Cosmogenic 3He and 10Be chronologies of the late Pinedale northern Yellowstone ice cap, Montana, USA
- Joseph M. Licciardi*1,
- Peter U. Clark*1,
- Edward J. Brook*2,
- Kenneth L. Pierce*3,
- Mark D. Kurz*4,
- David Elmore*5 and
- Pankaj Sharma*5
- 1Department of Geosciences, Oregon State University, Corvallis, Oregon 97331, USA
- 2Department of Geology, Washington State University, Vancouver, Washington 98686, USA
- 3U.S. Geological Survey, Northern Rocky Mountain Science Center, Montana State University, Bozeman, Montana 59717, USA
- 4Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
- 5Department of Physics, PRIME Lab, Purdue University, West Lafayette, Indiana 47907, USA
Abstract
Cosmogenic 3He and 10Be ages measured on surface boulders from the moraine sequence deposited by the northern outlet glacier of the Yellowstone ice cap indicate that the outlet glacier reached its terminal position at 16.5 ± 0.4 3He ka and 16.2 ± 0.3 10Be ka, respectively. Concordance of these ages supports the scaled production rates used for 3He (118.6 ± 6.6 atoms · g−1 · yr−1) and 10Be (5.1 ± 0.3 atoms · g−1 · yr−1) (±2σ at high latitudes at sea level). Two recessional moraines upvalley from the terminal moraine have mean ages of 15.7 ± 0.5 10Be ka and 14.0 ± 0.4 10Be ka, respectively, and a late-glacial flood bar was deposited at 13.7 ± 0.5 10Be ka. These cosmogenic chronologies identify a late Pinedale glacial maximum in northern Yellowstone that is significantly younger than previously thought, and they suggest deglaciation of the Yellowstone plateau by ∼14 10Be ka.
Footnotes
-
↵*Present address: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA; jlicciardiwhoi.edu.
-
↵GSA Data Repository item 2001127, Table 1, Helium data for Eightmile terminal moraines, and Table 2, Beryllium data for Yellowstone moraines, is available on request from Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301, editing@geosociety.org, or at www.geosociety.org/pubs/ft2001.htm.
-
- Accepted August 7, 2001.
- Received April 23, 2001.
- Revision received July 20, 2001.
- Geological Society of America
