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The Cantley Site:

Obstacle marks

Photo: Geodoxa

In June 2017, Geodoxa made the first 3D photogrammetric survey over the ancient gravel pit in Cantley, Quebec. A gigantic outburst of subglacial water eroded away many meters thick of marble of Grenville age (Precambrian). The marble contains harder volcanic inclusions more resistant to water abrasion leaving obstacle marks/tails on their lee side.


This video was presented at the CANQUA/AMQUA 2018 conference in Ottawa to prepare viewers for a field trip to the amazing site of Cantley, Quebec. The field trip was led by David R. Sharpe of the Geological Survey of Canada. The site was sculpted by catastrophic subglacial water at the end of the last Ice Age. The main s-forms are obstacle marks caused by the presence of harder granitic inclusion inside the white marble.

Cantley mable.JPG

In Cantley, the bedrock is composed of a marble spotted with a multitude of volcanic inclusions of all sizes ranging from millimeters to a few meters in diameter. These inclusions are composed of an intrusive volcanic rock much harder than the marble. During the subglacial flood these inclusions resisted better than marble.

 The following 3D models are drone photogrammetric surveys of the Cantley site.


Geology of the area

Cantley Megaobstacle Mark

Site 1 - Giant obstacle marks

Cantley Wall

Site 2 - Wall of erosion marks with a vertical cavetto

Tear shape obstacle mark

Site 3 - Tear shape obstacle mark. Ice abrasion of a glacier cannot carve such a shape with a over hanging roof.

Cantley gneiss

Site 4 - Gneiss rock East side of the road. The road marks the contact/fault between the 2 sorts of rock.

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