Type area: The type area of the Wabash Formation is in that part of the upper Wabash Valley extending from Carroll County to Huntington County, Indiana (Droste and Shaver, 1986).
History of usage:
The Wabash Formation was named in 1964 for all then so-called "Niagaran" rocks in northern Indiana lying above the Louisville Limestone and exclusive of Silurian rocks then assigned to the Salina Formation (Pinsak and Shaver, 1964, p. 34-47; Droste and Shaver, 1986). This definition included the preexisting units called the Mississinewa Shale, the Liston Creek Limestone, the New Corydon Limestone (nontypical, of Cumings and Shrock, 1928a, p. 113-117), and the Noblesville Dolomite (obsolete at that time, of Kindle and Breger, 1904, p. 407) (Droste and Shaver, 1986).
Four principal lithologies that intergrade and replace one another spatially characterize the Wabash Formation: (1) calcareous silty dolostone and dolomitic silty limestone that are gray, dense to fine grained, and massive (when fresh) and that are characteristic of, but not confined to, the Mississinewa Shale Member in the lower part of the formation; (2) limestone, dolomitic limestone, and dolostone that are light colored, mostly finely granular, cherty but otherwise fairly pure, and slabby bedded (in weathered exposures) and that are characteristic of, but not confined to, the upper part of the formation, especially the Liston Creek Limestone Member and less so the Kenneth Limestone Member; (3) dolostone and dolomitic limestone that are generally in shades of light tan to dark brown (but including grayish and greenish colors), are generally micritic to fine grained, are generally nonfossiliferous, and become strikingly color banded and thinly laminated over broad areas and that are characteristic of the Kokomo Limestone Member and especially of the upper Wabash rocks (unnamed to member) in the northern two tiers of Indiana counties; some greenish shale is included in the latter lithology in those northern counties; and (4) light-colored granular massive vuggy, nearly pure dolostone and limestone and bluish-gray carbonate mudstone that are widely distributed in bank, reef, reef-detrital, and biohermal facies throughout much of the formation (Droste and Shaver, 1986).
The hundreds of classically studied macrofossils from Wabash reef and interreef rocks have been assigned stratigraphically secure positions (Shaver, 1974). Among those to which greatest biostratigraphic importance may be attached are the pentamerid brachiopods Kirkidium cf. K. knighti (low in the formation) and K. cf. K. laqueatum (high in the formation), the graptolite Monograptus falciformis (= M. bohemicus; low in the formation), and the mollusk Megalomus canadensis (known high in the formation but probably has a lower range to below the formation) (Droste and Shaver, 1986).
Regional Indiana usage:
Illinois Basin (COSUNA 11)
New Corydon Limestone, Niagaran [rocks], Noblesville Dolomite
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.
Bristol, H. M., 1974, Silurian pinnacle reefs and related oil production in southern Illinois: Illinois State Geological Survey Illinois Petroleum 102, 98 p.
Cumings, E. R., and Shrock, R. R., 1928, Niagaran coral reefs of Indiana and adjacent states and their stratigraphic relations: Geological Society of America Bulletin, v. 39, p. 579-620.
Cumings, E. R., and Shrock, R. R., 1928, The geology of the Silurian rocks of northern Indiana: Indiana Department of Conservation Publications 75, 226 p.
Droste, J. B., and Shaver, R. H., 1980, Recognition of buried Silurian reefs in southwestern Indiana: Journal of Geology, v. 88, p. 567-587.
Droste, J. B., and Shaver, R. H., 1986, Wabash Formation, 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. 163-165.
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.
Lowenstam, H. A., 1949, Niagaran reefs in Illinois and their relation to oil accumulation: Illinois State Geological Survey Report of Investigations 145, 36 p.
Rexroad, C. B., Noland, A. V., and Pollock, C. A., 1978, Conodonts from the Louisville Limestone and the Wabash Formation (Silurian) in Clark County, Indiana, and Jefferson County, Kentucky: Indiana Geological Survey Special Report 16, 15 p.
Shaver, R. H., 1974, The Niagaran (Middle Silurian) macrofaunas of northern Indiana–review, appraisal, and inventory: Indiana Academy of Science Proceedings, v. 83, p. 301-315.
Shaver, R. H., Ault, C. H., Ausich, W. I., Droste, J. B., Horowitz, A. S., James, W. C., Okla, S. M., Rexroad, C. B., Suchomel, D. M., and Welch, J. R., 1978, The search for a Silurian reef model–Great Lakes area: Indiana Geological Survey Special Report 15, 36 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 (firstname.lastname@example.org)Date last revised: June 14, 2017