Type locality: Sandstones, 200 to 250 ft (61 to 76 m) thick and exposed in bluffs near Munising, Alger County, Michigan, were designated the Munising Sandstone by Lane and Seaman (1907, p. 680, 692) (Droste and Patton, 1986).
History of usage:
This unit was proposed to help clarify the stratigraphic relationships in rocks that were included earlier in the Lake Superior Sandstone (Droste and Patton, 1986). East of Copper Range, Upper Peninsula of Michigan, the light-colored rocks of the Munising lie above the brightly colored red and brown sandstone of the Jacobsville Sandstone (Droste and Patton, 1986). Use of the term "Munising" was extended into the Lower Peninsula of Michigan by Catacosinos (1973) to include there the Eau Claire Formation, the Galesville Sandstone, and the Franconia Formation (Droste and Patton, 1986). The name was further extended to Indiana use, with group status, by Droste and Patton (1985), where it includes the Eau Claire, Davis, and Franconia Formations and the Galesville and Ironton Sandstones (Droste and Patton, 1986).
The Munising Group of the Potsdam Supergroup in Indiana (Droste and Patton, 1985) is conformable with the Mount Simon Sandstone below (Droste and Patton, 1986). It ranges from less than 600 ft (183 m) to more than 1,500 ft (457 m) in thickness (Droste and Patton, 1986). In southwestern Indiana the only formation of the Munising Group present, the Eau Claire Formation, lies with gradational contact below the Potosi Dolomite (Droste and Patton, 1986). Throughout much of Indiana the Munising consists of the Eau Claire Formation below and the Davis Formation above, the Davis also lying conformably below the Potosi (Droste and Patton, 1986). In northwestern Indiana the Munising consists of, in ascending order, the Eau Claire Formation, the Galesville and Ironton Sandstones, and the Franconia Formation (Droste and Patton, 1986). Here, too, the Potosi Dolomite conformably overlies the Munising rocks (Droste and Patton, 1986). Southward and eastward from northwestern Indiana, therefore, the top of the Munising descends stratigraphically through a lateral transition zone with the Potosi Dolomite (Droste and Patton, 1986).
Given the relations noted above, the upper part of the Munising in northwestern Indiana is presumably late Franconian in age, whereas its upper part in southwestern Indiana is presumably late Dresbachian in age (Droste and Patton, 1986). The overall Munising Group of Indiana correlates with a sequence of siliciclastic and carbonate rocks in Illinois that has a southward, stratigraphically descending transition zone between the two basic lithologies similar to that noted above for Indiana (Droste and Patton, 1986). In part of northern Illinois, therefore, the Munising-correlative rocks consist dominantly of siliciclastic rocks of the Eau Claire Formation and overlying rocks through the Franconia Formation, there assigned to the Potsdam Sandstone Megagroup by Buschbach (1975) (Droste and Patton, 1986). In much of the rest of Illinois the Munising correlatives, although known by the same formation names, have an increased carbonate content and were assigned to the Knox Dolomite Megagroup by Buschbach (Droste and Patton, 1986). The southern Indiana Munising rocks, however, consist only of the Eau Claire and therefore correlate only with the Eau Claire of Illinois (Droste and Patton, 1986).
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.
Buschbach, T. C., 1975, Cambrian System, in Willman, H. B., Atherton, Elwood, Buschbach, T. C., Collinson, Charles, Frye, J. C., Hopkins, M. E., Lineback, J. A., and Simon, J. A., Handbook of Illinois stratigraphy: Illinois State Geological Survey Bulletin 95, p. 34-46.
Catacosinos, P. A., 1973, Cambrian lithostratigraphy of Michigan Basin: American Association of Petroleum Geologists Bulletin, v. 57, p. 2,404-2,418.
Droste, J. B., and Patton, J. B., 1986, Munising 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. 98-99.
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.
Janssens, Adriaan, 1973, Stratigraphy of the Cambrian and Lower Ordovician rocks in Ohio: Ohio Geological Survey Bulletin 64, 197 p.
Lane, A. C., and Seaman, A. E., 1907, Notes on the geological section of Michigan—Pt. 1, The pre-Ordovician: Journal of Geology, v. 15, p. 680-695.
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 (firstname.lastname@example.org)Date last revised: April 5, 2017