Evidence Suggesting a Meteorite Impact Origin for Lac Couture, Quebec.

Lac Couture is a circular lake of diameter 16 km with a central island-free area of 10 km diameter and depth 150 m. The central area is surrounded by a shallower zone characterized by numerous islands and peninulas all of which show marked indications of glacial action, the direction of ice movement being from east to west. An examination of the bedrock of the islands showed many locations of heavy shattering with some indications of stratified gneisses tilting away from the lake center. Most of the islands and peninsulas examined showed numerous boulders and other types of glacial debris, and on a number of islands on the westward side of the lake this debris included large quantities of rock breccia of the type normally associated with meteorite impact. Since no evidence was found of consolidated sediments in the lake or sedimentary rock fragments in the glacial debris, it was concluded that the rock breccia had been dredged from the lake bottom by glacial action. The evidence as a whole suggests an ancient and eroded meteorite crater of approximately 12 km diameter, of which the circular fringe of islands and peninsulas represents the remains of the rim, formerly several hundred meters in height.