Age:

Cambrian and Ordovician

Type designation:

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 association of the name “Knox,” at formation or group rank, with thick bodies of rock dominated by dolostone has been made throughout the central United States (Droste and Patton, 1986). Additionally in Illinois, the name evolved to "Knox Dolomite Megagroup" (Swann and Willman, 1961, p. 477), which contains relatively pure dolostone generally underlying the St. Peter Sandstone and overlying rocks of the Potsdam Sandstone Megagroup (Droste and Patton, 1986).

The earliest use of the name Knox in Indiana is unknown, but "Knox Dolomite" was the long-preferred use (Droste and Patton, 1986).

Change in rank: In 1985, the term "Knox Supergroup" was introduced to Indiana use by Droste and Patton. Nomenclaturally, it consists of, in ascending order, the Potosi Dolomite, the Prairie du Chien Group (consisting of the Oneota and Shakopee Dolomites), and the Everton Dolomite (Droste and Patton, 1986).

Description:

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).

Except for fragmented rocks in the chaotic structure exposed in the Kentland Quarry in Newton County, the Knox Supergroup is present everywhere only in the subsurface of Indiana (Droste and Patton, 1986). The Newton County exposures are of faulted blocks of the Shakopee Dolomite (Gutschick, 1983; Droste and Patton, 1986). The Knox ranges from less than 20 ft (6 m) to more than 4,500 ft (1,372 m) in thickness (Droste and Patton, 1986). Twenty feet (part of the Potosi Dolomite) is all that remains in the area of one northwestern Indiana well beneath the major erosional unconformity that separates the Knox from the overlying St. Peter Sandstone (Droste and Patton, 1986). In contrast in southwestern Indiana, more than 4,500 ft (1,372 m) of the Knox is preserved beneath the unconformity with the overlying St. Peter (Droste and Patton, 1986). There the Everton Dolomite (Whiterockian Stage) makes up the youngest part of the Knox Supergroup (Droste and Patton, 1986). In northeastern Indiana, where the preserved Knox is more than 600 ft (183 m) thick, the Oneota Dolomite part of the Knox (Canadian Stage) lies unconformably below the Joachim Dolomite (Blackriverian Stage) (Droste and Patton, 1986).

Correlations:

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).

Economic Importance:

Petroleum production: The following petroleum fields have produced oil from the Knox Supergroup (Cambrian-Ordovician) in Indiana: Trenton and Spencer Consolidated (Cazee, 2004).

Regional Indiana usage:

Illinois Basin (COSUNA 11)
Supergroup: Knox Supergroup
Illinois Basin Margin (COSUNA 12)
Supergroup: Knox Supergroup
Cincinnati Arch (COSUNA 13)
Supergroup: Knox Supergroup
Kankakee Arch (COSUNA 14)
Supergroup: Knox Supergroup
Michigan Basin (COSUNA 15)
Supergroup: Knox Supergroup

Misc/Abandoned Names:

None

Geologic Map Unit Designation:

OCk

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.

References:

Cazee, J. T., 2004, Petroleum exploration, development, and production in Indiana during 2002: Indiana Geological Survey, Mineral Economic Series 49, 50 p.

Droste, J. B., and Patton, J. B., 1985, Lithostratigraphy of the Sauk Sequence in Indiana: Indiana Geological Survey Occasional Paper 47, 24 p.

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.

Droste, J. B., and Shaver, R. H., 1983, Atlas of early and middle Paleozoic paleogeography of the southern Great Lakes area: Indiana Geological Survey Special Report 32, 32 p.

Gutschick, R. C., 1983, Geology of the Kentland Dome structurally complex anomaly–northwestern Indiana (Field Trip 5), 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 (7^th 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.