The Online Handbook of Illinois Stratigraphy (ILStrat)
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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.
Elwood Atherton, Charles Collinson, and Jerry A. Lineback
Mammoth Cave Limestone Megagroup (Miller, 1917, p. 3; Swann and Willman, 1961, p. 481).
The Mammoth Cave Limestone Megagroup is named for Mammoth Cave, Kentucky. The name was introduced, first as a formation name and later as a series name, for the relatively pure limestone in the interval from the base of the St. Louis Limestone to the base of the Big Clifty Sandstone.
The Mammoth Cave Limestone Megagroup occurs throughout the area of Mississippian rocks in Illinois, but it thins from nearly 2000 feet in extreme southern Illinois to little more than 100 feet in east-central Illinois (fig. M-8). It crops out extensively along the Mississippi and Illinois Valleys in western Illinois and along the Mississippi and Ohio Valleys in southern Illinois. <center> {| class="wikitable" style="text-align: center;" |- |<gallery caption="" widths=250px heights=250px perrow=4> Figure_M-8.jpg|{{file:Figure_M-8.jpg}} </gallery> |} </center>
The Mammoth Cave Limestone Megagroup (Miller, 1917, p. 3; Swann and Willman, 1961, p. 481) consists of the dominantly limestone groups and formations that overlie the siliceous elastic rocks of the Knobs Megagroup and occur below the lowest well developed sandstone formations of late Valmeyeran or early Chesterian age at the base of the Pope Megagroup. The Mammoth Cave is entirely Mississippian in age, but both upper and lower contacts are time-transgressive and are marked by a series of step-like, vertical cut-offs (figs. 14, M-3). <center> {| class="wikitable" style="text-align: center;" |- |<gallery caption="" widths=250px heights=250px perrow=4> Figure_14.jpg|{{file:Figure_14.jpg}} Figure_M-3.jpg|{{file:Figure_M-3.jpg}} </gallery> |} </center>
place a <pre><br></pre>at the end of a line to get a line return MILLER, A. M., 1917, Table of geological formations of Kentucky: University Bookstore, 7 p.; reprinted in Miller, 1919, p. 9-15.<br> SWANN, D. H., and H. B. WILLMAN, 1961, Megagroups in Illinois: American Association of Petroleum Geologists Bulletin, v. 45, p. 471-483; Illinois State Geological Survey Reprint 1961-N.
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