Age:

Pennsylvanian

Type designation:

Type locality: Newton and Weller (1937, p. 18) described the Cohn Cyclothem and Cohn Coal in an exposure in the NE¼ sec. 1, T. 11 N., R. 12 W., Clark County, Illinois, 2 miles (3.2 km) northwest of Cohn (now called Livingston) (Wier, 1986).

History of usage:

Revised rank: This coal was later designated the Cohn Coal Member by Kosanke and others (1960, p. 41) in Illinois (Wier, 1970, 1986).

Extended: Wier (unpublished manuscripts; 1970, p. 38) noted that the Cohn was accepted as a member of the Mattoon Formation in Indiana (Wier, 1986).

Description:

The Cohn Coal Member is 2 inches (<0.1 m) thick in the type area and is 20 ft (6 m) above the top of the Livingston Limestone Member of the Bond Formation (Wier, 1970, 1986).

Distribution: The only known occurrence of the Cohn coal in Indiana is at Merom, Sullivan County (W½ sec. 7, T. 7 N., R. 10 W.), where it is more than a foot (0.3 m) thick and has been mined on a small scale (Wier, 1970, 1986).

Boundaries:

The Cohn Coal Member is underlain by 4 to 5 ft (1.2 to 1.5 m) of clay and overlain by a foot (>0.3 m) of light-gray shale (Wier, 1970, 1986).

Regional Indiana usage:

Illinois Basin (COSUNA 11)
Supergroup: none
Group: McLeansboro Group
Formation: Mattoon Formation
Member: Cohn Coal Member

Misc/Abandoned Names:

None

Geologic Map Unit Designation:

*mtc

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:

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.

Kosanke, R. M., Simon, J. A., Wanless, H. R., and Willman, H. B., 1960, Classification of the Pennsylvanian strata of Illinois: Illinois State Geological Survey Report of Investigations 214, 84 p.

Newton, W. A., and Weller, J. M., 1937, Stratigraphic studies of Pennsylvanian outcrops in part of southwestern Illinois: Illinois State Geological Survey Report of Investigations, 45, 31 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.

Wier, C. E., 1970, Cohn Coal Member, 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. 38.

Wier, C. E., 1986, Cohn Coal Member, 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. 30–31.