Type section: The Lee Creek Member of the Brassfield Limestone was named by Nicoll and Rexroad (1968, p. 9) for the very dolomitic upper part of the Brassfield in southeastern Indiana and adjacent Kentucky (Rexroad, 1986). The type section is just below a long-abandoned road near the head of a short tributary of Lee Creek in the NE¼SE¼SE¼ sec. 36, T. 3 N., R. 9 E., Jefferson County, Indiana (Rexroad, 1986).
The Lee Creek Member is fine-grained dolostone that varies from tan to red brown and in places has a greenish cast (Rexroad, 1986). Glauconite, mostly in sand-sized grains, is common, especially near the top of the unit (Rexroad, 1986). Bedding is thin and tends to be irregular. Maximum measured thickness (Nicoll and Rexroad, 1968) is 4.3 ft (1.3 m), but the member is commonly less than 1 foot (0.3 m) thick. It is generally present from Mt. Washington, Bullitt County, Kentucky, as far north as Madison, Jefferson County, Indiana (Rexroad, 1986). It is discontinuously present north of Madison and is recognized in Decatur and Switzerland Counties (Rexroad, 1986).
Apparently its relation to the underlying Brassfield proper varies from unconformable to conformable (Rexroad, 1986). It is unconformably overlain by the Osgood (a member of the Salamonie Dolomite in Indiana and a formation in Kentucky) (Rexroad, 1986).
The conodont fauna of the Lee Creek Member falls mostly within the Ozarkodina celloni Assemblage Zone (Nicoll and Rexroad, 1968), which correlates with the C5 division of the Telychian Stage in the upper part of the type Llandoverian Series in Great Britain. The same conodont fauna has been reported from the middle part of the Brandon Bridge Member of the Joliet Formation of northeastern Illinois (Liebe and Rexroad, 1977), the Seventy-Six Shale Member of the Bainbridge Formation in southwestern Illinois (Satterfield and Thompson, 1975), and the top of the Noland Formation and at one locality in the base of the Estill Shale in Kentucky (Rexroad and Nicoll, 1972; Rexroad and Kleffner, 1984; Rexroad, 1986). This zone indicates an early Niagaran age in the North American standard (Rexroad, 1986).
Regional Indiana usage:
Cincinnati Arch (COSUNA 13)
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.
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.
Liebe, R. M., and Rexroad, C. B., 1977, Conodonts from Alexandrian and early Niagaran rocks in the Joliet, Illinois, area: Journal of Paleontology, v. 51, p. 844-857.
Nicoll, R. S., and Rexroad, C. B., 1968, Stratigraphy and conodont paleontology of the Salamonie Dolomite and Lee Creek Member of the Brassfield Limestone (Silurian) in southeastern Indiana and adjacent Kentucky: Indiana Geological Survey Bulletin 40, 73 p.
Rexroad, C. B., 1986, Lee Creek 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. 75-76.
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., and Nicoll, R. S., 1972, Conodonts from the Estill Shale (Silurian, Kentucky and Ohio) and their bearing on multielement taxonomy: Geologica et Palaeontologica, Special Volume 1, p. 57-74.
Satterfield, I. R., and Thompson, T. L., 1975, Seventy-Six Shale, a new member of the Bainbridge Formation (Silurian) in southeastern Missouri, in Studies in stratigraphy: Missouri Geological Survey Report of Investigations 57, p. 109-119.
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: February 10, 2015