Age:

Pennsylvanian

Type designation:

Type section: Wier (1970) designated the type section of the Pirtle Coal Member of the Shelburn Formation in the SE¼SE¼SW¼ sec. 15, T. 7 N., R. 8 W. in Sullivan County, Indiana (Wier and Ault, 1986).

History of usage:

The Pirtle Coal Member of the Shelburn Formation was formally named by Wier (1970) for exposures of Ashley's (1899) Coal VIIa near the Pirtle Cemetery in secs. 15 and 27, T. 8 N., R. 8 W., Sullivan County, Indiana (Wier and Ault, 1986).

Description:

The Pirtle Coal Member is thickest in Sullivan County and in northern Knox County, where the coal is bright banded and shaly in places (Wier, 1970; Wier and Ault, 1986). It averages 1 to 1.5 ft (0.3 to 0.5 m) in thickness and lies more than 60 ft (18 m) above the Danville Coal Member of the Dugger Formation (Wier, 1970; Wier and Ault, 1986). The Pirtle coal is very thin in Vigo and Vermillion Counties or is absent (Wier, 1970; Wier and Ault, 1986). It is seen in few places in outcrop in Gibson and Posey Counties but may not be recognized on many geophysical logs because of its thinness (Wier and Ault, 1986).

Regional Indiana usage:

Illinois Basin (COSUNA 11)
Supergroup: none
Group: McLeansboro Group
Formation: Shelburn Formation
Member: Pirtle Coal Member
Illinois Basin Margin (COSUNA 12)
Supergroup: none
Group: McLeansboro Group
Formation: Shelburn Formation
Member: Pirtle Coal Member

Misc/Abandoned Names:

Coal VIIa

Geologic Map Unit Designation:

*shp

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:

Ashley, G. H., 1899, The coal deposits of Indiana: Indiana Department of Geology and Natural Resources Annual Report 23, p. 1–1,573.

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.

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, Pirtle 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. 134.

Wier, C. E., and Ault, C. H., 1986, Pirtle 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. 113.