Geology of the County

In Breckinridge County, water is obtained from consolidated sedimentary rocks of Mississippian through Pennsylvanian age and from unconsolidated sediments of Quaternary age. Geologists call the oldest rocks found at the surface in Breckinridge County the St. Louis Limestone. The most common rock types in Breckinridge County are Mississippian limestones, which were deposited 350 million years ago in the bottom of a warm, shallow sea. At the end of the Mississippian Period, 320 million years ago, the seas receded and sediments of the Pennsylvanian were deposited. The warm climate of the Pennsylvanian allowed extensive forests and great coastal swamps to grow at the edges of water bodies. Marine waters advanced and receded many times, which produced many layers of sandstone, shale, and coal. Vegetation of all sorts fell into the water and was buried under blankets of sediments, which over long geologic time were compressed into coal. The nonvegetative sediments such as sand, clay, and silt were compressed into sandstone and shale. Over the last million years, Quaternary sediments have been deposited along the larger streams and rivers.

Geologic Formations in the County
Unconsolidated deposits
Alluvium (Qa), glacial sediments (Qg)

Ste. Genevieve Limestone (Mgl)
St. Louis Limestone (Mgl)

Caseyville Formation (Pca)
Bethel Sandstone of the Mooretown Formation (Mms)

Coals, sandstones, and shales
Tradewater Formation (Pt)

Interbedded limestones, sandstones, and shales
Buffalo Wallow Formation, Tar Springs Sandstone (Mcu)
Glen Dean Limestone, Hardinsburg Sandstone (Mcl)
Golconda Formation (Haney Limestone, Big Clifty Sandstone, Beech Creek Limestone Members) (Mcl)
Girkin Formation (Reelsville Limestone, Sample Sandstone, Beaver Bend and Paoli Limestone) (Mcl)

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

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