IGNIS
Harrodsburg Limestone

Age:

Mississippian

Type designation:

Type section: The Harrodsburg Limestone was named by Hopkins and Siebenthal (1897, p. 296-297) for the town of Harrodsburg in southern Monroe County, Indiana (Rexroad, 1986). The type section in the NE¼SW¼ sec. 32, T. 7 N., R. 1 W., on the north bluff of Judah Creek is poorly exposed (Rexroad, 1986).

Reference sections: Exposures 1 mile (1.6 km) north of Harrodsburg along former Indiana Highway 37 in the SE¼ sec. 20, T. 7 N., R. 1 W., have been used as a reference section (Rexroad, 1986). A section exposing the top of the Borden Group, the Harrodsburg Limestone, and the Salem Limestone is less than 0.25 miles (0.4 km) east of that section in the cut on present Indiana Highway 37 in the same quarter section (Rexroad, 1986). Another reference section is the cut along the dam-access road at the Monroe Reservoir in the NE¼SE¼ sec. 28, T. 7 N., R. 1 W. (Rexroad, 1986).

History of usage:

The lower part of the Harrodsburg was divided into the Leesville and Guthrie Creek Members by Stockdale (1939) (Rexroad, 1986). These units were reduced to the status of beds by Nicoll and Rexroad (1975).

Rexroad (1986) noted that the concept of the Harrodsburg Limestone has undergone numerous modifications since the term was first proposed for rocks between the Borden Group and the Salem Limestone of modern usage.

Description:

The Harrodsburg Limestone is dominantly a well-cemented bioclastic calcarenite and calcirudite but includes some dolostone, shale, very argillaceous limestone, and minor amounts of chert (Rexroad, 1986). An impure unit, which includes geodes and silicified material, is present in some places from 1 to 11 ft (0.3 to 3.4 m) above the base of the formation (Rexroad, 1986). Geodes and chert are uncommon elsewhere in the Harrodsburg (Rexroad, 1986). Shale is present in places in beds as much as 2 ft (0.6 m) thick. In the upper part of the formation some lenses nearly 20 ft (6 m) thick are almost identical in lithology to common Salem lithologies, although in general they are more firmly cemented (Rexroad, 1986). The bioclastic part of the limestone is dominated by crinoid fragments and contains some bryozoans and brachiopods (Rexroad, 1986). In the upper part of the Harrodsburg thick beds of fenestrate-bryozoan coquina are present (Rexroad, 1986).

Distribution: The Harrodsburg is present throughout the Indiana part of the Illinois Basin, and its outcropping margin forms an arc extending from Parke County south-southeastward to Harrison County (Rexroad, 1986). Northwest of Parke County it is overlapped by Pennsylvanian rocks of the Mansfield Formation (Rexroad, 1986). The Harrodsburg is almost 70 ft (21 m) thick in its type area and appears to thin both to the north and the south along its outcrop belt (Rexroad, 1986). It thickens somewhat in the subsurface but in most places is no more than 120 ft (37 m) thick above the Borden delta (Rexroad, 1986). Basinward from the paleotopographic margin of the delta, however, the formation is thicker (Rexroad, 1986). It is nearly 300 ft (92 m) thick in Vanderburgh County (Lineback, 1966).

Boundaries:

The northern boundary of the Harrodsburg is obscured by Pennsylvanian overlap where the Mansfield Formation locally overlies it unconformably (Rexroad, 1986). Otherwise, the Harrodsburg is overlain conformably and gradationally by the Salem Limestone, and it conformably overlies the Ramp Creek Formation (Rexroad, 1986).

Correlations:

Conodonts show that the Harrodsburg is the age equivalent of the upper three-fourths of the Warsaw Shale and the lower part of the Salem Limestone of the Mississippi Valley sequence (Nicoll and Rexroad, 1975, p. 16). The Harrodsburg is also considered to be partly equivalent to the Warsaw Limestone of Kentucky (Shaver, 1984), a name that had often been applied directly in Indiana as late as the time of P. B. Stockdale's work (Rexroad, 1986). According to Lineback (1966), the Harrodsburg is the upper member of the Ullin Limestone, which derived its name from southern Illinois (Rexroad, 1986).

Regional Indiana usage:

Illinois Basin (COSUNA 11)
Supergroup: none
Group: Sanders Group
Formation: Harrodsburg Limestone
Illinois Basin Margin (COSUNA 12)
Supergroup: none
Group: Sanders Group
Formation: Harrodsburg Limestone
Cincinnati Arch (COSUNA 13)
Supergroup: none
Group: Sanders Group
Formation: Harrodsburg Limestone

Misc/Abandoned Names:

Lower Harrodsburg Limestone, Upper Harrodsburg Limestone

Geologic Map Unit Designation:

Mh

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.)

Map showing the COSUNA areas (heavy black line) that approximate regional bedrock outcrop patterns and major structural features in Indiana, and the COSUNA numbers (large bold font) for these areas. The COSUNA boundaries are limited to state and county boundaries that facilitate coding.

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

Map showing major tectonic features that affect bedrock geology 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 (7th ed.): Washington, D.C., U.S. Geological Survey, 289 p.

Hopkins, T. C., and Siebenthal, C. E., 1897, The Bedford Oolitic Limestone: Indiana Department of Geology and Natural Resources Annual Report 21, p. 289-427.

Lineback, J. A., 1966, Deep-water sediments adjacent to the Borden Siltstone (Mississippian) delta in southern Illinois: Illinois State Geological Survey Circular 401, 48 p.

Nicoll, R. S., and Rexroad, C. B., 1975, Stratigraphy and conodont paleontology of the Sanders Group (Mississippian) in Indiana and adjacent Kentucky: Indiana Geological Survey Bulletin 51, 33 p.

Rexroad, C. B., 1986, Harrodsburg 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. 57-59.

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.

Stockdale, P. B., 1939, Lower Mississippian rocks of east-central interior (U.S.): Geological Society of America Special Paper 22, 248 p.



For additional information contact:

Nancy Hasenmueller (hasenmue@indiana.edu)
Date last revised: July 29, 2016

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