Defiance Member

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Lithostratigraphy: Ottawa Limestone Megagroup >>Ancell Group >>Joachim Dolomite >>Defiance Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Blackriveran 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 Defiance Member of the Joachim Dolomite (Templeton and Willman, 1963, p. 60).


Named for Defiance, St. Charles County, Missouri, 3 miles northeast of the type section.

Other names


Type section

Type location

The type section of the Defiance Member is located in the same exposure as the Boles Member in a quarry on the north side of the Missouri Valley 1 mile southwest of Matson, St. Charles County (NE cor. SE NE SW 4, 44N- 2E), where the member is 20.5 feet thick.

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

The Defiance Member is located on top of the Boles Member of the Joachim Dolomite Formation.

Extent and thickness

The Defiance Member is exposed in Illinois only in the Mississippi bluffs at West Point Landing, Calhoun County. The Defiance Member is usually 20-40 feet thick and dominantly silty dolomite.


The Defiance Member contains numerous algal domes, and beds of limestone are common in the southern part of the outcrop area. The Defiance Member is similar in lithology to the Augusta Member.




Well log characteristics


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