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

„Ï KAPLAN, M.; CORONATO, A., HULTON, N., RABASSA, J., STONE, J., KUBIK, P.

GEOMORPHOLOGY

Elsevier

Lugar: Amsterdam; Año: 2007 p. 284 - 301

0169-555X

We measured in situ 10Be, 26Al, and 36Cl on glacial deposits as old as 1.1 Myr in the southernmost part of Patagonia and on northern Tierra del Fuego to understand rates of boulder and moraine degradation, and by inference landscape change. Nucleide concentrations indicate that surface boulders have been exposed for far less time than the ages of moraines they sit upon. The moraines are themselves constrained by previously obtained  40Ar/39Ar ages on interbedded lava flows or U series/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 caused the erratics to have a large age variance and often short exposure histories, despite that some morainal landforms are 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 Patagonia imply different geomorphic processes operating in southernmost Patagonia. We infer a faster rate of landscape degradation towards the higher latitudes where conditions have been colder and wetter.