Differential thermal analysis of the sediments of the Lake Agassiz basin in Metropolitan Winnipeg, Manitoba
Wicks, Frederick John
Samples of the Keewatin (Gray) till bed, the blue-gray and brown clay beds of Lake Agassiz I Unit, and the yellow silt, greenish brown clay and fine sand beds of Lake Agassiz II Unit were collected from 2 sample locations in the Metropolitan Winnipeg area. Differential thermal analysis under dynamic gases, nitrogen, oxygen and carbon dioxide, of nearly 60 samples followed up by X-ray powder diffraction photographs, X-ray fluorescence analysis, and standard chemical analysis of 9 selected samples showed a common mineralogy between all the beds except the fine sand bed of Lake Agassiz II Unit. The dominant clay mineral component of the clay fraction was identified as an interstratified dioctahedral illite-montmorillonite, X-ray diffraction analysis indicated that the coarse clay fraction tended to be more dominantly illite and the fine clay fraction tended to be more dominantly montmorillonite, but differential thermal analysis showed both fractions to be similar interstratified illite-montmorillonite. ... Interpretation of the mineralogy of the beds showed that most of the material in the till originated from the Paleozoic carbonate rocks, with lesser contributions from the Precambrian rocks and minor contributions from the Cretaceous shales. Lake Agassiz I beds received most of their material from the Cretaceous shales with contributions from the glacier steadily decreasing as it retreated northward. The yellow silt bed was interpreted as receiving its material as wind blown till from the northwest, with the fine clay layers originating from minor fluvial or intermittent lacustrine activity. The greenish brown clay bed had a similar mineralogy and origin as the brown clay. The fine sand bed appeared to the originated from a nearby dolomite outcrop probably Stony Mountain, through fluvial activity.