Map and Chart--KGS

Abstract

This map shows the geologic age of rocks and sediments at the surface in Kentucky. Sedimentary rocks, deposited from about 465 to 290 million years ago during the Ordovician, Silurian, Devonian, Mississippian, and Pennsylvanian Periods, crop out across the state. The rocks mainly consist of shale, limestone, sandstone, and siltstone. As shown in the cross sections, these surface rocks are underlain by older unexposed rocks of Precambrian, Cambrian, and Ordovician age.

Small bodies of igneous rocks were intruded into the state's bedrock about 270 million years ago during the Permian Period. They crop out in Elliott County of northeastern Kentucky, and in Crittenden and Livingston Counties of western Kentucky.

Younger unconsolidated sediments were deposited during the Cretaceous, Tertiary, and Quaternary Periods, from about 95 million years ago to the present time. They cover far western Kentucky and occur across the state in stream valleys and, locally, on uplands. The sediments commonly are composed of clay, silt, sand, and gravel. In northern Kentucky, Quaternary sediments include glacial deposits laid down within the last million years during the Ice Age.

The present distribution of rocks and sediments at the surface in Kentucky mainly reflects uplift and downwarping of major structural features and subsequent episodes of erosion. Subsidence in the Appalachian Basin and Illinios Basin has preserved younger coal-bearing rocks of Pennsylvanian age in eastern and western Kentucky, respectively. These younger rocks were eroded from the uplifted Cincinnati Arch in central Kentucky, a process that eventually uncovered Ordovician deposits, the oldest exposed rocks in the state. Vertical and lateral movements along faults have displaced strata in parts of Kentucky. Much younger Cretaceous, Tertiary, and Quaternary sediments were deposited in the downwarped Mississippi Embayment of far western Kentucky, a northern extension of the Gulf Coastal Plain.

Publication Date

2000

Series

Series XII

Report Number

Map and Chart 20

Digital Object Identifier (DOI)

https://doi.org/10.13023/kgs.mc20.12

Notes

Cartography by Terry Hounshell

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