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Dynamic response of the southwestern Laurentide Ice Sheet during the last deglaciation
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- Author / Creator
- Norris, Sophie
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This thesis utilises geomorphic mapping, cosmogenic nuclide dating, and numerical modelling, to reconstruct the timing and deglacial dynamics of the southwestern Laurentide Ice Sheet (SWLIS). A paucity of geomorphic data within the interior portions of the SWLIS is addressed through the mapping of a 150,000 km2 region of northern Alberta and Saskatchewan. Multi-generation glacial landforms present a complex glacial geomorphic signal within the region, suggesting the SWLIS underwent several glaciodynamic shifts during the last deglaciation.A new database of 26 10Be surface exposure ages from glacial erratics spanning a 1200 km transect across the SWLIS is then presented. This chronology is combined with pre-existing luminescence, 10Be surface exposure ages, and ‘high quality’ minimum radiocarbon chronologies, exclusive of dates on bulk sediments, terrestrial shells, or mixed assemblages, to provide an updated chronology for the retreat of the SWLIS. These data indicate that initial detachment of the SWLIS from its convergence with the Cordilleran Ice Sheet occurred at ~15.0 ka BP, concurrent with, or possibly somewhat before the abrupt warming at the onset of the Bølling-Allerød, and retreated >1200 km to its Younger Dryas position in ≤2500 yrs. Synthesis of pre-existing ice flow mapping and new surficial geomorphology, allows the identification of discrete ice flowsets, including those potentially formed by palaeo-ice streams. Reconciling these ice flow dynamics with the new chronology reveals a complex pattern of ice stream behaviour characterised by substantial flow switches and reconfigurations. This reconstruction suggests the SWLIS underwent ice sheet scale reorganisation at least three times in ~2500 yrs. These rapid, decadal to centennial, changes in ice stream orientations demonstrate both, how ice streams can influence an ice sheet’s broader response to external climate forcing, and how ice sheets, through changes to ice flow regime, are highly sensitive to rapid climate change.The role of meltwater discharge from large proglacial lakes associated with rapid deglaciation is then examined. Geomorphic and sedimentological evidence from the Beaver River Spillway, eastern Alberta, provides a rarely preserved example of catastrophic meltwater drainage associated with deglaciation. Modelling results indicate peak discharge within Beaver River Spillway was approximately 14 000–26 000 m³ s-1 and maintained a minimum flow duration of 3-5 days. This case study not only demonstrates the catastrophic nature of meltwater drainage from the SWLIS but also demonstrates the role of easily erodible glacial sediment as a control on meltwater channel evolution and morphology within the Canadian Prairies.
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- Subjects / Keywords
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- Graduation date
- Fall 2020
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.