NATURE AND TIMING OF MELTWATER PROCESSES IN SOUTHEASTERN MANITOBA, CANADA

Many southeastern Manitoba landforms and near surface sediments, including eskers, gravel sheets, and large moraine complexes, are attributed to meltwater processes during the Late Wisconsinan glaciation. This study explores the nature and timing of these processes.

Short, narrow, sand and gravel eskers and channel fills, ranging from <1 km to >10 km in length, stratigraphically overlie tills in the Interlake and Southern Uplands regions and are draped by Lake Agassiz clay in the Red River Lowland. These landforms record late-glacial R-channel and N-channel flow into Lake Agassiz. Gravel sheets (1 to 2 m thick, 1 to >10 km2 area), that occasionally exhibit an anabranched morphology, overlie tills in the Interlake and Southern Uplands regions. These sheets are more indicative of waning flow deposition from broad late-glacial meltwater flows into Lake Agassiz.

The Belair Moraine, which extends ~100 km along the eastern shore of Lake Winnipeg, is composed of an arcuate belt of stacked tabular beds and broad scour-fills in sand and gravel that rise 30 m to 50 m above the surrounding Red River Lowland. Stratigraphically, the Belair Moraine (i) overlies a till surface, (ii) is discontinuously overlain by carbonate-rich diamicton on its northwest flank, and (iii) is transitional to, and partly overlain by, Lake Agassiz silt-clay rhythmites. The stratigraphic architecture, upward and southeasterly fining lithofacies, and southeasterly paleoflow directions indicate that the Belair Moraine was rapidly deposited as a series of high-energy, coalescing subaqueous outwash fans in Lake Agassiz at the grounding-line of the northwesterly receding ice mass. A drop in lake level may explain both subaqueous fan deposition and till plastering on the up-ice side. Southeasterly cross-cutting channels, and subdued relief between Birds Hill and Mars Hill may be attributed to subsequent meltwater erosion under a near-floating ice margin corresponding to an ice advance into a rising Lake Agassiz.