Bullhead Group is a

stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostrati ...

unit of

Lower Cretaceous Lower may refer to: *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Lower Wick is a small hamlet located in the county of Gloucestershire, England. It is situated about five miles south west of Dursley, eight ...

age Age or AGE may refer to: Time and its effects * Age, the amount of time someone or something has been alive or has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...

in the

Western Canada Sedimentary Basin The Western Canadian Sedimentary Basin (WCSB) underlies of Western Canada including southwestern Manitoba, southern Saskatchewan, Alberta, northeastern British Columbia and the southwest corner of the Northwest Territories. This vast sedimentary ...

of northeastern

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, ...

and western

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 ...

. It was first defined by F.H. McLearn in 1918 as the Bullhead Mountain Formation, but later was upgraded to group status. It consists of the

Cadomin Cadomin is a hamlet in the west-central Alberta, Canada within Yellowhead County. It is located along the McLeod River in the foothills of the Rocky Mountains, approximately south of Hinton near the Bighorn Highway. It is served by a spur of th ...

and

Gething Formation Gething Formation is a stratigraphic unit of Lower Cretaceous ( Aptian) age in the Western Canada Sedimentary Basin. It is present in northeastern British Columbia and western Alberta, and includes economically important coal deposits. The forma ...

s, although some early workers included the

Bluesky Formation The Bluesky Formation is a stratigraphic unit of Lower Cretaceous age in the Western Canada Sedimentary Basin. It takes the name from the hamlet of Bluesky, and was first described in Shell's ''Bluesky No. 1'' well by Badgley in 1952. Lithology ...

and others in the group.Stott, D.F. 1965. Lower Cretaceous Bullhead and Fort St John Groups, between Smoky and Peace Rivers, Rocky Mountain foothills, Alberta and British Columbia. Geological Survey of Canada, Bulletin 152, 279 p. .

Lithology

Bullhead Group includes the conglomerate and quartzose

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 Cadomin Formation at the base, and grades to

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

mudstone 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. ...

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

and

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dea ...

seams of the overlying Gething Formation. Those sediments were deposited in

alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to semiarid climates, but a ...

braided river 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 l ...

deltaic A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more rare ...

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 Coa ...

environments.

Distribution

The Bullhead Group is present in the foothills of the

Northern Rocky Mountains The Northern Rocky Mountains, usually referred to as the Northern Rockies, are a subdivision of the Canadian Rockies comprising the northern half of the Canadian segment of the Rocky Mountains. While their northward limit is easily defined as the ...

and the adjacent plains, extending from the

Tuchodi River The Tuchodi River is a stream in the Northern Rocky Mountains of northern British Columbia, Canada. The river flows through the Northern Rocky Mountains Provincial Park in a northeasterly direction to the Muskwa River. Its name comes from Slavey ...

of British Columbia in the north to 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 . Fro ...

of Alberta in the south. It thins eastward from about in the western foothills of northeastern British Columbia to about in the Peace River plains, reaching zero near Fort St. John. The most complete section is found in the type locality of the Gething Formation in the

Peace River The Peace River (french: links=no, rivière de la Paix) is a river in Canada that originates in the Rocky Mountains of northern British Columbia and flows to the northeast through northern Alberta. The Peace River joins the Athabasca River in th ...

Canyon immediately downstream from the

W. A. C. Bennett Dam The W. A. C. Bennett Dam is a large hydroelectric dam on the Peace River in northern British Columbia, Canada. At high, it is one of the world's highest earth fill dams. Construction of the dam began in 1961 and culminated in 1968. At the dam ...

.Glass, D.J. (editor) 1997. Lexicon of Canadian Stratigraphy, vol. 4, Western Canada including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba. Canadian Society of Petroleum Geologists, Calgary, 1423 p. on CD-ROM. .

Relationship to other units

The Bullhead Group overlies a major regional

unconformity 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 o ...

caused by pre-Bullhead erosion. It rests unconformably on the

Fernie Formation The Fernie Formation is a stratigraphic unit of Jurassic age. It is present in the western part of the Western Canada Sedimentary Basin in western Alberta and northeastern British Columbia.Poulton, T.P., Tittemore, J. and Dolby, G. 1990. Jurassic ...

, the

Nikanassin Formation The Nikanassin Formation is a stratigraphic unit of Late Jurassic (Portlandian) to Early Cretaceous (Barremian) age.Poulton, T.P., Tittemore, J. and Dolby, G. 1990. Jurassic strata of northwestern (and west-central) Alberta and northeastern Britis ...

, the

Minnes Group The Minnes Group, originally named the Minnes Formation, is a geologic unit of Late Jurassic, latest Jurassic to Early Cretaceous, earliest Cretaceous age in the Western Canadian Sedimentary Basin, Western Canada Sedimentary Basin. It is present i ...

or 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. I ...

, depending on the location and the extent of the erosion. It is overlain conformably by the

glauconitic Glauconite is an iron potassium phyllosilicate ( mica group) mineral of characteristic green color which is very friable and has very low weathering resistance. It crystallizes with a monoclinic geometry. Its name is derived from the Greek () m ...

sandstones and marine shales at the base of the Fort St. John Group.

References

{{WCSB, Northwest_Plains=yes Western Canadian Sedimentary Basin Cretaceous British Columbia Geologic groups of British Columbia Barremian Stage Aptian Stage Albian Stage Geologic groups of Alberta