IGNIS
Cataract Formation

Age:

Silurian

Type designation:

Type locality: The Cataract Formation was named by Schuchert (1913) for a part of what was commonly called the Medina Sandstone at Niagara Falls (Rexroad, 1986).

History of usage:

Extension and rank revision: Rexroad (1980) introduced the name “Cataract Formation” for usage in the northeastern part of Indiana, which is a marginal part of the Michigan Basin. The Cataract was reduced to formational rank, and the other named units were considered to be members (Rexroad, 1980).

Description:

Where it is undivided, the Cataract Formation is generally a dolostone that is more impure and argillaceous in its middle and upper parts (Rexroad, 1986). The Cataract Formation in Indiana consists of, in ascending order, the Manitoulin Dolomite, Cabot Head, and Stroh Members (Rexroad, 1980). The dolostones of the Manitoulin are variable; above them the Cabot Head is a mixture of shale and argillaceous dolostone that generally has a greenish cast (Rexroad, 1986). Similarly, the overlying Stroh Member consists of argillaceous dolostone and shale (Rexroad, 1986). The dolostone tends to be gray or tannish gray but commonly has a greenish cast, and the shale is commonly green (Rexroad, 1986). The thickest Cataract, slightly more than 100 ft (30 m), is in the extreme northeast corner of the state, and the thinnest, somewhat less than 10 ft (3 m), is along the axis of the Madison Trend (Rexroad, 1980), a north-southward-trending, structurally high feature in eastern northern Indiana. In Indiana, the three members can be recognized only north of Adams County, and so the Cataract Formation is undivided as to member in its southernmost extent (Rexroad, 1986).

Correlations:

The Manitoulin and the Cabot Head of Indiana are continuous with the same named units in Michigan, and the Stroh part is continuous with the Clinton Group (undifferentiated) of Michigan (Rexroad, 1986). The upper Cataract (Stroh Member) to the south and the west is in a facies relationship with the basal beds of the Salamonie Dolomite (Rexroad, 1986). The middle Cataract member (Cabot Head) pinches out to the south and the west, although in part it is in a facies relationship with the underlying lower member (Manitoulin), which in turn is in a facies relationship with the Brassfield Limestone to the south and the Sexton Creek Limestone to the west (Rexroad, 1986). The lower and middle Cataract rocks (Manitoulin and Cabot Head) contain conodonts of the Distomodus kentuckyensis Assemblage Zone of generally middle Llandoverian age, and the upper member (Stroh) has conodonts representative of the upper part of the Pterospathodus amorphognathoides-KockelelIa ranuliformis Assemblage Zone and is of early Wenlockian age (Rexroad, 1980).

Regional Indiana usage:

Kankakee Arch (COSUNA 14)
Supergroup: none
Group: none
Formation: Cataract Formation
Michigan Basin (COSUNA 15)
Supergroup: none
Group: none
Formation: Cataract Formation

Misc/Abandoned Names:

None

Geologic Map Unit Designation:

Sc

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:

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.

Rexroad, C. B., 1980, Stratigraphy and conodont paleontology of the Cataract Formation and the Salamonie Dolomite (Silurian) in northeastern Indiana: Indiana Geological Survey Bulletin 58, 83 p.

Rexroad, C. B., 1986, Cataract 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. 27-28.

Schuchert, Charles, 1913, The Cataract; a new formation at the base of the Siluric in Ontario and New York: Geological Society of America Bulletin, v. 24, p. 107.

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: February 12, 2016

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