Age:

Pennsylvanian

Type designation:

Type section: The name “Silverwood” was applied by Alexander (1943, p. 143) to a well-developed cyclothem and limestone exposed near Silverwood, Fountain County, Indiana, about 0.25 miles (0.4 km) north of Indiana Highway 234 on the east side of Coal Creek (Hutchison, 1970; Hutchison and Hasenmueller, 1986). This exposure in the SE¼NW¼ sec. 36, T. 18 N., R. 9 W., was mistakenly cited by Alexander as in the NE¼SW¼ sec. 36, T. 18 N., R. 8 W. (Hutchison and Hasenmueller, 1986).

History of usage:

Hutchison (1970; 1976, p. 19, 50) assigned the limestone member rank in the Staunton Formation and designated the above exposure as the type section, although he, too, listed incorrect locations, the NE¼SW¼ sec. 36, T. 18 N., R. 8 W., in 1970 and the NE¼SW¼ sec. 36, T. 18 N., R. 9 W., in 1976 (Hutchison and Hasenmueller, 1986).

Description:

The Silverwood Limestone Member consists of three benches (Alexander, 1943; Hutchison, 1970; Hutchison and Hasenmueller, 1986). The upper bench at the type section is dark-blue fossiliferous limestone, which is 0.2 ft (0.06 m) thick and has distinctive cone-in-cone structure (Alexander, 1943; Hutchison, 1970; Hutchison and Hasenmueller, 1986). The middle bench is a calcareous fossiliferous shale, 0.75 ft (0.23 m) thick, and the lower and more persistent bench is dark-gray fossiliferous limestone, 0.3 ft (0.09 m) thick (Alexander, 1943; Hutchison, 1970; Hutchison and Hasenmueller, 1986).

Correlations:

The Silverwood Cyclothem, according to Alexander (1943), extends as far north as Fall Creek in north-central Warren County and includes Coal II of Parke and Clay Counties as defined by Ashley (1909) (Hutchison, 1970; Hutchison and Hasenmueller, 1986). In Fountain County, however, the Silverwood Limestone Member lies about 50 ft (15 m) above Coal II, and it correlates with one or more of a group of marine zones in the middle part of the Staunton Formation (Hutchison, 1961, 1970; Hutchison and Hasenmueller, 1986). This zone can be traced along the outcrop and in the subsurface from Warren County to the Ohio River (Hutchison, 1970; Hutchison and Hasenmueller, 1986).

The Silverwood has been correlated with the Stonefort Limestone Member of Illinois (Peppers and Popp, 1979, p. 71; Hutchison and Hasenmueller, 1986).

Regional Indiana usage:

Illinois Basin (COSUNA 11)
Supergroup: none
Group: Raccoon Creek Group
Formation: Staunton Formation
Member: Silverwood Limestone Member
Illinois Basin Margin (COSUNA 12)
Supergroup: none
Group: Raccoon Creek Group
Formation: Staunton Formation
Member: Silverwood Limestone Member

Misc/Abandoned Names:

None

Geologic Map Unit Designation:

*sts

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:

Alexander, J. W., 1943, Key beds of the Pennsylvanian section of eastern Vermilion County, Illinois, and Vermillion, Warren, and Fountain Counties, Indiana: Illinois State Academy of Science Transactions, v. 36, p. 141–144.

Ashley, G. H., 1909, Supplementary report to the report of 1898 on the coal deposits of Indiana: Indiana Department of Geology and Natural Resources Annual Report 33, p. 13–150.

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.

Hutchison, H. C., 1961, Distribution, structure, and mined areas of coals in Fountain and Warren Counties and the northernmost part of Vermillion County, Indiana: Indiana Geological Survey Preliminary Coal Map 9, scale 1:126,720.

Hutchison, H. C., 1970, Silverwood Limestone 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. 168.

Hutchison, H. C., 1976, Geology of the Catlin-Mansfield area, Parke and Putnam Counties, Indiana: Indiana Geological Survey Bulletin 54, 57 p.

Hutchison, H. C., and Hasenmueller, W. A., 1986, Silverwood Limestone Member, 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. 145.

Peppers, R. A., and Popp, J. T., 1979, Stratigraphy of the lower part of the Pennsylvanian System in southeastern Illinois and adjacent portions of Indiana and Kentucky, in Palmer, J. E., and Dutcher, R. R., eds., Depositional and structural history of the Pennsylvanian System of the Illinois Basin–Pt. 2, Invited papers, Ninth International Congress Carboniferous Stratigraphy and Geology, Illinois Geological Survey Guidebook Series 15a, p. 65–72.

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.