The La Loche Formation is a geologic formation of early

Middle Devonian In the geological timescale, the Middle Devonian epoch (from 393.3 ± 1.2 million years ago to 382.7 ± 1.6 million years ago) occurred during the Devonian period, after the end of the Emsian age. The Middle Devonian epoch is subdivided into two ...

( Eifelian) age in the Western Canada Sedimentary Basin. It is present in northeastern

Alberta Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...

and northwestern

Saskatchewan Saskatchewan is a Provinces and territories of Canada, province in Western Canada. It is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and to the south by the ...

and was first described by A. W. Norris in 1963, who named it for a Roman Catholic Mission at

Lac La Loche Lac La Loche is a lake in north west Saskatchewan near the Alberta border. The lake is part of the Churchill River system that flows into the Hudson Bay. The La Loche River at the southern end flows into Peter Pond Lake which is connected ...

. Its type section is located at Contact Rapids on the Clearwater River in Saskatchewan, northwest of Lac La Loche. It is not fossiliferous.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. .

Lithology

The basal portion of the La Loche Formation consists of pale brown to reddish, fine- to coarse-grained arkosic and conglomeratic

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

s that may include weathered, angular clasts of the underlying

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...

granitic A granitoid is a broad term referring to a diverse group of coarse-grained igneous rocks that are widely distributed across the globe, covering a significant portion of the Earth's exposed surface and constituting a large part of the continental ...

gneiss Gneiss (pronounced ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. This rock is formed under p ...

. Planar

bedding Bedding, also called bedclothes or bed linen, is the materials laid above the mattress of a bed for hygiene, warmth, protection of the mattress, and decorative effect. Bedding is the removable and washable portion of a human sleeping environment ...

cross-bedding In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The origina ...

, and graded bedding are common in the sandstones. Sandy dolomite,

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

, and thin beds of anhydrite and

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk ...

are present in the upper portion. The formation is not fossiliferous.

Environment of deposition

The La Loche Formation marked the beginning of the deposition of the Elk Point Group at the onset of a

marine transgression A marine transgression is a geologic event where sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling with water ...

over the Canadian Shield. The Shield had been exposed to a long period of

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

, and the basal portion of the La Loche is regolithic; that is, it is composed of

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...

, and

gravel Gravel () is a loose aggregation of rock fragments. Gravel occurs naturally on Earth as a result of sedimentation, sedimentary and erosion, erosive geological processes; it is also produced in large quantities commercially as crushed stone. Gr ...

derived from the underlying Precambrian rocks that was lying on the Precambrian surface at that time. Bedding textures indicate fluvial to marginal marine depositional environments.

Distribution and thickness

The La Loche Formation is present in northeastern Alberta and northwestern Saskatchewan. It is up to thick in

outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth and other terrestrial planets. Features Outcrops do not cover the majority of the Earth's land surface because in most p ...

, and ranges from about to thick in the subsurface around

Fort McMurray Fort McMurray ( ) is an urban service area in the Regional Municipality of Wood Buffalo in Alberta, Canada. It is located in northeast Alberta, in the middle of the Athabasca oil sands, surrounded by boreal forest. It has played a significa ...

, Alberta. It is thickest in low areas on the Precambrian surface and thin to absent over high areas.

Relationship to other units

The La Loche Formation is the basal unit of the Elk Point Group and rests unconformably on the eroded Canadian Shield. It is gradationally overlain by the

Contact Rapids Formation The Elk Point Group is a stratigraphic unit of Early to Middle Devonian age in the Western Canada and Williston sedimentary basins. It underlies a large area that extends from the southern boundary of the Northwest Territories in Canada to Nor ...

in the Clearwater River area, and by the Chinchaga or the

Keg River Formation The Keg River Formation is a stratigraphic unit of Givetian age in the Western Canada Sedimentary Basin. Description It takes the name from the Keg River, a community along the Peace River, and was first described in the California Standar ...

in the Slave River area north of

Lake Athabasca Lake Athabasca ( ; French: ''lac Athabasca''; from Woods Cree: , " herethere are plants one after another") is in the north-west corner of Saskatchewan and the north-east corner of Alberta between 58° and 60° N in Canada. The lake is ...

. It may be considered equivalent to the Contact Rapids or Chinchaga Formation in some areas, and may also be referred to as the Basal

red beds Red beds (or redbeds) are sedimentary rocks, typically consisting of sandstone, siltstone, and shale, that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain t ...

or the Granite Wash.

References

{{Western Canadian Sedimentary Basin, Northeast_Plains=yes, Saskatchewan=yes Western Canadian Sedimentary Basin Devonian Alberta Devonian Saskatchewan Geologic formations of Saskatchewan Geologic formations of Alberta Middle Devonian Series Sandstone formations of Canada Mudstone formations of Canada Conglomerate formations