April 30th, 2014 ~ Vol. 84 No. 17
Looking Back - John Kinnear
Geology Rocks – Literally – Part Two
Crowsnest Pass Herald Front Page
John Kinnear Photo
Crowsnest Formation aka Crowsnest Volcanics
Let see now. Where were we? Oh yeah, we wuz headin’ west out of Coleman on an amateur geology road tour. Last week’s wanderings ended at the Cadomin conglomerate just west of town. Just past there one passes by yet another west dipping section of the aforementioned Beaver Mines formation, just before you cross McGillivray Creek. If you look carefully on the east side of the Beaver Mines formation here you will see a curious reddish vertical intrusion into the bedding. It appears to be a clastic dyke, a seam of reddish sedimentary material that has thrust up into a vertical crack in the formation. Seems like the whole Pass has been thrust one way or another!

About a kilometer west from here, just past the government shed corners heading up the hill, you will find what is known as the infamous Crowsnest Formation volcanics. The rock in this massive road cut began as a lava flow (lahar) and has been dated to between 94 million and 90 million years old. So where was the volcano that this flow came from? Apparently it was roughly located near Cranbrook about 100 kilometers away. So did the lava flow that far? Nope, the most lava will flow is around 10 km. These volcanics were eventually thrust northeastward to their present location during what they call the mountain-building period. Like I said, a lot of shoving around went on back then.

The volcanic lava hardened into what is called trachyte which is rock composed of pinkish feldspar and greenish pyroxene; minerals that are common to rock that have been erupted like basalt. Within the volcanics also are black melanite crystals known as phenocrysts which are basically crystals that have grown in the igneous rock. As a young boy I used to work hard to dig out these mini “black diamonds” from their matrix. In the geologic world the Crowsnest Volcanics are referred to as Blairmorite but as far as I am concerned they should be called Colemanite!

From the pullout at the volcanics one has a spectacular view of Crowsnest Mountain and the Flathead Range to the south. A remarkable feature that is not apparent in this view is that there is a massive thrust fault that runs through the Flathead Range north into Crowsnest Ridge and Mount Tecumseh and on further north through the High Rock Range west of Crowsnest Mountain. It is known as the Lewis Thrust fault and runs for 425 km (Glacier Park to Canmore!) and the horizontal displacement along this fault is in the order of 115 km. Now that’s some thrust fault.

It runs down low through the bottom third of all these mountains and under Crowsnest Mountain just above the tree line. Erosion has wiped out evidence of it between the Crow and the High Rock Range (Atlas Road valley) and left the Crow sitting all by itself making it a klippe which is by definition an erosional remnant of a thrust sheet. Chief Mountain down near Waterton and Mt Hosmer near Fernie are also known as klippes. So if you were to walk up the Crow until you reached that Lewis thrust fault contact and followed it horizontally you would wind up walking all the way around the mountain.
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The Crow as we know has older rock (Livingstone, Banff and Palliser formations) on top of younger rock (Belly River Group) which basically makes it an upside down mountain. There are a lot of these formation reversals in the Rockies thanks to major and minor faulting.

Just past the Bohomolec Ranch there is a rock cut you pass through that is another interesting geological formation. It is known as the Cardium and is gray-green sandstone that is only 50 -100 meters thick. It lies between two shale formations known as the Wapiabi and Blackstone. I worked in oil and gas many years ago and the Cardium Sand is a most prolific producer of oil. In fact it accounts for 11 percent of all conventional oil in Western Canada. It is the perfect reservoir rock, meaning it has permeability and porosity. That is to say it has lots of small spaces that hydrocarbons can migrate into and lots of connections between the spaces so that when penetrated its oil will flow freely to the well.

The Wapiabi Formation at Bohomolecs also runs through the east half of Coleman and within its black shale one can find scaphites, ancient sea cephalopods sometimes called ammonites. I found a fine specimen exposed in the ditch right next to the Best Canadian Motor Inn. These little chambered boat-shaped shells are found in the Late Cretaceous Western Interior Seaway, an ancient seaway that reached from the Arctic Ocean all the way to Gulf of Mexico. The Cardium sand, which is referred to as a clastic, was in fact deposited in this very long ancient strait. Clastics by definition are just chunks and smaller grains of rock broken off other rocks by physical weathering.

Our final stop on this geological meander will be at the big rock cut at Crowsnest Lake. On the east side of this cut the Lewis thrust fault emerges and west of there we find a massively long stretch of limestone from what is called the middle carbonates. In the midst of this cut is a narrow dark band of rock known as the Exshaw Formation. Last June the water was running down there like a river and in the process wiped out some rather interesting concretions that were exposed in this black shale that lies between the Palliser and Banff formations. The Exshaw is only about 7 meters thick and is a hydrocarbon-soaked marine shale found throughout a lot of North America despite its thinness. If you were to chuck a piece of it into a fire it would glow. When you look up at Mt. Hosmer from Fernie you can see this vertical narrow black band very clearly at the top of the mountain.

Just a brief glimpse at some of the amazing geology of the Crowsnest Pass. Don’t you think it is time we interpreted it with pullouts and signage?
April 30th ~ Vol. 84 No. 17
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