IGNIS
Vernon Fork Member

Age:

Devonian

Type designation:

Type section: The name “Vernon Fork Member” was given by Droste and Shaver (1975, p. 404-406) to the rocks often called the laminated beds, Laminated Zone, chalk beds, or fine-grained dolomite of the Jeffersonville Limestone (Droste and Shaver, 1986). The type area was designated as the area near Vernon and North Vernon along Vernon Fork of the Muscatatuck River, Jennings County, Indiana (Droste and Shaver, 1986). (Butlerville quadrangle).

Principal reference section: Droste and Shaver (1975) designated a principal reference section in the Berry Materials Corp. quarry (now named the North Vernon Quarry) at the north edge of North Vernon (NE¼ sec. 34, T. 7 N., R. 8 E.) (Droste and Shaver, 1986). At this reference section the Vernon Fork Member, containing the Tioga Bentonite Bed, is 17 ft (5 m) thick and lies between the Paraspirifer acuminatus Zone (above) and the Amphipora Zone (below) of the Jeffersonville; the top of the Geneva Dolomite Member is about 6 ft (1.8 m) farther down (Droste and Shaver, 1986). At the same time the Pendleton Sandstone Bed was assigned to the Vernon Fork (Droste and Shaver, 1986).

Description:

View description from:
Compendium of Paleozoic Rock-Unit
Stratigraphy in Indiana
(1986)

Regional Indiana usage:

Illinois Basin (COSUNA 11)
Supergroup: none
Group: Muscatatuck Group
Formation: Jeffersonville Limestone
Member: Vernon Fork Member
Illinois Basin Margin (COSUNA 12)
Supergroup: none
Group: Muscatatuck Group
Formation: Jeffersonville Limestone
Member: Vernon Fork Member
Cincinnati Arch (COSUNA 13)
Supergroup: none
Group: Muscatatuck Group
Formation: Jeffersonville Limestone
Member: Vernon Fork Member
Kankakee Arch (COSUNA 14)
Supergroup: none
Group: Muscatatuck Group
Formation: Jeffersonville Limestone
Member: Vernon Fork Member

Misc/Abandoned Names:

chalk beds, fine-grained dolostone of the Jeffersonville Limestone, laminated beds, Laminated Zone

Geologic Map Unit Designation:

Djv

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:

Conkin, J. E., and Conkin, B. M., 1979, Selected glossary of eastern North American Devonian stratigraphy, pyroclastics, bone beds, disconformities, and correlation: Louisville, Ky., University of Louisville Studies in Paleontology and Stratigraphy 9, 32 p.

Droste, J. B., and Shaver, R. H., 1975, The Jeffersonville Limestone (Middle Devonian) of Indiana—stratigraphy, sedimentation, and relation to Silurian reef-bearing rocks: American Association of Petroleum Geologists Bulletin, v. 59, p. 393-412.

Droste, J. B., Shaver, R. H., 1986, Vernon Fork 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. 160-162.

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 (hasenmue@indiana.edu)
Date last revised: August 6, 2013

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