Buckhorn Member

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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

Primary source

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.

Contributing author(s)

H. B. Willman and T. C. Buschbach


Original description

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.

Other names

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


Type section

Type location

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.

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

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

Economic importance



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