Historical:Wilmette Bed

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Handbook of Illinois Stratigraphy
Series Bulletin 95
Author H. B. Willman, Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, Jack A. Simon
Date 1975
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Lithostratigraphy: Lake Michigan Formation >>South Haven Member >>Wilmette Bed
Chronostratigraphy: Cenozoic Erathem >>Quaternary System >>Holocene Series


John C. Frye and H. B. Willman

Name Origin

The Wilmette Bed of the Sheboygan Member of the Lake Michigan Formation (Lineback et al., 1970, p. 11) is named for Wilmette, Cook County.

Type Section

The type section is in the type section of the Sheboygan Member, interval 112-219.3 cm in core 143.

Extent and Thickness

It is 3-9 inches thick, and it occurs only in the area of southern Lake Michigan where water depth exceeds 270 feet.


It is a bed of gray clay, with some silt and sand, in the middle of the Sheboygan Member.


LINEBACK, J. A., N. J. AYER, and D. L. GROSS, 1970, Studies of Lake Michigan bottom sediments- No. 3. Stratigraphy of unconsolidated sediments in the southern part of Lake Michigan: Illinois State Geological Survey Environmental Geology Notes 35, 35 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation