Pendleton Sandstone Bed
  

Vernon Fork Member,

Devonian System


Type section and history of name: The Pendleton Sandstone was named by Cox (1869, p. 7) for Pendleton, Madison County, Ind., where a friable white sandstone, as much as 15 feet (4.6 m) thick, was exposed at the falls of Fall Creek in sec. 16, T. 18 N., R. 7 E. Damming of the creek and mining the sand apparently have obscured the exposure. According to Orr and Pierce (1973, p. 326-329), a type section was not originally designated, and in their later designation of a type section (center S2SW¼ sec. 16, T. 18 N., R 7 E., at the falls of Fall Creek in Fall Park, north edge of Pendleton) 7.6 feet (2.3 m) of the Pendleton Sandstone was described as lying conformably below the Jeffersonville Limestone (Devonian) and disconformably above the Wabash Formation (Silurian). The term, at formation rank, had sporadic use in many Indiana reports before the time of Orr and Pierce, who also assigned formation rank, and in 1975 it was assigned the rank of bed in the Vernon Fork Member of the Jeffersonville Limestone (Droste and Shaver, 1975a, p. 405-406) .

Description: At the type section the Pendleton Sandstone Bed consists of white and varicolored fine-grained well-sorted calcareous sandstone that is fairly pure but that is partly ferruginous, laminated, and fossiliferous (Orr and Pierce, 1973, p. 328-329). Early reports refer to a conglomerate in its upper part, but Orr and Pierce suspected that these reports actually referred to blocks of concrete.

Although Devonian sand is very common, such concentrations of sand as in the Pendleton are rare at the bottom of or within Middle Devonian rocks in central Indiana the Pendleton concentration grades both vertically and laterally into pale-colored fine-grained to micritic sandy to sparsely sandy and sand-free dolomites. Pendleton recognition becomes, therefore, very much a subjective matter, and its distribution should be considered as spotty at best and in thicknesses less than that of the type section.

At its type section the Pendleton disconformably overlies Silurian rocks (Cox, 1869) that were identified as the Mississinewa Shale Member (lower part of the Wabash Formation) by Burger and Patton (1970, p. 129) and simply as the Wabash by Orr and Pierce (197.8), who identified reworked Silurian conodonts of Ludlovian age in the Pendleton. The Pendleton type section, however, is very near the northern limit of distribution of the Geneva Dolomite Member (Jeffersonville Limestone) (Becker, 1974, fig. 14), and Droste and Shaver (1975a, fig. 4) considered the Pendleton southward from its type section to be stratigraphically above the Geneva, that is, to be one and the same with sandy basal Vernon Fork rocks where these rocks are high in sand content. The lower Pendleton contact is a conformable one, therefore, wherever this bed occurs in central Indiana south of Madison County. The Pendleton is overlain conformably by fine-grained Vernon Fork dolomites that are unnamed at bed rank. A part of these observations are contrary to the opinions of Orr and Pierce (1978, p. 829), who recommended that the Pendleton be so identified wherever arenaceous carbonate rocks appear at the base of Middle Devonian rocks, whether the base be identified as the Geneva Dolomite Member or the Jeffersonville proper.

The discussion above suggests questionable status for the Pendleton. Considering its type-section relations and the position as-signed by Orr and Pierce (1978) and Droste and Shaver (1975a), it is both within the Jeffersonville and at its base. Because the Geneva is considered to be facies of other lower Jeffersonville rocks, including the Vernon Fork in part, the Pendleton, as defined most lately, may be diachronous at best, if not also totally separated within itself in more than one stratigraphic position. To assure consistency, short of new definition, the Pendleton should be considered as restricted to areas south and west of the Kankakee and Cincinnati Arches, that is, primarily to the area of Geneva distribution. Otherwise, confusion with sands as old as earliest Middle Devonian or late Early Devonian in the Illinois and Michigan Basins would result (for example, with the Dutch Creek Sandstone Member and with the Sylvania Sandstone equivalent, which has been identified only tentatively in far northern Indiana).

Correlation: Although some reports (for example, Hall, 1879a, p. 60, and Ells, 1958, p. 16), partly on the basis of faunal evidence, correlated the Pendleton with Lower Devonian rocks of New York (Schoharie Grit) and Michigan (Garden Island Formation), some other reports have not. For example, Sutton (1944) correlated the Pendleton with basal Jeffersonville and Geneva rocks, that is, with what is called elsewhere in this compendium the Dutch Creek Sandstone Member; Orr and Pierce (1973) agreed; Fagerstrom (1971, p. 69) doubted that the Pendleton fauna permitted precise correlation; and as already noted Droste and Shaver assigned the Pendleton a position mostly within the Jeffersonville and above the Geneva (middle Eifelian).

Because sand is so common within or at the base of several Middle Devonian rock units, whether or not these units are basalmost in the local Devonian section, many of the older reports of Pendleton and Pendleton-correlative rocks must be individually appraised.






 
 
 
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