Type locality: This unit was originally named the Clore Formation by Stuart Weller (1913, p. 129) for exposures near Clore School, Randolph County, Illinois (Gray, 1970, 1986).
History of usage:
Revised assignment: The unit was restricted and designated the Clore Limestone by Weller (1920, p. 212-213), who described it as a crystalline to shaly limestone and calcareous shale as much as 40 ft (12 m) thick (Gray, 1970, 1986).
limestone interbedded with shale are typical of the upper 15 to 30 ft (4.6 to 9.1 m) of the unit. The shales between the upper and lower limestone intervals are various shades of gray and green. The silty and sandy shales are interbedded with sandstones. Very fine grained to fine-grained white to light-gray sandstones are in beds of shaly sandstone a few feet thick to intervals of massive sandstone as much as 50 ft (15 m) thick (Droste and Keller, 1995). The Clore increases in thickness from less than 60 ft (18 m) near the eastern outcrop to more than 100 ft (30 m) along the Indiana-Illinois state line (Droste and Keller, 1995).
The Clore overlies the Palestine Formation and is overlain by the Degonia Formation or by the Mansfield Formation (Morrowan) where uppermost Chesterian formations have been removed by pre-Pennsylvanian erosion (Gray, 1986; Droste and Keller, 1995).
The following petroleum fields have produced oil from the Clore Formation (Mississippian) in Indiana: Black River Consolidated, Caborn West, College Consolidated, Griffin Consolidated, Lamott Consolidated, Mt. Vernon Consolidated, Mumford Hills, Springfield Consolidated, Welborn Consolidated, Welborn North Consolidated, and West Hovey (Cazee, 2004).
Regional Indiana usage:
Illinois Basin (COSUNA 11)
Geologic Map Unit Designation:
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.
Atherton, Elwood, Collinson, Charles, and Lineback, J. A., 1975, Mississippian 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. 123-163.
Gray, H. H., 1970, Clore Limestone, in Shaver, R. H., Burger, A. M., Gates, G. R., Gray, H. H., Hutchison, H. C., Keller, S. J., Patton, J. B., Rexroad, C. B., Smith, N. M., Wayne, W. J., and Wier, C. E., Compendium of rock-unit stratigraphy in Indiana: Indiana Geological Survey Bulletin 43, p. 36-37.
Gray, H. H., 1986, Clore Limestone, 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. 30.
Hansen, W. R., 1991, Suggestions to authors of the reports of the United States Geological Survey (7th ed.): Washington, D.C., U.S. Geological Survey, 289 p.
Malott, C. A., and Esarey, R. E., 1940, Outcrop of the Chester Series of southern Indiana: Indiana-Kentucky Geological Society, May 18, 1940, 9 p. [mimeo.].
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.
Swann, D. H., 1963, Classification of Genevievian and Chesterian (Late Mississippian) rocks of Illinois: Illinois State Geological Survey Report of Investigations 216, 91 p.
Weller, Stuart, 1913, Stratigraphy of the Chester Group in southwestern Illinois: Illinois State Academy of Science Transactions, v. 6, p. 118-129.
Weller, Stuart, 1920, The geology of Hardin County and the adjoining part of Pope County: Illinois State Geological Survey Bulletin 41, 416 p.
For additional information, contact:
Nancy Hasenmueller (firstname.lastname@example.org)Date last revised: March 4, 2021