Geology of the Cantley Quarry

May 13, 2019

Last Sunday afternoon, David Sharpe, a glaciologist with the Geological Survey of Canada, conducted a tour of the glacially-sculpted rocks at the Cantley Quarry. The attendees of the tour included members of the MFNC and MVFN club.

Excavation works at the quarry exposed bedrock which consists of Precambrian marble containing more resistant granitic and volcanic inclusions. These rocks were altered by a metamorphic event that occurred about 1 billion years ago. The bedrock exposures show glacial erosional textures as a result of a glaciation event that ended about 12,000 years ago. Surrounding the quarry and at higher levels are sand and gravel layers and beaches that were formed by the Champlain Sea, a part of the Atlantic Ocean that covered the area following the end of the glaciation period.

The erosional textures and forms, displayed very clearly in the marble, consist of obstacle marks, hollows, depressions, channels, scratches and gashes. These textures are best explained by the rapid flow of sediment-laden and turbulent melt water underneath the glacier and the abrasion of the glacier against the rock. The presence and association of textures produced both by water erosion and ice abrasion suggest that the glacier was alternately lifted from the rock bed during periods of water flow at the base of the glacier and subsequently reattached during periods of low or no flow. 

In his explanation of these textures, Dr. Sharpe emphasized the importance of the scientific method of looking for many lines of evidence to support observations.

It was a very enjoyable afternoon and David was an excellent guide to this amazing place. Also nice was the chance for members of MFNC to meet some of the folks from MVFN club. For an excellent overview of the site see the video by Guy Leduc, https://youtu.be/uYp8noIc_UK