COROSSOL STRUCTURE

Type: Central peak
Location: N 50°03′ W 66°23′ – underwater in the Gulf of St. Lawrence
Diameter: 4.0 Km;
Age: >12,900 years^a – PLEISTOCENE
Possible central peak crater

^a Calibrated ¹⁴C ages of shells in the sediments can be extrapolated to give an estimate of the age of the base of the sedimentary sequence of ~12,900 cal BP

The Corossol Crater is a complex crater ~4 km in diameter with a central uplift, a prominent moat, and multiple, low-relief ridges. Quebec, Canada.

Introduction

The Corossol crater (50°3’N, 66°23’W) was first discovered by the Canadian Hydrographic Service about 10 years ago while mapping the entrance to the Sept Iles harbour, Gulf of St Lawrence, Canada. It is a complex circular structure about 4 km in diameter with a central uplift that rises to about -70 m and an annular valley ~160 m deep. There are no other circular structures nearby.” (Higgins et al, 2011).

The Corossol Crater’s Origins Are Slowly Revealed

In 2001, a hydrographic survey conducted by the Canadian Hydrographic Service in Mont-Joli, on behalf of the National Defence, revealed the existence of a strange underwater crater. Found near Sept-Îles at a depth of 40 metres, this circular structure generated considerable interest among researchers, geologists and geomorphologists, who saw it as an “enigmatic form” of “great interest.”

Since then, scientific teams have sampled sediments and taken other measurements to determine the nature and age of the crater. The structure has a raised central core and concentric rings whose morphology and geometry resemble those of craters created by complex impacts. An article recently published in the international journal Meteoritics and Planetary Scienceestablishes that the age limits of this formation fall between 470 million years (Ordovician) and 12 600 years BP (Before Present). According to study results, the most realistic hypothesis suggests a violent impact, probably from a meteorite. The study indicates that other radiometric measurements are required to confirm these conclusions.

Scientists named the Corossol Crater after a ship from King Louis XIV’s fleet that ran aground near Sept-Îles in 1693. This discovery demonstrates how much remains to be done to truly broaden our knowledge on the country’s as yet unexplored seabeds.

The authors of the article The Corossol structure: a possible impact crater on the seafloor of the northwestern Gulf of St. Lawrence, Eastern Canada are researchers from the Université Laval (Patrick Lajeunesse and Jacques Locat), the Université du Québec à Rimouski (Guillaume Saint-Onge), the Geological Survey of Canada (Mathieu J. Duchesne), the Université du Québec à Chicoutimi (Michael Higgins), Kent State University (Joseph Ortiz), and Fisheries and Oceans Canada’s Canadian Hydrographic Service (Richard Sanfaçon). (InfoOcean Quebec Bulletin December 2013 – January 2014/Volume 16/Number 6)

Age of impact

At present it is only possible to give age limits. The maximum age is very difficult to establish. Clearly, it is younger than Ordovician, but it is not clear if it is younger or older than the cuestas. The paucity of sediments in the crater might be taken to indicate that it is young. The minimum age was established using data from a ~7 metre core taken in the central trough, which almost reached the basement, as defined by seismic data. Calibrated 14C ages of shells in the sediments can be extrapolated to give an estimate of the age of the base of the sedimentary sequence of ~12,900 cal BP, if no hiatus or older sediments were preserved between the base of the core and the bedrock. This is taken to be the youngest possible age of the impact.” (Higgins et al, 2011).

Suevite breccia clast dredged from the central uplift and the innermost annular rim. A) Scanned image of a thin section in non-polarised light. Limestone clasts are medium-grey. B) Planar deformation features in a crystal of quartz. Cross-polarised light. C) Broken fragment of a glassy droplet. Darker areas have a composition close to apatite, pale areas are pyritic. In the matrix calcite is pale and dolomite is darker. Back-scattered electron image. D) Carbonatitic material infilling between limestone fragments. Euhedral crystals are Dolomite. Plane-polarised light.

Ironically, while serving in the Royal Canadian Navy, I participated in naval exercises throughout these islands without realizing I was sailing over the Corossol crater.

References

[see – METEORITE]

Brent Dalrymple, Radiometric Dating Does Work! Reports of the National Center for Science Education

M. D. Higgins, P. Lajeunesse, G. St-Onge, J. Locat, M. Duchesne, J. Ortiz, R. Sanfaçon, BATHYMETRIC AND PETROLOGICAL EVIDENCE FOR A YOUNG (PLEISTOCENE?) 4-KM DIAMETER IMPACT CRATER IN THE GULF OF SAINT LAWRENCE, CANADA. 42nd Lunar and Planetary Science Conference (2011)