New Harmony Group
  

(JBD & RHS)

Ulsterian Series,

Devonian System


Type section and use of name: The name New Harmony Group was given by Becker and Droste (1978, p. 4) to the subsurface Lower Devonian rocks that are penetrated between the depths of 4,987 and 5,478 feet (4,996 and 5,480 feet on electric log) (1,521 and 1,671 m) in the Superior No. C-17 Ford well, White County, Ill. Data for this section are available in Collinson and others (1967), Schwalb (1975), and Droste and Shaver (in preparation), and samples are on file in the Indiana Geological Survey as well as elsewhere. The name is taken from New Harmony, Posey County, Ind., which is very near the Ford well and on the east bank of the Wabash River.

The group was further defined to include in generally ascending order the Grassy Knob Chert and the Backbone Limestone and the Clear Creek Chert.

Description: The New Harmony consists of two basic kinds of variably colored, mostly pale carbonate rocks: (1) very fine grained to medium-grained, sparsely cherty limestone and dolomite to almost pure chert and (2) very light colored medium- to coarse-grained high-purity bioclastic limestone and dolomite. The former are in more central Illinois Basin locations and consist of the Grassy Knob and Clear Creek Cherts, whereas the latter are the Backbone Limestone in the more basin-marginal area. Each basic facies has tongues of the other facies.

The bottom of the group in Indiana is the probably conformable contact between 20 to 30 feet (6 to 9 m) of white coarse-grained bioclastic limestone (above) and the drab fine-grained Bailey Limestone (Silurian, below). The New Harmony underlies the sandy dolomite of the Dutch Creek Sandstone Member (Jeffersonville Limestone, mostly Middle Devonian in age) or underlies Jeffersonville rocks unnamed to member where the Dutch Creek is not recognized. This contact ranges from conformable (southwestward) to unconformable (northeastward). (See Shaver and others, 1985.)

In Indiana the New Harmony Group is limited to the subsurface in an area of about eight-county size in the southwesternmost part of the state (Becker, 1974, fig. 11), where it ranges from a northeastern eroded edge to almost 900 feet in thickness in Posey County. (See Becker and Droste, 1978, fig. 4A, and Droste and Shaver, in preparation, fig. 8.)

Correlation: As of early 1985 the name New Harmony had not been used in published literature for the Illinois and Kentucky parts of the Illinois Basin, but the constituent formations are known by the same names in those states, where a fourth formation, the Flat Gap Limestone, is also recognized and may be wholly or partly equivalent of lower New Harmony rocks of Indiana. (See Shaver and others, 1985.)

Faunal data from the subsurface New Harmony are sparse but include records of a Devonian conodont species, Icriodus latericrecens huddlei (as reported by Becker, 1974, p. 24-28), that is common to the Oriskany Sandstone (Ulsterian) of New York. The bottom part of the New Harmony Group, m its extension in Illinois to include uppermost rocks of the Bailey Limestone (as defined there), contains the conodont Icriodus woschmidti, which denotes a Gedinnian age in global terms (early Ulsterian, American terms). (See Becker and Droste, 1978, p. 4-5.) These and other fossils (not recorded in Indiana, however) suggest an age range from Gedinnian to Emsian inclusive (Ulsterian).






 
 
 
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