Three Forks Group
Introduction The '''Three Forks Group''' is a stratigraphical unit of Famennian age in the Williston Basin.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 , but can be as thin as .
Subdivisions  Sub-unit  Age  Lithology  Max.Thickness  ReferenceBakken Formation  Kinderhookian  bituminous shale  Lyleton Formation  Famennian  red dolomitic and silty shale, argillaceous dolomite  Big Valley Formation  Famennian  mudstone  Torquay Formation  Famennian  brown dolomite, shale
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.
References