Cambrian and Ordovician
Type area: The Knox Dolomite was named by Safford (1869, p. 151) for about 4,000 ft (1,220 m) of heavy-bedded ridge-making dolostone in Knox County, Tennessee (Droste and Patton, 1986).
History of usage:
Early use of name: In the one original publication the name “Knox”was also applied to a shale and to a sandstone and was used as a group (Droste and Patton, 1986). The early ambiguities were resolved by renaming the Knox Shale as the "Conasauga Shale" and the Knox Sandstone as the "Rome Formation" (Droste and Patton, 1986).
The Knox Supergroup in Indiana consists of the relatively pure dolostone lying conformably above the Potsdam Supergroup (Cambrian: St. Croixan) and underlying unconformably the Ancell Group (Ordovician: Chazyan and Blackriverian) (Droste and Patton, 1986). At its base the Knox grades laterally into the Potsdam (Droste and Patton, 1986). In Indiana the Potsdam-to-Knox gradation embraces approximately the stratigraphic interval of the Franconian Stage (Droste and Patton, 1986).
Given the constitution of the Knox noted above, its apparent time-stratigraphic range in Indiana is from the Dresbachian (Cambrian) to upper Whiterockian (Ordovician) (Droste and Patton, 1986). For details of rock-unit correlation throughout the Midwest, see Droste and Shaver (1983, fig. 2) and Shaver (1984); see also the general discussion under "Potsdam Supergroup" (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 featuers in Indiana.
Major tectonic features that affect bedrock geology in Indiana.
Droste, J. B., and Patton, J. B., 1986, Knox Supergroup, 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. 69-70.
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.
Safford, J. M., 1869, Geology of Tennessee: Nashville, Tenn., S. C. Mercer, Printer of the State, 550 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.
Swann, D. H., and Willman, H. B., 1961, Megagroups in Illinois: American Association of Petroleum Geologists Bulletin, v. 46, p. 471-483.
For additional information, contact:
Nancy Hasenmueller (firstname.lastname@example.org)Date last revised: September 22, 2017