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Cosmogenic nuclide exposure ages for moraines in the Lago San Martin Valley, Argentina

Published online by Cambridge University Press:  20 January 2017

Neil F. Glasser*
Affiliation:
Centre for Glaciology, Institute of Geography and Earth Sciences, Aberystwyth University, Ceredigion SY23 3DB, Wales, UK
Krister N. Jansson
Affiliation:
Department of Physical Geography and Quaternary Geology, University of Stockholm, SE-106 91, Stockholm, Sweden
Bradley W. Goodfellow
Affiliation:
Geological and Environmental Sciences, 450 Serra Mall, Stanford University, Stanford, CA 94305, USA
Hernan de Angelis
Affiliation:
Department of Physical Geography and Quaternary Geology, University of Stockholm, SE-106 91, Stockholm, Sweden
Helena Rodnight
Affiliation:
Institute for Geology and Palaeontology, University of Innsbruck, Innrain 52, 6020 Innsbruck, Austria
Dylan H. Rood
Affiliation:
Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, L-397 Livermore, CA 94550, USA
*
Corresponding author.

Abstract

At several times during the Quaternary, a major eastward-flowing outlet glacier of the former Patagonian Ice Sheet occupied the Lago San Martin Valley in Argentina (49°S, 72°W). We present a glacial chronology for the valley based on geomorphological mapping and cosmogenic nuclide (10Be) exposure ages (n = 10) of boulders on moraines and lake shorelines. There are five prominent moraine belts in the Lago San Martin Valley, associated with extensive sandar (glaciofluvial outwash plains) and former lake shorelines. Cosmogenic nuclide exposure ages for boulders on these moraines indicate that they formed at 14.3 ± 1.7 ka, 22.4 ± 2.3 ka, 34.4 ± 3.4 ka to 37.6 ± 3.4 ka (and possibly 60 ± 3.5 ka), and 99 ± 11 ka (1σ). These dated glacier advances differ from published chronologies from the Lago San Martin Valley based on 14C age determinations from organic sediments and molluscs in meltwater channels directly in front of moraines or in kettleholes within end moraine ridges. The moraine boulder ages also point to possible pre-LGM glacial advances during the last glacial cycle and a key observation from our data is that the LGM glaciers were probably less extensive in the Lago San Martin Valley than previously thought.

Type
Research Article
Copyright
University of Washington

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