Age:

Silurian

Type designation:

Type area: Foerste (1904, p. 33) used the name “Kokomo limestone” for a limestone at Kokomo, Indiana, which had previously been called the “Waterlime" (Droste and Shaver, 1986).

Type section: Cumings and Shrock (1927, p. 76) restricted the name “Kokomo limestone” to the thinly laminated limestone lying between Mississinewa shale below and a cherty limestone above, containing the brachiopod horizon (Droste and Shaver, 1986). Cumings and Shrock (1927) noted that the formation was well exposed at the quarry on West Markland Avenue in Kokomo (SW¼ sec. 36, T. 24 N., R. 3 E.) (Droste and Shaver, 1986).

Reference section: The type quarry was filled in during the 1960s, which led Shaver (1970, p. 84) to designate the Kokomo rocks cored at the edge of the quarry in Indiana Geological Survey drill hole 72 (Indiana Geological Survey Petroleum Database Management System No. 140455) in LaFountain Res., T. 24 N., R. 3 E., as the principal reference section (Droste and Shaver, 1986).

History of usage:

Change in rank: The rank of the Kokomo was reduced to that of member in the Salina Formation (Pinsak and Shaver, 1964, p. 50; Droste and Shaver, 1986).

Reassignment: The Kokomo Limestone Member was later transferred to the Wabash Formation when the latter unit was assigned to the elevated-in-rank Salina Group (Droste and Shaver, 1982, p. 21; Droste and Shaver, 1986).

Description:

The Kokomo Limestone Member characteristically consists of banded tan and gray micritic to very fine grained, thinly laminated and dolomitic limestone (Droste and Shaver, 1986). Besides the thin lamination, which may be considered as made up of couples, each consisting of a dark lamina and a light lamina, a more gross alternation of light and dark beds characterizes the Kokomo in some places (Droste and Shaver, 1986). At such places the thin lamination is pervasive through the gross couples whose separate light and dark parts are 2 to 10 ft (0.6 to 3.0 m) thick (Droste and Shaver, 1986). In addition, as many as four still larger units have been traced in the Cass County area (Tollefson, 1979).

The basis for such recognition has been, besides the gross lithology noted above, the different combinations of lesser Kokomo lithologies that consist of intraformational breccias and contorted beds (considered to represent soft-sediment deformation), algal stromatolites, cut-and-fill structures, molds of evaporate crystals, and other features generally ascribed to very shallow subtidal to intratidal environments, including environments of desiccation (Droste and Shaver, 1986). In some places macro-fossiliferous rocks are present in parts of the Kokomo and include the tabulate coral Halysites, so-called "dwarf" cephalopods of the Protokionoceras type, eurypterids, and leperditiid ostracods in coquinas (Droste and Shaver, 1986).

In the reference core, the Kokomo is about 50 ft (15 m) thick; in the type area, including Cass County, it ranges from zero to about 125 ft (38 m) in thickness, the zero being a depositional zero for a facies relationship and in the above-mentioned areas beyond the type area, reported thicknesses range from 30 to 125 ft (9 to 38 m) (Droste and Shaver, 1986).

Distribution: Distribution of the Kokomo beyond its type area in Howard County and the adjacent Cass County area is poorly understood, although various notations of Kokomo rocks in the Jasper County and Allen County areas have been made from about the turn of the century (Droste and Shaver, 1986). Pinsak and Shaver in their 1964 Salina thickness map (pl. 2) defined an approximate Kokomo distribution in the Cass County and Howard County area, but beyond that area they applied the term "Kokomo" only in Allen County (p. 79) (Droste and Shaver, 1986). More recently, the term "Kokomo" has been assigned to rocks in Marshall and Pulaski Counties in areas that are variably north and south of the Fort Wayne Bank (Droste and Shaver, 1983), but Okla (1976, p. 38) recognized the Kokomo only in the counties around the type area (Droste and Shaver, 1986). Physical continuity of the Kokomo in typical lithology among all these occurrences seems most unlikely (Droste and Shaver, 1986).

Boundaries:

As recorded especially by Droste and Shaver (1983), the Kokomo variably overlies parts of the cherty Liston Creek Limestone Member (Wabash Formation), very likely conformably or with only very minor localized unconformity, and in some places the Kokomo completely replaces the Liston Creek and rests directly on the Mississinewa Shale Member (Wabash Formation) (Droste and Shaver, 1986). In the Silurian outcrop area of central northern Indiana and in the subsurface just to the north, the Kokomo underlies either the cherty Kenneth Limestone Member (Wabash Formation) conformably or the Muscatatuck Group (Middle Devonian) unconformably (Droste and Shaver, 1986).

The Kokomo-Kenneth contact appears sharp in places but not in others, and evidence of unconformity of regional scope is lacking (Droste and Shaver, 1986). In fact, the Kokomo-Liston Creek relations (noted above) and the existence of a probable Kokomo reef facies (for example, see Indiana University Paleontology Seminar, 1980) appear to deny strongly the classic idea of the Kokomo having grossly unconformable relations with the reef-bearing rock units that include without doubt all the other members of the Wabash Formation (Droste and Shaver, 1986).

