Age:

Ordovician

Type designation:

Type area: The name “Everton Limestone” was first given by Ulrich (1907, p. 251-252) to exposures in deep ravines a few miles south of the Missouri-Arkansas state line near Everton, Boone County, Arkansas.

History of usage:

Extended and revised rank: The Everton, as traced to Illinois, was first classified as a group (Templeton and Willman, 1963) and then with formation rank as the Everton Dolomite (Willman and Buschbach, 1975; Droste, Patton, and Rexroad, 1986).

Extended: This unit was recognized in Indiana (Droste, Abdulkareem, and Patton, 1982; Rexroad, Droste, and Ethington, 1982) and was there also designated the Everton Dolomite (Droste, Patton, and Rexroad, 1986).

Assignment: Droste and Patton (1985) assigned the Everton of Indiana to the Knox Supergroup (Droste, Patton, and Rexroad, 1986).

Description:

Well samples and core from a well that penetrates the Everton Dolomite in southwestern Indiana indicate that the Everton is a medium-gray to brownish-black fine- to medium-grained dolostone interbedded with shaly dolostone and fine- to medium-grained quartz sandstone (Droste, Abdulkareem, and Patton, 1982). Core from an interval about 25 ft (8 m) thick shows breccia zones throughout (Droste, Patton, and Rexroad, 1986).

Distribution: In Indiana the Everton Dolomite occurs only in the subsurface in the southwestern part of the state and is known from only a few wells that penetrate the upper part of the formation before reaching total depth (Droste, Patton, and Rexroad, 1986).

Boundaries:

The Everton Dolomite is unconformably overlain by the St. Peter Sandstone, and on the basis of data from wells in Illinois and Kentucky, it is thought to overlie unconformably the Shakopee Dolomite (Droste, Patton, and Rexroad, 1986).

Correlations:

Conodonts recovered from an Everton core from southwestern Indiana are dominated by Paraprioniodus costatus and Leptochirognathus quadratus and indicate a Whiterockian age (Rexroad, Droste, and Ethington, 1982), that is, an age younger than that traditionally assigned to any part of the Knox of Indiana (previously assigned a Trempealeauan and Canadian age) (Droste, Patton, and Rexroad, 1986). This association is indicative of Middle Ordovician faunas 2-4 of Sweet, Ethington, and Barnes (1971) (Droste, Patton, and Rexroad, 1986). The upper Knox assignment was made, however, as one possible solution to nomenclatural problems arising from the incompletely known stratigraphic relations of the Everton (Droste, Patton, and Rexroad, 1986). Although these lower relations are unknown in Indiana, the Everton of Indiana is probably closely correlatable with the formation by the same name in its type area in northern Arkansas and in Missouri, Illinois, and Kentucky (Droste, Patton, and Rexroad, 1986).

Regional Indiana usage:

Illinois Basin (COSUNA 11)
Supergroup: none
Group: none
Formation: Everton Dolomite

Misc/Abandoned Names:

None

Geologic Map Unit Designation:

Oe

Note: Hansen (1991, p. 52) in Suggestions to authors of the reports of the United States Geological Survey noted that letter symbols for map units are considered to be unique to each geologic map and that adjacent maps do not necessarily need to use the same symbols for the same map unit. Therefore, map unit abbreviations in the Indiana Geologic Names Information System should be regarded simply as recommendations.

COSUNA areas and regional terminology

Names for geologic units vary across Indiana. The Midwestern Basin and Arches Region COSUNA chart (Shaver, 1984) was developed to strategically document such variations in terminology. The geologic map (below left) is derived from this chart and provides an index to the five defined COSUNA regions in Indiana. The regions are generally based on regional bedrock outcrop patterns and major structural features in Indiana. (Click the maps below to view more detailed maps of COSUNA regions and major structural features in Indiana.)

COSUNA areas and numbers that approximate regional bedrock outcrop patterns and major structural features in Indiana.

Major tectonic features that affect bedrock geology in Indiana.

References:

Droste, J. B., Abdulkareem, T. F., and Patton, J. B., 1982, Stratigraphy of the Ancell and Black River Groups (Ordovician) in Indiana: Indiana Geological Survey Occasional Paper 36, 15 p.

Droste, J. B., and Patton, J. B., 1985, Lithostratigraphy of the Sauk Sequence in Indiana: Indiana Geological Survey Occasional Paper 47, 24 p.

Droste, J. B., Patton, J. B., and Rexroad, C. B., 1986, Everton Dolomite, in Shaver, R. H., Ault, C. H., Burger, A. M., Carr, D. D., Droste, J. B., Eggert, D. L., Gray, H. H., Harper, Denver, Hasenmueller, N. R., Hasenmueller, W. A., Horowitz, A. S., Hutchison, H. C., Keith, B. D., Keller, S. J., Patton, J. B., Rexroad, C. B., and Wier, C. E., Compendium of Paleozoic rock-unit stratigraphy in Indiana–a revision: Indiana Geological Survey Bulletin 59, p. 44–45.

Hansen, W. R., 1991, Suggestions to authors of the reports of the United States Geological Survey (7^th ed.): Washington, D.C., U.S. Geological Survey, 289 p.

Rexroad, C. B., Droste, J. B., and Ethington, R. L., 1982, Conodonts from the Everton Dolomite and the St. Peter Sandstone (lower Middle Ordovician) in a core from southwestern Indiana: Indiana Geological Survey Occasional Paper 39, 13 p.

Shaver, R. H., coordinator, 1984, Midwestern basin and arches region–correlation of stratigraphic units in North America (COSUNA): American Association of Petroleum Geologists Correlation Chart Series.

Sweet, W. C., Ethington, R. L., and Barnes, C. R., 1971, North American Middle and Upper Ordovician conodont faunas: Geological Society of America Memoirs 127, p. 163–193.

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

Ulrich, E. O., 1907, [untitled chapter], in Purdue, A. H., Cave-sandstone deposits of the southern Ozarks: Geological Society of America Bulletin, v. 18, p. 251–256.

Willman, H. B., and Buschbach, T. C., 1975, Ordovician System, in Willman, H. B., Atherton, Elwood, Buschbach, T. C., Collinson, Charles, Frye, J. C., Hopkins, M. E., Lineback, J. A., and Simon, J. A., Handbook of Illinois stratigraphy: Illinois State Geological Survey Bulletin 95, p. 47–87.