Age:

Mississippian

Type designation:

Type locality: The name "Coldwater Shales" was originally used by Lane (1893, p. 66) for outcrops of light-colored greenish to bluish and darker shales along Coldwater River in Branch County, Michigan (Keller and Burger, 1970; Keller and Rexroad, 1986).

History of usage:

Extended: Keller and Burger (1970, p. 39) noted that the name “Coldwater Shale” is used in Indiana for the southern extension of the Michigan rocks by the same name into northeastern Indiana, north of the Cincinnati Arch.

Description:

The Coldwater is typically a gray to greenish-gray, slightly silty shale bearing red shale stringers near the bottom (Keller and Rexroad, 1986). In some places there are lenses of brown dolostone or limestone throughout the section. A distinctive red shale, 5 to 20 ft (1.5 to 6.1 m) thick and sometimes called the “Coldwater Red Rock,” is at the base of the unit (Keller and Rexroad, 1986).

Distribution: The Coldwater reaches a thickness greater than 500 ft (152 m) in Steuben County (Keller and Burger, 1970; Keller and Rexroad, 1986). Distribution: The Coldwater Shale is known in Indiana only in the subsurface because its position at the bedrock surface is deeply buried by glacial drift (Johnson and Keller, 1972; Keller and Burger, 1970; Keller and Rexroad, 1986). Because of pre-Pleistocene erosion, it is not present west of Elkhart County or south of northern DeKalb County and Noble County (Keller and Rexroad, 1986).

Boundaries:

The Coldwater conformably overlies the Sunbury and Ellsworth Shales (Keller and Burger, 1970; Keller and Rexroad, 1986).

Correlations:

The Coldwater Shale of Indiana is Kinderhookian in age and correlates with the Coldwater Shale in Michigan and the Cuyahoga Formation in Ohio (Keller and Rexroad, 1986). In southern Indiana the lower part of the Rockford Limestone and the uppermost parts of the Ellsworth and Clegg Creek Members of the New Albany Shale are equivalent to the Coldwater (Shaver, 1984; Keller and Rexroad, 1986).

Regional Indiana usage:

Michigan Basin (COSUNA 15)
Supergroup: none
Group: none
Formation: Coldwater Shale

Misc/Abandoned Names:

Coldwater Red Rock

Geologic Map Unit Designation:

Mcw

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.

Johnson, G. H., and Keller, S. J., 1972, Geologic map of the 1° x 2° Fort Wayne quadrangle, Indiana, Michigan, and Ohio, showing bedrock and unconsolidated deposits: Indiana Geological Survey Regional Geologic Map No. 8, Part A [bedrock units], scale 1:250,000.

Keller, S. J., and Burger, A. M., 1970, Coldwater Shale, 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. 39–40.

Keller, S. J., and Rexroad, C. B., 1986, Coldwater Shale, 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. 31.

Lane, A. C., 1893, [On Paleozoic rocks], in Wadsworth, M. E., Report of the State Geologist for 1891-92: Michigan Geological Survey Report for 1891-92, p. 59–73.

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.