The Elk Point Group is a stratigraphic unit of

Early Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * Early ...

to Middle Devonian

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 and Williston sedimentary basins. It underlies a large area that extends from the southern boundary of the

Northwest Territories The Northwest Territories (abbreviated ''NT'' or ''NWT''; french: Territoires du Nord-Ouest, formerly ''North-Western Territory'' and ''North-West Territories'' and namely shortened as ''Northwest Territory'') is a federal territory of Canada. ...

in Canada to North Dakota in the United States. It has been subdivided into numerous formations, number of which host major petroleum and natural gas reservoirs.

Lithology

The formations of the Elk Point Group are composed primarily of carbonate rocks (

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

and limestone) and evaporitic rocks ( halite, anhydrite and potash), with lesser amounts of

dolomitic Dolomite () is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite. An alternative name sometimes used for the dolomiti ...

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. ...

and

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 ...

.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. .

Paleontology

Some of the carbonate formations of the Elk Point Group contain rich assemblages of marine invertebrate fossils, including many species of brachiopods,

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

bivalve 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 ...

cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...

s, crinoids, ostracods and corals. The evaporitic formations are unfossiliferous or contain a few

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

s and

algal Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

remains.

Environment of Deposition

The formations of the Elk Point Group were deposited in a marine embayment that stretched from an open ocean in the present-day

of Canada to North Dakota in the United States, covering an area roughly half as large as that covered by today's Mediterranean Sea. At times of low water levels and excessive

evaporation Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...

, halite and other evaporite minerals were deposited in sabkha, supratidal flat and coastal lagoon environments, and at times of higher water levels carbonate platform sedimentation and reef growth were dominant.

Distribution and Thickness

The Elk Point Group extends from the southern boundary of the

through northwestern British Columbia, Alberta, Saskatchewan, and southwestern Manitoba in Canada, and continues into eastern Montana and North Dakota in the United States.Meijer Drees, N.C. 1986. Evaporitic deposits of western Canada. Geological Survey of Canada, paper 85-20. It reaches a maximum thickness of about in eastern Alberta.

Stratigraphy

The Elk Point Group was named for the town of

Elk Point, Alberta Elk Point is a town located in east-central Alberta, Canada. It is located on Highway 41. A number of oil related businesses have located in Elk Point. Agriculture is also important in the Elk Point area. Elk Point is located on the North Sas ...

by J.R. McGehee in 1949.McGehee, J.R., 1949. Pre-Waterways Paleozoic stratigraphy of Alberta Plains. Bull.

American Association of Petroleum Geologists The American Association of Petroleum Geologists (AAPG) is one of the world's largest professional geological societies with more than 40,000 members across 129 countries as of 2021. The AAPG works to "advance the science of geology, especially as ...

, 33:4, p. 603-613. Core from a well that was drilled near Elk Point has been designated as the type section (Anglo-Canadian Elk Point No. 11, 2-11-57-5W4). The group is subdivided into the Lower and Upper Elk Point Group, each of which is further subdivided into formations according to the dominant

lithologies The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lit ...

, as shown in the tables below. The Lower Elk Point Group comprises all strata lying below the

Winnipegosis 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 North ...

(in the south) 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 tributary of the Peace River, and was first described in the California Standard Steen ...

(in the north) and is present only in the deepest parts of the basin. The Upper Elk Point Group, which is present throughout the basin, includes those formations and all overlying formations to the base of the

Manitoba Group The Manitoba Group is a stratigraphical unit of middle to late Devonian age in the Western Canadian Sedimentary Basin. The group takes its name from the province of Manitoba, and was first defined by A.D. Baillie in 1953. Lithology The Manito ...

(in the south) or the

Beaverhill Lake Group The Beaverhill Lake Group is a geologic unit of Middle Devonian to Late Devonian (late Givetian to Frasnian) age in the Western Canada Sedimentary Basin that is present in the southwestern Northwest Territories, northeastern British Columbia and A ...

(in the north).

Subdivisions

In northern Alberta and central Alberta, the Elk Point Group contains the following subdivisions, from top to base: ;In southern Alberta The Elk Point Group is dolomitic and is not differentiated. ;In Saskatchewan, Manitoba and Montana

Relationship to Other Units

The Elk Point Group is conformably overlain by the

in Manitoba and Saskatchewan, and by the

in Alberta. It rests

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 o ...

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, 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 the ...

basement rocks In geology, basement and crystalline basement are crystalline rocks lying above the mantle and beneath all other rocks and sediments. They are sometimes exposed at the surface, but often they are buried under miles of rock and sediment. The baseme ...

in northern Alberta, on

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

strata in northeastern Alberta and in Saskatchewan, and on Ordovician to

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

formations in western Alberta, Saskatchewan and southwestern Manitoba. In the Northwest Territories, some of its uppermost units are exposed at surface or are unconformably overlain by Cretaceous strata. The Lower Elk Point Group is equivalent to the

Stone Formation In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its chemical composition, and the way in which it is formed. Rocks form the Earth's o ...

and its equivalents, and the Headless and Nahanni Formations, in northerneastern British Columbia and the southwestern Northwest Territories. In the same areas, the Upper Elk Point includes the Pine Point Group, and is equivalent to parts of the

Horn River Formation The Horn River Formation (also ''Horn River Shale'') is a stratigraphic unit of Devonian (early Givetian to late Frasnian) age in the Western Canadian Sedimentary Basin. It is a thick sequence of marine sediments that was first described in out ...

Besa River Formation The Besa River Formation is a stratigraphical unit of Devonian age in the Western Canadian Sedimentary Basin. It takes the name from Besa River, a tributary of the Prophet River, and was first described in outcrop near the Muskwa River, in the ...

, and others.

Petroleum and Natural Gas

The porous carbonate rocks of the Elk Point Group host major petroleum and natural gas reservoirs. As of 1994, the Initial Established Recoverable Petroleum Reserves and the Cumulative Petroleum Production for the group were estimated at 339.3 and 240.4 million cubic metres, respectively. For natural gas, the Initial Established Marketable Reserves and the Cumulative Production were estimated at 142.7 and 79.5 billion cubic metres, respectively.

References

{{Western Canadian Sedimentary Basin, Northeast_Plains=yes, Northwest_Plains=yes, South AB=yes, Saskatchewan=yes Geologic groups of the United States Geologic formations of Canada Oil-bearing shales in Canada Oil-bearing shales in the United States Western Canadian Sedimentary Basin Devonian Alberta Devonian British Columbia Devonian Montana Devonian North Dakota Devonian Northwest Territories Devonian Saskatchewan Geologic groups of Montana Geologic groups of North Dakota Stratigraphy of Alberta Stratigraphy of British Columbia Stratigraphy of Saskatchewan Devonian System of North America Devonian southern paleotropical deposits Lower Devonian Series Middle Devonian Series Devonian southern paleotemperate deposits