Mahomet Sand Member

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Lithostratigraphy: Banner Formation >>Mahomet Sand Member
Chronostratigraphy: Cenozoic Erathem >>Quaternary System >>Pleistocene Series

Primary source

Willman, H. B., and John C. Frye, 1970, Pleistocene Stratigraphy of Illinois: Illinois State Geological Survey Bulletin 94, 204 p.

Contributing author(s)

H. B. Willman and John C. Frye


Original description

Mahomet Sand Member, Banner Formation (Horberg, formally 1953; in abstract 1946a).


The Mahomet Sand Member was named by Horberg for Mahomet, Champaign County, near which it is encountered in numerous wells (Horberg, 1953, wells 155, 156, 157, pl. 1, section J-J').

Other names


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Stratigraphic relationships

The Mahomet Sand is classified here as a member of the Banner Formation. It occupies the same stratigraphic position as the Sankoty Sand Member, but it consists of about equal amounts of sand and gravel, contains many silt beds, and lacks the polished pink quartz grains that distinguish the Sankoty.

Extent and thickness

The Mahomet Sand Member occurs in the Mahomet Bedrock Valley (Horberg, 1945, 1953), mainly in De Witt, Macon, Piatt, and Champaign Counties, but it probably extends eastward into Indiana. It is as much as 150 feet thick.





Well log characteristics


Age and correlation

Horberg considered the Mahomet Sand to be Nebraskan in age because of possible Nebraskan-age till along the north side of the lower Mahomet Valley, but the presence of Nebraskan drift in the valley has not been confirmed, and it appears more likely that the Mahomet Sand is pro-Kansan outwash. The Mahomet Sand has been described and the position of the valley somewhat modified in reports by Heigold, McGinnis, and Howard (1964), Manos (1961), Walker, Bergstrom, and Walton (1965), Piskin and Bergstrom (1967), and Stephenson (1967).

Environments of deposition

Economic importance



BERGSTROM, R. E., and T. R. WALKER, 1956, Ground-water geology of the East St. Louis area, Illinois: Illinois State Geological Survey Report of Investigations 191, 44 p.
HEIGOLD, P. C., L. D. McGINNIS, and R. H. HOWARD, 1964, Geologic significance of the gravity field in the DeWitt-McLean County area, Illinois: Illinois State Geological Survey Circular 369, 16 p.
HORBERG, C. L., 1945, A major buried valley in east-central Illinois and its regional relationships: Journal of Geology, v. 53, no. 5, p. 349-359.
HORBERG, C. L., 1946a, Pleistocene deposits below the Wisconsin drift in Illinois [abs.]: Geological Society of America Bulletin, volume 57, p. 1204.
HORBERG, C. L., 1953, Pleistocene deposits below the Wisconsin drift in northeastern Illinois: Illinois State Geological Survey Report of Investigations 165, 61 p.
MANOS, CONSTANTINE, 1961, Petrography of the Teays-Mahomet Valley deposits: Journal of Sedimentary Petrology, v. 31, no. 3, p. 456-466.
PISKIN, KEMAL, and R. E. BERGSTROM, 1967, Glacial drift in Illinois: Thickness and character: Illinois State Geological Survey Circular 416, 33 p.
STEPHENSON, D. A., 1967, Hydrogeology of glacial deposits of the Mahomet Bedrock Valley in east-central Illinois: Illinois State Geological Survey Circular 409, 51 p.
WALKER, W. H., R. E. BERGSTROM, and W. C. WALTON, 1965, Preliminary report on the ground-water resources of the Havana region in west-central Illinois: Illinois State Geological Survey and Illinois State Water Survey Cooperative Ground-Water Report 3, 61 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation