Geology of the County

In Casey County, water is obtained from consolidated sedimentary rocks of Ordovician, Devonian, and Mississippian age and from unconsolidated sediments of Quaternary age. Geologists call the oldest rocks found at the surface in Casey County the Cumberland Formation. This formation was deposited in warm seas 450 million years ago during the Ordovician Period. Lying above the Ordovician rocks is the Devonian New Albany Shale, 400 million years old, which was formed when the deep sea floor became covered with an organic black muck. The muck is now hard black shale (an oil shale) and is one of the most distinctive of all geologic formations in Kentucky. The Mississippian sandstones and siltstones are the result of a great influx of mud, silts, and sands brought in by rivers and streams from uplands many miles away and deposited as a great delta. The Mississippian limestone found in Casey County was deposited 350 million years ago in the bottom of a warm, shallow sea. Over the last million years, unconsolidated Quaternary sediments have been deposited along the larger streams and rivers.

Geologic Formations in the County
Unconsolidated deposits
Alluvium (Qa)

Ste. Genevieve Limestone (Mgl)
St. Louis Limestone (Mgl)
Salem and Warsaw Formations (Msh)
Fort Payne Formation (Mbf)

Interbedded clay shales, siltstones, and sandstones
Borden Formation (MDbb)

Fractured shales
New Albany Shale (MDnb)
Boyle Dolomite (MDnb)

Interbedded limestones and shales
Drakes Formation (Od), (Odc)
Ashlock Formation and Calloway Creek Limestone (Oaf)
Cumberland Formation, Leipers Limestone, Catheys Formation (Ocl)

For more information, see the definitions of geologic terms and rock descriptions, a geologic map of Casey County, a summary of the geology of Kentucky, and a discussion of fossils and prehistoric life in Kentucky.

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