Madison Group
{{Short description|Geologic formation in the western United States}}
{{Infobox Rockunit
| name = Madison Limestone
| image = SunRiver.JPG
| caption = Thrust segment of the Madison Limestone, Sun River canyon, Montana
| type = Geological formation
| age = {{fossil range|Mississippian|Mississippian|Mississippian}}
| period = Mississippian
| prilithology = Limestone
| otherlithology = Shale
| namedfor = Madison Range
| namedby = A.C. Peale, 1893Peale, A.C., 1893. The Paleozoic section in the vicinity of Three Forks, Montana. United States Geological Survey, Bull. 110, p.9-56.
| region = South Dakota, Montana, Idaho, Colorado, Arizona, Alberta, Saskatchewan, Manitoba, Utah
| country = United States, Canada
| coordinates =
| unitof =
| subunits =
| underlies = Big Snowy Group
| overlies = Bakken Formation (Three Forks Group)
| thickness = up to {{convert|2100|ft|m|-1}}{{Cite web|url=http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl?00053:008973|title=Madison Group|author=Lexicon of Canadian Geologic Units|accessdate=2009-03-26}}
| extent =
| area =
| map =
| map_caption =
}}
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. The Madison and its equivalent strata extend from the Black Hills of western South Dakota to western Montana and eastern Idaho, and from the Canada–United States border to western Colorado and the Grand Canyon of Arizona.
Age and nomenclature
The Madison is formally known as the Madison Group. In Montana, where its thickness reaches {{convert|1700|ft|m|-1}}, the group is subdivided into the Mission Canyon Formation and Lodgepole Formation. Equivalents of the Madison are named the Pahasapa Limestone in the Black Hills, Leadville Limestone (Colorado), Guernsey Limestone (Wyoming), and Redwall Limestone in the Grand Canyon. The upper part of the Madison Group, the Charles Formation in the subsurface of North Dakota and northern Montana, is not strictly an equivalent of the Madison Limestone as usually defined.Mississippian System, by Lawrence C. Craig, in Geologic Atlas of the Rocky Mountain Region, Rocky Mountain Association of Geologists, Denver, CO, 1972: p. 100-110
Most of the Madison Limestones were deposited during Early to Middle Mississippian time (Tournaisian to Visean stages), about 359 to 326 million years ago. Older North American usage lists the Madison as being laid down during the Kinderhookian, Osagian, and Meramecian stages.
Neither a type locality nor derivation of the name was designated when the term Madison Limestone was first used by Peale (1893),[http://3dparks.wr.usgs.gov/coloradoplateau/lexicon/madison.htm Peale, A.C., 1893, The Paleozoic section in the vicinity of Three Forks, Montana, with petrographic notes by G.P. Merrill: U.S. Geological Survey Bulletin, 110, 56 p.] but since the original work focused on the area of Three Forks, Montana, it is likely that the name relates to outcrops along the Madison River, Montana. A reference section has been designated on the north side of Gibson Reservoir in SE/4 sec. 36, T. 22 N., R. 10 W., Patricks Basin quad, Teton Co., Montana.Mudge, M.R., Sando, W.J. and Dutro, J.T., Jr., 1962, Mississippian rocks of the Sun River Canyon area, Sawtooth Range, Montana: American Association of Petroleum Geologists Bulletin, v. 46, no. 11, p. 2003-2018
Lithology
Limestones and dolomites dominate the Madison. Because the rock is highly soluble, it often develops caves and karst topography. Lewis and Clark Caverns, Montana, is an example of a cave developed in the Madison. The rocks were deposited in a generally shallow marine setting, indicated by the richly fossiliferous rocks of the Madison. In the Williston Basin, water was shallow enough for oolite shoals to develop; they later became reservoirs for oil.[http://aapgbull.geoscienceworld.org/cgi/content/abstract/39/11/2170 Mississippian Madison group stratigraphy and sedimentation in Wyoming and southern Montana, by John Michael Andrichuk, AAPG Bulletin; November 1955; v. 39; no. 11; p. 2170-2210]
The gray cliffs along the Missouri River in the Gates of the Mountains, Montana are formed by Madison Limestone.River Log and Road Log: Thrust Faulting near Gates of the Mountains, Lombard, Lewis & Clark Canyon, Montana Geological Society 1994 Guidebook, James L. Cannon, Gary G. Thompson, and John R. Warne, editors
Subdivisions
;Montana-Wyoming-Manitoba
The following formations are recognized in Montana, Wyoming and Manitoba, from top to base:
;Saskatchewan
The following subdivisions (of formation rank) are recognized in Saskatchewan, from top to base:
See also
References
{{reflist}}
{{Western Canadian Sedimentary Basin| Saskatchewan=yes}}
Category:Geologic groups of the United States
Category:Geologic groups of Saskatchewan
Category:Mississippian United States
Category:Carboniferous Arizona
Category:Carboniferous Colorado
Category:Carboniferous Montana
Category:Carboniferous North Dakota
Category:Carboniferous South Dakota
Category:Carboniferous Saskatchewan
Category:Carboniferous geology of Utah
Category:Carboniferous geology of Wyoming
Category:Western Canadian Sedimentary Basin
Category:Geologic groups of Idaho
Category:Geologic groups of Colorado
Category:Geologic groups of Arizona
Category:Geologic groups of Montana
Category:Geologic groups of North Dakota
Category:Geologic groups of South Dakota
Category:Geologic groups of Utah
Category:Geologic groups of Wyoming
Category:Geologic groups of Alberta
Category:Carboniferous System of North America
Category:Limestone groups of the United States
Category:Limestone groups of Canada