Clay Deposits of the Tuscaloosa Group in Alabama*

Otis M. Clarke Jr.
Geological Survey of Alabama
* Published by permission of State Geologist, Geological Survey of Alabama.

Abstract: Sediments of the Tuscaloosa Group, Upper Cretaceous Age, crop out in an arc that extends from North Carolina through the kaolin districts of South Carolina and Georgia, across Alabama, Tennessee, Kentucky and into southern Illinois. Deposits of clay, sand, and gravel were formed in a variety of geologic environments that include marine, lacustrine, lagoonal, fluvial and deltaic deposition. They accumulated on an eroded surface of pre-Triassic rocks.

In eastern Alabama clay beds within the Tuscaloosa Group that occur close to the contact of the pre-Cretaceous crystalline rocks comprise detrital accumulations derived from saprolite, and consist of kaolinite, montmorillonite, chlorite and quartz. Clays occurring somewhat stratigraphically higher in this section are mixtures of illite, kaolinite, quartz and minor amounts of montmorillonite and chlorite.

Westward in Alabama, clay in the Tuscaloosa Group occurs as thick irregular pockets and lenses of montmorillonite clay, whereas, in northwestern Alabama the clay is kaolinite with variable amounts of illite and montmorillonite. Some of the clay deposits in this area have been lateritized, resulting in the formation of bauxitic clay, which is a mixture of gibbsite and kaolinite.

Clays and Clay Minerals; 1963 v. 12; no. 1; p. 495-507; DOI: 10.1346/CCMN.1963.0120143
© 1963, The Clay Minerals Society
Clay Minerals Society (www.clays.org)