Historical:Anvil Rock Sandstone Member
M. E. Hopkins and J. A. Simon
The Anvil Rock Sandstone Member of the Carbondale Formation (Owen, 1856, p. 45) is named for an anvil-shaped float block along a bluff 1.5 miles north of Dekoven Station, Union County, Kentucky. The name "Anvil Rock" was applied by Hopkins (1958) and Potter and Simon (1961) to a major channel sandstone, which replaces the Herrin Coal along a sinuous band extending through Montgomery, Bond, Clinton, Washington, Jefferson, and Franklin Counties (fig. P-13) in Illinois.
Extent and Thickness
The sandstone underlies the Bankston Fork Limestone and overlies the gray shale above the Conant Limestone throughout southern Illinois, where it occurs as a channel sandstone as much as 80 feet thick. East of the Du Quoin Monocline the Anvil Rock occurs as a channel sandstone or, more commonly, as a sheet sandstone up to 20 feet thick (Hopkins, 1958; Potter and Simon, 1961).
The Anvil Rock Sandstone is now considered to be in part contemporaneous with the Herrin Coal and the immediately overlying gray silty shale. In the sheet facies it is normally a fine-grained, relatively impure, quartz sandstone incorporating considerable argillaceous material, but in the channel facies it is medium grained and less argillaceous. In the deeper channels the sandstone cuts through several underlying stratigraphic units, including the Herrin (No. 6) Coal. Some channels are only a few hundred feet across, but the major ones are up to 2 miles wide. In the sheet facies the dominant sedimentary structure is ripple bedding. In the channel facies, planar and trough cross-bedding are common.
HOPKINS, M. E., 1958, Geology and petrology of the Anvil Rock Sandstone of southern Illinois: Illinois State Geological Survey Circular 256, 49 p.
OWEN, D. D., 1856, Report of the geological survey in Kentucky made during the years 1854 and 1855: Kentucky Geological Survey Bulletin, v. I, Series 1, 416 p.
POTTER, P. E., and J. A. SIMON, 1961, Anvil Rock Sandstone and channel cutouts of Herrin (No. 6) Coal in west-central Illinois: Illinois State Geological Survey Circular 314, 12 p.
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