Historical:Elm Member

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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
Link Web page
PDF PDF file
Store ISGS Store

Lithostratigraphy: Ottawa Limestone Megagroup >>Platteville Group >>Plattin Subgroup >>Nachusa Formation >>Elm Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Blackriveran Stage
Allostratigraphy: Tippecanoe Sequence

Authors

H. B. Willman and T. C. Buschbach

Name Origin

The Elm Member of the Nachusa Formation (Templeton and Willman, 1963, p. 89) is named for Elm Street in Dixon, Lee County, just southwest of the type section.

Type Section

The type section of the Elm Member is part of the Nachusa Formation type section (a quarry on the east edge of Dixon (SE SE SW 33, 22N-9E) where it is 2.8 feet thick.

Other Names

The Elm Member is equivalent to the Glenburnie Member, a similar shaly unit, in the Chaumont Formation in New York.

Extent and Thickness

The Elm Member is widely present, but it is absent in subsurface in western Illinois. It is 1-4.5 feet thick in the northern outcrop area, is 7 feet thick in Calhoun County and near Ste. Genevieve, Missouri, and it thickens southward to 15 feet at Cape Girardeau.

Description

The Elm Member consists of argillaceous, gray, cherty dolomite or limestone and is mainly nonfucoidal. It is thin bedded and has thin shale partings. It commonly weathers to a smooth surface, which distinguishes it from the members above and below that have pitted surfaces.

References

TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation
7930
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