputed in situ tephras. In contrast, the majority of cosmogenic exposure ages are younger. Third, geomorphic and weathering processes are active today in Dry Valleys, indicating a younger landscape than Miocene age implied by the ancient tephra eruption ages.
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