The Big Clifty Sandstone is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolita ...

and

Kentucky Kentucky ( , ), officially the Commonwealth of Kentucky, is a state in the Southeastern region of the United States and one of the states of the Upper South. It borders Illinois, Indiana, and Ohio to the north; West Virginia and Virginia to ...

. It is a subunit of the Golconda Formation in

and is correlative with the Fraileys Shale to which it grades to in southern

. The Big Clifty and Golconda are part of the

Chesterian The Mississippian ( , also known as Lower Carboniferous or Early Carboniferous) is a subperiod in the geologic timescale or a subsystem of the geologic record. It is the earlier of two subperiods of the Carboniferous period lasting from roughly ...

Series of late Mississippian age. The Big Clifty Sandstone was deposited in deltaic to marginal marine environment by the paleo Michigan River which in modern directions flowed south from the Canadian shield, the sediment source, and then westward depositing sediment across Illinois, Kentucky, and Indiana, as the

Big Clifty Formation The Big Clifty Formation is a geologic formation in Indiana. It preserves fossils dating back to the Carboniferous period. In Illinois and Kentucky, the Big Clifty is referred to as the Big Clifty Sandstone and has been assigned to the Golconda ...

of the Stephensport Group. At

Mammoth Cave National Park Mammoth Cave National Park is an American national park in west-central Kentucky Kentucky ( , ), officially the Commonwealth of Kentucky, is a state in the Southeastern region of the United States and one of the states of the Upper Sout ...

the Big Clifty overlies the

Girkin Formation The Girkin Formation is a geologic formation located in the Chester Escarpment of central Kentucky, USA. It comprises a level of Mammoth Cave and lies above the Ste. Genevieve Limestone and St. Louis Limestone and below the Big Clifty Sandstone ...

, the uppermost of three cave forming carbonate formations which the Mammoth-Flint Ridge cave system spans.Palmer, A.N., 1981, Geologic Guide to Mammoth Cave National Park: Teaneck, N.J., Zephyrus Press, 210 p. Below the

are the

Ste. Genevieve Limestone The Ste. Genevieve Limestone is a geologic formation named for Ste. Genevieve, Missouri where it is exposed and was first described. It is a thick-bedded limestone that overlies the St. Louis Limestone. Both are Mississippian in age. The St. Loui ...

, and the

St. Louis Limestone The St. Louis Limestone is a large geologic formation covering a wide area of the midwest of the United States. It is named after an exposure at St. Louis, Missouri. It consists of sedimentary limestone with scattered chert beds, including the ...

respectively. The chemically resistant sediments comprising the Big Clifty, and similar siliciclastics, act as a caprock over the dissolving carbonates. The presence of the Big Clifty is one of several contributory factors that create favorable conditions for the formation, and subsequent preservation, of connected cavernous porosity in the Mammoth-Flint Ridge cave system. The Big Clifty Sandstone also appears as sandstone knobs throughout south-central Kentucky, including the Pilot Rock on the border of Todd County.

References

Geologic formations of Kentucky Geologic formations of Illinois {{US-geologic-formation-stub