CGRG Bibliography of Canadian Geomorphology
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Author : Gosse, J.; Gray, J.; and Grant, D.
Date : 2002.
Title : Uses of in situ cosmogenic nuclides for supporting geomorphology and ice cover simulations for Atlantic Canada.
Publication : Atlantic Canada Glacier Ice Dynamics Workshop, May 22-24, 2002. Dalhousie University, Halifax, Nova Scotia.
Issue :
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Abstract
In glaciated regions, concentrations of cosmogenic nuclides can be used for more than just tracking deglaciation. The isotopes can be used to provide information regarding the duration of ice cover, the duration that the ice margin fluctuated near its maximum position, and the conditions of ice-bed interaction. In Atlantic Canada, studies involving one or more isotopes have been used to support interpretations based upon geomorphological observations on highland plateaus and dissecting valleys. With single isotopes, it seems wherever we have sampled, the highest summits in the Torngat Mountains and Long Range Mountains have been covered by ice of the last glaciation. In Newfoundland, deglaciation of plateau ice caps (a single perched block has an exposure age of 18 kyr) seems to have preceded deglaciation of the fjords (e.g. Ten Mile Pond Moraine). In Labrador, ages on all erratics dated on summits fall within the Younger Dryas chron, the proposed age of the last component of the latest local (Saglek) glaciation. Unlike the erratics, ages on bedrock or felsenmeer blocks show a distinct trend with elevation. Bedrock surfaces in the lowest (LGM) weathering zones have single isotope exposure ages consistent with radiocarbon chronology of deglaciation. This suggests that any inherited nuclides produced in the rock surface prior to glaciation were completely removed by glacial erosion. However, at higher altitudes, the single isotope exposure ages in bedrock are older than the ages in the lowest weathering zone and older than the ages of adjacent erratics. This suggests that some concentration of nuclides in bedrock in the higher weathering zones survived glaciation. Because the erratics indicate the terrain was completely ice covered, the difference in nuclide concentrations can only be explained by decreases in the glacial erosion of the bedrock with height. Ratios of two nuclides (26Al/10Be) show similar patterns. Samples from bedrock on the highest summits have ratios indicating that the exposure was interrupted by long periods of shielding (by ice?) or that the surface was episodically eroded (plucked) to depths greater than 60 cm, but not sufficiently deep to remove all inherited values. Samples from bedrock in the lowest weathering zone have ratios that imply continuous, uninterrupted exposure to cosmic rays, indicating no inheritance from exposure prior to the last glacial cover.
Bibliography of Canadian Geomorphology