Type locality: The name “Geneva Limestone” was first used by Collett (1882, p. 63, 81, and 82) for exposures of a buff dolomitic limestone exposed along the Flat Rock River near Geneva, Shelby County, Indiana (Burger and Patton, 1970; Droste and Shaver, 1986).
History of usage:
Foerste (1898, p. 234-235) called these same rocks the Shelby Bed. Most early usage, however, was "Geneva," and in accord with the advice of Kindle (1901, p. 536), the term “Shelby” was abandoned (Droste and Shaver, 1986).
The Geneva Dolomite Member is typically a calcareous dolostone that is buff to chocolate brown, rather soft, granular, and vuggy and that contains bands and partings of carbonaceous material (Burger and Patton, 1970; Droste and Shaver, 1986). It is massive to thick bedded in its lower part and more commonly thin bedded in its upper part (Burger and Patton, 1970; Droste and Shaver, 1986). The distinctive colors are due to a high organic content, and near-surface beds are commonly oxidized to pale tan, cream, or even white. White crystalline, coarsely cleavable calcite masses (spar) ranging from 1 inch to more than 1 foot (0.3 m) in cross section, resulting from calcification of fossils, are scattered through the fine-grained dolomite matrix (Burger and Patton, 1970; Droste and Shaver, 1986). Some calcite masses make up beautifully preserved, taxonomically identifiable fossil casts (Droste and Shaver, 1986). Chert is present in some sections, and quartz sand is especially common in basal rocks.
Despite the abundance of fossil material in the Geneva, age assessment and correlation have long been controversial for at least three reasons: (1) preservation for taxonomic purposes is poor, (2) outcrop and subsurface studies tend to support different conclusions, and (3) age and correlation are partly matters of different definitions of what shall constitute the Geneva (Droste and Shaver, 1986).
Regional Indiana usage:
Illinois Basin (COSUNA 11)
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 features in Indiana.
Major tectonic features that affect bedrock geology in Indiana.
Burger, A. M., and Patton, J. B., 1970, Geneva Dolomite, 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. 62-64.
Collett, John, 1882, Geology of Shelby County: Indiana Department of Geology and Natural History Annual Report 11, p. 55-88.
Dawson, T. A., 1941, Outcrop in southern Indiana, pt. 1 of The Devonian formations of Indiana: Indiana Division of Geology, 48 p.
Droste, J. B., and Shaver, R. H., 1975, The Jeffersonville Limestone (Middle Devonian) of Indiana—stratigraphy, sedimentation, and relation to Silurian reef-bearing rocks: American Association of Petroleum Geologists Bulletin, v. 59, p. 393-412.
Droste, J. B., and Shaver, R. H., 1986, Geneva Dolomite 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. 50-52.
Foerste, A. F., 1898, A report on the Niagara limestone quarries of Decatur, Franklin, and Fayette Counties, with remarks on the geology of the Middle and Upper Silurian rocks of these and neighboring (Ripley, Jennings, Bartholomew, and Shelby) counties: Indiana Department of Geology and Natural Resources Annual Report 22, p. 195-256.
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.
Kindle, E. M., 1901, The Devonian fossils and stratigraphy of Indiana: Indiana Department of Geology and Natural Resources Annual Report 25, p. 529-758.
Kindle, E. M., 1913, The unconformity at the base of the Onondaga Limestone of New York and its equivalent west of Buffalo: Journal of Geology, v. 21, p. 301-319.
Meents, W. F., and Swann, D. H., 1965, Grand Tower Limestone (Devonian) of southern Illinois: Illinois State Geological Survey Circular 389, 34 p.
Patton, J. B., and Dawson, T. A., 1955, Stratigraphy, in Murray, H. H., compiler, Sedimentation and stratigraphy of the Devonian rocks of southeastern Indiana: Indiana Geological Survey Field Conference Guidebook 8, p. 16, 21-22, 25-26, and 37-43.
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.
Sutton, D. G., and Sutton, A. H., 1937, Middle Devonian of southern Indiana: Journal of Geology, v. 45, p. 320-331.
Wilmarth, M. G., 1938, Lexicon of geologic names of the United States (including Alaska): U.S. Geological Survey Bulletin 896, 2,396 p.
For additional information, contact:
Nancy Hasenmueller (email@example.com)Date last revised: June 30, 2017