Bankston Fork Limestone Member
Willman, H. B., Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, and Jack A. Simon, 1975, Handbook of Illinois Stratigraphy: Illinois State Geological Survey Bulletin 95, 261 p.
M. E. Hopkins and J. A. Simon
The Bankston Fork Limestone Member of the Carbondale Formation (Cady, 1926, p. 261-262).
Named for Bankston Creek in Saline County.
The type section consists of outcrops along the south side of Bankston Creek (NE NW 19, 9S-5E).
Extent and thickness
It occurs in southwestern, central, eastern, and southeastern Illinois, where it is commonly several feet thick but seldom over 6 feet. It does not occur west of the Illinois River or in northern Illinois. It commonly is not present over the thick portions of the Anvil Rock Sandstone.
The Bankston Fork is a fine-grained, argillaceous, thick-bedded limestone that is dolomitic in places (fig. P-3B). It is commonly nodular in the upper and lower portions and is generally divided into two benches by a greenish gray shale several inches thick.
Well log characteristics
It is sparsely fossiliferous, its open-marine fauna dominated by brachiopods, fusulinids, and a few crinoids.
Age and correlation
The Bankston Fork correlates with the Universal Limestone Member of Indiana and is present in parts of western Kentucky, where it locally is as much as 8 feet thick.
Environments of deposition
CADY, G. H., 1926, Areal geology of Saline County: Illinois Academy of Science Transactions, v. 19, p. 250-272.
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