Backbone Limestone
Lithostratigraphy: Hunton Limestone Megagroup >>Backbone Limestone
Chronostratigraphy: Paleozoic Erathem >>Devonian System >>Lower Devonian Series
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)
Charles Collinson and Elwood Atherton
Name
Original description
The Backbone Limestone (Savage, 1920, p. 169-178).
Derivation
Named for an isolated ridge called the Backbone along the Mississippi River north of Grand Tower, Jackson County.
Other names
History/background
Type section
Type location
The type section of the Backbone Formation is in a quarry at the south end of the ridge (SE SW SW 24, 10S-4W), where only the upper 38 feet of the formation, overlain by the Clear Creek Chert, is exposed.
Type author(s)
Type status
Reference section
Reference location
Reference author(s)
Reference status
Stratigraphic relationships
The Backbone Limestone overlies the Grassy Knob Chert.
Extent and thickness
The Backbone Limestone appears to be as much as 200 feet thick where it rims the deep part of the Illinois Basin, but it becomes thinner within the deeper part and in places is absent (Collinson et al., 1967a). In the outcrop area in Jackson and Union Counties, the Backbone Limestone is about 100 feet thick, but it thins southward and is absent (or becomes cherty and is not recognized) in the Devonian outcrop area in Alexander County.
Lithology
The Backbone Limestone consists of light gray, massive, crystalline, pure limestone that commonly contains many large crinoid stems and a few scattered chert nodules.
Core(s)
Photograph(s)
Contacts
Well log characteristics
Fossils
The Backbone has a large fauna that is dominated by brachiopods, notably Acrospirifer murchisoni and Costispirifer arenosus, but gastropods, bryozoans, conodonts, and trilobites are common.
Age and correlation
The fossils indicate a correlation with the Oriskany in New York. The Backbone is continuous with the Little Saline Limestone in Missouri.
Environments of deposition
Economic importance
Remarks
References
COLLINSON, CHARLES, L. E. BECKER, G. W. JAMES, J. W. KOENIG, and D. H. SWANN, 1967a, Illinois Basin, in International symposium on the Devonian System: Alberta Society of Petroleum Geologists, v. 1, p. 940-962; Illinois State Geological Survey Reprint 1968-G.
SAVAGE, T. E., 1920, Devonian formations of Illinois: American Journal of Science, v. 49, p. 169-182.
ISGS Codes
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