Type section: The Edwardsville Formation was named by Stockdale (1931, p. 220) for Edwardsville, Floyd County, Indiana. The type section is along former Indiana Highway 62 a short distance northeast of the town near the center of the NE¼ sec. 1, T. 3 S., R. 5 E. (Georgetown quadrangle) (Rexroad, 1986).
History of usage:
Summary of early history: Stockdale included strata between his Floyds Knob Formation below and his Harrodsburg Limestone above (Rexroad, 1986). The latter included the Ramp Creek as its basal member (Rexroad, 1986). The Floyds Knob was later designated as the basal member of the Edwardsville, and the Ramp Creek was given formational status (Nicoll and Rexroad, 1975, p. 3; Rexroad, 1986). The Edwardsville of present usage overlies the Spickert Knob Formation and underlies the Ramp Creek Formation (Rexroad, 1986).
Siltstone, sandy shale, and sandstone are the dominant lithologies along most of the Edwardsville Formation outcrop above the Floyds Knob Limestone Member; however, limestone is present in places (Gates and Rexroad, 1970; Rexroad, 1986). The Edwardsville represents delta-platform sedimentation, and according to Stockdale (1931) is from 40 to 200 ft (12 to 61 m) thick in Indiana (Gates and Rexroad, 1970; Rexroad, 1986).
The Edwardsville is conformable with the underlying delta-slope sediments of the Spickert Knob Formation, although cessation of deposition must have occurred locally (Rexroad, 1986). The overlying Ramp Creek Formation, or the Muldraugh Formation along the distal margin of the Edwardsville, appears to be disconformable, because the boundary is marked by a sharp lithologic break and a bed of glauconite occurs at the top of the Edwardsville along most of its outcrop (Rexroad, 1986).
The Edwardsville Formation is thought to correlate with part of the Keokuk Limestone of the Mississippi Valley because conodonts from the Floyds Knob Limestone Member at its base and from the lower part of the overlying Ramp Creek Formation compare closely with Keokuk conodonts (Nicoll and Rexroad, 1975, p. 16; Rexroad, 1986). Further, the famous Crawfordsville crinoid beds, consisting of fossiliferous siltstones and lesser amounts of crinoidal limestone and lying partly in the stratigraphic position of the Edwardsville in Montgomery County, Indiana, are Keokuk in age according to Van Sant and Lane (1964, p. 30-33) (Rexroad, 1986).
Regional Indiana usage:
Illinois Basin Margin (COSUNA 12)
Crawfordsville crinoid beds, Riverside Sandstone
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.
Gates, G. R., Rexroad, C. B., 1970, Edwardsville 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. 50-51.
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.
Hopkins, T. C., 1896, The Carboniferous sandstones of western Indiana an economic report on the sandstones of a portion of western Indiana, accompanied by two atlas sheets showing the outcrops and distribution of the sandstone: Indiana Department of Geology and Natural Resources Annual Report 20, p. 186-327.
Rexroad, C. B., 1986, Edwardsville 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. 41-42.
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.
Stockdale, P. B., 1931, The Borden (Knobstone) rocks of southern Indiana: Indiana Department of Conservation Publications 98, 330 p.
Van Sant, J. F., and Lane, N. G., 1964, Crawfordsville (Indiana) crinoid studies: University of Kansas Paleontological Contributions, Echinodermata, art. 7, 136 p.
For additional information, contact:
Nancy Hasenmueller (firstname.lastname@example.org)Date last revised: April 6, 2016