Cosmogenic nuclide measurements in southernmost South America and implications for landscape change

Publication Type  Journal Article
Year of Publication  2007
Authors  Kaplan, M. R.; Coronato, A.; Hulton, N. R. J.; Rabassa, J. O.; Kubik, P. W.; Freeman, S. P. H. T.
Journal Title  Geomorphology
Volume  87
Issue  4
Pages  284-301
Journal Date  Jul 1
ISBN Number  0169-555X
Accession Number  ISI:000251894700004
Key Words  cosmogenic; geomorphology; quaternary; glacial geology; south america; argentina; lago buenos-aires; production-rates; last glaciation; bahia inutil; chronology; quaternary; argentina; landforms; cl-36; moraines

We measured in situ Be-10, Al-16 and Cl-16 on glacial deposits as old as 1.1 Myr in the southernmost part of Patagonia and on northern Tierra del Fuego to understand boulder and moraine and, by inference, landscape changes. Nuclide concentrations indicate that surface boulders have been exposed for far less time than the ages of moraines they sit upon. The moraine ages are themselves constrained by previously obtained Ar-40/Ar-39 ages on interbedded lava flows or U-series and amino acid measurements on related (non-glacial) marine deposits. We suggest that a combination of boulder erosion and their exhumation from the moraine matrix could cause the erratics to have a large age variance and often short exposure histories, despite the fact that some moraine landforrns are demonstrably 1 Myr old. We hypothesize that fast or episodic rates of landscape change occurred during glacial times or near the sea during interglacials. Comparison with boulder erosion rates and exhumation histories derived for the middle latitudes of semi-arid Patagonia imply different geomorphic processes operating in southernmost South America. We infer a faster rate of landscape degradation towards the higher latitudes where conditions have been colder and wetter. (c) 2006 Elsevier B.V. All rights reserved.


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URL  <Go to ISI>://000251894700004
DOI  DOI 10.1016/j.geomorph.2006.10.005