Age:

Silurian

Type designation:

Type area: The term “Bainbridge Limestone” was first given (E. O. Ulrich, as published by Buckley and Buehler, 1904, p. 110) to all the Silurian carbonate rocks that lie above what was then designated as the Girardeau Limestone and below the Bailey Limestone along a several-mile stretch of the Mississippi River bluffs above and below Bainbridge, Missouri, and Thebes, Illinois (Droste and Shaver, 1986).

History of usage:

Revised contact: Ulrich (1911, pl. 28) redefined the lower boundary as being with the Brassfield Limestone, which meant that he restricted the Bainbridge to what were then considered to be Niagaran rocks. During that period of study, what is now considered to be the Bailey part of the Bainbridge was thought to be Early Devonian in age (Droste and Shaver, 1986).

Revised rank and contents: Lowenstam (1949, p. 12) elevated the rank and assigned two formations to the Bainbridge Group, the St. Clair Limestone below and the Moccasin Springs Shale above, and also defined the relations of this group in the Illinois Basin (Droste and Shaver, 1986).

Extended: Becker (1974, p. 14) applied the name “Bainbridge Group” (St. Clair Limestone and Moccasin Springs Formation) to rocks that overlie the Sexton Creek Limestone and underlie the Bailey Limestone (Lower Devonian) in southwestern Indiana.

Redefined: Becker and Droste (1978, fig. 2 and p. 4) and Droste and Shaver (1980, fig. 4), realized that all but a small upper part of the Bailey Limestone was Silurian and redefined the Bainbridge Group to include the Bailey as its uppermost formation (Droste and Shaver, 1986).

Revised assignment: In Indiana the uppermost part of what had been called the Bailey was reassigned to the New Harmony Group (Lower Devonian) (Droste and Shaver, 1986).

Vertical cutoff: In this understanding, the Bainbridge Group has a vaguely defined vertical cutoff boundary in southwestern Indiana against rocks ranging upward from the Salamonie Dolomite through the Wabash Formation (Droste and Shaver, 1986). This boundary is in the area of extensive deposits of reef and reeflike rocks included in the feature called the Terre Haute Bank (Droste and Shaver, 1986).

Description:

Three rather distinctive lithologies of regional scope characterize the Bainbridge Group from the bottom part upward: (1) relatively pure white to pink, red, gray, and brown granular echinoderm-rich limestone (St. Clair Limestone); (2) multihued dense argillaceous to shaly, silty limestone and some shale (Moccasin Springs Formation); and (3) white, gray, and brown, very fine grained, cherty, and partly argillaceous limestone and some dolomitic limestone (Bailey Limestone) (Droste and Shaver, 1986).

A fourth distinctive lithology of the Bailey consists of rather pure light-colored granular carbonate rocks in reefs and banklike deposits that may extend vertically (for example, in pinnacle reefs as thick as 800 or 900 ft [244 or 274 m]) from within the St. Clair through the Bailey (Droste and Shaver, 1986).

Distribution: In its nonreef facies the Bainbridge thickens southwestward from about 200 ft (61 m) to about 400 ft (122 m) in the area of its southwestern Indiana distribution in the parts or whole of 10 counties (Droste and Shaver, 1986).

Boundaries:

The Bainbridge rests unconformably on the Sexton Creek Limestone and underlies the New Harmony Group (Lower Devonian) probably unconformably and conformably (Droste and Shaver, 1986).

Correlations:

The Bainbridge Group ranges from early Niagaran (late Llandoverian) in age through latest Silurian and can be correlated approximately with a great many midwestern and Midcontinent Silurian formations as shown in part by Shaver (1984) (Droste and Shaver, 1986). Direct-age data remain very sparse, however, and much of the suggested correlation is based on direct tracing and geophysical logging (Droste and Shaver, 1986).

Regional Indiana usage:

Illinois Basin (COSUNA 11)
Supergroup: none
Group: Bainbridge Group

Misc/Abandoned Names:

None

Geologic Map Unit Designation:

Sbb

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.

See also:

Salina Group

References:

Becker, L. E., 1974, Silurian and Devonian rocks in Indiana southwest of the Cincinnati Arch: Indiana Geological Survey Bulletin 50, 83 p.

Becker, L. E., and Droste, J. B., 1978, Late Silurian and Early Devonian sedimentologic history of southwestern Indiana: Indiana Geological Survey Occasional Paper 24, 14 p.

Buckley, E. R., and Buehler, H. A., 1904, Quarrying industry of Missouri: Missouri Bureau of Geology and Mines, 2nd Series, v. 2, 371 p.

Droste, J. B., and Shaver, R. H., 1980, Recognition of buried Silurian reefs in southwestern Indiana: Journal of Geology, v. 88, p. 567–587.

Droste, J. B., and Shaver, R. H., 1986, Bainbridge Group, 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. 9–10.

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.

Lowenstam, H. A., 1949, Niagaran reefs in Illinois and their relation to oil accumulation: Illinois State Geological Survey Report of Investigations 145, 36 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.

Ulrich, E. O., 1911, Revision of the Paleozoic systems: Geological Society of America Bulletin, v. 22, p. 281–680.