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Sun05May20192:00 pmCantley, Quebec
Guided Tour of the Sculpted Rocks at the Cantley Quarry
Leader: Dr. David Sharpe, GSC Geologist. David spoke to our club last year on glaciation.
Meet: Park on Chemin St-Andrew, just south of the quarry on the west side of highway 307, Cantley. The event will go on rain or shine.
The Cantley quarry is remarkable--beautiful and a very important geological site in our area, adding a great deal of information to the study of glaciation. Below is the abstract from a paper written about the site (Sharpe, D.R. and Le duc, G., 2018 ) for a CANQUA/AMQUA conference in Ottawa.
Several erosional forms on bedrock at Cantley, Quebec, differ from well-known glacial abrasion forms. The forms consist of obstacle marks, hollows, depressions, and channels, which are defined by sharp rims, smooth inner surfaces, divergent flow features, and remnant ridges. These forms are found on lee, lateral, and overhung rock surfaces. This assemblage of features is best explained by differential erosion produced by separation eddies along lines of flow reattachment. Rapid, sediment-laden, turbulent, subglacial melt-water flows likely produced the forms by corrasion and cavitation erosion.
Ice-abrasion forms, such as striations, and plucked forms such as gouges and crescentic fractures are also present at the Cantley site. Pitted forms, polishing, and carbonate precipitate are also present. The occurrence of abrasion, pitting, polishing, and lee-side carbonate precipitate with meltwater forms suggests that the meltwater flows were subglacial. Decoupling of abrading ice from its bed temporarily suspended glacial abrasion, whereas reattachment of ice to the bed may have led to the rounding of sharp edges and the production of striations superposed on the glaciofluvial forms.
The association of forms produced both by glaciofluvial erosion and ice abrasion suggests that the glacier was alternately lifted from, and reattached to, the bed during periodic subglacial floods. These floods may have affected the dynamics of the ice sheet, and depositional sequences related to high-energy meltwater outbursts were probably deposited in adjacent basins.
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