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.
H. B. Willman and T. C. Buschbach
The Buckhorn Member of the Dunleith Formation (Templeton and Willman, 1963, p. 119).
Named for Buckhorn Corners, Stephenson County, 2 miles east of the type section.
The Buckhorn is called the "Blue" in the lead-zinc district.
The type section of the Buckhorn Member of the Dunleith Formation is located in a quarry at Buena Vista (NW SW NE 15, 28N-7E), where the member is 8.3 feet thick.
The Buckhorn Member is the basal member of the Dunleith Formation.
Extent and thickness
The Buckhorn Member is commonly 5-8 feet thick but is generally absent in southwestern Illinois, where it is overlapped by the St. James Member.
The Buckhorn consists of argillaceous, medium to coarse, blue-gray dolomite heavily speckled with black, particularly at the top. It contains green shale partings and in the northwestern area is slightly sandy. It locally contains several very thin layers of bentonite.
Well log characteristics
Paucicrura [Dalmanella] rogata is especially common in the Buckhorn Member.
Age and correlation
With the overlying St. James Member, it is equivalent to the Ion Member at the top of the Decorah in the region northwest of Illinois.
Environments of deposition
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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