The Blairmore Group, originally named the Blairmore Formation, is a geologic unit of Early Cretaceous age in the Western Canada Sedimentary Basin that is present in southwestern

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...

and southeastern

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

. It is subdivided into four

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

Cadomin Formation The Cadomin Formation is a stratigraphic unit of Early Cretaceous (Barremian to Aptian) age in the western part of the Western Canada Sedimentary Basin. It is extends from southeastern British Columbia through western Alberta to northeastern Bri ...

, Gladstone,

Beaver Mines Beaver Mines is a hamlet in southern Alberta, Canada within the Municipal District of Pincher Creek No. 9. It is located in the foothills of the Canadian Rockies on Highway 507, approximately west of Pincher Creek. History The community wa ...

and Ma Butte , all of which are defined by type sections, most of which contain plant fossils. In some areas the Blairmore contains significant

reservoirs A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including control ...

of natural gas.

Lithology

The Blairmore group includes the conglomerate and

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...

ose

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s of the

at the base, and grades to sandstone, siltstone, mudstone, and

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

in the overlying formations. The Cadomin Formation has beds of quartzose sandstone and, in some sections, especially in the eastern foothills, is totally quartzose sandstone. It is normally a very durable,

siliceous Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

pebble conglomerate. A sequence of interbedded, highly variable-proportioned grey mudstone to sandstone layers makes up the bottom portion of the underlying Gladstone Formation. Sandstones, whose grain size rarely exceeds fine, frequently show a noticeable upward decline in grain size. Dark grey,

argillaceous Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay minerals ...

limestone and fossiliferous calcareous shale make up the top Gladstone Formation. Limestone deposits are few or nonexistent north of the Clearwater River (52°N). Both the Beaver Mines Formation in the south and the Mountain Park Formation in the north are made up of interbedded mudstone to very fine-grained sandstone with minor but noticeable thicker and coarser sandstone units that have abrupt bases and fining upward grain size. Conglomerate beds make up a small portion. The marine mudstone Moosebar Member of the Malcolm Creek Formation, which is restricted to the region north of Waiparous Creek (51°20'N), is overlain by the notable sandstone-dominated Torrens Member and the coal-bearing Grande Cache Member. Mudstone to very fine-grained sandstone, as well as layers of conglomerate and coarser sandstone, make up the Ma Butte Formation. The

and Ma Butte formations in the upper part of the group also include minor beds of

bentonite Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-m ...

and

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...

. In the type area,

tuffaceous Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock c ...

mudstones Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' ...

are widespread in the top portion of the formation, but they vanish to the northwest along the foothills. North of the Clearwater River, the structure is completely missing. Various shades of red and green, frequently speckled south of the

Bow River The Bow River is a river in Alberta, Canada. It begins within the Canadian Rocky Mountains and winds through the Alberta foothills onto the prairies, where it meets the Oldman River, the two then forming the South Saskatchewan River. These w ...

, are particularly prevalent. Except in the Mountain Park Formation, where greenish grey predominates in more southerly areas and is increasingly prominent higher, grey prevails to the north. In the

Smoky River The Smoky River is a river in western Alberta, Canada. It is a major tributary of the Peace River. The descriptive name refers to the presence of "smouldering beds of coal in the riverbank" noted by the Cree Indians. It drains an area of . F ...

region, the uppermost part of the formation, the proportion of the section with a conspicuously greenish tint is restricted to a subtle shade of greenish-grey as it declines northward.

Stratigraphy

The Blairmore Group is subdivided into the following formations from top to base: Some early workers included the

Crowsnest Formation The Crowsnest Formation, also called the Crowsnest Volcanics, is a geological formation in southwestern Alberta, Canada, on the southwestern margin of the Western Canada Sedimentary Basin. It was named for the Crowsnest Pass near Coleman, Alberta. ...

, which overlies the Ma Butte Formation, at the top of the Blairmore Group, but that practice has been abandoned.

Distribution and Thickness

The name Blairmore Group is applicable in the foothills and mountains of southwestern Alberta and southeastern British Columbia, from the Canada–United States border northward to the Clearwater River. The equivalent strata north of the Clearwater River, which were originally assigned to the Blairmore Group, differ in that they contain major coal deposits and they have therefore been reassigned to the Luscar Group.Langenberg, W.C. and McMechan, M.E. 1985. Lower Cretaceous Luscar Group (revised) of Alberta's northern and north-central foothills. Bulletin of Canadian Petroleum Geology, v. 33, p. 1-11. The Blairmore Group has a maximum thickness of about . The Ma Butte portion has a thickness of The Fernie Basin's maximum reported thickness is estimated to be . The easternmost foothills have reported thicknesses of roughly , indicating a clear west to east thinning. In the northwest, thicknesses of 400 to 600 m (1312 to 1968 ft) are common in the foothills.

Relationship to other units

The Blairmore Group

unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

overlies the

Kootenay Group The Kootenay Group, originally called the Kootenay Formation, is a geologic unit of latest Jurassic to earliest Cretaceous age in the Western Canada Sedimentary Basin that is present in the southern and central Canadian Rockies and foothills. ...

and is gradationally overlain by the Crowsnest Formation or, where the Crowsnest Formation is absent, is disconformably overlain by the Alberta Group. It is equivalent to the Luscar Group north of the Clearwater River and to the

Mannville Group The Mannville Group is a stratigraphical unit of Cretaceous age in the Western Canadian Sedimentary Basin. It takes the name from the town of Mannville, Alberta, and was first described in the ''Northwest Mannville 1'' well by A.W. Nauss in 194 ...

in the plains to the east. In northwestern Montana the Cut Bank Sandstone correlates with the Cadomin Formation; the lower Kootenai Formation, including the Draney Limestone with the Beaver Mines Formation; and the lower Blackleaf Formation with the Ma Butte Formation.

Environment of deposition and paleontology

The Blairmore Group is a westward-thickening clastic wedge of clastic

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

s derived from the erosion of newly uplifted mountains to the west. The sediments were transported eastward by river systems and deposited in a variety of

braided stream A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in English usage, '' aits'' or ''eyots''. Braided streams tend to occur in rivers with high sediment ...

, river channel,

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

, and

coastal plain A coastal plain is flat, low-lying land adjacent to a sea coast. A fall line commonly marks the border between a coastal plain and a piedmont area. Some of the largest coastal plains are in Alaska and the southeastern United States. The Gulf Co ...

environments along the western edge of the

Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, and the Western Interior Sea) was a large inland sea that split the continent of North America into two landmasses. The ancient sea ...

. Its formations include a variety of plant fossils,

trace fossil A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...

s, bivalves, and

microfossils A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, ...

References