Type designation:

Type section: The Spickert Knob Formation was named by Rexroad and Lane (1984) for exposures in Floyd County, Indiana, near Spickert Knob along Spickert Knob Road and adjacent gullies to the northeast (Rexroad, 1986). This is Stockdale's section 16 (1931, p. 115), which is in the NE¼ sec. 21 and SE¼ sec. 16, T. 2 S., R. 6 E., and extends a few tens of yards into sec. 22 (New Albany quadrangle) (Rexroad, 1986).

Reference sections:

(1) The type section of the former Locust Point Formation along a secondary road ascending the Knobstone Escarpment at the Ohio River in the NW¼NE¼ sec. 13, T. 4 S., R. 5 E., Harrison County (Stockdale, 1931, p. 114; Rexroad, 1986).

(2) A section east of Edwardsville along former Indiana Highway 62 and the Southern Railroad and mainly in the NW¼ sec. 6, T. 3 S., R. 6 E., and NE¼ sec. 1, T. 3 S., R. 5 E. (Stockdale, 1931, p. 221; Rexroad, 1986).

(3) A section exposed along Indiana Highway 135 near Millport in the NW¼ sec. 29, T. 4 N., R. 4 E., Washington County (Kammer, Ausich, and Lane, 1983, p. 62-65; Rexroad, 1986).

History of usage:

The Spickert Knob is the precise equivalent of Stockdale's (1929) Locust Point and Carwood Formations, which in practice could not be separated as mappable units and which form a single depositional unit (Rexroad, 1986).


The Spickert Knob Formation consists of rocks between the New Providence Shale below and the Edwardsville Formation above (Rexroad, 1986). It is dominated by siltstone but includes abundant silty shale, some sandstone, and minor amounts of limestone (Rexroad, 1986). The formation tends to be more shaly and argillaceous in the lower part and to be dominated by massive siltstone in the upper part, but it is a complex of discontinuous lenses that were deposited as shifting and coalescing delta lobes and sublobes. Ironstone nodules and geodes are irregularly distributed in the formation (Rexroad, 1986).

In its type area the Spickert Knob Formation ranges between about 228 and 300 ft (69 and 92 m) in thickness (Rexroad, 1986). It maintains approximately this range in most of the outcrop area, although its thickness is subject to the vagaries characteristic of deltaic deposition (Rexroad, 1986). The Spickert Knob was truncated by erosion before Pennsylvanian sedimentation, however, in the area of Warren County (Rexroad, 1986). Southwestward from the outcrop belt, the formation thins away from the source area of the deltaic sediments and is not recognizable separately from the New Providence Shale and the Edwardsville Formation in the subsurface of southwestern Indiana (Rexroad, 1986).


Both boundaries are conformable and to some degree have intertonguing relationships (Rexroad, 1986). The formation represents delta-slope deposits (Rexroad, 1986).


The Spickert Knob Formation is approximately equivalent to the Nancy Member and the Holtsclaw Siltstone Member of the Borden Formation in north-central Kentucky (Rexroad, 1986). A variety of faunal elements (for example, brachiopods, crinoids, and cephalopods) in the formation have ranges that include or fall within the time-stratigraphic limits of the Keokuk Limestone of the Mississippi Valley (Kammer, Ausich, and Lane, 1983; Rexroad, 1986). Because the conodonts recovered from the New Providence Shale below (Rexroad and Scott, 1964) and the Floyds Knob Limestone Member of the Edwardsville Formation above (Gates and Rexroad, 1970; Whitehead, 1978) are of Keokuk-depositional age, the Spickert Knob, therefore, must also be equivalent to part of the Keokuk Limestone (Rexroad, 1986).

Regional Indiana usage:

Illinois Basin Margin (COSUNA 12)
Supergroup: none
Group: Borden Group
Formation: Spickert Knob Formation
Cincinnati Arch (COSUNA 13)
Supergroup: none
Group: Borden Group
Formation: Spickert Knob Formation

Misc/Abandoned Names:

Carwood Formation, Locust Point Formation

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.


Gates, G. R., and Rexroad, C. B., 1970, Borden Group, 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. 20-22.

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.

Kammer, T. W., Ausich, W. I., and Lane, N. G., 1983, Paleontology and stratigraphy of the Borden delta of southern Indiana and northern Kentucky (Field Trip 2), 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, p. 37-71.

Rexroad, C. B., 1986, Spickert Knob 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. 148-149.

Rexroad, C. B., and Lane, N. G., 1984, Spickert Knob Formation (new), Borden Group, in Indiana: Indiana Geological Survey Occasional Paper 43, 4 p.

Rexroad, C. B., and Scott, A. J., 1964, Conodont zones in the Rockford Limestone and the lower part of the New Providence Shale (Mississippian) in Indiana: Indiana Geological Survey Bulletin 30, 54 p.

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., 1929, Facies of the Borden rocks of southern Indiana [abs.]: Ohio Journal of Science, v. 29, p. 170.

Stockdale, P. B., 1931, The Borden (Knobstone) rocks of southern Indiana: Indiana Department of Conservation Publications 98, 330 p.

Whitehead, N. D., III, 1978, Lithostratigraphy, depositional environments, and conodont biostratigraphy of the Muldraugh Formation (Mississippian) in southern Indiana and north-central Kentucky: Southeastern Geology, v. 19, p. 83-109.

For additional information contact:

Nancy Hasenmueller (
Date last revised: May 4, 2017