Historical:Defiance Member

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Handbook of Illinois Stratigraphy
Series Bulletin 95
Author H. B. Willman, Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, Jack A. Simon
Date 1975
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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


H. B. Willman and T. C. Buschbach

Name Origin

The Defiance Member of the Joachim Dolomite (Templeton and Willman, 1963, p. 60), which overiles the Boles Member, is named for Defiance, St. Charles County, Missouri, 3 miles northeast of the type section.

Type Section

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.

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.

Stratigraphic Position

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


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.


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