Type section: The name “Limberlost Dolomite” was originally used by Droste and Shaver (1976, p. 4) for exposures of dolostone in the Limberlost area near Geneva in Adams and Jay Counties, Indiana (Droste and Shaver, 1986). They designated the type section in the John W. Karch Stone Co. quarry 4.5 miles (7.2 km) east-southeast of Geneva, Adams County (SW¼SW¼ sec. 31, T. 25 N., R. 15 E.) (New Corydon quadrangle).
History of usage:
Change in rank: The Limberlost Dolomite Member was originally ranked as a formation by Droste and Shaver (1976, p. 4) (Droste and Shaver, 1986). In 1982, Droste and Shaver reduced the Limberlost Dolomite to member status and designated it as the bottommost unit in the Pleasant Mills Formation (Droste and Shaver, 1986).
The Limberlost is made up of several subtly different carbonate facies, the dominant one consisting of light-brown micritic to fine-grained rather pure dolostone (Droste and Shaver, 1986). Variations include fine-grained, faintly to strongly laminated and color-banded dolostone, oolitic dolostone, coarser grained bioclastic vuggy dolostone, and bluish-gray mudstone dolostone (the latter two lithologies in association with reef-flank and reef-core rocks) (Droste and Shaver, 1986).
The Limberlost is underlain by the Salamonie Dolomite and is overlain by the Waldron Member of the Pleasant Mills Formation (Droste and Shaver, 1986). Both the lower and the upper Limberlost contacts appear to be conformable, but there probably is minor unconformity in some places along the lower contact, for example, possibly in the reference-section quarry in Randolph County (Droste and Shaver, 1986).
A common late Llandoverian-middle Wenlockian (late Alexandrian-middle Niagaran) guide fossil, the brachiopod Pentamerus oblongus, is found at its highest stratigraphic range in the Limberlost (Droste and Shaver, 1986). It is followed closely above in middle Pleasant Mills and Louisville rocks by species of the pentamerid genus Rhipidium (late Wenlockian-early Ludlovian) (Droste and Shaver, 1986).
Regional Indiana usage:
Illinois Basin Margin (COSUNA 12)
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 features in Indiana.
Major tectonic features that affect bedrock geology in Indiana.
Droste, J. B., and Shaver, R. H., 1986, Limberlost Dolomite Member, 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. 79-80.
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.
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.
For additional information, contact:
Nancy Hasenmueller (email@example.com)Date last revised: June 13, 2017