The Elk Point Group is a stratigraphic unit of Early to Middle Devonian age in the Western Canada and Williston sedimentary basins. It underlies large area that extends from southern boundary of the Northwest Territories in Canada to North Dakota in the United States. It has been subdivided into numerous formations, many which host major petroleum and natural gas reservoirs.
|Elk Point Group|
Stratigraphic range: Early to Middle Devonian
|Sub-units||Upper and Lower Elk Point Group|
|Underlies||Beaverhill Lake Group, Manitoba Group|
|Overlies||Precambrian to Silurian formations|
|Thickness||up to 610 metres (2,000 ft)|
|Primary||Dolomite, halite, anhydrite|
|Other||Limestone, shale, potash|
|Country||Canada United States|
|Named for||Elk Point|
|Named by||J.R. McGehee|
The formations of the Elk Point Group are composed primarily of carbonate rocks (dolostone and limestone) and evaporitic rocks (halite, anhydrite and potash), with lesser amounts of dolomitic mudstone and shale.
Some of the carbonate formations of the Elk Point Group contain rich assemblages of marine invertebrate fossils, including many species of brachiopods, gastropods, bivalves, cephalopods, crinoids, ostracods and corals. The evaporitic formations are unfossiliferous or contain a few spores and algal remains.
The formations of the Elk Point Group were deposited in a marine embayment that stretched from an open ocean in the present-day Northwest Territories 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, 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.
The Elk Point Group extends from the southern boundary of the Northwest Territories through northwestern British Columbia, Alberta, Saskatchewan, and southwestern Manitoba in Canada, and continues into eastern Montana and North Dakota in the United States. It reaches a maximum thickness of about 610 metres (2,000 ft) in eastern Alberta.
The Elk Point Group was named for the town of Elk Point, Alberta by J.R. McGehee in 1949. 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, as shown in the tables below.
The Lower Elk Point Group comprises all strata lying below the Winnipegosis Formation (in the south) or the Keg River Formation (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 (in the south) or the Beaverhill Lake Group (in the north).
|Watt Mountain Formation||Givetian||red and green shale, sandstone, anhydrite, dolostone, limestone||74.4 m (240 ft)|||
|Gilwood Member||Givetian||coarse quartz and feldspathic sandstone||15.2 m (50 ft)|||
|Presqu'ile Formation||Givetian||crystalline dolostone||300 m (980 ft)|||
|Sulphur Point Formation||Givetian||fossiliferous limestone, green shale||106 m (350 ft)|||
|Muskeg Formation||Givetian||anhydrite, salt, dolostone, limestone||270 m (890 ft)|||
|Zama Member||Givetian||sucrosic dolostone||24 m (80 ft)|||
|Keg River Formation||Givetian||porous dolostone, wackestone limestone, includes the Rainbow Member (dolomitized reef)||300 m (980 ft)|||
|Contact Rapids Formation||Eifelian to Givetian||argillaceous dolostone, dolomitic shale||48.8 m (160 ft)|||
|Chinchaga Formation||Eifelian to Givetian||anhydrite, crystalline dolostone, quartz sandstone, dolomitic shale, halite||76 m (250 ft)|||
|Cold Lake Formation||Eifelian||halite, dolomitic shale||117 m (380 ft)|||
|Ernestina Lake Formation||Eifelian||red shale (base), carbonates, anhydrite (top)||23 m (80 ft)|||
|Lotsberg Formation||Eifelian||halite, calcareous shale||229 m (750 ft)|||
|La Loche Formation (Basal red beds)||Eifelian||red dolomitic or calcareous shales, silty or sandy, quartzose sandstone||30 m (100 ft)|||
The Elk Point Group is dolomitic and is not differentiated.
|Dawson Bay Formation||Givetian||dolomitic mudstone, crystalline limestone, argillaceous carbonate, bituminous limestone, dolostone, anhydrite, halite||50 m (160 ft)|||
|Prairie Evaporite Formation||Givetian||halite, anhydrite, dolostone, dolomitic mudstone, limestone, potash||218 m (720 ft)|||
|Winnipegosis Formation||Givetian||dolostone, bituminous carbonates, anhydrite||100 m (330 ft)|||
|Ashern Formation||Eifelian to Givetian||argillaceous dolostone and dolomitic shale and siltstone; minor anhydrite||55 m (180 ft)|||
|Meadow Lake Formation||Eifelian||dolostone with mudstone interbeds, limestone and sandstone at base||56 m (180 ft)|||
The Elk Point Group is conformably overlain by the Manitoba Group in Manitoba and Saskatchewan, and by the Beaverhill Lake Group in Alberta. It rests unconformably on Precambrian basement rocks in northern Alberta, on Cambrian strata in northeastern Alberta and in Saskatchewan, and on Ordovician to Silurian 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 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, Besa River Formation, and others.
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.
