7 field seasons and 250 cosmogenic exposure ages: laurentide ice sheet history and dynamics
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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? - PowerPoint PPT PresentationTRANSCRIPT
7 field seasons and 250 cosmogenic exposure ages:Laurentide Ice Sheet history and dynamics
The Clyde River project, on northeastern Baffin Island
4 Questions to consider:
1. Why can’t blockfields be used as evidence for LGM refugia?
2. Recall that we’re presently in the “Goldilocks Paradigm.” Howis the Goldilocks model incorrect?
3. What are weathering zones really telling us?
4. What is potentially wrong with a story that is based on only a fewcosmogenic exposure ages?
10 km NClyde Foreland
Differentially-weathered fiord landscapes
Future work . . .
Extent of “fresh” zone indicates extent of LGM ice
Weathered uplands are covered, but not eroded, during the LGM
Tor: ≥67.5±7.2 ka
Boulder: 17.5±1.9 ka
Tor:≥64.1±2.2 (Be)≥61.4 ± 2.7 (Al)
Boulder:10.2±1.1
Cobble:11.6±0.9 (Be)14.8±1.7 (Al)
Future work . . .
Future work . . .
Updated from Briner et al., 2003,QSR
Locations of “LGM” erratics
380-430 m
410-610 m520-580 m620-690 m
? ??
?
Cold-based
Cold-based
warm-based
Shearzone Shear
zone
Ice Stream
Cold-based
Cold-based
warm-based
Shearzone Shear
zone
Ice Stream
South
North
10 km N
South North
glacially scoured
N S
no evidence of glacial erosion
glacially scoured
N S
no evidence of glacial erosion
some evidence of glacial modification
glacially scoured
N S
28.3+0.7 ka 32.5+1.1 ka
10.2+0.5 ka34.2+0.9 ka
9.5+0.7 ka23.3+0.7 ka
9.5+0.3 ka23.7+1.0 ka
11.4+0.5 ka11.6+0.3 ka80.0+3.4 ka
9.4+0.4 ka
22.0+0.7 ka
Cosmogenic Exposure ages: Bedrock and Erratics
28.3+0.7 ka 32.5+1.1 ka
10.2+0.5 ka34.2+0.9 ka
9.5+0.7 ka23.3+0.7 ka
9.5+0.3 ka23.7+1.0 ka
11.4+0.5 ka11.6+0.3 ka80.0+3.4 ka
9.4+0.4 ka
22.0+0.7 ka
erosive ice (>2 m of erosion)
erosive ice (<2 m of erosion)some glacial modification of upland bedrock
highest areas: no observable glacial modification
Clarke et al., in prep.
Future work . . .
Future work . . .
Future work . . .
Future work . . .
What we’ve learned:
?? ?
1. LGM ice at shelf break2. Uplands covered by cold-based ice
3. WZs mark of basal thermal regimes
4. Ice streams occupied fiords
weatheredfresh
10 km N
5.5±0.3
5.1±0.34.0±0.3
3.9±0.3
50.0±1.230.1±0.755.8±1.3
5.5±0.3
5.1±0.34.0±0.3
3.9±0.3
50.0±1.230.1±0.755.8±1.3
Al/Be burial age:~430 ka
Byrd Glacier, Antarctica
LANDSAT-1 image
Lambert Glacier: an Antarctic ICE STREAM
JPL - RADARSAT AMP
ice-sheet scalepatterns in basal thermal regime…
JPL - RADARSAT AMP
4 Questions to consider:
1. Why can’t blockfields be used as evidence for LGM refugia?
2. Recall that we’re presently in the “Goldilocks Paradigm.” Howis the Goldilocks model incorrect?
3. What are weathering zones really telling us?
4. What is potentially wrong with a story that is based on only a fewcosmogenic exposure ages?
2D numerical glacier model run in MatLab
Bob Anderson and Mark Kessler (University of Colorado)
Published:Kessler et al. 2006
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Erosion is deepest as it crosses the crest.Erosion accelerates through time
X-section of a typical Baffin Island Fjord
> 2 km
100 km
Bob Anderson, Mark Kessler
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