Wilcox Formation

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Lithostratigraphy: Embayment Megagroup >>Wilcox Formation
Chronostratigraphy: Cenozoic Erathem >>Tertiary System >>Eocene Series

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)

H. B. Willman and John C. Frye


Original description

Wilcox Formation (Crider and Johnson, 1906, p. 5, 9).


Named for Wilcox County, Alabama.

Other names

It was formerly called Lagrange in Illinois (Lamar and Sutton, 1930).


Type section

Type location

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

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Stratigraphic relationships

Extent and thickness

The Wilcox Formation is exposed in Illinois only in Pulaski County (Pryor and Ross, 1962), along the east side of the Cache River south of Unity, particularly in a pit where 20 feet of sand of the Wilcox Formation overlies the Porters Creek Formation and is overlain by the Mounds Gravel (SE SW SW 7, 16S-1W) (Pryor and Ross, 1962). It is only 20-30 feet thick in the outcrop area, but it thickens southward and is as much as 250 feet thick in subsurface near Cairo, Alexander County.


The Wilcox Formation varies from white, fine to medium, slightly micaceous sand to gray, nearly white, silty or sandy clay.




Well log characteristics


Age and correlation

The Wilcox Formation probably is equivalent to only part of the Wilcox farther south in Kentucky and Tennessee.

Environments of deposition

The Wilcox Formation was deposited in a delta at the head of the embayment.

Economic importance



CRIDER, A. F., and L. C. JOHNSON, 1906, Summary of the underground water resources of Mississippi: USGS Water Supply Paper 159, 86 p.
LAMAR, J. E., and A. H. SUTTON, 1930, Cretaceous and Tertiary sediments of Kentucky, Illinois, and Missouri: American Association of Petroleum Geologists Bulletin, v. 14, p. 845-866.
PRYOR, W. A., and C. A. ROSS, 1962, Geology of the Illinois parts of the Cairo, La Center, and Thebes Quadrangles: Illinois State Geological Survey Circular 332, 39 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation