By the mid-1970s, oil and gas exploration by industry had revealed a thick succession of strata on the continental margin off Nova Scotia. The Geological Survey of Canada’s Atlantic office in Dartmouth, Nova Scotia, was charged with investigating the broad history of these strata.
During the investigation, a circular subsurface structure on the southwestern Scotian margin was discovered. Thinking that it could be a possible trap for oil or gas, Union Oil drilled an exploration well, Montagnais I-94, in 1974. The well proved dry, but it cut through over 500 metres of broken and once-melted rock. Considered at first to be of volcanic origin, further research suggested that the Montagnais structure originated from an extraterrestrial impact.
This has since been confirmed, making Montagnais the first-recognized impact structure formed from a meteorite striking the seafloor. Fossil evidence shows that the impact occurred some 50 million years ago. More recently, a huge underwater landslide associated with the Montagnais structure has been recognized, and the deposit from it is one of the largest-known of its kind.
Category: Science Advances
Jansa, L.F. and Pe-Piper, G., 1987. Identification of an underwater extraterrestrial impact crater; Nature, v. 327, p. 612–614. doi:10.1038/327612a0
Deptuck, M. and Campbell, D.C., 2012. Widespread erosion and mass failure from the ~51 Ma Montagnais marine bolide impact off southwestern Nova Scotia, Canada; Canadian Journal of Earth Sciences, v. 49, p. 1567–1594. doi:10.1139/e2012-075