The Madison Limestone is a thick sequence of mostly carbonate

Carbonate minerals

Carbonate minerals are those minerals containing the carbonate ion: CO32-.-Anhydrous carbonates:*Calcite group: Trigonal**Calcite CaCO3**Gaspeite CO3**Magnesite MgCO3**Otavite CdCO3**Rhodochrosite MnCO3**Siderite FeCO3**Smithsonite ZnCO3...

 rocks of Mississippian age in the Rocky Mountain and Great Plains

Great Plains

The Great Plains are a broad expanse of flat land, much of it covered in prairie, steppe and grassland, which lies west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S...

 areas of western United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. The rocks serve as an important aquifer

Aquifer

An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...

 as well as an oil reservoir

Oil reservoir

A petroleum reservoir, or oil and gas reservoir, is a subsurface pool of hydrocarbons contained in porous or fractured rock formations. The naturally occurring hydrocarbons, such as crude oil or natural gas, are trapped by overlying rock formations with lower permeability...

 in places. The Madison and its equivalent strata extend from the Black Hills

Black Hills

The Black Hills are a small, isolated mountain range rising from the Great Plains of North America in western South Dakota and extending into Wyoming, USA. Set off from the main body of the Rocky Mountains, the region is something of a geological anomaly—accurately described as an "island of...

 of western South Dakota

South Dakota

South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...

 to western Montana

Montana

Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

 and eastern Idaho

Idaho

Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....

, and from the Canadian border to western Colorado

Colorado

Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...

 and the Grand Canyon

Grand Canyon

The Grand Canyon is a steep-sided canyon carved by the Colorado River in the United States in the state of Arizona. It is largely contained within the Grand Canyon National Park, the 15th national park in the United States...

 of Arizona

Arizona

Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...

.

Age and nomenclature

The Madison is formally known as the Madison Group

Geologic unit

A geological unit is a volume of rock or ice of identifiable origin and age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features that characterize it....

. In Montana, where its thickness reaches 1700 feet (518.2 m), 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.

Most of the Madison Limestones were deposited during Early to Middle Mississippian time (Tournaisian

Tournaisian

The Tournaisian is in the ICS geologic timescale the lowest stage or oldest age of the Mississippian, the oldest subsystem of the Carboniferous. The Tournaisian age lasted from 359.2 ± 2.5 Ma to 345.3 ± 2.1 Ma...

 to Visean

Viséan

The Visean, Viséan or Visian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the second stage of the Mississippian, the lower subsystem of the Carboniferous. The Visean lasted from 345.3 ± 2.1 to 328.3 ± 1.6 Ma...

 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), but since the original work focused on the area of Three Forks, Montana

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 Missouri River. The population was 1,728 at the 2000 census...

, it is likely that the name relates to outcrops along the Madison River

Madison River

The Madison River is a headwater tributary of the Missouri River, approximately 183 miles long, in Wyoming and Montana. Its confluence with the Jefferson and Gallatin rivers near Three Forks, Montana form the Missouri 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.

Lithology

Limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

s and dolomite

Dolomite

Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....

s dominate the Madison. Because the rock is highly soluble, it often develops caves and karst

KARST

Kilometer-square Area Radio Synthesis Telescope is a Chinese telescope project to which FAST is a forerunner. KARST is a set of large spherical reflectors on karst landforms, which are bowlshaped limestone sinkholes named after the Kras region in Slovenia and Northern Italy. It will consist of...

 topography. Lewis and Clark Caverns

Lewis and Clark Caverns

Lewis and Clark Caverns State Park is located in southeastern Jefferson County, Montana. The primary feature of the park is its namesake cavern....

, 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

Williston Basin

The Williston Basin is a large intracratonic sedimentary basin in eastern Montana, western North and South Dakota, and southern Saskatchewan known for its rich deposits of petroleum and potash. The basin is a geologic structural basin but not a topographic depression; it is transected by the...

, water was shallow enough for oolite

Oolite

Oolite is a sedimentary rock formed from ooids, spherical grains composed of concentric layers. The name derives from the Hellenic word òoion for egg. Strictly, oolites consist of ooids of diameter 0.25–2 mm; rocks composed of ooids larger than 2 mm are called pisolites...

 shoals to develop; they later became reservoirs for oil.
The gray cliffs along the Missouri River

Missouri River

The Missouri River flows through the central United States, and is a tributary of the Mississippi River. It is the longest river in North America and drains the third largest area, though only the thirteenth largest by discharge. The Missouri's watershed encompasses most of the American Great...

 in the Gates of the Mountains, Montana

Gates of the Mountains Wilderness

The Gates of the Mountains Wilderness is located in the U.S. state of Montana. Created by an act of Congress in 1964, the wilderness is managed by Helena National Forest...

 are formed by Madison Limestone.

Subdivisions

Montana-Wyoming-Manitoba
The following formations are recognized in Montana

Montana

Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

, Wyoming

Wyoming

Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

 and Manitoba

Manitoba

Manitoba is a Canadian prairie province with an area of . The province has over 110,000 lakes and has a largely continental climate because of its flat topography. Agriculture, mostly concentrated in the fertile southern and western parts of the province, is vital to the province's economy; other...

