Late Quaternary till stratigraphy of southeastern Manitoba based on clast lithology
Keatinge, Penelope Rosanna Gann
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Lithological analyses were made on the 4 to 16 mm and 1 to 2 mm particles in samples of till which were collected from boreholes and surface samples sites in southeastern Manitoba. On the basis of these analyses and on the basis of matrix texture and stratigraphic position, a Quaternary stratigraphy was established in southeastern Manitoba. Two main groups of till units were found, one containing abundant igneous and metamorphic clasts and few carbonate clasts, the other containing few igneous and metamorphic clasts and abundant carbonate rock fragments. Ten till units were identified in the study area... These units have been correlated with the units in northwestern Ontario, southeastern Manitoba, and also with units in North Dakota and Minnesota on the basis of their similar lithologic characteristics and stratigraphic position. In general, the sandier, Precambrian-rich till units were deposited by ice moving across the Precambrian Shield from the east or northeast, while the less sandy, carbonate-rich tills were deposited by ice advancing across the Paleozoic strata from the north or northwest. The exact ages of the lower three till units are uncertain. The Woodmore Formation and Stuartburn Formation were deposited by an ice advance from the northwest before 39 000 years B.P. and may be early Wisconsinan or pre-Wisconsinan in age. Deposition of the first late Wisconsinan till, the Senkiw and Whiteshell Formations, took place after 22 260 years B.P. when ice moved into the area from the northeast. following this, ice advanced from the north or northwest depositing the Roseau and Sprague Formations. Retreat of this ice sheet and subsequent readvance before about 12 800 years B.P. deposited the Marchand Formation. The last advance into the study area deposited the Steinbach till before about 8 000 B.P.