Geologic units in Shelby county, Alabama

Additional scientific data in this geographic area

Parkwood Formation and Floyd Shale undifferentiated (Pennsylvanian-Mississippian) at surface, covers 23 % of this area

Parkwood Formation -- 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. Floyd Shale -- Dark-gray shale, sideritic in part; thin beds of sandstone, limestone and chert are locally present; beds of partly bioclastic, partly argillaceous limestone are abundant in parts of Calhoun and Cherokee Counties.

Pottsville Formation (upper part) (Pennsylvanian) at surface, covers 21 % of this area

Interbedded dark-gray shale, siltstone, medium-gray sandstone, and coal in cyclic sequences. The members present in the Cahaba synclinorium in descending order include: the Straven Conglomerate Member, Rocky Ridge Sandstone Member, and Chestnut Sandstone Member. The members present in the Coosa synclinorium in descending order include: Straight Ridge Sandstone Member and Wolf Ridge Sandstone Member.

Newala Limestone (Ordovician) at surface, covers 9 % of this area

Light to dark-gray thick-bedded micritic and peloidal limestone and minor dolomite.

Kahatchee Mountain Group; Waxahatchee Slate (Precambrian?-Cambrian?) at surface, covers 7 % of this area

Dark-gray to grayish-green thin-bedded, micaceous metasiltstone, slate, and fine-grained quartzite.

Pottsville Formation (lower part) (Pennsylvanian) at surface, covers 7 % 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. In both the Cahaba and Coosa synclinoria the members in descending order include: the Pine Sandstone Member and the Shades Sandstone Member. Top of unit is mapped at top of Pine Sandstone Member.

Knox Group undifferentiated in part (Ordovician-Cambrian) at surface, covers 6 % of this area

Light-gray to light-brown locally sandy dolomite, dolomitic limestone, and limestone; characterized by abundant light-colored chert.

Floyd Shale (Mississippian) at surface, covers 5 % of this area

Dark-gray shale, sideritic in part; thin beds of sandstone, limestone and chert are locally present; beds of partly bioclastic, partly argillaceous limestone are abundant in parts of Calhoun and Cherokee Counties.

Chepultepec and Copper Ridge Dolomites undifferentiated (Ordovician-Cambrian) at surface, covers 5 % of this area

Light-gray to dark-bluish-gray thick-bedded dolomite and interbedded light-gray limestone; includes abundant chert.

Parkwood Formation (Pennsylvanian-Mississippian) at surface, covers 3 % 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.

Tuscumbia Limestone and Fort Payne Chert undifferentiated (Mississippian) at surface, covers 2 % of this area

Tuscumbia Limestone -- light to dark-gray fossiliferous and oolitic partly argillaceous and cherty limestone. Apparently present only along part of the northwest limb of the Coosa synclinorium. Fort Payne Chert -- dark-gray to light-gray limestone with abundant irregular light-gray chert nodules and beds. Commonly present below the Fort Payne is greenish-gray to grayish-red phosphatic shale (Maury Formation) which is mapped with the Tuscumbia Limestone and Fort Payne Chert undifferentiated.

Rome Formation (Cambrian) at surface, covers 2 % of this area

Variegated thinly interbedded mudstone, shale, siltstone, and sandstone; limestone and dolomite occur locally. Quartzose sandstone commonly present near top of formation.

Brierfield Dolomite (Cambrian) at surface, covers 1 % of this area

Medium to dark-bluish-gray thick-bedded siliceous dolomite; characterized by locally abundant chert with irregular cavities.

Ketona Dolomite (Cambrian) at surface, covers 1 % of this area

Light to medium-gray thick-bedded coarsely crystalline dolomite.

Longview Limestone (Ordovician) at surface, covers 1 % of this area

Longview Limestone - light to medium-gray thick-bedded cherty limestone and dolomite, locally sandy.

Athens Shale (Ordovician) at surface, covers 1 % of this area

Black graptolitic shale, locally contains interbedded dark-gray limestone.

Little Oak and Lenoir Limestones undifferentiated (Ordovician) at surface, covers 0.9 % of this area

Dark-gray argillaceous, fossiliferous medium to thick-bedded limestone; locally contains rare chert in upper part and an interval of fenestral mudstone in lower part (Mosheim Limestone Member of the Lenoir Limestone). Between Siluria and Pelham in Shelby County, the Little Oak and Lenoir Limestones are seperated by a tongue of the Athens Shale.

