# Madison Group

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{{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](/source/Sun_River) canyon, Montana
| type           = [Geological formation](/source/Geological_formation)
| age            = {{fossil range|Mississippian|Mississippian|[Mississippian](/source/Mississippian_age)}}
| period         = Mississippian
| prilithology   = [Limestone](/source/Limestone)
| otherlithology = [Shale](/source/Shale)
| namedfor       = [Madison Range](/source/Madison_Range)
| namedby        = A.C. Peale, 1893<ref>Peale, A.C., 1893. The Paleozoic section in the vicinity of Three Forks, Montana. [United States Geological Survey](/source/United_States_Geological_Survey), Bull. 110, p.9-56.</ref>
| region         = [South Dakota](/source/South_Dakota), [Montana](/source/Montana), [Idaho](/source/Idaho), [Colorado](/source/Colorado), [Arizona](/source/Arizona), [Alberta](/source/Alberta), [Saskatchewan](/source/Saskatchewan), [Manitoba](/source/Manitoba), [Utah](/source/Utah)
| country        = [United States](/source/United_States), [Canada](/source/Canada)
| coordinates    = 
| unitof         = 
| subunits       = 
| underlies      = Big Snowy Group
| overlies       = [Bakken Formation](/source/Bakken_Formation) ([Three Forks Group](/source/Three_Forks_Group))
| thickness      = up to {{convert|2100|ft|m|-1}}<ref name=lexicon>{{Cite web|url=http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl?00053:008973|title=Madison Group|author=[Lexicon of Canadian Geologic Units](/source/Lexicon_of_Canadian_Geologic_Units)|accessdate=2009-03-26}}</ref>
| extent         = 
| area           = 
| map            = 
| map_caption    = 
}}

The '''Madison Limestone''' is a thick sequence of mostly [carbonate rock](/source/carbonate_rock)s of [Mississippian](/source/Mississippian_age) age in the [Rocky Mountain](/source/Rocky_Mountain) and [Great Plains](/source/Great_Plains) areas of the western [United States](/source/United_States). The rocks serve as an important [aquifer](/source/aquifer) as well as an [oil reservoir](/source/oil_reservoir) in places. The Madison and its equivalent strata extend from the [Black Hills](/source/Black_Hills) of western [South Dakota](/source/South_Dakota) to western [Montana](/source/Montana) and eastern [Idaho](/source/Idaho), and from the [Canada–United States border](/source/Canada%E2%80%93United_States_border) to western [Colorado](/source/Colorado) and the [Grand Canyon](/source/Grand_Canyon) of [Arizona](/source/Arizona).

==Age and nomenclature==

The Madison is formally known as the Madison [Group](/source/Geologic_unit). 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](/source/Leadville_Limestone) (Colorado), Guernsey Limestone (Wyoming), and [Redwall Limestone](/source/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.<ref>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</ref>

Most of the Madison Limestones were deposited during Early to Middle Mississippian time ([Tournaisian](/source/Tournaisian) to [Visean](/source/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),<ref>[https://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.]</ref> but since the original work focused on the area of [Three Forks, Montana](/source/Three_Forks%2C_Montana), it is likely that the name relates to outcrops along the [Madison River](/source/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.<ref>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</ref>

==Lithology==

[Limestone](/source/Limestone)s and [dolomite](/source/Dolomite_(rock))s dominate the Madison. Because the rock is highly soluble, it often develops caves and [karst](/source/karst) topography. [Lewis and Clark Caverns](/source/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](/source/Williston_Basin), water was shallow enough for [oolite](/source/oolite) shoals to develop; they later became reservoirs for oil.<ref>[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]</ref> 
The gray cliffs along the [Missouri River](/source/Missouri_River) in the [Gates of the Mountains, Montana](/source/Gates_of_the_Mountains_Wilderness) are formed by Madison Limestone.<ref>''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</ref>

==Subdivisions==
;Montana-Wyoming-Manitoba
The following formations are recognized in [Montana](/source/Montana), [Wyoming](/source/Wyoming) and [Manitoba](/source/Manitoba), from top to base:
{|class="wikitable"
|-
! [Sub-unit](/source/Geological_unit) !! [Age](/source/Geochronology) !! Lithology !! Max.<br>Thickness !! Reference
|-
|[Charles Formation](/source/Charles_Formation) || [Mississippian](/source/Mississippian_age) || [dolomitic](/source/Dolomite_(mineral)) limestone || {{convert|244|m|ft|-1|abbr=on}}
|<ref>{{Cite web|url=http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl?00053:002766|title=Charles Formation|author=[Lexicon of Canadian Geologic Units](/source/Lexicon_of_Canadian_Geologic_Units) |accessdate=2010-01-07}}</ref>
|-
|Mission Canyon Formation || [Osagian](/source/Osagian) || white bioclastic limestone, oolitic [calcarenite](/source/calcarenite), occasionally [dolomitized](/source/dolomitized); [anhydrite](/source/anhydrite) in the [Williston Basin](/source/Williston_Basin) || {{convert|183 |m|ft|-1|abbr=on}}
|<ref>{{Cite web|url=http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl?00053:009922|title=Mission Canyon Formation|author=[Lexicon of Canadian Geologic Units](/source/Lexicon_of_Canadian_Geologic_Units) |accessdate=2010-01-07}}</ref>
|-
|[Lodgepole Formation](/source/Lodgepole_Formation) || [Kinderhookian](/source/Kinderhookian) || lime [mudstones](/source/mudstones), [shale](/source/shale), [chert](/source/chert), contains [bitumen](/source/bitumen) || {{convert|245|m|ft|-1|abbr=on}}
|<ref>{{Cite web|url=http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl?00053:008638|title=Lodgepole Formation|author=[Lexicon of Canadian Geologic Units](/source/Lexicon_of_Canadian_Geologic_Units) |accessdate=2010-01-07}}</ref>
|}

