Sedimentology, stratigraphy, and chronology of the Northwestern Outlet of glacial Lake Agassiz, northeastern Alberta

• Author / Creator

  Young, Joseph

• Lake Agassiz was dammed on the retreating southern and western margins of the Laurentide Ice Sheet during the end of the last Ice Age. Periodic discharges of freshwater from the lake basin have been implicated in altering oceanic circulation and impacting global climate. Meltwater from a rapid decrease in lake level at the start of the Moorhead Phase has been hypothesized as the initiation mechanism for the Younger Dryas cold reversal (~12.9 to 11.5 ka yr BP). However, the timing and routing of this event is still disputed, as there is evidence for both easterly and northwestward drainage during this time. This thesis presents a twofold contribution to understanding the timing, dynamics, and significance of glacial Lake Agassiz meltwater centred on the Moorhead Phase.
  
  Radiocarbon data pertaining to the Moorhead and subsequent Emerson Phases from the Lake Agassiz basin was collated and assessed using manual and statistical filters to vet the dataset. Approximately one third of existing dates were found to be inadequate chronological constraints. A Bayesian model was then applied to the filtered dataset to produce refined age ranges for the start and end of each lake phase. The modelled onset of the Moorhead Phase suggests a lack of contemporaneity to the onset of the Younger Dryas. We suggest further high-quality radiocarbon dates are needed in the Lake Agassiz basin to more robustly constrain lake dynamics during this time. This does not necessarily preclude Lake Agassiz from being the forcing mechanism but underlies the need for further high-quality radiocarbon dates in the lake basin.
  Sediments associated with the northwestern outlet of Lake Agassiz were examined in the lower Athabasca River valley north of Fort McMurray, Alberta. Three distinct sedimentological reaches are identified, containing eleven principal units that bracket catastrophic Lake Agassiz during the Moorhead Phase. Our data permit the development of a new depositional model that suggests catastrophic drainage occurred into a lower stage of glacial Lake McConnell, with a subsequent transgression and deposition of a distal braided delta. Bitumen-mitigated radiocarbon ages from the distal braided delta complex indicate the northwestern outlet was well operational by at least 10.2 14C ka yr BP until 9.6 14C ka yr BP.

• Subjects / Keywords

  • Sedimentology
  • Fort McMuray
  • Lake Agassiz
  • Younger Dryas

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3Q81581N

• 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.