A Glacial History of Roberts Massif, Central Transantarctic Mountains, Antarctica, Using Cosmogenic 3He, 10Be, and 21Ne Surface Exposure Ages
Ice-free areas at high elevation in the central Transantarctic Mountains preserve moraines and drift deposits that delineate the former thickness and extent of the East Antarctic Ice Sheet (EAIS); cosmogenic exposure ages on these features indicate when the ice sheet was as or more extensive than to...
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| Format: | Text |
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DigitalCommons@UMaine
2018
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| Online Access: | https://digitalcommons.library.umaine.edu/etd/2941 https://digitalcommons.library.umaine.edu/context/etd/article/3951/viewcontent/Balter__Alexandra_Final_1.11.19.pdf |
| Summary: | Ice-free areas at high elevation in the central Transantarctic Mountains preserve moraines and drift deposits that delineate the former thickness and extent of the East Antarctic Ice Sheet (EAIS); cosmogenic exposure ages on these features indicate when the ice sheet was as or more extensive than today. Approximately 30 existing cosmogenic-nuclide exposure ages from scattered locations within these deposits suggest that some moraines and drift sheets are at least 5 Ma old. Those ages imply that the age range of these deposits may span warm periods during the Miocene and Pliocene, during which the EAIS is hypothesized to have been much smaller than present and which constitute potentially important geologic analogues for future warm climates. Therefore, to evaluate the long-term stability of the ice sheet, I have obtained 3He, 10Be, and 21Ne exposure ages from 150 glacially-transported clasts on distinct ice-marginal landforms at Roberts Massif at the head of Shackleton Glacier. The majority of these data comprise 3He measurements on pyroxene extracted from Ferrar dolerite clasts and prepared using a refined HF etching method that improves both measurement throughput and reproducibility. I address the common problem of scatter in exposure ages due to cosmogenic-nuclide inheritance by (i) measuring large numbers of exposure ages, including ~7 from each landform, and (ii) resampling and averaging approaches based on both statistical criteria and field observations of boulder characteristics and geomorphic context. Moraines at Roberts Massif are openwork boulder belts characteristic of deposition by cold-based ice, which is consistent with present climate and glaciological conditions. Additionally, the lack of glaciofluvial deposits at Roberts Massif suggests that temperatures have not been sufficiently warm to induce surface melting of the ice at this location since at least the beginning of my glacial record. Apparent exposure ages at this site range from ~400 ka to 13 Ma, with individual moraine ages as old as ~8 ... |
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