Strawbridge Member

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Lithostratigraphy: Ottawa Limestone Megagroup >>Platteville Group >>Plattin Subgroup >>Quimbys Mill Formation >>Strawbridge 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 Strawbridge Member of the Quimbys Mill Formation (Templeton and Willman, 1963, p. 92).


Named for Strawbridge, Lafayette County, Wisconsin, 3 miles southwest of the type section.

Other names


Type section

Type location

The type section of the Strawbridge Member is located in the same type section as Quimbys Mill (a small quarry near Etna, Lafayette County, Wisconsin (SE SE 11, 1N-1E)) where it is 7.8 feet thick.

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

The Strawbridge Member is at the top of the Quimbys Mill Formation.

Extent and thickness

The Strawbridge Member is about 7 feet thick in the northern outcrop area in Illinois and 10-15 feet thick in the southern outcrop area.


The Strawbridge Member is similar in lithology to the Shullsburg Member but is less argillaceous, generally thicker bedded, and has fewer and thinner shale partings. It is partly cherty, especially at the top, in northern Illinois.




Well log characteristics


The Strawbridge Member contains numerous fucoids, which are scarce in the older members of the formation and much smaller than those in the underlying Nachusa Formation.

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