cosmogenic exposure dating -principles and applications quaternary glacial history of beringia...
TRANSCRIPT
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Cosmogenic exposure dating
-principles and applications
Quaternary glacialhistory of Beringia-overview with casestudies
Late Quaternary glacial historyof the Eastern Canadian Arctic
-the Clyde River Project
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Firstly, it is great to be here!
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My biased reading suggestions:(be familiar with lots more, but be sure to read these)
Quaternary glacial history of Beringia
Late Quaternary glacial history of the Eastern Canadian Arctic
1. Brigham-Grette, 2001, QSR v. 20, p. 15-24.2. Briner and Kaufman, submitted, Journal of Quaternary Science.Read this for discussion:3. letter to the editor debate on ‘Beringian Ice Sheet’ - Brigham-Grette and Gualtieri et al., 2004; Grosswald and Hughs, 2004, QR, v. 62.
1. England, 1998, JQS, v. 13, p. 275-280.2. Miller et al., 2002, QSR, v. 21, p. 33-48.
vs.3. Briner et al., 2006, GSAB, v. 118, p. 406-420.
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Cosmogenic Exposure Dating
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3 Questions to consider:
1. How would you explain cosmogenic exposure dating to your Dad (elementary school teacher) and Mom (engineer)?
2. What are three ways that cosmogenic radionuclides are used?
3. How would you critique a dataset of cosmogenic exposure ages?
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GEOREF hits of "cosmogenic" and "glaci*"
0.00
5.00
10.00
15.00
20.00
25.00
30.00
1930 1940 1950 1960 1970 1980 1990 2000 2010
Year
Number of records
Series1
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Surface Exposure Datingthe basics
lava flowold landscapelandslidemoraineCosmic Radiation
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Gosseand Phillips,2001
woah
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CosmoIsotopeproductionversus depth
Gosseand Phillips,2001
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The case of glacial erosion
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Gosse and Phillips, 2001
quartz
whole rock
calcite
parent
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N =
P
λ
( 1 − e
− λ t
)
t =
ln 1 −
N λ
P
⎛
⎝
⎞
⎠
− λ
.
N=concentrationP=production rateλ=decay constantT=time
Exposure dating requires:
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Production of cosmogenic radionuclides varies spatially
Gosseand Phillips,2001
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Stone, 2000
Air Pressure
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Complication: Surface erosion
Steig et al.,1998
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Shielding of cosmic rays by surrounding topography
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Complication:Seasonal snow cover
Gosseand Phillips,2001
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Use CRONUS-Balco age calculator
http://hess.ess.washington.edu/math/
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Application #1: exposure dating
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Complication: degrading landforms
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Result of moraine degradation
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Complication: isotopic inheritanceApplication #2: glacial erosion
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1.Know pre-existing cosmogenic isotope concentration2.Measure what is left3.Calculate depth of glacial erosion
Solving for glacial erosion
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Briner and Swanson, 1998, GEOLOGY
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Low elevation
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10Be = 9.4±0.4 ka
Low elevation
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Intermediate elevation
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22.0±0.7 ka
Intermediate elevation
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High elevation
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84.4±2.0 ka
High elevation
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Low-elevation bedrock(n=10)
Intermediate-elevation bedrock(n=11)
High-elevation bedrock(n=12)
Relative Probability
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High elevation
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High elevation
102.3±3.4 ka
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High elevation
11.4±0.5 ka
102.3±3.4 ka
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Erratics from intermediate and high elevation bedrock(n=27)
Low-elevation bedrock(n=10)
Intermediate-elevation bedrock(n=11)
High-elevation bedrock(n=12)
Relative Probability
Briner et al., 2006, GSAB
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Cold-based
Cold-based
warm-based
Shearzone
Shearzone
Ice Stream
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Application #3: burial studies
11.4±0.5 ka
102.3±3.4 ka
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Tor exposed at surface becomes saturated with 10Be and 26Al
10Be and 26Al accumulate in upper ~2 m of rock
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Tor shielded by cold-based ice
Once shielded:
10Be and 26Al radioactively decay differentially
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With constant exposureratio of isotope production eventually decreases
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Upon burial or shieldingratio decreases below the constant exposure line
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84.4±2.0 ka
High elevation
Al/Be burial age:~420 ka
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High elevation
102.3±3.4 ka
Al/Be burial age:~475 ka
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High elevation
11.4±0.5 ka
102.3±3.4 ka
Al/Be burial age:~475 ka
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Overview: 1. Exposure dating2. Glacial erosion3. Burial history