Age:

Ordovician

Type designation:

Type section: The St. Peter Sandstone was named by Owen (1847, p. 169-170) for the exposures along the river then called St. Peter (now the Minnesota River) in southern Minnesota (Gray, 1970; Droste, Patton, and Rexroad, 1986). A St. Peter type section was later designated (Stauffer, 1934) as the exposures in the bluff at the junction of the Minnesota and Mississippi Rivers (Droste, Patton, and Rexroad, 1986).

Description:

Generally the St. Peter Sandstone in Indiana is composed of fine to medium well-rounded and well-sorted frosted grains of quartz that are weakly cemented (Droste, Abdulkareem, and Patton, 1982; Droste, Patton, and Rexroad, 1986). In some places secondary quartz overgrowth and siliceous intergranular cement have resulted in well-indurated rather than friable sandstone (Droste, Patton, and Rexroad, 1986). In some southern Indiana localities the St. Peter has carbonate cement and thin interbeds of carbonate rocks, generally dolostone (Droste, Patton, and Rexroad, 1986).

Generally the thickness of the St. Peter ranges from 0 foot at its depositional limit to about 140 ft (43 m) (Droste, Patton, and Rexroad, 1986). Sharp differences in thickness over a few tens of miles are the result of moderate relief developed along the unconformity on the subjacent Knox rocks and of facies changes from St. Peter rocks to Dutchtown or Joachim rocks within short distances (Droste, Patton, and Rexroad, 1986). Within the continuous body of the St. Peter, abruptly increased thickening over short distances is also known but not well understood (Droste, Patton, and Rexroad, 1986). For example, in a square mile (2.6 km2) (sec. 6, T. 31 N., R. 7 W., Jasper County, Indiana) the sandstone increases from 60 to 335 ft (18 to 102 m) in thickness as evidenced by two wells (Droste, Patton, and Rexroad, 1986).

Distribution: The St. Peter in Indiana is restricted to the subsurface in the western half of the state except for the chaotic structure exposed in the Kentland structure in Newton County, Indiana (Gutschick, 1983).

Boundaries:

The lower part of the St. Peter Sandstone interfingers with the Dutchtown Formation (Droste, Patton, and Rexroad, 1986). The upper St. Peter grades laterally into the Joachim Dolomite, which is Blackriverian in age. In only one well in northwestern Indiana is the St. Peter known to constitute the entire Ancell Group (Droste, Patton, and Rexroad, 1986). In that well the St. Peter is overlain, probably unconformably, by the Pecatonica Formation of the Black River Group (Droste, Patton, and Rexroad, 1986). Elsewhere in Indiana the St. Peter is overlain conformably by either the Dutchtown Formation or the Joachim Dolomite (Droste, Patton, and Rexroad, 1986). The St. Peter overlies unconformably the Everton Dolomite in southwestern Indiana and the Shakopee Dolomite, the Oneota Dolomite, or the Potosi Dolomite elsewhere in the state (Droste, Patton, and Rexroad, 1986).

Correlations:

The St. Peter Sandstone of Indiana correlates generally with the St. Peter Sandstone of Illinois, Michigan, Ohio, and Kentucky (Droste, Patton, and Rexroad, 1986). Its lower part is known to be Chazyan in age because of its conodonts that are closely similar to those from the Dutchtown Formation in its type locality in Missouri (Rexroad, Droste, and Ethington, 1982; Repetski, 1973) and from the lower part of the Wells Creek Dolomite in the subsurface of eastern Tennessee (Votaw and Repetski, 1982; Droste, Patton, and Rexroad, 1986). The conodonts of this lower part of the St. Peter represent parts of faunas 5 and 6 of Sweet, Ethington, and Barnes (1971). The upper part of the formation is probably Blackriverian in age (Droste, Patton, and Rexroad, 1986).

Regional Indiana usage:

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

Misc/Abandoned Names:

None

Geologic Map Unit Designation:

Osp

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:

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., Patton, J. B., and Rexroad, C. B., 1986, St. Peter Sandstone, 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. 127–128.

Gray, H. H., 1970, St. Peter Sandstone, 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. 148–149.

Gutschick, R. C., 1983, Geology of the Kentland Dome structurally complex anomaly–northwestern Indiana (Field Trip 5), 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 (7^th ed.): Washington, D.C., U.S. Geological Survey, 289 p.

Owen, D. D., 1847, Preliminary report of the geological survey of Wisconsin and Iowa: U.S. Gen. Land Office Report, 1847, p. 160–173.

Repetski, J. E., 1973, The conodont fauna of the Dutchtown Formation (Middle Ordovician) of southeast Missouri: Columbia, University of Missouri, master's thesis, 182 p.

Rexroad, C. B., Droste, J. B., and Ethington, R. L., 1982, Conodonts from the Everton Dolomite and the St. Peter Sandstone (lower Middle Ordovician) in a core from southwestern Indiana: Indiana Geological Survey Occasional Paper 39, 13 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.

Stauffer, C. R., 1934, Type Paleozoic sections in the Minnesota Valley: Journal of Geology, v. 42, p. 337–357.

Sweet, W. C., Ethington, R. L., and Barnes, C. R., 1971, North American Middle and Upper Ordovician conodont faunas: Geological Society of America Memoirs 127, p. 163–193.

Votaw, R. B., and Repetski, J. E., 1982, Conodonts from the Stones River Group (Middle Ordovician) of the central basin of Tennessee [abs.]: Geological Society of America Abstracts with Programs, v. 14, p. 291.