Type designation:

Type locality: The Sisson Member was named by Keller and Becker (1980, p. 11) for a crossroads community in southern Knox County, Indiana. The type section is in the T & H Corp. No. 1 Lane well (Indiana Geological Survey Petroleum Database Management System No. 121491) from 2,105 to 2,226 ft (642 to 679 m) in sec. 10, T. 1 N., R. 10 W.

Reference sections: Keller and Becker (1980, p. 11) designated reference sections for the Sisson as the interval from 2,690 to 2,845 ft (819.9 to 867.2 m) in the Turner No. 1 Jones well (Indiana Geological Survey Petroleum Database Management System No. 131277) in sec. 3, T. 3 S., R. 11 W. in Gibson County and the interval from 3,383 to 3,555 ft (1,031.1 to 1,083.6 m) in the Sun Oil No. 1 Reynolds well (Indiana Geological Survey Petroleum Database Management System No. 109132) in sec. 3, T. 4. S., R. 13 W. in Posey County.


The Sisson is recognized only in the subsurface and is the basal member of the St. Louis Limestone in an area that extends from Knox, Daviess, Dubois, and Perry Counties southwestward (Gray, 1986). It is distinguished by skeletal limestone much like that in the Salem Limestone but commonly a little more fine grained; also present are fine-grained dolostone, crystalline limestone, thin green and black shale, and anhydrite (Gray, 1986). Over most of the area of its recognition the member is 110 to 160 ft (34 to 49 m) thick, but in Posey County thicknesses of more than 200 ft (60 m) are known (Keller and Becker, 1980; Gray, 1986).

Most previous workers have assigned rocks of the Sisson Member to the Salem Limestone, and in Illinois these rocks are still so classified (Gray, 1986). Excluding these rocks from the Salem, however, and regarding them as a distinctive member of the St. Louis avoid creating a step effect in the Salem-St. Louis contact; that contact, therefore, is now at a uniform horizon throughout the state (Gray, 1986).

Regional Indiana usage:

Illinois Basin (COSUNA 11)
Supergroup: none
Group: Blue River Group
Formation: St. Louis Limestone
Member: Sisson Member

Misc/Abandoned Names:


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 featuers in Indiana.

Major tectonic features that affect bedrock geology in Indiana.


Gray, H. H., 1986, Sisson 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. 145-146.

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.

Keller, S. J., and Becker, L. E., 1980, Subsurface stratigraphy and oil fields in the Salem Limestone and associated rocks in Indiana: Indiana Geological Survey Occasional Paper 30, 63 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.

For additional information contact:

Nancy Hasenmueller (
Date last revised: June 14, 2017