Historical:Walnut Grove Limestone 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
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Lithostratigraphy: Hunton Limestone Megagroup >>Lingle Formation >>Walnut Grove Limestone Member
Chronostratigraphy: Paleozoic Erathem >>Devonian System >>Middle Devonian Series
Allostratigraphy: Kaskaskia Sequence

Authors

Charles Collinson and Elwood Atherton

Name Origin

The Walnut Grove Limestone Member of the Lingle Formation (North, 1969, p. 29-30), the uppermost member, is named for Walnut Grove Church, Union County, 1 mile southeast of the type section.

Type Section

The type section of the Walnut Grove Member is an outcrop near the head of a small tributary of Clear Creek (SE SE SW 22, 11S-2W), where the member is 29 feet thick.

Extent and Thickness

The Walnut Grove occurs only in and near the outcrop area in Jackson, Union, and Alexander Counties (fig. D-15), and its maximum thickness is about 50 feet.

Description

The Walnut Grove Member is cherty, very silty, glauconitic, spore-bearing, fine-grained, fossiliferous limestone locally interbedded with very dark brown, calcareous shale. The Rendleman Oolite Bed near the base is a distinctive key bed.

Fossils

Fossils include crinoids, corals, brachiopods, and sporangites.

References

NORTH, W. G., 1969, Middle Devonian strata of southern Illinois: Illinois State Geological Survey Circular 441, 45 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation
5980
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