Abstract

Fire Lake depression, which is 9 km long, 5 km wide, and about 100 m deep, was formed by surface removal of about 40 m of drift, mainly till, and 60 m of Cretaceous sands, silts, and clays. The depression, which was formed during the last glaciation, was partly filled with hummocky glaciolacustrine sands and silts. The bedrock beneath the depression is slickensided, folded, brecciated, softened, and gouged, typical of structures formed by shear.The physical dimensions, stratigraphy, structure, and age (last glaciation) indicate that the Fire Lake depression was formed by glacial erosion. The folding, faulting, brecciation, gouge, and softening of the bedrock beneath the depression are indicative of shear and suggest glacial thrusting. The process of glacial thrusting was not verified, however, because the sediments excavated from the depression were not found. The fact that the base of the depression corresponds to the uppermost, most clayey bed (least shear resistance) suggests that the depression was formed during one episode of glacial erosion.

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