Historical:Buckhorn 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 >>Galena Group >>Kimmswick Subgroup >>Dunleith Formation >>Buckhorn Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Trentonian Stage
Allostratigraphy: Tippecanoe Sequence


H. B. Willman and T. C. Buschbach

Name Origin

The Buckhorn Member of the Dunleith Formation (Templeton and Willman, 1963, p. 119), the basal member, is named for Buckhorn Corners, Stephenson County, 2 miles east of the type section.

Type Section

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.

Other Names

The Buckhorn is called the "Blue" in the lead-zinc district.


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.

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.


Paucicrura [Dalmanella] rogata is especially common in the Buckhorn 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