Type locality: The term "Prairie du Chien Formation" was introduced by Bain (1906, p. 18) to replace "Lower Magnesian" of earlier reports that referred to exposures near Prairie du Chien, Crawford County, Wisconsin, where this unit consists of as much as 300 ft (91 m) of dolostone and sandstone (Droste and Patton, 1986).
History of usage:
The Prairie du Chien has been intensely studied in the subsurface of Illinois, where it consists of, in ascending order, the Gunter Sandstone, the Oneota Dolomite, the New Richmond Sandstone, and the Shakopee Dolomite (Willman and Templeton, 1951; Droste and Patton, 1986). In Illinois it is accorded group status as it is in most other places of recognition (Droste and Patton, 1986). The Illinois understanding of the group was extended to Indiana by Droste and Patton (1985), but with this modification: Neither the Gunter Sandstone nor the New Richmond Sandstone is recognized in Indiana, so that the Prairie du Chien Group consists of the Oneota Dolomite below and the Shakopee Dolomite above (Droste and Patton, 1986).
The Prairie du Chien Group is recognized throughout the subsurface of Indiana except for the area of one well in northwesternmost Indiana where pre-Middle Ordovician erosion removed the entire group (Droste and Patton, 1986). Faulted blocks of the Shakopee Dolomite in the Kentland structure, Newton County, Indiana (Gutschick, 1983), are the only Prairie du Chien exposures in the state (Droste and Patton, 1986). The group is overlain unconformably by rocks of the Ancell Group in most of Indiana, by the Everton Dolomite in southwestern Indiana, and by the Black River Group in isolated parts of eastern Indiana where Ancell rocks are absent because of nondeposition (Droste and Patton, 1986). The Prairie du Chien increases in thickness from its eroded limit in northwestern Indiana to more than 2,000 ft (610 m) in southwestern Indiana (Droste and Patton, 1986).
The Prairie du Chien of Indiana is represented by this same name in Illinois, Wisconsin, and Michigan, and it is equivalent to the upper part of the undifferentiated Knox Dolomite of Ohio and to the Beekmantown Dolomite, the Gunter Sandstone, the Gasconade Dolomite, the Roubidoux Formation, the Jefferson City Dolomite, and the Cotter Dolomite of Kentucky (Droste and Patton, 1986). (See Droste and Shaver, 1983, and Shaver, 1984.)
Regional Indiana usage:
Illinois Basin (COSUNA 11)
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 features in Indiana.
Major tectonic features that affect bedrock geology in Indiana.
Bain, H. F., 1906, Zinc and lead deposits of the upper Mississippi Valley: U.S. Geological Survey Bulletin 194, 135 p.
Droste, J. B., and Patton, J. B., 1986, Prairie du Chien Group, 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. 119-120.
Gutschick, R. C., 1983, Geology of the Kentland Dome structurally complex anomaly, northwestern Indiana (Field Trip 15), in Shaver, R. H., and Sunderman, J. A., eds., Field trips in midwestern geology: Bloomington, Indiana, Geological Society of America, Indiana Geological Survey, and Indiana University Department of Geology, v. 1., p. 105-138.
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.
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.
Willman, H. B., and Templeton, J. S., 1951, Cambrian and Lower Ordovician exposures in northern Illinois: Illinois State Academy of Science Transactions, v. 44, p. 109-125.
For additional information, contact:
Nancy Hasenmueller (firstname.lastname@example.org)Date last revised: November 22, 2016