Age:

Mississippian

Type designation:

Type section: In exposures in cuts on Illinois Highway 37, 4 miles (6.4 km) northwest of Karnak, in SW¼SW¼ sec. 32, T. 13 S., R. 2 E., and NW¼NW¼ sec. 5, T. 14 S, R. 2 E., Dongola quadrangle, Johnson County, Illinois (Swann, 1963, p. 28-29, 71).

History of usage:

Named: The Karnak Limestone Member of the Ste. Genevieve Limestone was named by Swann (1963, p. 28).

Extended: Droste and Carpenter (1990, p. 15, 25) adopted the name “Karnak Member” of the Ste. Genevieve Limestone for use in the subsurface of Indiana.

Description:

The Karnak Member of the Ste. Genevieve Limestone is predominantly limestone and has good lateral continuity and high resistivity on electric logs (Droste and Carpenter, 1990, p. 25; figs. 8, 9, 10, and 11). The uppermost bed of the Ste. Genevieve in the outcrop area, the Bryantsville Breccia Bed, is placed in the Karnak Member. The Karnak Member generally ranges from 20 to 45 ft (6.1 to 13.7 m) in thickness in the deeper subsurface where the overlying Joppa Member of the Ste. Genevieve is recognized (Droste and Carpenter, 1990, p. 25).

Distribution: Droste and Carpenter (1990) recognized the Karnak Member in the subsurface in southwestern Indiana. In the area of outcrop, the upper Ste. Genevieve is composed of limestone typical of the Karnak Member of the deeper subsurface. Therefore, in the shallow subsurface and outcrop areas, all the rocks of the Ste. Genevieve above the Fredonia Member are placed in the Karnak by Droste and Carpenter (1990, p. 25).

Boundaries:

The uppermost bed of the Ste. Genevieve Limestone in the outcrop area, the Bryantsville Breccia Bed, marks the top of the Karnak Member. Where the Bryantsville Breccia is absent, the shale and sandstone of the overlying Aux Vases Member of the Paoli Limestone are easily differentiated from the carbonate rocks of the Ste. Genevieve Limestone in samples and on logs (Droste and Carpenter, 1990, p. 27).

Correlations:

The Karnak Member of Indiana is equivalent to the Karnak Limestone Member of the Ste. Genevieve Limestone of Illinois (Droste and Carpenter, 1990).

Regional Indiana usage:

Illinois Basin (COSUNA 11)
Supergroup: none
Group: Blue River Group
Formation: Ste. Genevieve Limestone
Member: Karnak Member
Illinois Basin Margin (COSUNA 12)
Supergroup: none
Group: Blue River Group
Formation: Ste. Genevieve Limestone
Member: Karnak Member

Misc/Abandoned Names:

Levias Member (middle part)

Geologic Map Unit Designation:

Msgk

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.

References:

Droste, J. B., and Carpenter, G. L., 1990, Subsurface stratigraphy of the Blue River Group (Mississippian) in Indiana: Indiana Geological Survey Bulletin 62, 45 p.

Hansen, W. R., 1991, Suggestions to authors of the reports of the United States Geological Survey (7^th ed.): Washington, D.C., U.S. Geological Survey, 289 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.

Swann, D. H., 1963, Classification of Genevievian and Chesterian (Late Mississippian) rocks of Illinois: Illinois State Geological Survey Report of Investigations 216, 91 p.