[meteorite-list] Corossol Impact Structure, Quebec, Canada

From: Paul H. <inselberg_at_meteoritecentral.com>
Date: Fri, 18 Oct 2013 8:29:29 -0400
Message-ID: <20131018082929.ZJKZW.57792.imail_at_eastrmwml106>

Back in 2011, Higgins et al. (2011) published an extended
abstract about what they called the Corossol Impact
Crater, which is a 4-km diameter impact structure that
lies off of the coast of Sept-Iles in Gulf of St Lawrence,
Canada. They suggested that it might be as young as
12,900 BP based upon calibrated radiocarbon dates
from shells in marine sediments that directly overlie the
structure.

However, I am skeptical of it being a terminal Pleistocene
crater in that the colored relief map shown in that extended
abstract show a badly eroded impact structure that has
been strongly modified by erosion. The feature shown in
Figure 1 looks nothing like a pristine impact crater that was
created close to 12,900 years ago. In addition the calibrated
radiocarbon date corresponds exactly to the point in time
that various maps showing reconstructing the deglaciation
of North America indicate that this part of Canada became
ice-free as the Laurentide Ice Sheet melted back. Thus, the
12,900 BP date could very well be a minimum date that
indicates only when the site of the impact structure became
ice-free and sediments containing datable could
accumulate after being scoured by a continental ice sheet.
Finally, Higgins et al. (2011) pointed out that this impact
structure could be any age between 12,900 BP and local
470 million year old sedimentary rocks. This left it as an
uncertain candidate for a terminal Pleistocene impact.

More recently, I found an abstract by Locat et al. (2012).
After an analysis of "excellent" multibeam sonar coverage
of the area, they concluded on the basis of its surface
morphology that this impact structure exhibited the
characteristics of glacial erosion. Based upon other
morphological criteria, they estimated the minimum age
of this impact structure to about 20 million years. They
assigned a tentative age to it that ranged between 20 to
470 million years. Although this is still quite a range of
age, the estimated minimum age of 20 million years,
if it holds, would make it far too old to be the result of
an terminal Pleistocene impact. Also, a 20 million year
minimum age seems to be far more consistent with the
eroded appearance of this impact structure than a
12,900 BP age. if this impact structure is glacially
eroded, then it would even more unlikely that this is
the result of a terminal Pleistocene impact given the
glacial history of the region. However, further research
into the age of this impact structure is still needed.

Reference Cited

Higgins M. D., P. Lajeunesse, G. St-Onge, J. Locat, M.
Duchesne, J. Ortiz, and R. Sanfacon, 2011, 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), Abstract #1504.

Locat, J., P. Lajeunesse, G. St-Onge, M. Duchesne,
M. D. Higgins, R. Sanfacon, and J. Ortiz, 2012, A
morphological analysis for estimating the age of a
possible impact structure; the Corossol Structure
on the seafloor of the northwestern Gulf of St
Lawrence Eastern Canada. Congres Geologique
International, Resumes. vol. 34, pp. 3440.

Yours,

Paul H.
Received on Fri 18 Oct 2013 08:29:29 AM PDT