Fairplay Member

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Lithostratigraphy: Ottawa Limestone Megagroup >>Galena Group >>Kimmswick Subgroup >>Dunleith Formation >>Fairplay Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Trentonian Stage
Allostratigraphy: Tippecanoe Sequence

Primary source

Willman, H. B., Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, and Jack A. Simon, 1975, Handbook of Illinois Stratigraphy: Illinois State Geological Survey Bulletin 95, 261 p.

Contributing author(s)

H. B. Willman and T. C. Buschbach


Original description

The Fairplay Member of the Dunleith Formation (Templeton and Willman, 1963, p. 121).


Named for the town of Fairplay, Grant County, Wisconsin, 6 miles northeast of the type section.

Other names


Type section

Type location

The type section of the Fairplay Member is part of the Dunleith Formation type section (in an exposure in the Mississippi River bluffs on the north side of East Dubuque (SE 19, 29N-2W)), where the Fairplay Member is 19.8 feet thick.

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

The Fairplay Member of the Dunleith Formation overlies the Eagle Point Member.

Extent and thickness

The Fairplay Member is commonly 14-20 feet thick.


In the type section the Fairplay consists of relatively pure, lithographic limestone and is the top of the northern limestone facies. It is largely free of chert, but scattered nodules appear locally. The upper 1-3 feet is persistently argillaceous or shaly. These characteristics extend into the northern dolomite facies, but the member is not differentiated in the southern limestone facies.




Well log characteristics


Receptaculites oweni is common in many beds of the Fairplay Member, and the Fairplay is the Lower Receptaculites Zone.

Age and correlation

Environments of deposition

Economic importance



TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation