IGNIS
Ancell Group

Age:

Ordovician

Type designation:

Type locality: A composite type section was formally designated by Templeton and Willman (1963, p. 29) in the bluffs north of Ancell, between Dutchtown and Rock Levee, Missouri (Droste and Patton, 1986).

Description:

The Ancell Group of Indiana (Droste, Abdulkareem, and Patton, 1982) consists of three formations, in ascending order, these are the St. Peter Sandstone, the Dutchtown Formation, and the Joachim Dolomite (Droste and Patton, 1986). These three formations are in partial facies relationships with one another (Droste and Patton, 1986).

Distribution: On some of the highest erosion remnants along the unconformity at the top of the Knox, the Ancell rocks may be entirely missing, so that rocks of the Black River Group lie superjacent to Knox rocks (Droste and Patton, 1986). Generally the Ancell Group thickens from less than 50 ft (15 m) in northern Indiana to more than 450 ft (137 m) in southwestern Indiana (Droste and Patton, 1986). Rocks of the Ancell are present in faulted blocks in the Kentland structure in Newton County, Indiana (Gutschick, 1983; Droste and Patton, 1986).

Boundaries:

The Ancell lies with unconformity on the rocks of the Knox Supergroup as follows: in northwestern Indiana on the Potosi Dolomite (Trempealeauan), in southwestern Indiana on the Everton Dolomite (Whiterockian), and elsewhere in the state on the Prairie du Chien Group (Canadian) (Droste and Patton, 1986).

Correlations:

The Ancell Group of Indiana correlates with the Ancell Group of Illinois; with the St. Peter Sandstone and the Glenwood Formation of Michigan; with the lower part of the Black River Limestone, the Wells Creek Formation, and the St. Peter Sandstone of Ohio; and with the lower part of the High Bridge Group and the Wells Creek Dolomite of central Kentucky and the St. Peter Sandstone and the Dutchtown Formation of western Kentucky (Droste and Shaver, 1983; Shaver, 1984; Droste and Patton, 1986).

Regional Indiana usage:

Illinois Basin (COSUNA 11)
Supergroup: none
Group: Ancell Group
Illinois Basin Margin (COSUNA 12)
Supergroup: none
Group: Ancell Group
Cincinnati Arch (COSUNA 13)
Supergroup: none
Group: Ancell Group
Kankakee Arch (COSUNA 14)
Supergroup: none
Group: Ancell Group
Michigan Basin (COSUNA 15)
Supergroup: none
Group: Ancell Group

Misc/Abandoned Names:

None

Geologic Map Unit Designation:

Oa

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:

Droste, J. B., Abdulkareem, T. F., and Patton, J. B., 1982, Stratigraphy of the Ancell and Black River Groups (Ordovician) in Indiana: Indiana Geological Survey Occasional Paper 36, 15 p.

Droste, J. B., and Patton, J. B., 1986, Ancell 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. 4-5.

Droste, J. B., and Shaver, R. H., 1983, Atlas of early and middle Paleozoic paleogeography of the southern Great Lakes area: Indiana Geological Survey Special Report 32, 32 p.

Gutschick, R. C., 1983, Geology of the Kentland Dome structurally complex anomaly, northwestern Indiana (Field Trip 15), in Shaver, R. H., and Sunderman, J. A., eds., Field trips in midwestern geology: Bloomington, Indiana, Geological Society of America, Indiana Geological Survey, and Indiana University Department of Geology, v. 1., p. 105-138.

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.

Templeton, J. S., and Willman, H. B., 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.



For additional information contact:

Nancy Hasenmueller (hasenmue@indiana.edu)
Date last revised: November 22, 2016

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