Part 1

Geology

of

the

Bow River region

Geology of Canada Canada is comprised of three major physiographic regions: the Canadian Shield is the country’s

geological core and is comprised of igneous and metamorphic rocks that are 1 to 4 billion years

old; the Interior Plains sedimentary basin contains deposits from terrestrial and marine

environments that are 560 to 10 million years old; and the Rocky Mountains, which were

constructed by tectonic activity 170 to 55 million years ago.

Over the past 800,000 years Canada has experienced a series of glacial episodes, culminating in

the Wisconsin period of glaciation that reached its maximum extent (see picture below) about

20,000 years ago. At this time, there was an extensive glacier called the Laurentide sheet to the

North East and a Cordilleran sheet covering the Rockies in the West. The flow of ice and melting

of glaciers carved out the terrain and deposited sand and gravel on it, creating the topography

that we see today.

Geology of Alberta If we were to take a cross-section of the rocks in Alberta it would look like the diagram below.

The principal rocks that can be observed at the surface are Cretaceous and Tertiary sandstones

and mudstones, blanketed by Quaternary sand and gravel glacial deposits. Upper Devonian

limestones are also important in Alberta – they are mostly deep below the ground, outcropping

only in the East of the province, and are the primary source of oil and gas in the Province.

Geology of the Bow River region The rock outcrops in the Bow River area comprise Cretaceous, Tertiary, and Quaternary

sedimentary deposits.

Eon Era Formation Facies

Cainozoic

Quaternary Glacial and river deposits

Tertiary Paskapoo Fluvial sandstones, siltstones and mudstones, with some pebble-conglomerate and coal.

Mesozoic Cretaceous

Belly River Fluvial, deltaic, and shallow marine sandstones, siltstones & coals

Upper Benton Black marine shales

Cardium shore face and shallow marine sandstones with interbedded mudstones and gravel horizons.

Lower Benton Black marine shales

Blairmore Braided river, channel, floodplain, and coastal plain sandstone, siltstone and shale

The rocks that you see forming the landscape between Cochrane and Morley are a mixture of

Quaternary glacial surficial deposits and Tertiary and Cretaceous bedrock.

Cretaceous in Canada During the Cretaceous era (144 to 65 million years ago), creation of the Rocky Mountains was

ongoing and rocks on the east side of the mountains were warped downwards to create a basin

that became a North-South trending inland sea in which sediments were deposited.

Multiple fluctuations in sea level, with an amplitude of over 250m, resulted in the shallow sea

periodically deepening significantly, as sea levels rose, or becoming terrestrial, as sea levels

dropped. The sediments deposited during this time ranged from deep marine shales, through

shallow sea sands to fluvial and deltaic gravels, sands, siltstones, and coals.

The tectonic activity responsible for the creation of the mountains was also responsible for

folding and faulting of compacted Cretaceous sediments in what is now the foothills region.

In the Cretaceous, both terrestrial and marine environments supported a rich diversity of fauna

and flora.

Cretaceous terrestrial fauna & flora

Cretaceous marine fauna

Cretaceous in the Bow Valley region Terrestrial, shallow marine and deep marine environments are all represented in the rock

outcrops in the Bow Valley region.

Belly River Group The Belly River Group takes its name from the Belly River, a tributary of the Oldman River in

southern Alberta. The sediments were deposited in a terrestrial environment comprising rivers

and deltas and, when sea levels rose slightly, in shallow marine environments. The rocks

deposited are sandstones and siltstones with some minor coal, green shale and concretionary

beds.

Remains of the small ceratopsian dinosaur Montanoceratops have been found in the rocks of the

Belly River Group. It was a small sized, moderately-built, ground-dwelling, quadrupedal

herbivore, that could grow up to an estimated 3 m (9.8 ft) long.

Good outcrops of the Belly River group can be found immediately below Ghost Dam and in

Cochrane in the cliff section next to the Bow River about 200m West of Highway 22. Sedimentary

Depositional environment of Cardium

shore face & shallow marine sands, gravel and

mudstones with ripples, trace fossils & cockle shells

Depositional environment of Upper

Benton and Lower Benton

Deep, quiet sea below the wave base

allowing suspended clay minerals in the

water column to settle out

Depositional environment of Belly River

Group

Fluvial, deltaic, and shallow marine sands,

silts, and coals.

