Type Geologic group Named by A.C. Peale, 1893 Overlies Saskatchewan Group Primary Mudstone, Slate | Country Canada
United States Named for Three Forks Underlies Madison Group | |
Sub-units Bakken Formation, Lyleton Formation, Big Valley Formation, Torquay Formation Thickness 35 metres (110 ft) to 80 metres (260 ft) Regions Western Canadian Sedimentary Basin, Williston Basin | ||
The Three Forks Group is a stratigraphical unit of Famennian age in the Williston Basin.
Contents
It takes the name from the city of Three Forks, Montana, 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, mudstone and bituminous shale.
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 produced from the Three Forks Formation in the Williston Basin of North Dakota and south-eastern Saskatchewan 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 80 metres (260 ft), but can be as thin as 35 metres (110 ft).
Relationship to other units
The Three Forks Group conformably overlies the Saskatchewan Group and is disconformably overlain by the Madison Group.
It is equivalent to the sum of the Wabamun Group and Exshaw Formation in Alberta.