BRENT IMPACT CRATER – GROUND EXPLORATION – 4

Ground Exploration of the Brent Impact Crater – Part IV       (a detailed analysis of the fractured rock canyon)

by: Charles O’Dale

In the spring of 2025, the Ottawa RASC undertook an expedition back into the Brent Impact Crater to make a detailed analysis of the “fractured rock canyon” that I discovered almost 20 years ago.

The intrepid RASC crater explorers at Brent (L-R;  Chris, Louisa, Gillian, yours truly, Paul and Andrew. Here I am at my 79th birthday ready to trek through the bush to rediscover my fractured rock canyon AKA “mini grand canyon”. What could possibly go wrong??
In 2006 I took this image of the fractured rock wall (mini grand canyon) within the Brent Impact Crater. I was searching for breccia at the time and did not stop very long to appreciate what I found.

A bit of background to explain the fractured rock wall that we will document:
– the Brent Impact Crater is a large meteorite impact structure located within Algonquin Park in northern Ontario, Canada. The impact caused significant fragmentation of the surrounding rocks, with evidence of shattered rock on the crater walls and a talus slope of broken fragments. The crater is also partially filled with sedimentary rocks, with the fragmented rock layers extending to a depth of 2,000 feet;
– “the recognition of preserved shock effects has been the main factor behind the steady increase in the number of recognized impact structures since the 1960s” (Grieve 1991);
– bolide impact “shock-wave pressures differ in other important ways from pressures produced by more normal geological processes. The application of shock-wave pressures is both sudden and brief. A shock-wave traveling at several kilometres per second will traverse the volume of a mineral grain or a rock sample in microseconds, and both the onset and release of pressure are highly transient. Shock-deformation effects therefore reflect transient stress conditions, high strain rates, and rapid quenching that are inconsistent with the rates of normal geological processes” (French 1998);
–  while travelling north on the Trans Canada Highway from Ottawa, toward the Brent impact crater, a casual look at the various rock cuts will reveal increasing examples of “shattered rocks”. The damage to the rock walls increases the closer you get to the Brent impact crater.

Fossilized talus debris within the Brent Crater containing shattered bedrock caused by the impact transient pressures.
Paul sampling solid bedrock exposed on the crater rim. The fractured rocks in this area would have been removed by glaciers thousands of years ago.
This high altitude image of the Brent crater shows a vague circular area with two bordering lakes.
Within the crater, the fracture zone contains a wall of shattered rocks that is caused by the transient impact pressures (circled).
The fractured rock wall within the Brent Crater. The mini canyon through the shattered bedrock wall was created  by water erosion over many thousands of years.
Illustrated here (with my hiking poles for scale) is “the Precambrian crystalline igneous-metamorphic basement complex mainly of gneiss of granodioritic composition of the Grenville structural province” (Grieve, 1978), fractured by the bolide impact transient pressures.
Gillian, Andrew and me within the mini grand canyon. The crater wall is rising in the background.
This image from within the canyon illustrates our intrepid explorers climbing the crater wall.
A view of the fractured rock canyon looking back from the crater wall.

It was great to see the canyon again almost 20 years after my initial discovery. My 79-year-old legs survived!!

And finally, the small red dot under the wing of our airplane (GOZooM)  indicates the approximate position of the fractured rock canyon.