;Saskatchewan
The following subdivisions (of [formation](/source/Formation_(stratigraphy)) rank) are recognized in [Saskatchewan](/source/Saskatchewan), from top to base:
{|class="wikitable"
|-
! [Sub-unit](/source/Geological_unit) !! [Age](/source/Geochronology) !! Lithology !! Max.<br>Thickness !! Reference
|-
|Poplar Beds || [Meramecian](/source/Meramecian) || [limestone](/source/limestone), argillaceous [dolomite](/source/Dolomite_(rock)), [evaporite](/source/evaporite) || {{convert|152|m|ft|-1|abbr=on}}
|<ref>{{Cite web|url=http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl?00053:012052|title= Poplar Beds|author=[Lexicon of Canadian Geologic Units](/source/Lexicon_of_Canadian_Geologic_Units) |accessdate=2010-01-07}}</ref>
|-
|Ratcliffe Beds || [Osagian](/source/Osagian) || dense [dolomite](/source/Dolomite_(rock)), [mudstone](/source/mudstone) with three [anhydrite](/source/anhydrite) beds || {{convert|80|m|ft|-1|abbr=on}}
|<ref>{{Cite web|url=http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl?00053:012509|title=Ratcliffe Beds|author=[Lexicon of Canadian Geologic Units](/source/Lexicon_of_Canadian_Geologic_Units) |accessdate=2010-01-07}}</ref>
|-
|Midale Beds || [Osagian](/source/Osagian) || [oolitic](/source/oolite) to [pisolitic](/source/pisolitic) and skeletal [grainstone](/source/grainstone) to [packstone](/source/packstone) with vuggy porosity, [dolomite](/source/Dolomite_(rock)), porous [wackestone](/source/wackestone) || {{convert|45|m|ft|-1|abbr=on}}
|<ref name=Midale>{{Cite web|url=http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl?00053:009713|title=Midale Beds|author=[Lexicon of Canadian Geologic Units](/source/Lexicon_of_Canadian_Geologic_Units) |accessdate=2010-01-07}}</ref>
|-
|Frobisher Evaporite || [Osagian](/source/Osagian) || supratidal [anhydrite](/source/anhydrite) || {{convert|9|m|ft|-1|abbr=on}}
|<ref name=Midale/>
|-
|Kisbey Sandstone || [Osagian](/source/Osagian) || porous [silt](/source/silt)y [dolomite](/source/Dolomite_(rock)) and calcareous [sandstone](/source/sandstone) || {{convert|10|m|ft|-1|abbr=on}}
|<ref>{{Cite web|url=http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl?00053:007682|title=Kisbey Sandstone|author=[Lexicon of Canadian Geologic Units](/source/Lexicon_of_Canadian_Geologic_Units) |accessdate=2010-01-07}}</ref>
|-
|Alida Beds || [Osagian](/source/Osagian) || oolitic to pisolitic [grainstone](/source/grainstone) and [packstone](/source/packstone), silty and [dolomitic](/source/Dolomite_(mineral)) limestone, crinoidal limestones || {{convert|63|m|ft|-1|abbr=on}}
|<ref>{{Cite web|url=http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl?00053:000230|title=Alida Beds|author=[Lexicon of Canadian Geologic Units](/source/Lexicon_of_Canadian_Geologic_Units) |accessdate=2010-01-07}}</ref>
|-
|Tilston Beds || [Kinderhookian](/source/Kinderhookian) || oolitic, pisolitic and [crinoid](/source/crinoid)al grainstone and packstone; [chert](/source/chert)y or [dolomitic](/source/Dolomite_(mineral)) limestone, silty limestone, [anhydrite](/source/anhydrite) || {{convert|80|m|ft|-1|abbr=on}}
|<ref>{{Cite web|url=http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl?00053:015229|title=Tilston Beds|author=[Lexicon of Canadian Geologic Units](/source/Lexicon_of_Canadian_Geologic_Units) |accessdate=2010-01-07}}</ref>
|-
|Souris Valley Beds || [Kinderhookian](/source/Kinderhookian) || argillaceous limestone, calcareous [shale](/source/shale), [chert](/source/chert) || {{convert|176|m|ft|-1|abbr=on}}
|<ref>{{Cite web|url=http://cgkn1.cgkn.net/weblex/weblex_litho_detail_e.pl?00053:014089|title= Souris Valley Beds|author=[Lexicon of Canadian Geologic Units](/source/Lexicon_of_Canadian_Geologic_Units) |accessdate=2010-01-07}}</ref>
|}

==See also==
*[List of types of limestone](/source/List_of_types_of_limestone)

==References==
{{reflist}}

{{Western Canadian Sedimentary Basin| Saskatchewan=yes}}

Category:Geologic groups of the United States
Category:Geologic groups of Saskatchewan
Category:Mississippian Series
Category:Mississippian United States
Category:Carboniferous Arizona
Category:Carboniferous Colorado
Category:Carboniferous Idaho
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
Category:Shale groups of the United States
Category:Shale groups of Canada

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Adapted from the Wikipedia article [Madison Group](https://en.wikipedia.org/wiki/Madison_Group) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Madison_Group?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.