Historical:Mammoth Cave Limestone Megagroup

	Handbook of Illinois Stratigraphy
Series	Bulletin 95
Author	H. B. Willman, Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, Jack A. Simon
Date	1975
Link	Web page
PDF	PDF file
Store	ISGS Store

	Handbook of Illinois Stratigraphy
Series	Bulletin 95
Author	H. B. Willman, Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, Jack A. Simon
Date	1975
Link	Web page
PDF	PDF file
Store	ISGS Store

Lithostratigraphy: Mammoth Cave Limestone Megagroup
Chronostratigraphy: Paleozoic Erathem >>Mississippian Subsystem
Allostratigraphy: Kaskaskia Sequence

Authors

Elwood Atherton, Charles Collinson, and Jerry A. Lineback

Name Origin

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.

Extent and Thickness

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.

Fig. M-8 -- Thickness of the Mammoth Cave Limestone Megagroup. Thickness is shown where Chesterian strata are present.

Description

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).

Fig. 14 -- Pre-Pennsylvanian megagroups and sequences of Illinois (Swann and Willman, 1961). Fig. M-3 -- Classification of the Mississippian System.

References

MILLER, A. M., 1917, Table of geological formations of Kentucky: University Bookstore, 7 p.; reprinted in Miller, 1919, p. 9-15.
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.

ISGS Codes

Stratigraphic Code	Geo Unit Designation
4450	--