IGNIS
Brassfield Limestone

Age:

Silurian

Type designation:

Type section: The Brassfield Limestone was named by Foerste (1906, p. 18, 27) for exposures along the now-abandoned Louisville and Atlantic Railroad between Brassfield and Panola in Madison County, east-central Kentucky (Rexroad, 1986).

History of usage:

Extended: The Brassfield of Indiana was first called the Clinton Limestone (Foerste, 1896, 1897), a now-abandoned term because the Brassfield of Indiana is continuous with the type Brassfield in east-central Kentucky (Rexroad, 1970).

Contacts: In southeastern Indiana and adjacent Kentucky, the Lee Creek Member is now recognized at the top of the formation (Nicoll and Rexroad, 1968, p. 8-10; Rexroad, 1986). The Belfast Bed of Foerste (1896, p. 163-164), named for strata in Ohio on the eastern flank of the Cincinnati Arch, was tentatively included as a basal part of the Brassfield at one locality in Indiana (Rexroad, 1967; Burger, 1970, p. 12), but later Rexroad (1986) considered it to be absent from Indiana, possibly because of either nondeposition or facies change.

Description:

In Indiana, the Brassfield Limestone is generally a medium- to coarse-grained fossiliferous limestone having numerous irregular blebs and stringers of shale scattered throughout and in many places containing Ordovician pebbles in the lower part (Rexroad, 1970, 1986). Small amounts of fine-grained dolostone are present in most sections, and the Lee Creek Member is also a dolostone (Rexroad, 1986). Color is variable; yellowish brown to salmon pink is common, but near Richmond the basal part is nearly white and the upper part is dark gray and contains scattered yellow grains (Rexroad, 1970, 1986). The formation is generally less than 4 ft (1.2 m) thick along the outcrop belt, but its maximum thickness on outcrop is 14 ft (4.3 m) and in the subsurface is 20 ft (6 m) (Rexroad, 1986).

Distribution In Indiana, exposures of the Brassfield are found near Richmond and near Connersville and thence southwestward to the Ohio River near Charlestown (Rexroad, 1986). The Brassfield is absent from parts of Decatur, Ripley, Jennings, and Jefferson Counties (Rexroad, 1967).

Boundaries:

The Brassfield unconformably overlies the Whitewater Formation of Ordovician age and in turn is unconformably overlain by the Osgood Member of the Salamonie Dolomite or by the undifferentiated Salamonie (Rexroad, 1986).

In the subsurface, in about northern Randolph County and Delaware and Madison Counties, the Brassfield is in a facies relationship with the Manitoulin Dolomite and Cabot Head Members of the Cataract Formation (Rexroad, 1980; Rexroad, 1986). To the west the Brassfield merges with the Sexton Creek Limestone that underlies approximately the western two-thirds of Indiana (Rexroad and Droste, 1982; Rexroad, 1986).

Correlations:

The Brassfield Formation (Rexroad and others, 1965) of the Cincinnati Arch area is time transgressive, the Brassfield Limestone of Indiana being younger than the type Brassfield (Rexroad, 1970, 1986). In Indiana Brassfield conodonts below the Lee Creek belong in the Distomodus kentuckyensis Assemblage Zone of middle and later Llandoverian age; the Lee Creek Member is C5 in age in reference to the standard zonation of the Llandoverian Series of Great Britain (Nicoll and Rexroad, 1968). In some localities evidence is lacking of an unconformity between the Lee Creek and the underlying part of the Brassfield, which suggests that part of the Brassfield proper is as young as the C4 interval in the upper part of the type Llandoverian (Rexroad, 1986). The Indiana Brassfield correlates with the Noland Formation of east-central Kentucky, and the main part of the formation also correlates approximately with the Elwood and Kankakee Formations of northeastern Illinois (Rexroad, 1986). It is continuous with the Sexton Creek Limestone of western Indiana, Illinois, and Missouri and with the Manitoulin and Cabot Head rocks of the Cataract Group (Formation in Indiana) of the Michigan Basin (Rexroad, 1986).

