Sunday, June 24, 2007

La Rouge - Part Deux

This weekend marked the start of the Bass Season. For all the spring, the mother fishies have attended their nests. At the marina, we could see a stationary double whirlpool, as some very large bass, deep below, was fanning her eggs. I celebrated by actually buying worms, but we only caught nasty little rock bass. When I catch a largemouth, I let it go, and it never goes after my hook again. I only catch the visiting tourists!

Back to my story. Here I was, convinced that as long as I had nice tight, highly stressed rock, I wouldn't have any big old faults for many miles. But Rouge Valley was a puzzle. The only hope I had was that tons of 'glacial shove' features had been mapped there before, but we couldn't dismiss this big sucker. Here it is (I think):

Fortunately, people were taking this seriously and I had some money at my disposal. I configured this a big scientific endeavour where everything would be published (behind the paywall!). We had geologists map the whole valley. Nearly all features were classic ice shove, except one. We mapped that feature, and got the strike and dip. As you can see, the cliff side of the river is inaccessible, but the fault could be traced over the river to the nice flat side.

There, we laid out 6 boreholes that were going to be drilled down to my favourite limestone marker bed, that I felt in my bones would be as flat as a billiard table. The wildcat drilling began! People who can get access to the papers can read all the gory details, but the big fault petered out, and underneath all the holes was our glorious marker bed, as flat as the day it was made!

Still, it was amazing how deep the glacial damage had gone, and it clarified a lot of geological observations for me. All throughout Southern Ontario are these insidious clay zones, right in the middle of solid rock. The drillers hate them, because if they hit one when they're hung over, it can suddenly clog the water flow and blow the whole dang thing up! (Drillers are hung over a lot!).

As well, the foundation of the CN tower was full of these clay zones and mashed up rock. I am now convinced that nearly all the surface sedimentary rock in southern Ontario can be mushed up to a depth of 20-30 m, which makes it almost impossible to come to some tectonic conclusion by just stumbling over a surface fault. All the more fun for geophysics!

No comments: