Multiple Deglaciations of the Hudson Bay Lowlands, Canada, Since Deposition of the Missinaibi (Last-Integlacial?) Formation

Abstract

The stratigraphic record in the James and Hudson Bay Lowlands indicates that the sequence of glacial events at the geographical center of the 12.6 × 106 km2 Laurentide Ice Sheet may have been more complex than hitherto imagined. Isoleucine epimerization ratios of in situ and transported shells recovered from till and associated marine and fluvial sediments cluster into at least 4 discrete groups. Two alternative explanations of the data are offered, of which we strongly favor the first. Hypothesis 1: Setting the age of the “last interglacial” marine incursion, the Bell Sea, at 130,000 yr B.P. results in a long-term average diagenetic temperature for the lowlands of +0.6°C. Using this temperature enables us to predict the age of shells intermediate in age between the “last interglaciation” and the incursion of the Tyrrell Sea 8000 yr ago. Between these two interglacial marine inundations, Hudson Bay is predicted to have been free of ice along its southern shore about 35,000, 75,000, and 105,000 yr ago based on amino acid ratios from shells occurring as erratics in several superimposed tills and fluvial sediments. These results suggest (1) that traditional concepts of ice-sheet build-up and decay must be reexamined; (2) that “high” sea levels may have occurred during the Wisconsin Glaciation; and (3) that a critical reappraisal is required of the open ocean δ18O record as a simple indicator of global ice volume. An alternative, Hypothesis 2, is also examined. It is based on the assumption that the 35,000-yr-old deposits calculated on the basis of Hypothesis 1 date from the “last interglaciation”; this, in effect, indicates that the Missinaibi Formation, commonly accepted as sediments of the “last interglaciation,” are about 500,000 yr old and that the effective diagenetic temperature in the lowlands during approximately the last 130,000 yr has been close to −6°C. We argue for rejection of this alternative hypothesis.

Objective Reconstructions of the Late Wisconsinan Laurentide Ice Sheet and the Significance of Deformable Beds

“…If the bed under Hudson Bay is frozen solid, and is thus not deformable, then the steady state model ice sheet would look like Figure 2, whereas a long enough interval of time with a melted- There are some lines of evidence that suggest several cycles of growth and decay of the Hudson Bay ice during the Wisconsinan ice age. ANDREWS et al (1983) maintain from amino acid analysis of shells that southern Hudson Bay was ice-free at 35 ka, 75 ka,and 105 ka; i.e. that there were three complete cycles of growth and decay of ice over Hudson Bay during the last glaciation.…”

Are long subglacial bedforms indicative of fast ice flow?

“…As more evidence is being uncovered which suggests that former ice sheets changed their volume and area rapidly, the latter option becomes less likely (cf. Andrews et al 1983;Boulton & Clark 1990a, b;MacAyeal 1993). This led Stokes & Clark (1999) to postulate highly attenuated bedforms (elongation ratios >10:1) as a speci c geomorphological criterion for identifying palaeo-ice streams.…”

Significance of Sedimentological Studies on the Wisconsinan Stratigraphy of Southern Ontario

“…The result implies that there is no precise timing for channel formation postdating the deltaic Scarborough Sands and that high ice-marginal lakes may have occupied much of the western Lake Ontario basin during Wisconsinan time. This conclusion is at odds with interpretations from the Hudson Bay Lowlands (ANDREWS et al, 1983) that suggest several nonglacial (marine and therefore limited ice extent) episodes during Wisconsinan time based on amino acid results.…”