Blodgett Member

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Lithostratigraphy: Knox Dolomite Megagroup >>Prairie du Chien Group >>Oneota Dolomite >>Blodgett Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Canadian Series >>Trempealeauan Stage
Allostratigraphy: Sauk 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 Blodgett Member of the Oneota Dolomite (Buschbach, 1964, p. 45).


The Blodgett Member is named for the town of Blodgett, western Will County.

Other names


Type section

Type location

The type section of the Blodgett Member is located 3 miles northeast of Blodgett, western Will County, in a boring (NE NE SW 25, 34N-9E) and is represented by samples (sample set 6199) from 885-980 feet deep.

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

The Blodgett Member of the Oneota Dolomite is the upper, noncherty, or only slightly cherty, member.

Extent and thickness

The Blodgett is recognized in the northeastern quarter of the state, where it ranges from 90 to over 100 feet thick.


It is dolomite, sandy in part, very slightly glauconitic, light or pinkish gray, and medium to fine grained. Oolitic chert is present but not abundant. Thin green shale partings are widely spaced throughout the member.




Well log characteristics


Age and correlation

Environments of deposition

Economic importance



BUSCHBACH, T. C., 1964, Cambrian and Ordovician strata of northeastern Illinois: Illinois State Geological Survey Report of Investigations 218, 90 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation