Lithostratigraphy: Embayment Megagroup >>Wilcox Formation
Chronostratigraphy: Cenozoic Erathem >>Tertiary System >>Eocene Series
H. B. Willman and John C. Frye
The Wilcox Formation (Crider and Johnson, 1906, p. 5, 9) (fig. T-2) is named for Wilcox County, Alabama.
It was formerly called Lagrange in Illinois (Lamar and Sutton, 1930).
The Wilcox Formation probably is equivalent to only part of the Wilcox farther south in Kentucky and Tennessee.
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.
The Wilcox Formation was deposited in a delta at the head of the embayment.
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.
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