Charles Collinson and Elwood Atherton
The Coralville Member of the Cedar Valley Limestone (Keyes, 1912, p. 149; 1913, p. 205-206), the uppermost member, is named for Coralville, Johnson County, Iowa.
The type section of the Coralville Member is located in quarries 1 mile northeast of Coralville.
Extent and Thickness
The Coralville is present in Illinois only in the western part of the area of the Cedar Valley. It is as much as 25 feet thick and is unconformably overlain by the Sweetland Creek Shale of the New Albany Group.
The Coralville consists of brown, medium-grained dolomite that in places is a stromatoporoid reef.
The Coralville is abundantly fossiliferous; brachiopods, corals, bryozoans, and stromatoporoids are the most common fossils. The conodonts indicate that in places the boundary of the Middle and Upper Devonian Series lies within the Coralville (Collinson et al., 1967b), but most, if not all, of the Coralville in Illinois is Middle Devonian in age.
COLLINSON, CHARLES, M. P. CARLSON, F. H. DORHEIM, and J. W. KOENIG, 1967b, Central Iowa Basin, in International symposium on the Devonian System: Alberta Society of Petroleum Geologists, v. 1, p. 963-971; Illinois State Geological Survey Reprint 1968-G.
KEYES, C. R., 1912, Some provincial and local phases of the general geologic section of Iowa: Iowa Academy of Science Proceedings, v. 19, p. 147-151.
KEYES, C. R., 1913, Late Devonic sequence of the Iowa region (synopsis): Iowa Academy of Science Proceedings, v. 20, p. 205-206.
|Stratigraphic Code||Geo Unit Designation|