H. B. Willman and T. C. Buschbach
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.
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.
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.
|Geo Unit Designation