The Big Clifty Sandstone is a geologic formation in

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. It borders on Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash River, Wabash and Ohio River, Ohio rivers to its ...

and

Kentucky Kentucky (, ), officially the Commonwealth of Kentucky, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Illinois, Indiana, and Ohio to the north, West Virginia to the ...

. 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 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 Canadian Shield ( ), also called the Laurentian Shield or the Laurentian Plateau, is a geologic shield, a large area of exposed Precambrian igneous and high-grade metamorphic rocks. It forms the North American Craton (or Laurentia), th ...

, the sediment source, and then westward depositing sediment across Illinois, Kentucky, and Indiana, as the Big Clifty Formation of the Stephensport Group. At

Mammoth Cave National Park Mammoth Cave National Park is a national park of the United States in south-central Kentucky. It encompasses portions of Mammoth Cave, the longest known cave system in the world. The park's are located primarily in Edmonson County, with sma ...

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 Sandst ...

, 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, and the St. Louis Limestone 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 Sandstone formations of the United States {{US-geologic-formation-stub