Cosmogenic exposure dating -principles and applications

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 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.  Late Quaternary glacial history of the Eastern Canadian Arctic 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.

4. Cosmogenic Exposure Dating

5. 3 Questions to consider: • 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?

7. Surface Exposure Dating the basics

8. woah Gosse and Phillips, 2001

9. Cosmo Isotope production versus depth Gosse and Phillips, 2001

10. The case of glacial erosion

12. parent quartz whole rock calcite Gosse and Phillips, 2001

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

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

15. Air Pressure Stone, 2000

16. Complication: Surface erosion Steig et al., 1998

20. Shielding of cosmic rays by surrounding topography

21. Complication: Seasonal snow cover Gosse and Phillips, 2001

23. Use CRONUS-Balco age calculator http://hess.ess.washington.edu/math/

24. Application #1: exposure dating

26. Complication: degrading landforms

28. Result of moraine degradation

33. Complication: isotopic inheritance Application #2: glacial erosion

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

35. Briner and Swanson, 1998, GEOLOGY

36. Low elevation

37. Low elevation 10Be = 9.4±0.4 ka

38. Intermediate elevation

39. Intermediate elevation 22.0±0.7 ka

40. High elevation

41. High elevation 84.4±2.0 ka

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

43. High elevation

44. High elevation 102.3±3.4 ka

45. High elevation 11.4±0.5 ka 102.3±3.4 ka

46. Low-elevation bedrock (n=10) Intermediate-elevation bedrock (n=11) High-elevation bedrock (n=12) Erratics from intermediate and high elevation bedrock (n=27) Relative Probability Briner et al., 2006, GSAB

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

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

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

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