Weisner and Wilson Ridge Formations undifferentiated (Cambrian) at surface, covers 0.8 % of this area

Interbedded quartzose to slightly feldspathic sandstone and laterally continous conglomerate in ledge-forming units seperated by greenish-gray silty mudstone.

Conasauga Formation (Cambrian) at surface, covers 0.7 % of this area

Light to dark-gray finely to coarsely crystalline, medium to thick-bedded dolomite containing minor greenish-gray shale and light-bluish-gray chert. In the Columbiana area of Shelby County, the Conasauga is dominated by thin to medium-bedded, dark-gray dolomitic limestone and minor dark-gray shale. In Bibb County and southwestern Shelby County, the Conasauga consists of medium-bluish-gray fine-grained, thin-bedded argillaceous limestone and interbedded dark-gray shale. In the eastern Valley and Ridge the lower part includes dark-green to pale-olive fossiliferous shale with a few dark-gray limestone interbeds.

Bibb Dolomite (Cambrian) at surface, covers 0.5 % of this area

Dark-gray thick-bedded siliceous dolomite; characterized by locally abundant chert containing irregular cavities.

Athens Shale and Lenoir Limestone undifferentiated (Ordovician) at surface, covers 0.4 % of this area

Athens Shale -- black graptolitic shale, locally contains interbedded dark-gray limestone. Lenoir Limestone -- dark-gray medium to thick-bedded argillaceous limestone; locally contains an interval of fenestral mudstone at the base (Mosheim Limestone Member).

Newala and Longview Limestones undifferentiated (Ordovician) at surface, covers 0.4 % of this area

Light to dark-grey thick-bedded limestone and dolomite, cherty in part.

Kahatchee Mountain Group; Brewer Phyllite (Precambrian?-Cambrian?) at surface, covers 0.3 % of this area

Dusky-red micaceous slate and phyllite, locally containing interbedded micaceous arkosic quartzite and metasiltstone; locally at the base is interbedded calcite and dolomite marble.

Kahatchee Mountain Group; Stumps Creek Formation (Precambrian?-Cambrian?) at surface, covers 0.3 % of this area

Grayish-green micaceous metasiltstone and minor phyllite; grayish-green fine to medium-grained pyritic metasandstone in middle to upper part.

Metaclastic rocks of unknown affinity (Precambrian to Paleozoic) at surface, covers 0.2 % of this area

In the area south of Talladega, Talladega County, the unit includes greenish-gray chlorite-sericite phyllite; in small area south of Childersburg the unit consists of greenish-gray chlorite-sericite phyllite and slate locally containing interbeds of metagraywacke; and in the area east of Columbiana, Shelby County, the unit includes dark-greenish-gray slate and metasiltstone containing interbedded coarse-grained to conglomerate quartzite.

Kahatchee Mountain Group; Sawyer Limestone Member of Brewer Phyllite (Precambrian?-Cambrian?) at surface, covers 0.2 % of this area

Light to medium-gray argillaceous, silty to siliceous calcite and dolomite marble interbedded with phyllite and quartzite, locally cherty.

Shady Dolomite (Cambrian) at surface, covers 0.1 % of this area

Bluish-gray or pale-yellowish-gray thick-bedded siliceous dolomite; characterized by coarsely crystalline porous chert.

Tuscaloosa Group; Coker Formation (Cretaceous) at surface, covers < 0.1 % of this area

Light-colored micaceous very fine to medium sand, cross-bedded sand, varicolored micaceous clay, and a few thin gravel beds containing quartz and chert pebbles. Beds of thinly laminated finely glauconitic very fine to fine sand, silt and dark-gray carbonaceous clay (Eoline Member) occur locally in the lower part in western AL. Locally quartz and chert gravels at the base of the formation range in size from very fine pebbles to large cobbles. In southeastern Elmore County the formation includes marine sediments consisting of glauconitic, fossiliferous, quartzose fine to medium sand and medium-gray carbonaceous silty clay. Not mapped east of the Tallapoosa River.

Little Oak Limestone (Ordovician) at surface, covers < 0.1 % of this area

Dark-gray medium to thick-bedded fossiliferous, argillaceous to silty limestone containing chert nodules. Locally includes thin beds of bentonite in the upper part.

Kahatchee Mountain Group; Wash Creek Slate (Precambrian?-Cambrian?) at surface, covers < 0.1 % of this area

Grayish-green to black micaceous, partly carbonaceous to graphitic slate and metasiltstone containing interbedded light-gray to light-brown fine to coarse-grained metasandstone.