Keewatin Ice Sheet—Re-evaluation of the traditional concept of the Laurentide Ice Sheet

Abstract

Patterns of dispersal of distinctive Proterozoic and Paleozoic erratics across terrain formed on Archean and Aphebian crystalline rocks indicate that (1) ice never flowed from Hudson Bay into Keewatin in the region from the Manitoba border (lat 60°N) northward at least to lat 65°N; (2) westward-southwestward flow out of the bay, probably from a Labradorean dispersal center, interfaced with southward-and southeastwardflowing ice from the Keewatin dispersal center somewhere between Nelson River and Churchill; and (3) at least 300 km of dispersal of distinctive erratics observed from the vicinity of the last position of the Keewatin Ice Divide to the present coast of Hudson Bay required considerably more time than the 1,000 to 3,000 yr that the divide has traditionally been thought to have existed. In fact, the Keewatin Ice Divide and its precursors represent the centers of an independent, land-based ice sheet that probably existed throughout the period of Wisconsin Glaciation.

Deglaciation of the Laurentide Ice Sheet from the Last Glacial Maximum

“…The incorporation of deforming beds also generated multi-domed configurations that were deemed to be more compatible with the emerging geological evidence at that time (e.g. Shilts et al, 1979;Shilts, 1980;see Fig. 2).…”

“…2). This geometry attempted to reconcile new evidence from erratic dispersal trains that clearly indicated a complex multi-domed configuration (Shilts et al, 1979;Shilts, 1980). Dyke and Prest (1987) also discussed the importance of ice streams and the availability of 'soft' deformable sediments (cf.…”

Are long subglacial bedforms indicative of fast ice flow?

“…This ow-set has been mapped previously (e.g. Bird 1953;Lee 1959;Shilts et al 1979;Aylsworth & Shilts 1989a, b) and is also represented on the Glacial Geological Map of Canada (Prest et al 1968). Aylsworth & Shilts (1989b) speculated that the ow pattern could have been produced by an ice stream, and Boulton & Clark (1990b) attributed it to a late glacial event (c. 10 000 yrs BP) related to a southeast shift in the Keewatin Ice Divide.…”

Late Wisconsinan and Holocene History of the Laurentide Ice Sheet*

“…2). One type, typified by the Dubawnt dispersal train of Keewatin (SHILTS et al, 1979), consists of debris spread down ice from a relatively isolated source area; ice flowed across the entire region, including the source area, in the same direction for the same duration. The dispersal train provides information on direction of flow and useful information on distance of transport and rate of mixing with debris from sources down ice, but it does not provide information on relative rate of flow of the ice that formed the dispersal train compared to rate of flow of ice on either side.…”