Ground Exploration of the Brent Impact Crater – Part II
In April 2006 a group of keen amateur crater geologists (rockhounds) from the Ottawa RASC re-explored the Brent Crater. The purpose of the expedition was to find a deposit of impact breccia that I understood was on a creek bed somewhere in the south-east arc of the crater. Various papers on the Brent Crater that I had studied indicated this. My planning centered on the creeks in the south-east rim area and how we could systematically explore them. Again I chose the early spring for the expedition in order to avoid the “bugs”. Our search for the breccia deposit was in vain but we did encounter a spectacular structure related to the impact along with other geological impact features.
That morning we met at the lookout station that overlooks the crater. Our exploration started at a dry creek bed in the south-east corner of the crater bowl and following it down to the crater floor. There was very little exposed rock in any of the creek beds as the crater wall was thickly covered by glacial till. Our first stop (position A) was at the “shattered rock” cliff that I had visited on my first expedition (illustrated in Part I as position #6).
There is an “arc” of this shattered rock around the south-east bowl of the Brent Crater. From this first shattered rock exposure we descended to Tecumseh Lake that is situated on the floor of the crater. We then traveled north along the east shore of the lake to find the mouth of the second creek that I wanted to explore. We would follow this creek back up the crater rim in our search for the breccia. The slogging was pretty tough once we got off the groomed trail.
After lunch, our second tour into the crater started a bit further to the west, from the creek originating at Rand Lake. Again, there were no bedrock exposures along the creek as the glacial till was too thick. The creek did reveal talus deposits (position C) near the floor of the crater. The talus in the crater was formed when the crater wall was eroded creating built up piles of fallen rock fragments (talus). The motion from the water that filled the crater washed into the talus slope and eroded the sharp edges of the rock fragments and filled the spaces between the fragments with mud. Over time the mud solidified into gritty limestone.
