IGNIS
Point Pleasant Member

Age:

Ordovician

Type designation:

Type locality: The name “Point Pleasant Beds” was originally given by Orton (1873) to 50 ft (15 m) of blue limestone interbedded with shale along the Ohio River at Cincinnati (Keith, 1986).

Reference section: In Indiana, Keith (1986) designated a reference section in the pertinent rocks cored from the bedrock surface downward in Indiana Geological Survey drill hole (SDH) 133 (Indiana Geological Survey Petroleum Database Management System No. 126872) on the Robins farm in sec. 1, T. 2 N., R. 1 W., Switzerland County. About 90 ft (27 m) of Point Pleasant rocks were penetrated (Keith, 1986). The exact thickness is unknown because an upper weathered zone of a few feet was not cored (Keith, 1986).

History of usage:

At the type locality, the base of the beds is not exposed, but they were considered by Orton to be the lowermost unit of the Cincinnati Group (Keith, 1986).

These rocks were traced into north-central Kentucky by Foerste (1906) (Keith, 1986). The unit has had a complex history in terms of its varying rank assignment, but in Kentucky along the Ohio River across from Cincinnati and Switzerland County in Indiana, it is considered as the Point Pleasant Tongue of the Clays Ferry Formation (Swadley and others, 1975; Keith, 1986). Closely corresponding rocks in Indiana, of which only about 50 ft (17.5 m) are exposed at Patriot in Switzerland County, were included in the Lexington Limestone by Gray, Brown, and Lineback (1966) (Keith, 1986). These and similar rocks in the immediate subsurface area of eastern Switzerland County were named the Point Pleasant Member of the Lexington Limestone by Keith (1986).

Description:

The Point Pleasant Member of the Lexington Limestone is the upper of two named subdivisions of the Lexington in Indiana (Keith, 1986). (See the article on the Curdsville Member.) The Point Pleasant is medium-gray fossiliferous limestone that contains thin (1.5 ft or 0.5 m, average thickness) interbeds of calcareous shale (Keith, 1986). In SDH 133 the ratio of limestone to shale is about 2 to 1 (Keith, 1986). This unit is present in Indiana only in eastern Switzerland County, where it ranges from 0 to 90 ft (27 m) in thickness (Keith, 1986). To the north in Dearborn County and to the west in western Switzerland County, the Point Pleasant is replaced through what is believed to be a facies change into an unnamed limestone unit of the Lexington that is a clean fossiliferous limestone of a thickness about equal to that of the Point Pleasant (Keith, 1986). The Point Pleasant Member bears lithologic affinity both to other Lexington rocks, which in part underlie and in part are laterally equivalent to the Point Pleasant, and to the overlying Kope Formation of the Maquoketa Group (Keith, 1986).

Correlations:

The Point Pleasant correlates with part of the Kope Formation in Indiana and, as noted above, with rocks designated by the same name in Kentucky, which are there assigned to the Clays Ferry Formation rather than to the Lexington Limestone (Keith, 1986). The Point Pleasant also correlates with the formation of the same name in southwestern Ohio (Keith, 1986).

Regional Indiana usage:

Cincinnati Arch (COSUNA 13)
Supergroup: none
Group: none
Formation: Lexington Limestone
Member: Point Pleasant Member

Misc/Abandoned Names:

None

Geologic Map Unit Designation:

Olpp

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.)

Map showing the COSUNA areas (heavy black line) that approximate regional bedrock outcrop patterns and major structural features in Indiana, and the COSUNA numbers (large bold font) for these areas. The COSUNA boundaries are limited to state and county boundaries that facilitate coding.

COSUNA areas and numbers that approximate regional bedrock outcrop patterns and major structural features in Indiana.

Map showing major tectonic features that affect bedrock geology in Indiana.

Major tectonic features that affect bedrock geology in Indiana.

References:

Foerste, A. F., 1906, The Silurian, Devonian, and Irvine formations of east-central Kentucky, with an account of their clays and limestones: Kentucky Geological Survey Bulletin 7, 369 p.

Gray, H. H., Brown, G. D., Jr., and Lineback, J. A., 1966, Physical techniques of correlation applied to Upper Ordovician rocks of southeastern Indiana [abs.]: American Association of Petroleum Geologists Bulletin, v. 40, p. 615-616.

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.

Keith, B. D., 1986, Point Pleasant 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. 116.

Orton, Edward, 1873, Report on the third geological district–geology of the Cincinnati Group and of Hamilton, Clermont, Warren, Butler, and Clarke Counties: Ohio Geological Survey Report, v. 1, pt. 1, p. 365-480.

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.

Swadley, W. C., Luft, S. J., and Gibbons, A. B., 1975, The Point Pleasant Tongue of the Clays Ferry Formation, northern Kentucky, in Cohee, G. V., and Wright, W. B., Changes in stratigraphic nomenclature by the U.S. Geological Survey: U.S. Geological Survey Bulletin 1405-A, p. A30-A31.



For additional information contact:

Nancy Hasenmueller (hasenmue@indiana.edu)
Date last revised: April 13, 2017

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