ABSTRACT: Laurentide deglaciation.

CGRG Bibliography of Canadian Geomorphology
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Abstract

An updated sequence of maps illustrating the deglaciation of North America was recently released as Geological Survey of Canada Open File 1574. These represent extensive revisions of the Dyke and Prest (1987; GＰgraphie physique et Quaternaire, 41: 237-263) ice margin reconstructions. Age control on ice margins and glacial lake shorelines is provided by a chronological data set of about 4000 radiocarbon dates as well as key varve and tephra dates. Dates on problematic materials, such as marl, freshwater shells, lake sediment with low organic carbon content, marine sediment, bulk samples yielding probable blended ages, and most deposit-feeding marine molluscs from calcareous substrates were excluded. These culled samples, many of which had been used in previous reconstructions, yield ages that are too old. Retained marine shell dates were adjusted for regionally variable marine reservoir effects, based on a new set of radiocarbon measurements on pre-bomb molluscs from Pacific, Arctic, and Atlantic shores. These corrections range from 800 years in the Pacific Ocean and the Champlain Sea to 450 years in the SW Gulf of St. Lawrence, and hence are larger than the previous "conventional" correction, a uniform 400 years. The net effect is that deglaciation ages are diminished in most places by 1000-2000 years in comparison to Dyke and Prest (1987). However, the spatial pattern remains similar to previous reconstructions, being guided by the continental scale glacial geology. The revised deglaciation chronology places most of the major mid-deglaciation moraines into the Younger Dryas interval and brings the deglaciation of Hudson Bay into correlation with the 8200 cal yr BP event (Barber et al., 1999; Nature 400: 344-348).

Bibliography of Canadian Geomorphology