Francis Creek Shale Member

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Lithostratigraphy: Kewanee Group >>Carbondale Formation >>Francis Creek Shale Member
Chronostratigraphy: Paleozoic Erathem >>Pennsylvanian Subsystem >>Desmoinesian Series
Allostratigraphy: Absaroka 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)

M. E. Hopkins and J. A. Simon


Original description

The Francis Creek Shale Member of the Carbondale Formation (Savage, 1927, p. 309).


Named for Francis Creek in Fulton County.

Other names


Type section

Type location

The type locality is along the creek (NE SW 22, 5N-1E) (Wanless, 1929, p. 89; 1956, p. 10; 1957, p. 88, 203).

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

Extent and thickness

The shale is more than 80 feet thick in northeastern Illinois. It forms a large clastic wedge that extends across the northern part of the area of Pennsylvanian rocks and thins out to the west and south (Smith, 1970). It has not been recognized in southern Illinois.


The shale is medium gray and silty. It is best known for the famous Mazon Creek sideritic concretions that are found in the Kankakee-Will-Grundy Counties area and have yielded what is probably the best known Pennsylvanian flora in the United States (Noé, 1925). In Will County and at one place in Fulton County, concretions in the shale have a diverse fauna (Johnson and Richardson, 1970). The upper part of the Francis Creek commonly contains a few sandstone beds, probably equivalent to the Jake Creek Sandstone.




Well log characteristics


Age and correlation

Environments of deposition

Economic importance



JOHNSON, R. G., and E. S. RICHARDSON, JR., 1970, Fauna of the Francis Creek Shale in the Wilmington area: Illinois State Geological Survey Guidebook Series 8, p. 53-60.
NOÉ, A. C., 1925, Pennsylvanian flora of northern Illinois: Illinois State Geological Survey Bulletin 52, 113 p.
SAVAGE, T. E., 1927, Significant breaks and overlaps in the Pennsylvanian rocks of Illinois: American Journal of Science, v. 14, p. 307-316.
SMITH, W. H., 1970, Lithology and distribution of the Francis Creek Shale in Illinois: Illinois State Geological Survey Guidebook Series 8, p. 34.
WANLESS, H. R., 1929, Geology and mineral resources of the Alexis Quadrangle: Illinois State Geological Survey Bulletin 57, 230 p.
WANLESS, H. R., 1956, Classification of the Pennsylvanian rocks of Illinois as of 1956: Illinois State Geological Survey Circular 217, 14 p.
WANLESS, H. R., 1957, Geology and mineral resources of the Beardstown, Glasford, Havana, and Vermont Quadrangles: Illinois State Geological Survey Bulletin 82, 233 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation