Cosmogenic exposure dating of late Pleistocene moraine stabilization in Alaska

Jason P. Briner, Darrell S Kaufman, William F. Manley, Robert C. Finkel, Marc W. Caffee

Research output: Contribution to journalArticle

129 Citations (Scopus)

Abstract

Seventy-three new 10Be/26Al ages from 57 moraine boulders and 2 tors, together with 43 previously published cosmogenic exposure ages from 41 moraine boulders, allow us to critique the use of cosmogenic exposure (CE) dating of moraine boulders in Alaska. Boulder exhumation during moraine degradation likely gives rise to the largest uncertainty in constraining the timing of initial moraine stabilization following ice retreat. Isotopic inheritance appears to be most important for moraines deposited close to their cirque headwalls. Boulder-surface (bedrock) erosion rate can be roughly constrained and leads to a range in moraine stabilization ages. Snow-cover history is difficult to constrain, but its effect is thought to be minor for the tall boulders sampled. Despite these complications, the CE ages provide important new information regarding the timing of the last and penultimate glaciations in Alaska. Three penultimate moraines yielded CE ages that overlap with marine isotope stage (MIS) 4/early MIS 3 (45-65 ka) rather than MIS 6 (ca. 140 ka). Based on a combination of our new CE chronologies and existing 14C ages from six study areas, glaciers retreated from their local late Wisconsin maxima: ca. 24-27 ka, Kokrines Hills (west-interior Alaska); ca. 24-26 ka, northeastern Brooks Range (NE Alaska); ca. 21-23 ka, Yukon Tanana Upland (east-interior Alaska); ca. 22 ka, Ahklun Mountains (SW Alaska); ca. 20 ka, western Alaska Range (central Alaska); ca. 16-18 ka, Chuilnuk Mountains (SW Alaska). Overall, glacier retreat was concurrent with the peak of the last global glacial maximum, probably in response to limited moisture availability.

Original languageEnglish (US)
Pages (from-to)1108-1120
Number of pages13
JournalBulletin of the Geological Society of America
Volume117
Issue number7-8
DOIs
StatePublished - Jul 2005

Fingerprint

moraine
stabilization
Pleistocene
marine isotope stage
boulder
glacier retreat
ice retreat
cirque
mountain
erosion rate
snow cover
exhumation
glaciation
exposure
dating
chronology
bedrock
glacier
moisture
history

Keywords

  • Alaska
  • Cosmogenic exposure dating
  • Last glacial maximum
  • Moraine
  • Penultimate glaciation

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)

Cite this

Cosmogenic exposure dating of late Pleistocene moraine stabilization in Alaska. / Briner, Jason P.; Kaufman, Darrell S; Manley, William F.; Finkel, Robert C.; Caffee, Marc W.

In: Bulletin of the Geological Society of America, Vol. 117, No. 7-8, 07.2005, p. 1108-1120.

Research output: Contribution to journalArticle

Briner, Jason P. ; Kaufman, Darrell S ; Manley, William F. ; Finkel, Robert C. ; Caffee, Marc W. / Cosmogenic exposure dating of late Pleistocene moraine stabilization in Alaska. In: Bulletin of the Geological Society of America. 2005 ; Vol. 117, No. 7-8. pp. 1108-1120.
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abstract = "Seventy-three new 10Be/26Al ages from 57 moraine boulders and 2 tors, together with 43 previously published cosmogenic exposure ages from 41 moraine boulders, allow us to critique the use of cosmogenic exposure (CE) dating of moraine boulders in Alaska. Boulder exhumation during moraine degradation likely gives rise to the largest uncertainty in constraining the timing of initial moraine stabilization following ice retreat. Isotopic inheritance appears to be most important for moraines deposited close to their cirque headwalls. Boulder-surface (bedrock) erosion rate can be roughly constrained and leads to a range in moraine stabilization ages. Snow-cover history is difficult to constrain, but its effect is thought to be minor for the tall boulders sampled. Despite these complications, the CE ages provide important new information regarding the timing of the last and penultimate glaciations in Alaska. Three penultimate moraines yielded CE ages that overlap with marine isotope stage (MIS) 4/early MIS 3 (45-65 ka) rather than MIS 6 (ca. 140 ka). Based on a combination of our new CE chronologies and existing 14C ages from six study areas, glaciers retreated from their local late Wisconsin maxima: ca. 24-27 ka, Kokrines Hills (west-interior Alaska); ca. 24-26 ka, northeastern Brooks Range (NE Alaska); ca. 21-23 ka, Yukon Tanana Upland (east-interior Alaska); ca. 22 ka, Ahklun Mountains (SW Alaska); ca. 20 ka, western Alaska Range (central Alaska); ca. 16-18 ka, Chuilnuk Mountains (SW Alaska). Overall, glacier retreat was concurrent with the peak of the last global glacial maximum, probably in response to limited moisture availability.",
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