Type section: The name “Ramp Creek Member” was given by Stockdale (1929, p. 240) to a part of his Lower Harrodsburg Limestone (Rexroad, 1986). The type section is along a stream in the NW¼NW¼ sec. 35, T. 8 N., R. 1 W., Monroe County, Indiana, but the formation is now very poorly exposed there (Rexroad, 1986).
History of usage:
The name was modified by Smith (1965) to "Ramp Creek Limestone Member" and assigned to the Muldraugh Formation (Rexroad, 1986). Still later, this unit was elevated to formation status by Nicoll and Rexroad (1975) and assigned as the lowest unit in the Sanders Group (Rexroad, 1986).
The Ramp Creek Formation is dominantly a carbonate unit consisting of interbedded very fine grained dolostone and limestone but containing small amounts of siltstone and shale (Rexroad, 1986). Chert is common to abundant, and geodes are numerous, especially in the dolostone (Rexroad, 1986). The limestone is generally coarse bioclastic calcarenite and calcirudite (Rexroad, 1986). Although the formation is known to range from 16 to 34 ft (5 to 10 m) in thickness, it is characterized by a relatively uniform thickness of about 20 to 25 ft (6 to 8 m) and tends to be even bedded (Rexroad, 1986).
The boundary between the Ramp Creek and the underlying Borden Group is marked by a sharp lithologic break and in most places by a zone of glauconite at the top of the Borden that probably represent a brief hiatus in sedimentation (Rexroad, 1986). The Harrodsburg Limestone conformably overlies the Ramp Creek (Rexroad, 1986).
Nicoll and Rexroad (1975, p. 16, 17) correlated the uppermost part of the Ramp Creek Formation with the lowermost part of the Warsaw Shale of the Mississippi Valley on the basis of the presence of conodonts of the Taphrognathus varians-Apatognathus Assemblage Zone (Rexroad, 1986). They found conodonts indicative of the Gnathodus texanus-Taphrognathus Assemblage Zone in the rest of the formation and correlated it with the upper part of the Keokuk Limestone of the Mississippi Valley (Rexroad, 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 featuers in Indiana.
Major tectonic features that affect bedrock geology in Indiana.
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.
Hirt, D. S., 1991, Mississippian brachiopod biostratigraphy and the Osagean-Meramecian boundary in south-central Indiana: Journal of Paleontology, v. 65, p. 912-916.
Lineback, J. A., 1966, Deep-water sediments adjacent to the Borden Siltstone (Mississippian) delta in southern Illinois: Illinois State Geological Survey Circular 401, 48 p.
Rexroad, C. B., 1986, Ramp Creek 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. 121-122.
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.
Stockdale, P. B., 1929, Stratigraphic units of the Harrodsburg Limestone: Indiana Academy of Science Proceedings for 1928, v. 38, p. 233-242.
For additional information contact:
Nancy Hasenmueller (email@example.com)Date last revised: April 13, 2017