Historical:Blodgett 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: Knox Dolomite Megagroup >>Prairie du Chien Group >>Oneota Dolomite >>Blodgett Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Canadian Series >>Trempealeauan Stage
Allostratigraphy: Sauk Sequence


H. B. Willman and T. C. Buschbach

Name Origin

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

Type Section

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.

Extent and Thickness

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


The Blodgett Member of the Oneota Dolomite (Buschbach, 1964, p. 45) is the upper, noncherty, or only slightly cherty, member. 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.


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