Age:

Silurian

Type designation:

Type section: At Red Bridge in the bluff of the Mississinewa River, Wabash County, Indiana (south-central part of Reserve 26, T. 26 N., R. 6 E.) (Shaver, 1970; Droste and Shaver, 1986). The type section is now underwater in the Mississinewa Reservoir during at least part of the year, as is the former exposure of this bed within the Liston Creek type section (Shaver and others, 1961, fig. 5; Droste and Shaver, 1986).

Characteristic sections:

Good exposures of the Red Bridge remain along the Wabash River in western Wabash County (Droste and Shaver, 1986). One of these is in the Indiana Highway 13 and 15 road cuts in the south bluff south of Wabash (north-central part of sec. 18, T. 27 N., R. 6 E.), where the 1.4-ft (0.4-m) Red Bridge, basalmost Liston Creek, immediately overlies a 48-ft (15-m) section of the Mississinewa Shale Member (Wabash Formation) (Droste and Shaver, 1986). (See Pinsak and Shaver, 1964, p. 82.)

Another good section flanks the Shanty Falls Reef, south bluff of the river valley, 1 mile west of Wabash (N½ Reserve 55, T. 27 N., R. 6 E.) (Droste and Shaver, 1986). (See Cumings and Shrock, 1928, p. 76 and 151.)

History of usage:

Reduction in rank: The Red Bridge was named by Cumings and Shrock (1927, p. 74) as a formation and was later (Cumings and Shrock, 1928, p. 72) regarded as a member (Shaver, 1970; Droste and Shaver, 1986).

The Red Bridge was reduced to the status Red Bridge Limestone Bed (Liston Creek Limestone Member) by Pinsak and Shaver (1964, p. 39) (Shaver, 1970; Droste and Shaver, 1986). The name has had little or no use outside Wabash County, although glauconite is found elsewhere in the lower Liston Creek rocks, for example, in Howard County (Shaver and others, 1961, p. 13; Droste and Shaver, 1986).

Description:

The Red Bridge Limestone Bed is 1 to 6 ft (0.3 to 1.8 m) thick and is a light-colored fine-grained glauconitic dolomitic limestone that commonly weathers reddish brown and appears as a single bed on outcrop (Shaver, 1970; Droste and Shaver, 1986).

Regional Indiana usage:

Kankakee Arch (COSUNA 14)
Supergroup: none
Group: Salina Group
Formation: Wabash Formation
Member: Liston Creek Limestone Member
Bed: Red Bridge Limestone Bed

Misc/Abandoned Names:

None

Geologic Map Unit Designation:

Swrb

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:

Cumings, E. R., and Shrock, R. R., 1927, The Silurian coral reefs of northern Indiana and their associated strata: Indiana Academy of Science Proceedings, v. 36, p. 71–85.

Cumings, E. R., and Shrock, R. R., 1928, The geology of the Silurian rocks of northern Indiana: Indiana Department of Conservation Publication No. 75, 226 p.

Droste, J. B., and Shaver, R. H., 1986, Red Bridge Limestone Bed, 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. 122.

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.

Pinsak, A. P., and Shaver, R. H., 1964, The Silurian formations of northern Indiana: Indiana Geological Survey Bulletin 32, 87 p.

Shaver, R. H., 1970, Red Bridge Limestone Bed, 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. 138.

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.

Shaver, R. H., with contributions by Gray, H. H., Pinsak, A. P., Sunderman, J. A., Thornbury, W. D., and Wayne, W. J., 1961, Stratigraphy of the Silurian rocks of northern Indiana: Indiana Geological Survey Field Conference Guidebook 10, 62 p.