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April 23rd, 2014 ~ Vol. 84 No. 16
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Looking Back - John Kinnear
Geology Rocks - Literally - Part 1
Crowsnest Pass Herald Front Page
John Kinnear Photo
Cadomin conglomerate west of Coleman
We are blessed here in the Crowsnest Pass with some of the most spectacular scenery to be found anywhere. It is easy to become complacent about it all or forget to look around and marvel at the mountain landscapes that surround us.

That landscape has an incredibly complex geological structure to it that has been studied for over 150 years now by dozens of geologists. It started with George Mercer Dawson and J.B. Tyrell doing the first Government of Canada survey of the southern Rockies in 1883 and has been going on non-stop ever since. It is not unusual these days to see van loads of university students and their Profs stopped at some of the more high profile geological occurrences.

I thought it might be fun to thrust some of this geology at you the reader and in the process learn more about what it all means. And thrust is the right word here as the complexity of the Pass’ geology is a direct result of massive thrusting and folding and deformations as one of the earth’s tectonic plates shoved everything to the northeast for about 250 km. That is a lot of shoving and the end result is massive repeating of formations, older rock on top of younger rock and synclines and anticlines all over the place.

Let’s start at where Highway 22 hits Highway 3 and head west. Right off the bat as you look south from that intersection over top of the Crowsnest River you see a series of almost vertical formations of the Milk River Group one of which is known as the Virgelle Sandstone. It is massive white sandstone that forms the top of the ridge heading south from the river. The Virgelle is what they call a shore face and was formed from the beach sands of the ancient Colorado Sea. The amazing thing about the Virgelle is that is occurs west of this site at Lundbreck Falls where it is laying flat in what is called a “pop-up structure”. That is to say it is a horizontal wedge of what should be steeply dipping rock that popped up between two thrust faults. It the process we got an amazing water fall.

The Virgelle reoccurs several places heading west through the Pass including the big rock cut in Coleman just past the 7-11. My back yard butts up against the east side of that Virgelle ridge and it has caused me no end of headaches as it has banded zones of harder and softer sandstones. The softer ones erode easily and chunks of the harder zones above them break off (called jointing failures) and topple into my rock garden making a mess. When the 7-11 was replacing their fuel tanks a couple of years ago their excavation ran into the Virgelle and it resulted in them having to put smaller than designed tanks into the ground. Why? They just could not dig through this hard formation.
continued below...

Probably the most significant thing about the Virgelle is that way back to the east at the foot of the Livingstone Range is has a deposit of magnetite near the top of its formation that became the center of a fairly disturbing proposal to mine said magnetite. Hopefully this unwarranted disturbance of the magnificent eastern slopes of the Livingstone has gone away for good.

Returning to our eastern approach on Highway 3 you will find as you pass the Burmis Tree that you move through another massive sandstone feature just before you drop down to the Leitch Collieries turnoff. This is on the eastern side of the Blairmore Group, a very prominent formation throughout the Pass. It has distinctive greenish and maroon-colored sandstones and shale beds and the bottom of the formation is a massive sandstone conglomerate called the Cadomin. Just east of Leitch Collieries as the highway climbs towards the turnoff to Passburg you pass by a part of the Blairmore known as the Beaver Mines Formation. It is a big rock cut that has a mix of sandstones and shales and the continuous erosion of the softer rocks necessitates a yearly cleanup of the ditch there.

Iron provides the color in the Beaver Mines Formation with oxidized giving the purple layers and green coming from the layers that have been reduced (lost oxygen). Apparently some of the green color can also come from weathered volcanic dust carried on the wind from eruptions to the west. This formation reoccurs immediately west of the Bellevue Underground Mine on the highway and is prominent again west of Coleman just before the Coleman Collieries office.

The Blairmore Formation continues uninterrupted between Leitch and the west side of Frank except for very thin occurrences of the Kootenay Group. The Kootenay is the breadwinner around here and contains the coal bearing formation that attracted mining interests last century wherever it outcropped. That would be in Bellevue just east of the mine entrance, then in Blairmore near the old Greenhill’s mine site and then again in Coleman on the west side of town. The thin Kootenay formation outcrops run north/south in all three places hence so did the mines that drove into its coal outcrops.

You are driving on top of the Kootenay as you pass by the old Mohawk tipple and you stay on it until you drop down past the east entrance to Bellevue towards the old mine. As you head downhill the contact between the basal Blairmore Formation which is the massive Cadomin sand and the Kootenay Formation (coal visible on the right) is clearly in view. There is also a prominent exposure of the Cadomin just west of Coleman as you round the first corner out of town. The Cadomin is not that thick but man oh man is it hard. It is pebbles cemented together with microcrystalline quartz and sometimes looks like concrete. Some of the pebbling in it is green chert and we all know how hard that is. Ben Gadd in his book Geology Road Tours notes that the greenest of the chert pebbles in the Coleman outcrop of Cadomin look like those found in the Cache Creek Terrane which is hundreds of miles to the west. If this is true then finding them here tells us that rivers once flowed from central B.C. into Alberta.

Tune in next week when I will reverse thrust you all the way to Crowsnest Lakes. It’s not my fault tho!
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