H. B. Willman and T. C. Buschbach
The Boles Member of the Joachim Dolomite (Templeton and Willman, 1963, p. 60), which overlies the Augusta Member, is named for Boles, Franklin County, Missouri, 6 miles southwest of the type section.
The type section of the Boles Member is located 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 19.1 feet thick.
Extent and Thickness
The Boles Member is commonly about 20 feet thick, ranging from 15-30 feet.
It consists largely of thin to medium beds of dense silty dolomite and vuggy pure dolomite, separated by layers of dark red-brown to gray-green shale as much as 5 inches thick. Many bedding surfaces are ripple marked, and mud cracks are common. It contains several bands of white to black chert nodules and is the only persistent chert zone in the outcropping Joachim. However, chert is absent in places, and in subsurface in Illinois it occurs in other members of the Joachim. The Boles is distinguished from both the Augusta below and the Defiance above by its thin bedding, abundance of shale, and the chert bands.
TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.
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