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Moraine chronosequence of the Donnelly Dome region, Alaska |
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| Authors: | A Matmon JP Briner P Bierman |
| Institution: | a Institute of Earth Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel b Department of Geology, University at Buffalo, Buffalo, NY 14260, USA c CARVER GEOLOGIC Inc., PO Box 52, 12021 Middle Bay Drive, Kodiak, AK 99615, USA d Department of Geology and School of Natural Resources, University of Vermont, Burlington, VT 05405, USA e Earth and Planetary Science Department, University of California, Berkeley, CA 94720, USA f Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA |
| Abstract: | We present 10Be exposure ages from moraines in the Delta River Valley, a reference locality for Pleistocene glaciation in the northern Alaska Range. The ages are from material deposited during the Delta and Donnelly glaciations, which have been correlated with MIS 6 and 2, respectively. 10Be chronology indicates that at least part of the Delta moraine stabilized during MIS 4/3, and that the Donnelly moraine stabilized ∼ 17 ka. These ages correlate with other dates from the Alaska Range and other regions in Alaska, suggesting synchronicity across Beringia during pulses of late Pleistocene glaciation. Several sample types were collected: boulders, single clasts, and gravel samples (amalgamated small clasts) from around boulders as well as from surfaces devoid of boulders. Comparing 10Be ages of these sample types reveals the influence of pre/post-depositional processes, including boulder erosion, boulder exhumation, and moraine surface lowering. These processes occur continuously but seem to accelerate during and immediately after successive glacial episodes. The result is a multi-peak age distribution indicating that once a moraine persists through subsequent glaciations the chronological significance of cosmogenic ages derived from samples collected on that moraine diminishes significantly. The absence of Holocene ages implies relatively minor exhumation and/or weathering since 12 ka. |
| Keywords: | Cosmogenic exposure ages Moraines Alaska Delta Donnelly |
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