Geologic units in Franklin county, Alabama

Tuscaloosa Group; Gordo Formation (Cretaceous) at surface, covers 39 % of this area

Massive beds of cross-bedded sand, gravelly sand, and lenticular beds of locally carbonaceous partly mottled moderate-red and pale-red-purple clay; lower part is predominantly a gravelly sand consisting chiefly of chert and quartz pebbles. Not mapped east of the Tallapooza River.

Bangor Limestone (Mississippian) at surface, covers 31 % of this area

Medium-gray bioclastic and oolitic limestone, containing interbeds of dusky-red and olive-green mudstone in the upper part.

Pottsville Formation (lower part) (Pennsylvanian) at surface, covers 16 % of this area

Light-gray thick-bedded to massive pebbly quartzose sandstone, containing varying amounts of interbedded dark-gray shale, siltstone, and thin discontinuos coal. The Boyles Sandstone Member is a formally named unit in the lower part of the formation. Top of unit is mapped at the Black Creek coal.

Parkwood Formation (Pennsylvanian-Mississippian) at surface, covers 6 % of this area

Interbedded medium to dark-gray shale and light to medium-gray sandstone; locally contains dusky-red and grayish-green mudstone, argillaceous limestone, and clayey coal.

Eutaw Formation (Cretaceous) at surface, covers 4 % of this area

Light-greenish-gray to yellowish-gray cross-bedded, well-sorted, micaceous, fine to medium quartz sand that is fossiliferous and glauconitic in part and contains beds of greenish-gray micaceous, silty clay and medium-dark-gray carbonaceous clay. Light-gray glauconitic fossiliferous sand, thin beds of sandstone, and massive accumulations of fossil oyster shells occur locally in the upper part of the formation in western AL (Tombigbee Sand Member). In eastern AL thin to thick-bedded accumulations of the fossil oyster Ostrea cretacea Morton occur throughout much of the formation.

Hartselle Sandstone (Mississippian) at surface, covers 3 % of this area

Light-colored thick-bedded to massive quartzose sandstone, containing interbeds of dark-gray shale.

Eutaw formation (Upper Cretaceous) at surface, covers < 0.1 % of this area

More or less cross-bedded and thinly laminated glauconitic sand and clay; basal part includes the McShan formation, greenish-gray, micaceous, locally very glauconitic, very fine-grained sand and thin-bedded light-gray clay, small chert gravels may be present in basal beds, not recognized in northern Tishomingo County.

Alluvial, coastal and low terrace deposits (Holocene) at surface, covers < 0.1 % of this area

Varicolored fine to coarse quartz sand containing clay lenses and gravel in places. Gravel composed of quartz and chert pebbles and assorted metmorphic and igneous rock fragments in streams near the Piedmont. In areas of the Valley and Ridge province gravel composed of angular to subrounded chert, quartz, and quartzite pebbles. Coastal deposits include fine to medium quartz sand with shell fragments and accessory heavy minerals along Gulf beaches and fine to medium quartz sand, silt, clay, peat, mud and ooze in the Mississippi Sound, Little Lagoon, bays, lakes, streams, and estuaries.

Tuscaloosa formation (Upper Cretaceous) at surface, covers < 0.1 % of this area

Light and vari-colored irregularly bedded sand, clay, and gravel; gravel is mostly in lower portion.