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Cosmogenic exposure dating -principles and applications Quaternary glacial history of Beringia -overview with case studies Late Quaternary glacial history.

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Presentation on theme: "Cosmogenic exposure dating -principles and applications Quaternary glacial history of Beringia -overview with case studies Late Quaternary glacial history."— Presentation transcript:

1 Cosmogenic exposure dating -principles and applications Quaternary glacial history of Beringia -overview with case studies Late Quaternary glacial history of the Eastern Canadian Arctic -the Clyde River Project

2 Firstly, it is great to be here!

3 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 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 England, 1998, JQS, v. 13, p Miller et al., 2002, QSR, v. 21, p vs. 3. Briner et al., 2006, GSAB, v. 118, p

4 Cosmogenic Exposure Dating

5 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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7 Surface Exposure Dating the basics

8 Gosse and Phillips, 2001 woah

9 Cosmo Isotope production versus depth Gosse and Phillips, 2001

10 The case of glacial erosion

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12 Gosse and Phillips, 2001 quartz whole rock calcite parent

13 N=concentration P=production rate =decay constant T=time Exposure dating requires:

14 Production of cosmogenic radionuclides varies spatially Gosse and Phillips, 2001

15 Stone, 2000 Air Pressure

16 Complication: Surface erosion Steig et al., 1998

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20 Shielding of cosmic rays by surrounding topography

21 Complication: Seasonal snow cover Gosse and Phillips, 2001

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23 Use CRONUS-Balco age calculator

24 Application #1: exposure dating

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26 Complication: degrading landforms

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28 Result of moraine degradation

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33 Complication: isotopic inheritanceApplication #2: glacial erosion

34 1.Know pre-existing cosmogenic isotope concentration 2.Measure what is left 3.Calculate depth of glacial erosion Solving for glacial erosion

35 Briner and Swanson, 1998, GEOLOGY

36 Low elevation

37 10 Be = 9.4±0.4 ka Low elevation

38 Intermediate elevation

39 22.0±0.7 ka Intermediate elevation

40 High elevation

41 84.4±2.0 ka High elevation

42 Low-elevation bedrock (n=10) Intermediate-elevation bedrock (n=11) High-elevation bedrock (n=12) Relative Probability

43 High elevation

44 102.3±3.4 ka

45 High elevation 11.4±0.5 ka 102.3±3.4 ka

46 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

47 Cold- based Cold- based warm-based Shear zone Shear zone Ice Stream

48 Application #3: burial studies 11.4±0.5 ka 102.3±3.4 ka

49 Tor exposed at surface becomes saturated with 10 Be and 26 Al 10 Be and 26 Al accumulate in upper ~2 m of rock

50 Tor shielded by cold-based ice Once shielded: 10 Be and 26 Al radioactively decay differentially

51 With constant exposure ratio of isotope production eventually decreases

52 Upon burial or shielding ratio decreases below the constant exposure line

53 84.4±2.0 ka High elevation Al/Be burial age: ~420 ka

54 High elevation 102.3±3.4 ka Al/Be burial age: ~475 ka

55 High elevation 11.4±0.5 ka 102.3±3.4 ka Al/Be burial age: ~475 ka

56 Overview: 1. Exposure dating 2. Glacial erosion 3. Burial history


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