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).
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).
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).
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)
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.)
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 (7th 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.
For additional information contact:
Nancy Hasenmueller (firstname.lastname@example.org)Date last revised: February 15, 2016