Unit Name: Madison Group
Unit Type: Lithostratigraphic
Rank: Group
Status: Formal
Usage: Currently in use
Age Interval: Mississippian (359.2 - 318.1 ma)
Province/Territory: Saskatchewan; Idaho; Montana; Nebraska; North Dakota; South Dakota; Wyoming

Originator: Peale, A.C, 1893.

Type Locality:
North bank of Gallatin River, directly across from Logan, Gallatin County, Montana, S/2 Sec. 25, Twp. 2N, Rge. 2E. (Holland, 1952; Sloss and Hamblin, 1942).

The Madison Group ranges from 457 to 640 m (1,500 to 2,100 ft) in thickness near the type area of southwestern Montana and exhibits similar thick development southward into Idaho and eastward in central Montana and the Williston basin. The Madison thins progressively by truncation towards zero edges at the north (Saskatchewan), east (North Dakota) and south (Wyoming, Nebraska and South Dakota).

At the type section the Madison Group consists of a limestone sequence that contains argillaceous limestones and calcareous shales in the lower part and massive brecciated limestone zones in the upper part. The limestones exhibit increasing dolomite content southward to Wyoming, whereas anhydrite and salt occur in the upper part in eastern Montana and the Williston Basin. Three evaporite cycles are recognized.

The Madison lies directly on the Bakken Formation in the Williston Basin and on Devonian beds south of the limit of the Bakken. It is overlain by the Chesteran Big Snowy group in central Montana and parts of the Williston Basin, unconformably by Triassic or Jurassic to the north (northern Montana, Saskatchewan) and by Pennsylvanian strata in Wyoming. On a faunal basis the Madison of central Montana has been assigned to the Kinderhookian and Osagean stages. Several authors have arbitrarily considered the Charles Formation in the upper part of the Madison to be of Meramecian age.

Although Peale (1893) named the Madison Formation for "Lower Carboniferous" beds in the Three Forks area of Montana, he did not specify a type section. Weed (1899) considered the type section to be in the Madison Range, south of the Three Forks area. After evaluating Peale's published works Sloss and Hamblin (1942) and Holland (1952) concluded that the type section is at Logan. Following Peale's three-fold subdivision of the Madison into "Laminated limestones, Massive limestones, and Jaspery limestones" (bottom to top) Weed (1899) first referred to the Madison as a group divisible into "Paine shale, Woodhurst limestone, and Castle limestone". Collier and Cathcart (1922) formally divided the Madison Group into two formations: a lower, Lodgepole limestone (152 m, 499 ft), and an upper Mission Canyon limestone (244 m, 800 ft) from type exposures in the Little Rocky Mountain of northern Montana, and recommended application of these terms in Montana and Wyoming.

Other Citations:
Andrichuk, 1955; Collier and Cathcart, 1922; Holland, 1952; Kent, 1974; Nordquist, 1953; Peale, 1893; Sloss and Hamblin, 1942; Sloss and Laird, 1945; Weed, 1899.

Source: CSPG Lexicon of Canadian Stratigraphy, Volume 4, western Canada, including eastern British Columbia, Alberta, Saskatchewan and southern Manitoba; D.J. Glass (editor)
Contributor: D.M. Kent
Entry Reviewed: Yes
Name Set: Lithostratigraphic Lexicon
LastChange: 25 May 2004