Geologic units in Colbert county, Alabama

Tuscumbia Limestone (Mississippian) at surface, covers 38 % of this area

Light-gray limestone, partly oolitic near top; fine to very coarse-grained bioclastic crinoidal limestone common; light-gray chert nodules and concretions are scattered throughout and are abundant locally. The apparent thickness of the formation in this province varies due to differential dissolution of the carbonate in the unit.

Pride Mountain Formation (Mississippian) at surface, covers 23 % of this area

Medium to dark-gray shale, containing one to three units of a variable combination of sandstone and limestone in the lower part; locally contains rare interbeds of dusky-red and greenish-gray mudstone.

Hartselle Sandstone (Mississippian) at surface, covers 20 % of this area

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

Tuscaloosa Group; Gordo Formation (Cretaceous) at surface, covers 15 % 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 4 % of this area

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

Fort Payne Chert (Mississippian) at surface, covers 1 % of this area

Very light to light-olive-gray, thin to thick-bedded fine to coarse-grained bioclastic (abundant pelmatozoans) limestone containing abundant nodules, lenses and beds of light to dark-grey chert. Upper part of formation locally consists of light-bluish-gray laminated siltstone containing vugs lined or filled with quartz and scattered throughout the formation are interbeds of medium to greenish-gray shale, shaly limestone and siltstone. Commonly present below the Fort Payne is a light-olive-gray claystone or shale (Maury Formation) which is mapped with the Fort Payne. The apparent thickness of the Fort Payne in this province varies due to differnetial dissolution of carbonate in the formation.

Eutaw Formation (Cretaceous) at surface, covers 0.5 % 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.

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.

Chester group (Mississippian) at surface, covers < 0.1 % of this area

Sandstone, shale, and limestone.

Chester group (Mississippian) at surface, covers < 0.1 % of this area

Limestone, chert, and shale of Meramec, Osage, and Kinderhook age.

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.