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 Alberta. It was named by the geological staff of Imperial Oil in 1950 for Beaverhill Lake, Alberta, based on the core from a well that they had drilled southeast of the lake, near Ryley, Alberta (Anglo-Canadian Beaverhill Lake No. 2, 11-11-50-17W4).Petroleum is produced from the Swan Hills Formation of the Beaverhill Lake Group in the Swan Hills area of northern Alberta.Clearwater River (Saskatchewan)
The Clearwater River is located in the Canadian provinces of Saskatchewan and Alberta. It rises in the northern forest region of northwestern Saskatchewan and joins the Athabasca River in northeastern Alberta. It was part of an important trade route during the fur trade era and has been designated as a Canadian Heritage River.Deadwood Formation
The Deadwood Formation is a geologic formation of the Williston Basin and Western Canada Sedimentary Basin. It is present in parts of North and South Dakota and Montana in the United States, and in parts of Alberta, Saskatchewan, and southwestern corner of Manitoba in Canada. It is of Late Cambrian to Early Ordovician age and was named for exposures in Whitewood Creek near Deadwood, South Dakota. It is a significant aquifer in some areas, and its conglomerates yielded significant quantities of gold in the Black Hills of South Dakota.It preserves trace fossils such as Skolithos, and remains of Late Cambrian trilobites and brachiopods, as well as Ordovician fossils.Fossiliferous limestone
Fossiliferous limestone is any type of limestone, made mostly of calcium carbonate (CaCO3) in the form of the minerals calcite or aragonite, that contains an abundance of fossils or fossil traces. The fossils in these rocks may be of macroscopic or microscopic size. The sort of macroscopic fossils often include crinoid stems, brachiopods, gastropods, and other hard shelled mollusk remains.
In some cases, microfossils such as siliceous diatom shells in deposition may convert over time to opal and chert, providing the only inferred evidence of bioactivity preserved in limestone.
Fossiliferous limestone is termed biosparite limestone under the Folk classification of sedimentary rocks.
Lagerstätte are a class of fossil bearing rocks that includes fossiliferous limestoneLa Loche Formation
The La Loche Formation is a geologic formation of early Middle Devonian (Eifelian) age in the Western Canada Sedimentary Basin. It is present in northeastern Alberta and northwestern Saskatchewan and was first described by A. W. Norris in 1963, who named it for a Roman Catholic Mission at Lac La Loche. Its type section is located at Contact Rapids on the Clearwater River in Saskatchewan, northwest of Lac La Loche. It is not fossiliferous.Manitoba Group
The Manitoba Group is a stratigraphical unit of middle to late Devonian age in the Western Canadian Sedimentary Basin.
It takes the name from the province of Manitoba, and was first defined by A.D. Baillie in 1953.McMurray Formation
The McMurray Formation is a stratigraphic unit of Early Cretaceous age (late Barremian to Aptian stage) of the Western Canada Sedimentary Basin in northeastern Alberta. It takes the name from Fort McMurray, and was first described in the outcrops exposed along the banks of the Athabasca River, 5 kilometres (3.1 mi) north of Fort McMurray, by F.H. McLearn in 1917. It is a well-studied example of fluvial to estuarine sedimentation, and it is economically important because it hosts most of the vast bitumen resources of the Athabasca Oil Sands region.Muskeg Formation
The Muskeg Formation is a geologic formation of Middle Devonian (Givetian) age in the Western Canada Sedimentary Basin. It extends from the plains of northwestern Alberta to northeastern British Columbia, and includes important petroleum and natural gas reservoirs in the Zama lake and Rainbow Lake areas of northwestern Alberta.Potassium
Potassium is a chemical element with symbol K (from Neo-Latin kalium) and atomic number 19. It was first isolated from potash, the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals. All of the alkali metals have a single valence electron in the outer electron shell, which is easily removed to create an ion with a positive charge – a cation, which combines with anions to form salts. Potassium in nature occurs only in ionic salts. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction, and burning with a lilac-colored flame. It is found dissolved in sea water (which is 0.04% potassium by weight), and is part of many minerals.
Potassium is chemically very similar to sodium, the previous element in group 1 of the periodic table. They have a similar first ionization energy, which allows for each atom to give up its sole outer electron. That they are different elements that combine with the same anions to make similar salts was suspected in 1702, and was proven in 1807 using electrolysis. Naturally occurring potassium is composed of three isotopes, of which 40K is radioactive. Traces of 40K are found in all potassium, and it is the most common radioisotope in the human body.
Potassium ions are vital for the functioning of all living cells. The transfer of potassium ions through nerve cell membranes is necessary for normal nerve transmission; potassium deficiency and excess can each result in numerous signs and symptoms, including an abnormal heart rhythm and various electrocardiographic abnormalities. Fresh fruits and vegetables are good dietary sources of potassium. The body responds to the influx of dietary potassium, which raises serum potassium levels, with a shift of potassium from outside to inside cells and an increase in potassium excretion by the kidneys.
Most industrial applications of potassium exploit the high solubility in water of potassium compounds, such as potassium soaps. Heavy crop production rapidly depletes the soil of potassium, and this can be remedied with agricultural fertilizers containing potassium, accounting for 95% of global potassium chemical production.Prairie Evaporite Formation
The Prairie Evaporite Formation, also known as the Prairie Formation, is a geologic formation of Middle Devonian (Givetian) age that consists primarily of halite (rock salt) and other evaporite minerals. It is present beneath the plains of northern and eastern Alberta, southern Saskatchewan and southwestern Manitoba in Canada, and it extends into northwestern North Dakota and northeastern Montana in the United States.The formation is a major source of potash, most of which is used for fertilizer production. Salt is also produced from the formation, and solution caverns are created in its thick salt beds for natural gas storage.Yahatinda Formation
The Yahatinda Formation is a geologic formation of Middle Devonian (Givetian) age in the southwestern part of the Western Canada Sedimentary Basin in the mountains of southwestern Alberta. Its type locality lies the on the eastern face of Wapiti Mountain above Ya-Ha-Tinda Ranch at the eastern edge of Banff National Park. The Yahatinda contains a variety of Devonian fossils.