WEST

features such as cross-bedding, wood casts, coal seams, plant rootlets, pebble beds, shell

deposits and burrows can all be observed at these locations.

Upper and Lower Benton The Upper and Lower Benton comprises black marine shales that were deposited in the Upper

Cretaceous at a time of high sea level. The rock formation derives its name from Fort Benton, a

small city in Montana on the Upper Missouri River.

The shale is black because it was deposited in an anoxic (oxygen-free) environment and the

organic (black, carbon-based) detritus entrained in the clay and silt was preserved instead of

being degraded, which it would have been if the environment had been oxygen-rich. From time

to time storms would stir up sand in the adjascent shallow seas and flows of sandy debris would

hurtle downwards into the muddy sediments below.

Because these shales are soft, they tend to erode easily and outcops are difficult to find. An

excellent location to view these shales is in the cliffs on the West side of the Ghost River and the

North side of Ghost Lake.

Cardium The Cardium formation is named for the Cardium cockles that are commonly found in the rocks.

The sediments were deposited as shore face and shallow marine sandstones with interbedded

mudstones and gravel. Ripple marks, trace fossils and cockle shells are abundant.

Cardium rocks can be found at Seebe Dam, where the Kananaskis river joins the Bow River.

Blairmore The Blairmore Formation comprises the oldest Cretaceous rocks in Alberta; only the upper part

of this formation is present in the Bow Valley region.

These upper Blairmore sediments were laid down in fresh water in braided rivers on coastal

plains and comprise interbedded sands and shales – the beds are quite hard due to compaction

beneath later Cretaceous sediments and to subsequent tectonic deformation. The shales are

coloured in various shades of green, brown, red and black

Blairmore rocks are exposed on the Kananaskis River.

Tertiary in the Bow Valley region

Paskapoo The Paskapoo underlies much of southwestern Alberta, and takes its name from the Blindman

River - paskapoo means "blind man" in Cree. It was first described from outcrops along that river,

near its confluence with the Red Deer River by J.B. Tyrrell in 1887. It is important for its freshwater

aquifers, its coal resources, and its fossil record, as well as having been the source of sandstone

for the construction of fire-resistant buildings in Calgary during the early 1900s. Many of Calgary's

early landmark buildings, such as the Lougheed House, Burns Manor, and some of the buildings

along Stephen Avenue, were built using Paskapoo sandstone, and Calgary became known as the

Sandstone City. Paskapoo sandstone is still used in landscaping in the Calgary area today.

The Paskapoo Formation is of fluvial origin and consists primarily of sandstones, siltstones and mudstones, with lesser amounts of pebble-conglomerate and coal. The sediments were derived from the Canadian Cordillera during tectonic uplift and erosion; they were transported eastward by river systems and deposited in fluvial and floodplain environments. The sandstones were deposited in river channels. They are cross-bedded, medium- to coarse-grained, and locally conglomeratic. The siltstones and mudstones represent crevasse splay, overbank and shallow pond environments. They include plant fossils, rooted horizons and paleosols. Carbonaceous mudstones and coaly beds that represent oxygen-poor, swampy settings are thin and discontinuous, but common. Thick coal seams that formed in well-developed swamps are present only in the youngest portion of the formation, which is preserved near Hinton.

The Paskapoo Formation contains remains of vertebrates, especially mammals, and plants, freshwater fish, impressions of insect wings and larvae, and shells of freshwater molluscs.

Locally, an accessible outcrop of Paskapoo can be found in Cochrane Ranche by the statue of

“Men of Vision”.

Quaternary in the Bow Valley region As the Laurentide ice sheet retreated to the East, meltwater rivers flowed Westwards and

deposited a series of sand and gravel river terraces. Later, as the Cordilleran ice sheet in the

Rockies also began to melt, more river terraces were deposited.

In the Bow River region, a lake formed where the cordilleran meltwater met the retreating

Laurentide glacier.

A variety of glacial features were formed at this time, and can be seen across the region. An

excellent example of a drumlin field can be found at Morley flats.

Bones of vertebrates can be found in some glacial deposits, commonly the Mexican ass and the

Western bison.