The Three Forks Group is a stratigraphical unit of

Famennian The Famennian is the latter of two faunal stages in the Late Devonian Epoch. The most recent estimate for its duration estimates that it lasted from around 371.1 million years ago to 359.3 million years ago. An earlier 2012 estimate, still used b ...

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

Williston Basin The Williston Basin is a large intracratonic sedimentary basin in eastern Montana, western North Dakota, South Dakota, southern Saskatchewan, and south-western Manitoba that is known for its rich deposits of petroleum and potash. The basin is a ...

. It takes the name from the city of

Three Forks, Montana Three Forks is a city in Gallatin County, Montana, United States and is located within the watershed valley system of both the Missouri and Mississippi rivers drainage basins — and is historically considered the birthplace or start of the M ...

, and was first described in outcrop near the city by A.C. Peale in 1893 (for the Three Forks Shale).

Lithology

The Three Forks Group is composed of

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 ...

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 bituminous

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 ...

Hydrocarbon production

In the subsurface of the Williston Basin, the Three Forks is referred to as the Three Forks ''Formation'', which lies between the Birdbear Formation below, and the Bakken Formation above.

Oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...

produced from the Three Forks Formation in the Williston Basin of

North Dakota North Dakota () is a U.S. state in the Upper Midwest, named after the Native Americans in the United States, indigenous Dakota people, Dakota Sioux. North Dakota is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north a ...

and south-eastern

Saskatchewan Saskatchewan ( ; ) is a Provinces and territories of Canada, province in Western Canada, western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on t ...

is often included in production statistics with the overlying Bakken Formation. For instance, the Three Forks and Bakken were combined in estimates of potential production released by the United States Geological Survey on April 30, 2013. The estimate by the USGS projects that 7.4 billion barrels of oil can be recovered from the Bakken and Three Forks formations and 6.7 trillion cubic feet of natural gas and 530 million barrels of natural gas liquids using current technology.

Distribution

The Three Forks Group reaches a maximum thickness of , but can be as thin as .

Subdivisions

Relationship to other units

The Three Forks Group

conformably Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igne ...

overlies the

Saskatchewan Group The Saskatchewan Group is a Stratigraphy, stratigraphical unit of Frasnian Geochronology, age in the Western Canadian Sedimentary Basin. It takes the name from the province of Saskatchewan, and was first described in the ''Mobil Oil Woodley Sincl ...

and is disconformably overlain by the

Madison Group The Madison Limestone is a thick sequence of mostly carbonate rocks of Mississippian age in the Rocky Mountain and Great Plains areas of the western United States. The rocks serve as an important aquifer as well as an oil reservoir in places. Th ...

. It is equivalent to the sum of the Wabamun Group and Exshaw Formation in

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 ...

References

{{Western Canadian Sedimentary Basin, Saskatchewan=yes Stratigraphy of Saskatchewan Geologic groups of North Dakota Geologic groups of Montana Geologic groups of North America Carboniferous southern paleotemperate deposits Devonian southern paleotemperate deposits