Type locality: The Laurel Member was named as the "Laurel Formation" by Foerste (1896, p. 191) for exposures near Laurel in Franklin County, Indiana, but no type section was designated (Rexroad, 1970, 1986).
History of usage:
Restriction: The Laurel was originally defined as the unit between the Brassfield Limestone, which was then called the Clinton Limestone, and the Waldron Shale, and so it included rocks later assigned to the Osgood Member (Rexroad, 1970, 1986). In 1897, Foerste (p. 217) restricted the Laurel to beds above the Osgood (Rexroad, 1970, 1986).
The Laurel is generally light-gray to tan dense dolomitic limestone that has lenticular and nodular chert especially in the upper part (Rexroad, 1970, 1986). Although fossiliferous, recrystallization has destroyed many of the fossils (Rexroad, 1970, 1986). The member on outcrop ranges from about 27 to 55 ft (8 to 17 m) in thickness, and it thickens northward (Rexroad, 1970, 1986). The Laurel outcrop belt extends southward from Laurel to the Ohio River, through Kentucky, and into Tennessee (Rexroad, 1986). North of the type area and west from the outcrop belt in Indiana, the Osgood loses its distinctive lithology and cannot be separated from the Laurel, so that the two members form an undifferentiated part of the Salamonie Dolomite (Rexroad, 1986).
In most areas of outcrop, as at Fourteenmile Creek, the Laurel is conformable with the underlying Osgood and the overlying Waldron, but in places pre-Middle Devonian erosion has removed the overlying Silurian beds, and the Jeffersonville Limestone (Middle Devonian) unconformable rests on the Laurel (Rexroad, 1986).
The Laurel Member is continuous with a mostly upper part of the Salamonie Dolomite, and therefore the upper part of the Laurel is also equivalent to the Limberlost Dolomite Member of the Pleasant Mills Formation (Rexroad, 1986). It probably correlates with the Bisher Formation of southern Ohio and adjacent Kentucky, a unit that in British terms is early and middle Wenlockian in age (Niagara in the North American standard) (Rexroad and Kleffner, 1984; Rexroad, 1986). It also apparently correlates with the Laurel Limestone, the Euphemia Dolomite, and the Springfield Dolomite of west-central Ohio usage, with upper parts of the Joliet Dolomite of northeastern Illinois, with part of the St. Clair Limestone of southwestern Indiana and southeastern Illinois (Rexroad and Droste, 1982), and with all but the lower carbonate and shale beds of the Laurel of central Kentucky (Rexroad, Gray, and Noland, 1983; Rexroad, 1986). Generally, however, the Laurel is nearly synchronous from southeastern Indiana into central Tennessee (Rexroad, 1986).
Regional Indiana usage:
Illinois Basin Margin (COSUNA 12)
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.
Foerste, A. F., 1896, An account of Middle Silurian rocks of Ohio and Indiana: Cincinnati Society of Natural History Journal, v. 18, p. 161-200.
Foerste, A. F., 1897, A report on the geology of the Middle and Upper Silurian rocks of Clark, Jefferson, Ripley, Jennings, and southern Decatur Counties, Indiana: Indiana Department of Geology and Natural Resources Annual Report 21, p. 213-288.
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.
Rexroad, C. B., 1970, Laurel Member, 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. 88-89.
Rexroad, C. B., 1986, Laurel 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. 73-74.
Rexroad, C. B., and Droste, J. B., 1982, Stratigraphy and conodont paleontology of the Sexton Creek Limestone and the Salamonie Dolomite (Silurian) in northwestern Indiana: Indiana Geological Survey Special Report 25, 29 p.
Rexroad, C. B., and Kleffner, M. A., 1984, The Silurian stratigraphy of east-central Kentucky and adjacent Ohio, in Rast, Nicholas, and Hay, Helen, eds., Field trip guides for Geological Society of America annual meeting, Southeastern and North-Central Sections: Lexington, University of Kentucky and Kentucky Geological Survey, p. 44-65.
Rexroad, C. B., Gray, H. H., and Noland, A. V., 1983, The Paleozoic systemic boundaries of the southern Indiana-adjacent Kentucky area and their relations to depositional and erosional patterns (Field Trip 1), in Shaver, R. H., and Sunderman, J. A., eds., Field trips in midwestern geology: Bloomington, Indiana, Geological Society of America, Indiana Geological Survey, and Indiana University Department of Geology, v. 1, p. 1-36.
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)Date last revised: February 10, 2015