The Luscar Group is a geologic unit of

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

age 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 ...

that is present in the foothills of southwestern Alberta. It is subdivided into a series of

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 ...

s, some of which contain economically significant coal deposits that have been mined near

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 Luscar. Coal mining in those areas began in the early 1900s and continues near Luscar as of 2016.

Lithology

The Luscar Group includes the

conglomerate Conglomerate or conglomeration may refer to: * Conglomerate (company) * Conglomerate (geology) * Conglomerate (mathematics) In popular culture: * The Conglomerate (American group), a production crew and musical group founded by Busta Rhymes ** Co ...

and quartzose sandstones of the

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 ...

at the base, and the overlying formations consist of variable amounts of sandstone,

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 ...

and

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. ...

. There are major coal seams in the

Gates Formation The Fort St. John Group is a stratigraphic unit of Lower Cretaceous age in the Western Canada Sedimentary Basin. It takes the name from the city of Fort St. John, British Columbia and was first defined by George Mercer Dawson in 1881. Lithology ...

, and minor coal, argillaceous limestone and calcareous

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 ...

in the

Gladstone Formation The Gladstone Formation is a stratigraphic unit of Early Cretaceous (Aptian) age in the Western Canada Sedimentary Basin. It is present in the foothills of southwestern Alberta and is named for outcrops along Gladstone Creek, a tributary of the ...

. The

Moosebar Formation The Fort St. John Group is a stratigraphic unit of Lower Cretaceous age in the Western Canada Sedimentary Basin. It takes the name from the city of Fort St. John, British Columbia and was first defined by George Mercer Dawson in 1881. Litholo ...

consists primarily of mudstone and shale.

Stratigraphy

The strata encompassed by the Luscar Group were originally included in the

Blairmore Group 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 and southeastern British Columbia. It is subdivided into ...

. However, the Blairmore Group strata in the mountains and foothills of southwestern Alberta are of primarily nonmarine origin and are not coal-bearing, while those in the central and northern foothills include thick coal seams and a marine shale unit. Those strata were therefore reassigned to the Luscar Group. Langenberg, C.W. and McMechan, M.E. 1985. Lower Cretaceous Luscar Group (revised) of the northern and north-central foothills of Alberta. Bulletin of Canadian Petroleum Geology, vol. 33, p. 1-11.Langenberg, C.W. 1984. Structural and sedimentological framework of the Lower Cretaceous coal-bearing rocks of the Grande Cache area, Alberta. In: The Mesozoic of Middle North America, Canadian Society of Petroleum Geologists Memoir 9, p. 533-540. The type section for the Luscar Group consists of outcrops along the railroad tracks near the town of Cadomin. Luscar Group is subdivided into the following formations from top to base:

Distribution and thickness

The name Luscar Group is applicable in the northern and north-central foothills of southwestern Alberta, from the Clearwater River north to the

Kakwa River The Kakwa River is a tributary of the Smoky River in western Alberta, Canada. The river is named for ''Kakwa'', the Cree language, Cree word for porcupine. Porcupines are abundant in Kakwa Provincial Park and Protected Area. Tourism along the ri ...

near the Alberta- British Columbia boundary. Its thickness is difficult to determine accurately due to folding and faulting that characterize the Alberta foothills, but is estimated to be about in the type area.

Relationship to other units

The Luscar Group is correlative with the

of the southwestern Alberta foothills; with the Bullhead Group and the lower part of the

Fort St. John Group The Fort St. John Group is a stratigraphic unit of Lower Cretaceous age in the Western Canada Sedimentary Basin. It takes the name from the city of Fort St. John, British Columbia and was first defined by George Mercer Dawson in 1881. Lithology T ...

of northeastern British Columbia; and with 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 1945 ...

of the Alberta plains. It disconformably overlies either 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 ...

or 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 ...

, and is disconformably overlain by either the

Shaftesbury Formation The Fort St. John Group is a stratigraphic unit of Lower Cretaceous age in the Western Canada Sedimentary Basin. It takes the name from the city of Fort St. John, British Columbia and was first defined by George Mercer Dawson in 1881. Lithology ...

or Blackstone Formation, depending on the location.

Environment of deposition and paleontology

The Luscar Group is an eastward-thinning wedge of

clastic Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...

sediments 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,

river channel In physical geography, a channel is a type of landform consisting of the outline of a path of relatively shallow and narrow body of water or of other fluids (e.g., lava), most commonly the confine of a river, river delta or strait. The word is ...

, floodplain,

swamp A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...

, coastal plain, marginal marine and shallow marine environments along the western edge of the Western Interior Seaway. Its formations include a variety of plant fossils, trace fossils,

bivalves Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

, and foraminifera.

References

{{Reflist Geologic formations of Canada Stratigraphy of Alberta Lower Cretaceous Series of North America