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TitleEvidence from geomorphological mapping and terrestrial cosmogenic nuclides for relict glacial terrains preserved under the Keewatin Ice Divide, Nunavut, Canada
AuthorMcMartin, IORCID logo; Campbell, J E; Godbout, P -M; Gosse, J C; Tremblay, TORCID logo
SourceGeological Association of Canada, Program and Abstracts vol. 45, 2022 p. 155
LinksOnline - En ligne
Alt SeriesNatural Resources Canada, Contribution Series 20210663
PublisherGeological Association of Canada
MeetingGAC-MAC-IAH-CNC-CSPG Joint Meeting; Halifax; CA; May 15-18, 2022
Mediapaper; on-line; digital
File formatpdf
NTS55; 65; 56; 66
Lat/Long WENS-104.0000 -88.0000 68.0000 60.0000
Subjectsgeneral geology; Science and Technology; glacial features; ice morphology; ice; mapping techniques; glacial erosion; Keewatin; Keewatin Glacier; Keewatin Ice Divide
ProgramGEM-GeoNorth: Geo-mapping for Energy and Minerals GEM Program Coordination
Released2022 05 15
AbstractRelict glacial terrains were recently identified in large areas formerly covered by the northern portion of the Keewatin Ice Divide in the Kivalliq Region of Nunavut west of Hudson Bay, Canada. A gradual transition in the preservation of these relict terrains, based on geomorphology, elevation, drainage network, lake density, weathering, and terrestrial cosmogenic nuclide (TCN) abundances in bedrock, till, and boulder samples, is linked to differential glacial erosion. The unprecedented and comprehensive documentation of these preserved landscapes in central mainland Nunavut is based on the mapping of glacigenic features using high-resolution imagery (ArcticDEM and Landsat 8), ground-based observations, and surface materials composition. Between Baker Lake and Repulse Bay, extensive areas of uplands form a continuum ranging from weathered bedrock, blockfields, and diamictons with little to no evidence of glacial erosion to terrains with moderate glacial erosion, rare streamlined landforms, ice-marginal channels and discontinuous eskers. High proportions of secondary clay minerals and amorphous Fe-oxides in the clay fraction of the most weathered diamictons are observed. In contrast, along and on either side of the ice divide zone between Baker Lake and the Manitoba border to the south, warm-based assemblages of glacial features, thick glacial deposits, and palimpsest glacial landscapes reflect mobile outflow centres during the last glacial cycle(s). Our mapping and classification of these land systems is supported by relative TCN abundances. Paired 10Be and 26Al abundances are relatively high in relict terrains where 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 reflect the persistence of cosmogenic nuclides formed during prolonged exposure prior to burial and preserved through incomplete erosion under a variably cold-based ice divide and suggest that the uplands in the north have largely escaped the effects of the last glaciation(s). The presence of rare glacial erratics over the weathered bedrock suggests full glacial coverage with sporadic warm-based conditions. South of Baker Lake, five apparent 10Be ages on bedrock varying between 6.9 ± 0.5 ka and 9.0 ± 0.6 ka indicate no exposure inheritance or burial. The exposure ages, however, generally suggest that deglaciation occurred at least 1 kyr earlier than radiocarbon-based reconstructions. All these characteristics can help to evaluate the significance of inheritance for glacial erosion and to understand differences in the composition and provenance of surface materials between the fully cold-based relict landscapes and the adjacent fully warm-based glacial terrains.
Summary(Plain Language Summary, not published)
This abstract for a talk to be presented at the annual meeting of the Geological Association of Canada reports on old terrains in mainland Nunavut preserved from glacial erosion 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 during the GEM-2 Rae Synthesis of Glacial History and Dynamics and GEM-GeoNorth Hudson Glacial Records activities. The work was undertaken to provide new geological knowledge on the nature of glacial terrains and is important for mineral exploration using glacial sediment provenance to evaluate how the composition of surface materials may vary between the relict landscapes and younger terrains affected by the last glaciation. The findings will support informed decision making for resource exploration and land use management.

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