Age:

Mississippian

Type designation:

Type section: The Tobinsport Formation was named by Gray (1978, p. 10-11) for the settlement by that name at the southernmost point in Perry County, Indiana (Gray, 1986). A section near Tobinsport earlier described by Malott (1925, p. 117-118) was designated as the type (Gray, 1986).

Reference section: Gray (1978) designated Indiana Geological Survey drill hole 132 (Indiana Geological Survey Petroleum Database Management System No. 125735) near Oriole in northeastern Perry County as a reference section (SW¼ sec. 10, T. 4 S., R. 1 W., Branchville quadrangle) (Gray, 1986).

Description:

The Tobinsport Formation is dominantly shale and mudstone but includes four widespread members, the Bristow and Mount Pleasant Sandstone Members and the Siberia and Negli Creek Limestone Members (Gray, 1986).

The name “Tobinsport Formation” is restricted to surface use. The base of the formation is the top of the Leopold Limestone Member of the Branchville Formation (Gray, 1986). This contact is conformable. The formation is disconformably overlain by the Mansfield Formation (Morrowan), and so its thickness is variable (Gray, 1986). Where substantially all members of the formation are present, it is 90 to 125 ft (27 to 38 m) thick, but it is truncated northward by the disconformity, so that it extends only a short distance north of the north boundary of Perry County (Gray, 1986).

Correlations:

The Tobinsport Formation correlates with rocks within the Namurian Series (probably Zone E2) of European usage (Gray, 1986). Conodont faunas of rocks now a part of the Tobinsport Formation were studied by Collinson, Rexroad, and Thompson (1971), who assigned these rocks to the Kadognathus-Cavusgnathus naviculus Assemblage Zone of standard North American usage (Gray, 1986).

Droste and Keller (1995, fig. 3) correlated the Tobinsport Formation with the following units recognized in the subsurface of southwestern Indiana. In ascending order, the subsurface units are the upper part of the Menard Limestone, the Palestine Formation, the Clore Formation, the Degonia Formation, and the lower part of the Kincaid Limestone.

Regional Indiana usage:

Illinois Basin (COSUNA 11)
Supergroup: none
Group: Buffalo Wallow Group
Formation: Tobinsport Formation

Misc/Abandoned Names:

None

Geologic Map Unit Designation:

Mt

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:

Collinson, Charles, Rexroad, C. B., and Thompson, T. L., 1971, Conodont zonation of the North American Mississippian: Geological Society of America Memoirs 127, p. 353–394.

Droste, J. B., and Keller, S. J., 1995, Subsurface stratigraphy and distribution of oil fields of the Buffalo Wallow Group (Mississippian) in Indiana: Indiana Geological Survey Bulletin 63, 24 p.

Gray, H. H., 1978, Buffalo Wallow Group upper Chesterian (Mississippian) of southern Indiana: Indiana Geological Survey Occasional Paper 25, 28 p.

Gray, H. H., 1986, Tobinsport 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. 155–156.

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.

Malott, C. A., 1925, The upper Chester of Indiana: Indiana Academy of Science Proceedings, v. 34, p. 103–132.

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.