Type locality: In 1898 M. R. Campbell used the term “Lexington Limestone” for 150 ft (45 m) of gray thin-bedded limestone near Lexington, Kentucky, but he established no type section (Keith, 1986).
History of usage:
Overview (Keith, 1986): The name “Lexington Limestone” was first used by J. L. Campbell (1879) for an Ordovician limestone near Lexington in western Virginia. This unit was later renamed.
The Lexington Limestone is generally light- to medium-brownish-gray fossiliferous limestone (Keith, 1986). Interbeds of shale lithologically similar to the overlying Kope Formation of the Maquoketa Group are found in the upper part of the Lexington in Dearborn County (Keith, 1986). The Lexington also contains some darker argillaceous zones that are discussed below (Keith, 1986).
The Lexington Limestone conformably overlies the Plattin Formation of the Black River Group (Keith, 1986). The contact with the overlying Kope Formation is more complex, as described above, but appears to be conformable (Keith, 1986).
The Lexington Limestone of Indiana has been correlated with varying degrees of probability and certainty with the Trenton Limestone (Formation, Group) of Indiana, Michigan, and Ohio, the Kimmswick and Lexington Limestones of Kentucky, the Galena Group of Illinois, and the lower parts of the Kope Formation and the Maquoketa Group (Shale) of Indiana and Kentucky (Keith, 1986). The Lexington also correlates with rocks in southwestern Ohio extending up from the Lexington Limestone, through the Point Pleasant Formation, and into the lower part of the Kope Formation (Keith, 1986). (See Gutstadt, 1958; Gray, 1972; Waterman, 1975; Droste and Shaver, 1983; and Shaver, 1984.)
Regional Indiana usage:
Illinois Basin Margin (COSUNA 12)
Cynthiana Formation, Lexington-Cynthiana
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.
Black, D. F. B., Cressman, E. R., and MacQuown, W. C., Jr., 1965, The Lexington Limestone (Middle Ordovician) of central Kentucky: U.S. Geological Survey Bulletin 1224-C, p. 1-29.
Campbell, J. L., 1879, Silurian formation in central Virginia: American Journal of Science, ser. 3, v. 18, p. 16-29.
Campbell, M. R., 1898, Description of the Richmond quadrangle (Kentucky): U.S. Geological Survey Geologic Atlas, Folio 46, 4 p.
Foerste, A. F., 1906, The Silurian, Devonian, and Irvine formations of east-central Kentucky, with an account of their clays and limestones: Kentucky Geological Survey Bulletin 7, 369 p.
Gray, H. H., Brown, G. D., Jr., and Lineback, J. A., 1966, Physical techniques of correlation applied to Upper Ordovician rocks of southeastern Indiana [abs.]: American Association of Petroleum Geologists Bulletin, v. 40, p. 615-616.
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.
Keith, B. D., 1986, Lexington Limestone, 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. 77-78.
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.
Sweet, W. C., 1979, Conodonts and conodont biostratigraphy of post-Tyrone Ordovician rocks of the Cincinnatian region, in Pojeta, John, Jr., ed., Contributions to the Ordovician paleontology of Kentucky and nearby states: U.S. Geological Survey Professional Paper 1066-G, 26 p.
Waterman, A. S., 1975, Conodont biostratigraphy, paleontology, and paleoecology of the Trenton and Lexington Limestones in southeastern Indiana: Bloomington, Indiana University, master's thesis, 60 p.
For additional information, contact:
Nancy Hasenmueller (email@example.com)Date last revised: October 27, 2014