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The Clyde River project, on northeastern Baffin Island. 7 field seasons and 250 cosmogenic exposure ages: Laurentide Ice Sheet history and dynamics. 4 Questions to consider:. Why can’t blockfields be used as evidence for LGM refugia?
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The Clyde River project, on northeastern Baffin Island 7 field seasons and 250 cosmogenic exposure ages: Laurentide Ice Sheet history and dynamics
4 Questions to consider: Why can’t blockfields be used as evidence for LGM refugia? Recall that we’re presently in the “Goldilocks Paradigm.” How is the Goldilocks model incorrect? 3. What are weathering zones really telling us? What is potentially wrong with a story that is based on only a few cosmogenic exposure ages?
N 10 km Clyde Foreland
Extent of “fresh” zone indicates extent of LGM ice Future work . . .
Weathered uplands are covered, but not eroded, during the LGM
Boulder: 17.5±1.9 ka Tor: ≥67.5±7.2 ka
Tor: ≥64.1±2.2 (Be) ≥61.4 ± 2.7 (Al) Cobble: 11.6±0.9 (Be) 14.8±1.7 (Al) Boulder: 10.2±1.1
Future work . . . Updated from Briner et al., 2003, QSR
Locations of “LGM” erratics ? ? ? ? 520-580 m 620-690 m 410-610 m 380-430 m
Shear zone Shear zone warm-based Cold- based Cold- based Ice Stream
Shear zone Shear zone warm-based Cold- based Cold- based Ice Stream
N 10 km North South
North South
S N glacially scoured
S N no evidence of glacial erosion glacially scoured
S N no evidence of glacial erosion some evidence of glacial modification glacially scoured
Cosmogenic Exposure ages: Bedrock and Erratics 11.4+0.5 ka 11.6+0.3 ka 80.0+3.4 ka 9.5+0.3 ka 23.7+1.0 ka 28.3+0.7 ka 32.5+1.1 ka 22.0+0.7 ka 9.5+0.7 ka 23.3+0.7 ka 9.4+0.4 ka
highest areas: no observable glacial modification erosive ice (<2 m of erosion) some glacial modification of upland bedrock erosive ice (>2 m of erosion) 11.4+0.5 ka 11.6+0.3 ka 80.0+3.4 ka 9.5+0.3 ka 23.7+1.0 ka 28.3+0.7 ka 32.5+1.1 ka 22.0+0.7 ka 9.5+0.7 ka 23.3+0.7 ka 9.4+0.4 ka Clarke et al., in prep.
1. LGM ice at shelf break Uplands covered by cold-based ice WZs mark of basal thermal regimes 4. Ice streams occupied fiords ? ? ? What we’ve learned: weathered fresh
N 10 km
55.8±1.3 30.1±0.7 50.0±1.2 5.5±0.3 4.0±0.3 5.1±0.3 3.9±0.3
55.8±1.3 30.1±0.7 50.0±1.2 5.5±0.3 Al/Be burial age: ~430 ka 4.0±0.3 5.1±0.3 3.9±0.3
Byrd Glacier, Antarctica LANDSAT-1 image
Lambert Glacier: an Antarctic ICE STREAM JPL - RADARSAT AMP
ice-sheet scale patterns in basal thermal regime…
4 Questions to consider: Why can’t blockfields be used as evidence for LGM refugia? Recall that we’re presently in the “Goldilocks Paradigm.” How is the Goldilocks model incorrect? 3. What are weathering zones really telling us? What is potentially wrong with a story that is based on only a few cosmogenic exposure ages?
2D numerical glacier model run in MatLab Bob Anderson and Mark Kessler (University of Colorado) Published: Kessler et al. 2006