Clore Formation

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Lithostratigraphy: Pope Megagroup >>Clore Formation
Chronostratigraphy: Paleozoic Erathem >>Mississippian Subsystem >>Chesterian Series >>Elviran Stage
Allostratigraphy: Kaskaskia 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)

Elwood Atherton, Charles Collinson, and Jerry A. Lineback


Original description

Clore Formation (S. Weller, 1913, p. 120).


Named for Clore School, Randolph County.

Other names


Type section

Type location

The type section of the Clore Formation is in gullies near Clore School (SE cor. 20, 7S-6W).

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

The formation includes three members, a lower limestone and shale member (Cora), a middle sandstone and shale member (Tygett), and an upper limestone and shale member (Ford Station). Early geologists in places confused the Tygett Sandstone Member with either the Degonia Sandstone or the Palestine Sandstone and confined the Clore Formation to either the Cora or the Ford Station Member (Swann, 1963).

Extent and thickness

The Clore is 40-60 feet thick near its northern and northwestern limits, and it thickens southward to a little more than 120 feet in parts of Pope and Johnson Counties (fig. M-48). The Clore is thinned by sub-Degonia channels in many more places than are shown in figure M-48. In several areas, sub-Pennsylvanian channels also cut into the Clore.


The formation is dominantly shale throughout most of its extent, but the proportion of limestone increases southward. Near the southern outcrop belt the top is stepped up a few feet to include limestone equivalent farther north to the basal portion of the Degonia. At about the same place, the base is stepped down to include limestone equivalent to the uppermost portion of the Palestine.




Well log characteristics


Fossils are generally abundant in the Clore. The fauna is made up mainly of bryozoans and brachiopods. The genera Archimedes, Batostomella, and Rhombopora (fig. M-4) are conspicuous among the bryozoans, and B. nitidula is an index fossil. The brachiopods Spirifer increbescens and Composita subquadrata are especially abundant.

Age and correlation

Environments of deposition

Economic importance



SWANN, D. H., 1963, Classification of Genevievian and Chesterian (Late Mississippian) rocks of Illinois: Illinois State Geological Survey Report of Investigations 216, 91 p.
WELLER, STUART, 1913, Stratigraphy of the Chester Group in southwestern Illinois: Illinois Academy of Science Transactions, v. 6, p. 118-129.

ISGS Codes

Stratigraphic Code Geo Unit Designation