Sedimentology and geomorphology of the glacial Lake Hind area, southwestern Manitoba, Canada

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Sun, Chuanyu (Stephen).
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Glacial Lake Hind was a 4000 km2 ice-marginal lake which formed in southwestern Manitoba during the last deglaciation. It received meltwater from western Manitoba, Saskatchewan, and North Dakota via at least 10 channels, and discharged into glacial Lake Agassiz through the Pembina Spillway. Surface sediment outside of the area covered by glacial Lake Hind is dominantly till. There are two types of tills based on their carbonate content and calcite/dolomite ratios: one that has high carbonate content and a low calcium/dolomite ratio (Dh), which occurs east of glacial Lake Hind, and another that has low carbonate content and a high calcite/dolomite ratio (Dl), which occurs north, west, and south of glacial Lake Hind, and may underlie Lake Hind sediments. Four till units have been identified based on carbonate content, texture, and color. They are the Wawanesa till, Souris till, Fairfax till, and Carroll till. Sediments in the Lake Hind basin consist of up to 30 m of silt and clay, 25 m of sand and deltaic gravels. Much of the uppermost lacustrine sand in the central part of the basin has been reworked into aeolian dunes. No beaches have been recognized in the basin. Around the margins, clayey silt occurs up to an elevation of 457 m, and deltaic gravels occur at 434 - 462 m. In addition, there are a total of 12 deltas around the lake basin, and these can be divided into 3 groups based on the elevation of their surfaces: 1) above 457 m along the eastern edge of the basin and in the narrow southern end; 2) between 450 and 442 m at the western edge of the basin; and 3) below 442 m. The earliest stage of glacial Lake Hind began shortly after 12 ka, as a small lake formed between the eastern edge of the Souris Lobe and the western edge of the Red River Lobe in southwestern Manitoba. Two deltas at an elevation of above 457 m were formed in this lake. At the same time, the western edge of the Souris Lobe retreated far enough to allow glacial Lake Souris to expand northward along the western side of the basin from North Dakota; three deltas were built at an elevation of between 457 and 466 m in the Canadian part of this proglacial lake. Continued retreat of the Souris Lobe allowed the merger of glacial Lake Souris with the interlobate glacial Lake Hind. Subsequent erosion of the outlet into the Pembina valley allowed waters in the glacial Lake Hind basin to become isolated from glacial Lake Souris, and four deltas formed between 442 and 450 m by meltwater from the west. Next, a catastrophic flood from the Moose Mountain uplands in southeastern Saskatchewan flowed through the Souris River valley to glacial Lake Souris, in turn, spilling into Lake Hind and depositing another delta at an elevation of about 442 m. This resulted in further incision of the outlet into the deep and wide Pembina spillway, and a new level of glacial Lake Hind was established at 434 m. A second flood through the Souris River valley, this time from glacial Lake Regina, further eroded the outlet; most of glacial Lake Hind was drained as a result of this flood except for the deeper northern part. Coarse gravel was deposited by this flood, which differs from previous flood gravel because it is massive and contains less shale.