Oglesby Member

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Lithostratigraphy: Ottawa Limestone Megagroup >>Platteville Group >>Pecatonica Formation >>Oglesby Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Blackriveran 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 Oglesby Member of the Pecatonica Formation (Templeton and Willman, 1963, p. 77).


Named for Oglesby, La Salle County.

Other names


Type section

Type location

The type section of the Oglesby Member is in Matthiessen State Park east of Oglesby (NE NE NE 31, 33N-3E), where the member is 12 feet thick.

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

Extent and thickness

The Oglesby Member is absent in Illinois north of the type locality, but it is as much as 15 feet thick in southern Illinois.


The Oglesby Member is pure, light gray, white, or buff calcarenite that is laminated, rarely conglomeratic, and locally cross bedded. It is medium to coarse grained in the type locality but fine grained elsewhere. A strong iron-stained corrosion surface occurs on the top and is equivalent to a similar surface on the top of the Medusa Member in northern Illinois, where the Oglesby is absent.




Well log characteristics


Age and correlation

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