Regional Indiana usage:

Illinois Basin Margin (COSUNA 12)
Supergroup: none
Group: none
Formation: Brassfield Limestone
Cincinnati Arch (COSUNA 13)
Supergroup: none
Group: none
Formation: Brassfield Limestone
Kankakee Arch (COSUNA 14)
Supergroup: none
Group: none
Formation: Brassfield Limestone

Misc/Abandoned Names:

Clinton Limestone

Geologic Map Unit Designation:

Sb

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.)

Map showing the COSUNA areas (heavy black line) that approximate regional bedrock outcrop patterns and major structural features in Indiana, and the COSUNA numbers (large bold font) for these areas. The COSUNA boundaries are limited to state and county boundaries that facilitate coding.

COSUNA areas and numbers that approximate regional bedrock outcrop patterns and major structural features in Indiana.

Map showing major tectonic features that affect bedrock geology in Indiana.

Major tectonic features that affect bedrock geology in Indiana.

See also:

Cabot Head Member
Manitoulin Dolomite Member
Sexton Creek Limestone

References:

Burger, A. M., 1970, Belfast Member, in Shaver, R. H., Burger, A. M., Gates, G. R., Gray, H. H., Hutchison, H. C., Keller, S. J., Patton, J. B., Rexroad, C. B., Smith, N. M., Wayne, W. J., and Wier, C. E., Compendium of rock-unit stratigraphy in Indiana: Indiana Geological Survey Bulletin 43, p. 12.

Foerste, A. F., 1896, An account of Middle Silurian rocks of Ohio and Indiana: Cincinnati Society of Natural History Journal, v. 18, p. 161-200.

Foerste, A. F., 1897, A report on the geology of the Middle and Upper Silurian rocks of Clark, Jefferson, Ripley, Jennings, and southern Decatur Counties, Indiana: Indiana Department of Geology and Natural Resources Annual Report 21, p. 213-288.

Foerste, A. F., 1906, The Silurian, Devonian, and Irvine formations of east-central Kentucky, with an account of their clays and limestones: Kentucky Geological Survey Bulletin 7, 369 p.

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.

Nicoll, R. S., and Rexroad, C. B., 1968, Stratigraphy and conodont paleontology of the Salamonie Dolomite and Lee Creek Member of the Brassfield Limestone (Silurian) in southeastern Indiana and adjacent Kentucky: Indiana Geological Survey Bulletin 40, 73 p.

Rexroad, C. B., 1967, Stratigraphy and conodont paleontology of the Brassfield (Silurian) in the Cincinnati Arch area: Indiana Geological Survey Bulletin 36, 64 p.

Rexroad, C. B., 1970, Brassfield Limestone, in Shaver, R. H., Burger, A. M., Gates, G. R., Gray, H. H., Hutchison, H. C., Keller, S. J., Patton, J. B., Rexroad, C. B., Smith, N. M., Wayne, W. J., and Wier, C. E., Compendium of rock-unit stratigraphy in Indiana: Indiana Geological Survey Bulletin 43, p. 22-24.

Rexroad, C. B., 1980, Stratigraphy and conodont paleontology of the Cataract Formation and the Salamonie Dolomite (Silurian) in northeastern Indiana: Indiana Geological Survey Bulletin 58, 83 p.

Rexroad, C. B., 1986, Brassfield Limestone, 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. 20-21.

Rexroad, C. B., and Droste, J. B., 1982, Stratigraphy and conodont paleontology of the Sexton Creek Limestone and the Salamonie Dolomite (Silurian) in northwestern Indiana: Indiana Geological Survey Special Report 25, 29 p.

Rexroad, C. B., Branson, E. R., Smith, M. O., Summerson, Charles, and Boucot, A. J., 1965, The Silurian formations of east-central Kentucky and adjacent Ohio: Kentucky Geological Survey, ser. 10, Bulletin 2, 34 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 (hasenmue@indiana.edu)
Date last revised: February 15, 2016

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