Historical:Downeys Bluff Limestone

	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

	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: Pope Megagroup >>Paint Creek Group >>Cedar Bluff Limestone Group >>Downeys Bluff Limestone
Chronostratigraphy: Paleozoic Erathem >>Mississippian Subsystem >>Chesterian Series >>Gasperian Stage
Allostratigraphy: Kaskaskia Sequence

Authors

Elwood Atherton, Charles Collinson, and Jerry A. Lineback

Name Origin

The Downeys Bluff Limestone (Atherton, 1947, p. 129) is named for Downeys Bluff, Hardin County.

Type Section

The type section for the Downeys Bluff Limestone is in a bluff along the Ohio River (NW SE 5, 13S-8E).

Extent and Thickness

The Downeys Bluff generally is 20-30 feet thick in Gallatin, Saline, and parts of Jackson and adjacent counties (fig. M-34), where it consists of two limestone benches separated by a thin shale. Elsewhere the Downeys Bluff consists of only the upper of the two benches, generally 5-10 feet thick but locally 10-20 feet thick.

Fig. M-34 -- Thickness of the Downeys Bluff Limestone.

Stratigraphic Position

The Downeys Bluff was originally regarded as a member of the Paint Creek Formation in southwestern Illinois and of the Renault Formation in southeastern Illinois, but it was later traced across the Illinois Basin (Dana and Scobey, 1941). It is now a formation at the base of the Paint Creek Group in southwestern Illinois and at the top of the Cedar Bluff Group in southeastern Illinois (fig. M-25).

Fig. M-25 -- Columnar section of the Chesterian Series (after Swan, 1963), showing biozones (after Collinson et al., 1971). In the columnar section, the blank areas are shale.

Description

Where two benches of the Downeys Bluff are present, the upper is typically cherty and the lower is slightly silty or very finely sandy. Limestone of the Downeys Bluff is white or light brownish gray and crinoidal. Many crinoid segments are replaced by pink chert. The pink crinoids are an excellent diagnostic characteristic that is better developed in the western than in the eastern part of Illinois.

References

ATHERTON, ELWOOD, 1947, Some Chester outcrop and subsurface sections in southeastern Illinois: Illinois Academy of Science Transactions., v. 40, p. 122-131; 1948, Illinois State Geological Survey Circular 144.
DANA, P. L., and E. H. SCOBEY, 1941, Cross section of Chester of Illinois Basin: American Association of Petroleum Geologists Bulletin, v. 25, p. 871-882.

ISGS Codes

Stratigraphic Code	Geo Unit Designation
4470	Mdb