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TitleEvidence from geomorphological mapping and paired terrestrial cosmogenic nuclides for a relict cold-based landscape preserved under the Keewatin Ice Divide, Nunavut, Canada
AuthorMcMartin, IORCID logo; Godbout, P M; Gosse, J C; Campbell, J E; Tremblay, T; Roy, M; Schaefer, J M
SourceXXI INQUA Congress - Program with Abstracts; by INQUA; 2023 p. 1
Alt SeriesNatural Resources Canada, Contribution Series 20220375
PublisherInternational Union for Quaternary Research
MeetingXXI INQUA Congress; Rome; IT; July 14-20, 2023
Mediapaper; digital; on-line
File formatpdf
SubjectsScience and Technology; general geology; Keewatin Ice Divide; Geomorphology
ProgramGEM-GeoNorth: Geo-mapping for Energy and Minerals GEM Program Coordination
Released2023 07 14
AbstractRelict weathered terrains were recently identified and mapped in large areas formerly covered by the northern portion of the Keewatin Ice Divide based on high-resolution imagery (e.g., ArcticDEM and Landsat 8), ground-based observations, and surface materials composition. A gradual transition in the preservation of these relict terrains reflects changes in geomorphology, weathering, elevation, drainage network, and lake density. Over the Wager Plateau north of Baker Lake, extensive areas of uplands form a continuum ranging from abundant weathered diamictons, bedrock and blockfields, with little to no evidence of glacial erosion, to terrains with moderate glacial erosion, patchy weathering, sporadic streamlined landforms, a well-developed network of ice-marginal channels, and discontinuous eskers. In the large ice divide migration zone south of Baker Lake, a palimpsest glacial record (striations, landforms and dispersal trains) and stacked till sheets of different provenance reflect persistent warm-based conditions and mobile outflow centres during the last glacial cycle(s). Our classification of these polythermal terrains is supported by relative terrestrial cosmogenic nuclide (TCN) abundances in bedrock, till, and boulder samples. Paired 10Be and 26Al abundances are relatively high in relict terrains and apparent 10Be ages of surface bedrock vary from 21.9 ± 0.5 ka to 61.9 ± 1.2 ka (n = 10 ; LSDn Age ±1s int). These apparent ages suggest that cosmogenic nuclides formed during prolonged exposure prior to burial were preserved through incomplete erosion under a variably cold-based ice divide. The presence of rare glacial erratics over the weathered bedrock suggests full glacial coverage with sporadic warm-based conditions. In the fully warm-based terrains, apparent 10Be ages on striated outcrops and wave-washed bedrock marine limits vary between 6.9 ± 0.5 ka and 9.0 ± 0.6 ka (n=10 ) and indicate no exposure inheritance or burial. These exposure ages, however, generally suggest that deglaciation occurred at least 1 ka earlier than radiocarbon-based reconstructions. This work can improve the deglacial history and help to interpret and possibly quantify the impact of polythermal ice on the composition and provenance of surface materials with applications for mineral exploration in glaciated terrains.
Summary(Plain Language Summary, not published)
This abstract for a talk to be presented at the INQUA 2023 Congress reports on old terrains in mainland Nunavut preserved from glacial erosion under very cold conditions at the core of the Laurentide Ice Sheet and dating back to a time prior to the last glaciation (>75 000 years). The interpretations are based on the detailed mapping of glacial features using high-resolution imagery and innovative dating techniques used as part of the GEM-GeoNorth Western Hudson Bay Glacial Records activity. The work was undertaken to provide new geological knowledge on the nature of glacial terrains and is important to evaluate how the composition of surface materials may vary in polythermal landscapes therefore reducing risks for mineral exploration.

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