Geology of the County

In Graves County, water is obtained from unconsolidated sediments of Tertiary and Quaternary age. The oldest geologic formation exposed on the surface in Graves County is the Tertiary Porters Creek Formation. The Tertiary Period began 70 million years ago, and deposits consisted of marine and fresh- to brackish-water sediments. The distribution of deposits indicates that the area was near the northern limit of the Gulf Embayment (also called the Mississippi Embayment). Parts of the embayment must have been swampy, because thin beds of lignite (brown coal) and carbonaceous clays occur in the western half of the eight-county Jackson Purchase Region. These geological deposits are a marked contrast to the underlying older hard rocks, because most of the Cretaceous and younger sediments remain unconsolidated and soft. 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 and glacial outwash sediments (Qa)
Terrace gravel deposits and continental deposits (QTcl)

Jackson, Claiborne (Tjc), and Wilcox Formations (Tw)
Porters Creek Clay (Tp)

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

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