Type area: 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). The type area is in that part of the upper Wabash Valley extending from Carroll County to Huntington County, Indiana (Droste and Shaver, 1986).
History of usage:
After considerable post-1964 evidence had accumulated to show that appreciable facies relationship exists between the Wabash and Salina Formations, the Wabash definition was expanded to include the upper part of the Salina Formation as previously defined, and the Salina was given group status to include the Wabash and older rocks in northern Indiana down through the Louisville Limestone and the Limberlost Dolomite (Droste and Shaver, 1982) (Droste and Shaver, 1986). Before that time, however, Becker (1974), Becker and Droste (1978), Rexroad, Noland, and Pollock (1978), and Droste and Shaver (1980) had defined the southern Indiana occurrence to extend very nearly to the southeastern Silurian outcrop, there being narrowly overlapped in the subsurface by Middle Devonian rocks, and well into the Illinois Basin, there being terminated along a defined vertical cutoff against rocks of the middle and upper parts of the Bainbridge Group (Droste and Shaver, 1986). This cutoff leaves an area of about eight-county size unoccupied by Wabash rocks (as defined) in the southwest corner of Indiana (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)
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.)
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.
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 (email@example.com) orDate last revised: June 2, 2014
Walter Hasenmueller (firstname.lastname@example.org)