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Cosmogenic nuclide chronology of pre-last glacial maximum moraines at Lago Buenos Aires, 46�S, Argentina

Published online by Cambridge University Press:  20 January 2017

Michael R. Kaplan ,
Daniel C. Douglass ,
Bradley S. Singer ,
Robert P. Ackert  and
Marc W. Caffee
Michael R. Kaplan*
Affiliation:
Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 West Dayton Street, Madison, WI 53706, USA School of GeoSciences, University of Edinburgh, Edinburgh, EH8 9XP, Scotland, UK
Daniel C. Douglass
Affiliation:
Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 West Dayton Street, Madison, WI 53706, USA
Bradley S. Singer
Affiliation:
Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 West Dayton Street, Madison, WI 53706, USA
Robert P. Ackert
Affiliation:
Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, USA
Marc W. Caffee
Affiliation:
Department of Physics, Purdue University, West Lafayette, IN 47907-1396, USA
*
*Corresponding author. School of GeoSciences, University of Edinburgh, Edinburgh, EH8 9XP, Scotland, UK. Fax: +44 131 650 2524.E-mail address:[email protected] (M.R. Kaplan).
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Abstract

At Lago Buenos Aires, Argentina, 10Be, 26Al, and 40Ar/39Ar ages range from 190,000 to 109,000 yr for two moraines deposited prior to the last glaciation, 23,000�16,000 yr ago. Two approaches, maximum boulder ages assuming no erosion, and the average age of all boulders and an erosion rate of 1.4 mm/103 yr, both yield a common estimate age of 150,000�140,000 yr for the two moraines. The erosion rate estimate derives from 10Be and 26Al concentrations in old erratics, deposited on moraines that are >760,000 yr old on the basis of interbedded 40Ar/39Ar dated lavas. The new cosmogenic ages indicate that a major glaciation during marine oxygen isotope stage 6 occurred in the mid-latitude Andes. The next five youngest moraines correspond to stage 2. There is no preserved record of a glacial advance during stage 4. The distribution of dated boulders and their ages suggest that at least one major glaciation occurred between 760,000 and >200,000 yr ago. The mid-latitude Patagonian glacial record, which is well preserved because of low erosion rates, indicates that during the last two glacial cycles major glaciations in the southern Andes have been in phase with growth and decay of Northern Hemisphere ice sheets, especially at the 100,000 yr periodicity. Thus, glacial maxima are global in nature and are ultimately paced by small changes in Northern Hemisphere insolation.

Keywords

Exposure ageCosmogenic nuclideSouth AmericaGlacial geologyPaleoclimatologyGlaciationSouthern HemisphereMilankovitchQuaternary periodStage 6
Type
Research Article
Information
Quaternary Research , Volume 63 , Issue 3 , May 2005 , pp. 301 - 315
Copyright
University of Washington

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