CGRG Bibliography of Canadian Geomorphology
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Author : Gosse, J.C.; MacDonald, F.; Staiger, J.; Yang, G.; Bell, T.; Gray, J.; and Stea, R.
Date : 2005.
Title : Tightening the deglacial history and glacial erosion of Atlantic Canada: exposure ages of bedrock and boulders.
Publication : Joint Meeting of the Geological Association of Canada, the Mineralogical Association of Canada, the Canadian Society of Petroleum Geologists and the Canadian Society of Soil Sciences. May 15-18, 2005. Studley Campus of Dalhousie University, Halifax, Nova Scotia.
Issue :
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Abstract
Due partly to the complexities of topography and proximity to the sea, the Quaternary record of glaciation in Atlantic Canada has spanned a spectrum of conceptual models from complete cover by the LIS to isolated but coalescing ice caps punctuated with nunataks during at least the LGM. Since the initial measurements in western Newfoundland in 1993, cosmogenic nuclide data seem to support a growing account from offshore and other records of an intermediate degree of ice cover where summits were glaciated but by non-erosive ice. Boulders at Peggy's Cove have an exposure history of 16.0±0.2 ka (n=4), supporting the offshore moraine chronology and lake sediment chronologies in the region. However, bedrock ridges under those boulders yield ages from 16 to ~100 kyr, indicating that the ice sheet was not effective at eroding the coastal plain Halifax pluton. On the coastal highlands of western Newfoundland previously believed to be nunataks during the LGM, erratic boulders on the St. John's Highland (13.5±0.4 ka, n=4) and on Big Level (20.9±3.0, n=1) mark the timing of deglaciation which is consistent with existing radiocarbon chronology and interpretations of offshore multibeam bathymetry data. However, bedrock in the highland summits record a much longer exposure history, in places over half a million years, indicating that although the glacial ice cover was extensive, ice dynamics of a polythermal glacier inhibited erosion of the summits whereas erosion in the valleys was intense. This observation is consistent with the pattern of glacial erosion in the Torngat Mountains. On the subsummit plateaus where erratics average 11 ka (Younger Dryas chron), the bedrock they rest on range from 11 ka to > 350 ka. An increasing concentration with elevation above the valley floor is apparent and supports an erosion mechanism linked to the basal thermal regime of the ice. A clearer account of glacial erosion under polythermal ice has been recently documented with cosmogenic nuclides from paleo-Barnes Ice Cap drift on Baffin Island.
Bibliography of Canadian Geomorphology