Difference between revisions of "Sellers Limestone Bed"
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Revision as of 21:52, 23 July 2018
Nelson, W.J., 2018, Pennsylvanian Subsystem in Illinois. Edited and figures drafted by Jennifer M. Obrad. Illinois State Geological Survey Bulletin (in press).
Cox (1875, p. 205) was the first to describe “blue argillaceous shales, with numerous bands of carbonate of iron” containing marine invertebrate fossils, exposed along the Ohio River 0.5 mi (0.8 km) below Sellers’ paper mill. Wanless (1939, p. 36, 101) was apparently the first to use the name “Sellers limestone.”
The name refers to the vanished community of Sellers Landing on the Ohio River in Hardin County, Illinois (Figure 2-1). G. Eschol Sellers settled here in 1850 and operated a paper mill, coal mines, and a shipping terminal on the river (Sneed 1977). Cox (1875, p. 205, footnote) mentioned walking out some of the outcrops in the company of G.E. Sellers.
The Sellers locality was long known as one of the few sites where marine fossils could be found in the Caseyville. Until 1960, geologists referred loosely and informally to the Sellers limestone or marine zone. Seeking to formalize all Pennsylvanian nomenclature in Illinois, Kosanke et al. (1960) designated this the Sellers Limestone Member of the Caseyville Formation. However, given that the Sellers Limestone has never been identified away from its type locality, the rank of the unit is hereby reduced to Sellers Limestone Bed.
The type section is on the west bluff of the Ohio River about 0.5 mi (0.8 km) south of Sellers Landing in the SE¼ NE¼ SE¼ of Sec. 21, T11S, R10E, Hardin County, on the Dekoven 7.5-minute quadrangle. Various geologists have provided slightly different coordinates. Those given by H.R. Wanless in field notes dated 1938 appear to be the most accurate.
Given that the stratotype is the only known exposure, all the authors cited here described aspects of the section. A composite section (Figure 2-6) represents my attempt to consolidate the various published and unpublished descriptions.
No exposures other than the type are known to exist.
As shown in the Caseyville type section by Lee (1916), the Sellers Limestone is roughly midway between the Pounds and Battery Rock Sandstones and is above the Gentry Coal (formerly Battery Rock coal) (Figure 2-2, column 1). A more detailed composite section assembled from published text and unpublished field notes places the Sellers in the lower part of an upward-coarsening sequence approximately 70 to 80 ft (21 to 24 m) thick (Figure 2-6). At least two thin, unnamed coal seams and the associated underclay are at the base of the sequence. The limestone itself changes dramatically across a small gully on the bluff face. On the north side, the limestone forms a channel-shaped deposit and is at least 8 ft (2.4 m) thick. South of the gully, the Sellers is reduced to thin, tabular limestone and ironstone layers within dark gray shale.
Extent and thickness
The Sellers Limestone is known only at the type locality, where the thickness ranges from about 2 to 13 ft (0.6 to 3.9 m), including limestone and interbedded shale (Figure 2-6).
The most detailed description is that of Fraunfelter (1979), who indicated that the unit varies from a ledge of limestone about 8 ft (2.4 m) thick to a 10-ft (3.1-m) interval of gray shale having numerous thin interbeds of limestone and calcareous siltstone. Where the limestone is an 8-ft (2.4-m) ledge, it is medium gray, silty biomicrite (wackestone), slightly argillaceous and fossiliferous, “with randomly distributed whole to partly broken fossils or lenses of worn and broken fossils” (Figure 2-4, p. 75). Where the Sellers is mostly shale, the limestone beds are a few inches thick, medium to dark bluish-gray biomicrite (lime mudstone) containing “whole or partly broken, randomly distributed marine fossils or lenses of fossil ‘hash’” (Figure 2-4, p. 75). Near the top of the interval, the carbonates grade to calcareous siltstone lacking fossils.
As described, the contacts vary from sharp to gradational and show rapid lateral variation.
Well log characteristics
No boreholes are known to penetrate this unit.
Cox (1875) reported brachiopods, pelecypods, gastropods, and corals. Wanless (1939, p. 36) remarked that the Sellers yielded “nearly 100 species of marine invertebrates.” Unfortunately, no faunal list is known to exist. Fraunfelter (1979) observed gastropods, trilobites, pelecypods, blastoids, and shark’s teeth. Rexroad and Merrill (1985) described a conodont fauna.
Age and correlation
Rexroad and Merrill (1985, p. 49) are the only authors who brought fossil evidence to bear on correlation of the Sellers. They observed “evolutionary continuity” in conodonts from the Grove Church Member of the Kinkaid Formation (Mississippian) through several outcrops of the Wayside Member in Johnson and Union Counties, Illinois, to the Sellers Limestone, representing the most advanced forms. These authors did not discuss correlations outside southern Illinois or place any units into a regional chronostratigraphic framework. Many advances have been made in Pennsylvanian conodont biostratigraphy since 1985, so the potential exists for more precise regional and global correlation of the Sellers.
Environments of deposition
The relationships depicted in the composite section (Figure 2-6) suggest that the Sellers is an estuarine deposit resulting from marine flooding of an incised valley. The cross-bedded sandstone near the base of the section may be lowstand fluvial sediment topped by soil horizons and thin peat layers. Upon transgression, the valley was flooded sufficiently to permit carbonate precipitation and a diverse marine fauna. The carbonates were then buried by progressively coarser clastic sediment as the estuary was backfilled.
- Cox, E.T., 1875, Geology of Gallatin County: Geological Survey of Illinois, v. 6, p. 197–219.
- Fraunfelter, G.H., 1979, Lower Pennsylvanian limestones in the Illinois Basin, in J.E. Palmer, and R.R. Dutcher, eds., Depositional and structural history of the Pennsylvanian System of the Illinois Basin, Part 2: Invited papers: Illinois State Geological Survey, Field Trip 9/Ninth International Congress of Carboniferous Stratigraphy and Geology, Guidebook 15A, p. 73–75.
- Kosanke, R.M., J.A. Simon, H.R. Wanless, and H.B. Willman, 1960, Classification of the Pennsylvanian strata of Illinois: Illinois State Geological Survey, Report of Investigations 214, 84 p., 1 pl.
- Lee, W., 1916, Geology of the Shawneetown Quadrangle in Kentucky: Kentucky Geological Survey, Ser. 4, v. 4, part 2, 73 p.
- Rexroad, C.B., and G.K. Merrill, 1985, Conodont biostratigraphy and paleoecology of Middle Carboniferous rocks in southern Illinois: Frankfurt-am-Main, Germany, Courier Forschunginstitut Senckenberg, v. 74, p. 35–64.
- Sneed, G.J., 1977, Ghost towns of southern Illinois: Royalton, Illinois, G.J. Sneed, 309 p.
- Wanless, H.R., 1939, Pennsylvanian correlations in the Eastern Interior and Appalachian coal fields: Geological Society of America, Special Paper 17, 130 p., 9 pls.
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