Correlations:

Within the Wabash Formation, the Kokomo correlates, variably, with part of or nearly the whole of the Liston Creek Member (Droste and Shaver, 1986). In recent years it has been correlated with other rocks of the Salina Group in stratigraphically high positions, as high as the E unit of the Michigan and Appalachian Basins and higher (Droste and Shaver, 1986). Much confusion has attended past correlations, however, beginning with correlation with the Lower Devonian Waterlime Beds (so-called) of New York during the period on either side of 1900 (Droste and Shaver, 1986). The problem was one of commonality of the thinly laminated eurypterid-bearing beds and one of lack of normal-marine index fossils (Droste and Shaver, 1986). This problem continued as late as the time of publication of the 1956 bedrock-geology map of Indiana (Patton, 1956), and Pinsak and Shaver's (1964) and Okla's (1976) correlations possibly involve rocks that Droste and Shaver (1983) and Tollefson (1979) assigned to a pre-Mississinewa position as well as to a post-Mississinewa position (Droste and Shaver, 1986). Further, the Kokomo correlates, as do Liston Creek rocks, with much of the Bailey Limestone of the Illinois Basin (Droste and Shaver, 1986). The type Kokomo as well as some other parts of the Kokomo are known to underlie the Kenneth Limestone Member (Wabash Formation), whose brachiopods, conodonts, and ostracods collectively require a rather Late Silurian age assignment (Droste and Shaver, 1986). Moreover, conodonts identified as Spathognathodus eosteinhornensis and S. snajdri have been found in the Kokomo itself (Pollock and Rexroad, 1973; Droste and Shaver, 1986). For all these reasons, the Kokomo was assigned a latest Ludlovian to early Pridolian (middle Cayugan) age by Shaver (1984) (Droste and Shaver, 1986).

Economic Importance:

Industrial Minerals: Crushed stone products from the Kokomo Limestone Member (Silurian) include the following: aglime, crushed stone, dolomite, flagstone, limestone, riprap, screenings, and shot rock from quarries in Cass, Howard, and Miami Counties (Shaffer, 2016).

Regional Indiana usage:

Kankakee Arch (COSUNA 14)
Supergroup: none
Group: Salina Group
Formation: Wabash Formation
Member: Kokomo Limestone Member
Michigan Basin (COSUNA 15)
Supergroup: none
Group: Salina Group
Formation: Wabash Formation
Member: Kokomo Limestone Member

Misc/Abandoned Names:

Eurypterid Beds, Lower Helderberg, Lower Waterlime, Waterlime

Geologic Map Unit Designation:

Swkk

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:

Cumings, E. R., and Shrock, R. R., 1927, The Silurian coral reefs of northern Indiana and their associated strata: Indiana Academy of Science Proceedings, v. 36, p. 71–85.

Droste, J. B., and Shaver, R. H., 1982, The Salina Group (Middle and Upper Silurian) of Indiana: Indiana Geological Survey Special Report 24, 41 p.

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.

Droste, J. B., and Shaver, R. H., 1986, Kokomo Limestone 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. 70–72.

Foerste, A. F., 1904, The Silurian of northern Indiana, in Hopkins, T. C., A short description of the topography of Indiana, and of the rocks of the different geological periods to accompany the geological map of the state: Indiana Department of Geology and Natural Resources Annual Report 28, p. 33–39.

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.

Indiana University Paleontology Seminar, 1980, Stratigraphy, structure, and zonation of large Silurian reef at Delphi, Indiana: American Association of Petroleum Geologists Bulletin, v. 64, p. 115–131.

Okla, S. M., 1976, Subsurface stratigraphy and sedimentation of Middle and Upper Silurian rocks of northern Indiana: Bloomington, Indiana University, Ph.D. thesis, 153 p.

Patton, J. B., 1956, Geologic map of Indiana: Indiana Geological Survey Atlas of Mineral Resources of Indiana Map No. 9, scale 1:1,000,000.

Pinsak, A. P., and Shaver, R. H., 1964, The Silurian formations of northern Indiana: Indiana Geological Survey Bulletin 32, 87 p.

Pollock, C. A., and Rexroad, C. B., 1973, Conodonts from the Salina Formation and the upper part of the Wabash Formation (Silurian) in north-central Indiana: Geologica et Palaeontologica, v. 7, p. 77–92.

Shaffer, K. R., compiler, 2016, Directory of industrial mineral producers in Indiana: Indiana Geological Survey Directory 11-2016, 287 p.

Shaver, R. H., 1970, Kokomo Limestone 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. 84–85.

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.

Tollefson, L. J. S., 1979, Paleoenvironmental analysis of the Kokomo and Kenneth Limestone Members of the Salina Formation in the vicinity of Logansport, Indiana: Urbana, University of Illinois, master's thesis, 173 p.