Age:

Devonian

Type designation:

Type section: Campbell (1946, p. 845) noted that the type section of the “Blocher formation” was 1.5 miles (2.4 km) southeast of Blocher, Indiana, 1 mile (1.6 km) east of the Baltimore and Ohio Railroad, on Indiana Highway 56 (SE¼SW¼SW¼ sec. 9, T. 3 N., R. 8 E., Jefferson County, Blocher quadrangle [Lineback, 1968, 1970]).

History of usage:

Named: The name “Blocher formation” was first used by Campbell (1946, p. 840) for the brownish-black, slightly calcareous shale in the basal part of the New Albany Shale in the outcrop area in southeastern Indiana (Burger, 1970; Hasenmueller, 1986).

Revised contact: Murray and others, (1955, p. 43) noted that the Indiana Geological Survey uses the term "Blocher" with the rank of member.

Revised contact: The unit was redefined by Lineback (1968, 1970) to include the section up to the base of the Spathiocaris Zone of the Blackiston Formation of Campbell, which is now recognized as the Selmier Member of the New Albany Shale (Hasenmueller, 1986).

Description:

The Blocher Member of the New Albany Shale is a brownish-black to grayish-black, slightly calcareous fissile pyritic shale, which is light gray and has brown and yellow stains on weathered surfaces (Hasenmueller, 1986). Beds of dolostone, dolomitic sandstone, and gray shale are present in places, and a brownish-black calcareous mudstone is present in the basal part of the member in central Indiana (Hasenmueller, 1986). In surface exposures the Blocher Member ranges from 3 to 15 ft (0.9 to 4.6 m) in thickness. The Blocher is thinnest at Lexington, Scott County (Lineback, 1970), and reaches its maximum thickness of 67 ft (20 m) in Posey County (Hasenmueller and Bassett, 1981) (Hasenmueller, 1986).

Distribution: The Blocher Member is widely recognizable in the southeastern Indiana outcrop area and in the subsurface (Hasenmueller, 1986).

Boundaries:

The Blocher Member is overlain by the Selmier Member of the New Albany Shale. It overlies the North Vernon Limestone both conformably and unconformably (Droste and Shaver, 1986, p. 105.)

Correlations:

The Blocher Member of Indiana is correlative with the Blocher Shale mapped by North (1969, fig. 20) in Illinois, the Blocher Shale and the lower part of the Selmier Shale mapped by Cluff and others (1981) in Illinois, and the Blocher Member of the New Albany Shale mapped by Schwalb and Norris (1980) in western Kentucky (Hasenmueller and Bassett, 1981) (Hasenmueller, 1986). In Illinois evidence from geophysical logs and sample studies indicates that the lower part of the Blocher grades laterally into the upper part of the Lingle Formation in a westerly direction (North, 1969) (Hasenmueller, 1986). The Blocher Member is equivalent to the lower part of the Antrim Shale of the Michigan Basin and to the lower part of the Dowelltown Member of the Chattanooga Shale of Tennessee (Hasenmueller, 1986). Conodonts from the Blocher are indicative of the doI division of the German Devonian standard (Hasenmueller, 1986). (See Lineback, 1970; Hasenmueller and Bassett, 1981.) Based on the conodont fauna, Norby and Ettensohn (1992) noted that the Blocher, at its type section, contained the middle varcus subzone (middle Givetian) through at least the early falsiovalis zone (early Frasnian).

Regional Indiana usage:

Illinois Basin (COSUNA 11)
Supergroup: none
Group: none
Formation: New Albany Shale
Member: Blocher Member
Illinois Basin Margin (COSUNA 12)
Supergroup: none
Group: none
Formation: New Albany Shale
Member: Blocher Member
Cincinnati Arch (COSUNA 13)
Supergroup: none
Group: none
Formation: New Albany Shale
Member: Blocher Member
Kankakee Arch (COSUNA 14)
Supergroup: none
Group: none
Formation: New Albany Shale
Member: Blocher Member

Misc/Abandoned Names:

None

Geologic Map Unit Designation:

Dnab

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:

Burger, A. M., 1970, Blocher Member, in Shaver, R. H., Burger, A. M., Gates, G. R., Gray, H. H., Hutchison, H. C., Keller, S. J., Patton, J. B., Rexroad, C. B., Smith, N. M., Wayne, W. J., and Wier, C. E., Compendium of rock-unit stratigraphy in Indiana: Indiana Geological Survey Bulletin 43, p. 16–17.

Campbell, Guy, 1946, New Albany Shale: Geological Society of America Bulletin, v. 57, p. 829–908.

Cluff, R. M., Reinbold, M. L., and Lineback, J. A., 1981, The New Albany Shale Group of Illinois: Illinois State Geological Survey Circular 518, 83 p.

Droste, J. B., and Shaver, R. H., 1986, North Vernon Limestone, 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. 103–105.

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.

Hasenmueller, N. R., 1986, Blocher 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. 15.

Hasenmueller, N. R., and Bassett, J. L., 1981, Stratigraphy, in Hasenmueller, N. R., and Woodard, G. S., eds., Studies of the New Albany Shale (Devonian and Mississippian) and equivalent strata in Indiana: Indiana Geological Survey, p. 5–32.

Lineback, J. A., 1968, Subdivisions and depositional environments of New Albany Shale (Devonian-Mississippian) in Indiana: American Association of Petroleum Geologists Bulletin, v. 52, p. 1,291–1,303.

Lineback, J. A., 1970, Stratigraphy of the New Albany Shale in Indiana: Indiana Geological Survey Bulletin 44, 73 p.

Murray, H. H., compiler, with contributions by Dawson, T. A., Leininger, R. K., McGregor, D. J., Murray, H. H., Patton, J. B., and Wayne, W. J., 1955, Sedimentation and stratigraphy of the Devonian rocks of southeastern Indiana: Indiana Geological Survey Guidebook 8, 73 p.

Norby, R. D., and Ettensohn, F. R., 1992, Stratigraphy and biostratigraphy of the New Albany Shale (Devonian-Mississippian) in the Illinois Basin: American Association of Petroleum Geologists Bulletin, v. 76, no. 8, p. 1282; American Association of Petroleum Geologist Search and Discovery Article #91013©1992, http://www.searchanddiscovery.com/abstracts/html/1992/eastern/abstracts/1282c.htm, date accessed, June 20, 2017.

North, W. G., 1969, The Middle Devonian strata of southern Illinois: Illinois State Geological Survey Circular 441, 48 p.

Schwalb, H. R., and Norris, Ronald, 1980, Isopach map of Blocher Member of New Albany Shale, western Kentucky: Morgantown, W. Va., U.S. Department of Energy, Morgantown Energy Technology Center, METC\EGSP Series No. 902 [1981].

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.