Presentation Information
[U11-P03]Stratigraphic evidence for modern-like glacier extents in south-central Alaska within the last glacial period (MIS 3).
*Bruno Belotti1, Elizabeth Cassel1, Timothy Bartholomaus1, Michael Loso2, Michael Christoffersen3, John Holt4 (1.Department of Earth and Spatial Sciences, University of Idaho, Moscow, 83844, Idaho, United States, 2.Wrangell-St. Elias National Park and Preserve, Resource Stewardship and Science, Copper Center, 99573, Alaska, United States, 3.School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, 30332-0340, Georgia, United States, 4.Department of Geosciences, University of Arizona, Tucson, 85721, Arizona, United States)
Keywords:
Glacial sedimentology,MIS 3 interstadials,Chronostratigraphy,Climate Proxy,Glacial Minima
The last (Wisconsinan) glacial period was punctuated in North America by two glacial maxima, known as the Early and Late Wisconsinan glaciations. In Alaska, these maxima and their subsequent retreats have been the object of dating efforts to reconstruct local climatic events and compare them to global trends. Little is known, however, about the period of milder climate and reduced glacier extents that separated the Early and Late Wisconsinan maxima, likely spanning a significant portion of Marine Isotope Stage 3 (MIS 3).
Detailed sedimentological analysis from the northern margin of the Chitina River Valley in the Copper River Basin, Alaska, revealed a buried proglacial sequence composed of glaciofluvial stream deposits, glaciolacustrine muds, and ice-proximal subaqueous fan deposits, which indicates ice-free conditions at ~39 ka. Our palaeodepositional reconstructions show that the local glacier, a tributary to one of the largest ancient south-central Alaskan ice streams, had retreated to near its modern terminus position during early to mid MIS 3, indicative of a stadial-interstadial transition with modern-like glacier termini.
We attribute differences in facies stacking patterns to drastic fluctuations in local base level, driven by the formation and drainage of a regional ice-dammed lake (Palaeolake Atna). Our results offer new constraints on Late-Pleistocene glacial fluctuations in south-central Alaska, including new MIS 3 glacial minima, and provide insights into the relationships between climatic fluctuations, ice extents, and associated landscape evolution in the Copper River Basin.
Detailed sedimentological analysis from the northern margin of the Chitina River Valley in the Copper River Basin, Alaska, revealed a buried proglacial sequence composed of glaciofluvial stream deposits, glaciolacustrine muds, and ice-proximal subaqueous fan deposits, which indicates ice-free conditions at ~39 ka. Our palaeodepositional reconstructions show that the local glacier, a tributary to one of the largest ancient south-central Alaskan ice streams, had retreated to near its modern terminus position during early to mid MIS 3, indicative of a stadial-interstadial transition with modern-like glacier termini.
We attribute differences in facies stacking patterns to drastic fluctuations in local base level, driven by the formation and drainage of a regional ice-dammed lake (Palaeolake Atna). Our results offer new constraints on Late-Pleistocene glacial fluctuations in south-central Alaska, including new MIS 3 glacial minima, and provide insights into the relationships between climatic fluctuations, ice extents, and associated landscape evolution in the Copper River Basin.