Fraileys Shale

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Lithostratigraphy: Pope Megagroup >>Okaw Group >>Golconda Group >>Fraileys Shale
Chronostratigraphy: Paleozoic Erathem >>Mississippian Subsystem >>Chesterian Series >>Hombergian 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

Fraileys Shale (McFarlan et al., 1955, p. 18).


Named for Fraileys Landing (abandoned), Hardin County, about a mile northeast of the type section.

Other names


Type section

Type location

The type section of the Fraileys Shale is in a bluff along Haney Creek (NE NE SE 9, 12S-10E), where the formation is 94 feet thick.

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

Extent and thickness

The Fraileys Shale is 80-100 feet thick in most of Williamson County, and it thins irregularly northward to 30-40 feet in the northern and northeastern areas (fig. M-39). Great variations in thickness within short distances have a reciprocal relation with units above and below.


The Fraileys is dominantly shale, with minor amounts of limestone and, locally, sandstone. The Fraileys is dominantly dark gray shale. A bed of red shale a few feet below the top and a bed of siltstone just below the shale are persistent in the southern area. Limestone beds occur sporadically at numerous levels. A bed about 15 feet below the top is fairly persistent, but the others, mostly lenticular accumulations of fossil debris, thin rapidly and disappear within a short distance. Some of these beds contain abundant fragments of bright red, orange, and green fossils, mainly bryozoans but also a few oolites and other detrital grains. In the north, limestone is fairly abundant locally in the Fraileys, particularly in the lower part, and in places it is difficult to distinguish limestone at the base of the Fraileys from the underlying Beech Creek Limestone. Sandstone in the Fraileys, where present in significant amount, is assigned to the Big Clifty Sandstone Member.




Well log characteristics


The corkscrew-like axes of the bryozoan Archimedes reach a peak in number of species and abundance of specimens in the Fraileys and Haney Formations. A brachiopod faunal zone, the "Camarophoria"--Stenoscisma explanata Range Zone, extends from the Fraileys upward to the top of the Chesterian strata. The Pterotocrinus capitalis Range Zone is equivalent to the lower half of the Fraileys Shale.

Age and correlation

Environments of deposition

Economic importance

"Golconda shale" is an informal name applied to the Fraileys Shale. “Big Clifty” and “Jackson” are informal names applied to producing zones in the Big Clifty Sandstone Member of the Fraileys Shale.



MCFARLAN, A. C., D. H. SWANN, F. H. WALKER, and EDMUND NOSOW, 1955, Some old Chester problems-Correlations of lower and middle Chester formations of western Kentucky: Kentucky Geological Survey Bulletin 16, 37 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation