Davis Member

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Lithostratigraphy: Knox Dolomite Megagroup >>Franconia Formation >>Davis Member
Chronostratigraphy: Paleozoic Erathem >>Cambrian System >>Croixan Series >>Franconian Stage
Allostratigraphy: Sauk Sequence

Primary source

Willman, H. B., Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, and Jack A. Simon, 1975, Handbook of Illinois Stratigraphy: Illinois State Geological Survey Bulletin 95, 261 p.

Contributing author(s)

T. C. Buschbach


Original description

The Davis Member of the Franconia Formation (Buckley, 1907; 1909, p. 33).


Named for outcrops on Davis Creek, St. Francois County, southeast Missouri.

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Stratigraphic relationships

The Davis Member is the basal member of the Franconia Formation.

Extent and thickness

The Davis Member is recognized as a shaly sandstone unit at the base of the Franconia throughout all of Illinois except the extreme north, where the entire Franconia is represented by shaly and glauconitic sandstone, and in the southeast (Lawrence and Hamilton Counties), where the unit appears to have graded to dolomite and is included in the Knox Megagroup. It ranges from a few feet thick in the north to about 100 feet in the south.


The Davis grades from shaly sandstone in the north to silty, sandy, argillaceous dolomite in the south. The member is characterized by green, gray, or red shale partings and by flat-pebble conglomerate.




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Economic importance



BUCKLEY, E. R., 1907, Missouri Bureau of Geology and Mines, 2nd Series, v. 10, separate.
BUCKLEY, E. R., 1909, Geology of the disseminated lead deposits of St. Francois and Washington Counties: Missouri Bureau of Geology and Mines, 2nd Series, v. 9, part 1, 259 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation
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