Age:

Devonian

Type designation:

Type section: The Milan Center Dolomite Member was named for the middle Detroit River dolostone that is exposed in the Woodburn Quarry of May Stone and Sand, Inc., and that was cut in Indiana Geological Survey drill hole 188 (Indiana Geological Survey Petroleum Database Management System [PDMS] No. 133650 and Core File No. 452), eastern Allen County, Indiana (NE¼ sec. 23, T. 31 N., R. 14 E.) (Doheny, Droste, and Shaver, 1975, p. 28-30; Droste and Shaver, 1986).

Reference section: A principal reference section consists of the pertinent rocks cored in the Northern Indiana Public Service Co. August Taelman No. 1 well (Indiana Geological Survey PDMS No. 142195 and Core File No. 483), LaPorte County, Indiana (NE¼ sec. 16, T. 36 N., R. 1 W.) (Doheny, Droste, and Shaver, 1975, p. 29; Droste and Shaver, 1986).

History of usage:

The name was taken from Milan Center Township, in which the Woodburn Quarry is located (Doheny, Droste, and Shaver, 1975, p. 28-30; Droste and Shaver, 1986).

Description:

The Milan Center is dominantly a rich brown granular, finely vuggy dolostone that is a replacement of pelletoidal, oolitic, and bioclastic rocks that have been termed grainstones, packstones, and boundstones (Droste and Shaver, 1986). In areas of greatest thickness, a gray-yellow cherty dolostone is at the top of the member (Droste and Shaver, 1986).

The Tioga Bentonite Bed, consisting of an inch to a few inches (0.03 to 0.15 m) of metabentonite, is found in the Milan Center in a part of its distribution (Droste and Shaver, 1986).

Distribution: The greater distribution of the Milan Center is in northwestern Indiana, where it thickens from an erosional zero in the Lake County and Pulaski County areas to more than 40 ft (12 m) in St. Joseph County, but over most of northeastern Indiana the thickness ranges from zero (nondepositional?) to a few feet (Doheny, Droste, and Shaver, 1975, pl. 2D; Droste and Shaver, 1986). This eastward decrease in thickness is facies controlled; as the Milan Center thins, the underlying Grover Ditch thickens (Droste and Shaver, 1986).

Boundaries:

The Milan Center rests conformably on the Grover Ditch Member of the same formation and is generally overlain conformably by the Cranberry Marsh Member (Droste and Shaver, 1986). In two places, however, it is overlain unconformably by the Traverse Formation (Middle Devonian) in an overlapping manner (Droste and Shaver, 1986). One place is along the southward eroded limit of Detroit River rocks, and the other is in part of Noble County where the Cranberry Marsh Member apparently was not deposited (Droste and Shaver, 1986).

Correlations:

Index fossils have not been recovered from the Milan Center, but because the Milan Center is mostly a facies of the Grover Ditch and because the Tioga bentonite occurs in the topmost Milan Center rocks in part of northern Indiana, much of the Grover Ditch correlation can be applied to the Milan Center (Droste and Shaver, 1986). The Milan Center member is Eifelian in age (early Erian, North American standard) (Droste and Shaver, 1986). The greatest age for the Grover Ditch (possibly Emsian) does not apply, however, to the Milan Center (Droste and Shaver, 1986).

Regional Indiana usage:

Kankakee Arch (COSUNA 14)
Supergroup: none
Group: Muscatatuck Group
Formation: Detroit River Formation
Member: Milan Center Dolomite Member
Michigan Basin (COSUNA 15)
Supergroup: none
Group: Muscatatuck Group
Formation: Detroit River Formation
Member: Milan Center Dolomite Member

Misc/Abandoned Names:

None

Geologic Map Unit Designation:

Ddrmc

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 features in Indiana.

Major tectonic features that affect bedrock geology in Indiana.

References:

Doheny, E. J., Droste, J. B., and Shaver, R. H., 1975, Stratigraphy of the Detroit River Formation (Middle Devonian) of northern Indiana: Indiana Geological Survey Bulletin 53, 86 p.

Droste, J. B., and Shaver, R. H., 1986, Milan Center Dolomite 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. 92.

Hansen, W. R., 1991, Suggestions to authors of the reports of the United States Geological Survey (7^th 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.