, from top to base:

Sub-unit	Age Geochronology Geochronology is the science of determining the age of rocks, fossils, and sediments, within a certain degree of uncertainty inherent to the method used. A variety of dating methods are used by geologists to achieve this, and schemes of classification and terminology have been proposed...	Lithology	Max. Thickness	Reference
Charles Formation	Mississippian	dolomitic limestone Dolostone Dolostone or dolomite rock is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite. In old U.S.G.S. publications it was referred to as magnesian limestone. Most dolostone formed as a magnesium replacement of limestone or lime mud prior to lithification. It is...	244 m (800.5 ft)
Mission Canyon Formation	Osagian	white bioclastic limestone, oolitic calcarenite Calcarenite thumb|250px|The [[Pietra di Bismantova]] in central [[Italy]] is an example of calcarenite formation.Calcarenite is a type of limestone that is composed predominately, more than 50 percent, of detrital sand-size , carbonate grains... , occasionally dolomitized; anhydrite Anhydrite Anhydrite is a mineral – anhydrous calcium sulfate, CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium and strontium sulfates, as might be expected from the...  in the Williston Basin Williston Basin The Williston Basin is a large intracratonic sedimentary basin in eastern Montana, western North and South Dakota, and southern Saskatchewan known for its rich deposits of petroleum and potash. The basin is a geologic structural basin but not a topographic depression; it is transected by the...	183 m (600.4 ft)
Lodgepole Formation	Kinderhookian	lime mudstones, shale Shale Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering... , chert Chert Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements... , contains bitumen	245 m (803.8 ft)

Saskatchewan
The following subdivisions (of formation rank) are recognized in Saskatchewan

Saskatchewan

Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....

, from top to base:

Sub-unit	Age Geochronology Geochronology is the science of determining the age of rocks, fossils, and sediments, within a certain degree of uncertainty inherent to the method used. A variety of dating methods are used by geologists to achieve this, and schemes of classification and terminology have been proposed...	Lithology	Max. Thickness	Reference
Poplar Beds	Meramecian	limestone Limestone Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera.... , argillaceous dolomite Dolomite Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone.... , evaporite Evaporite Evaporite is a name for a water-soluble mineral sediment that result from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporate deposits, marine which can also be described as ocean deposits, and non-marine which are found in standing bodies of...	152 m (498.7 ft)
Ratcliffe Beds	Osagian	dense dolomites Dolomites The Dolomites are a mountain range located in north-eastern Italy. It is a part of Southern Limestone Alps and extends from the River Adige in the west to the Piave Valley in the east. The northern and southern borders are defined by the Puster Valley and the Sugana Valley... , mudstone Mudstone Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...  with three anhydrite Anhydrite Anhydrite is a mineral – anhydrous calcium sulfate, CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium and strontium sulfates, as might be expected from the...  beds	80 m (262.5 ft)
Midale Beds	Osagian	oolitic Oolitic Oolitic may refer to:* Oolite, a sedimentary rock consisting of ooids* Oolitic, Indiana, a town whose name came from the underlying limestone...  to pisolitic and skeletal grainstone Grainstone Under the Dunham classification, grainstones are grain-supported carbonate sedimentary rocks that contain no micrite. The spaces between grains are filled with sparry cement.-References:...  to packstone with vuggy porosity, dolomite Dolomite Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone.... , porous wackestone Wackestone Wackestone is a matrix-supported carbonate rock that contains over 10% allochems in a carbonate mud matrix. This is part of the Dunham classification of carbonate rocks. In the other widely used classification due to Folk, an equivalent description would be, for example, an oopelmicrite, where the...	45 m (147.6 ft)
Foirbisher Evaporite	Osagian	supratidal anhydrite Anhydrite Anhydrite is a mineral – anhydrous calcium sulfate, CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium and strontium sulfates, as might be expected from the...	9 m (29.5 ft)
Kisbey Sandstone	Osagian	porous silt Silt Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body... y dolomite Dolomite Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....  and calcareous sandstone Sandstone Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...	10 m (32.8 ft)
Alida Beds	Osagian	oolitic to pisolitic grainstone Grainstone Under the Dunham classification, grainstones are grain-supported carbonate sedimentary rocks that contain no micrite. The spaces between grains are filled with sparry cement.-References:...  and packstone, silty and dolomitic limestone Dolostone Dolostone or dolomite rock is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite. In old U.S.G.S. publications it was referred to as magnesian limestone. Most dolostone formed as a magnesium replacement of limestone or lime mud prior to lithification. It is... , crinoidal limestones	63 m (206.7 ft)
Tilston Beds	Kinderhookian	oolitic, pisolitic and crinoid Crinoid Crinoids are marine animals that make up the class Crinoidea of the echinoderms . Crinoidea comes from the Greek word krinon, "a lily", and eidos, "form". They live both in shallow water and in depths as great as 6,000 meters. Sea lilies refer to the crinoids which, in their adult form, are... al grainstone and packstone; chert Chert Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements... y or dolomitic crystalline limestone Dolostone Dolostone or dolomite rock is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite. In old U.S.G.S. publications it was referred to as magnesian limestone. Most dolostone formed as a magnesium replacement of limestone or lime mud prior to lithification. It is... , silty limestone, anhydrite Anhydrite Anhydrite is a mineral – anhydrous calcium sulfate, CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium and strontium sulfates, as might be expected from the...	80 m (262.5 ft)
Souris Valley Beds	Kinderhookian	argillaceous limestone, calcareous shale Shale Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering... , chert Chert Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...	176 m (577.4 ft)