Geologic units in Saint Clair county, Alabama

Additional scientific data in this geographic area

Pottsville Formation (upper part) (Pennsylvanian) at surface, covers 22 % 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.

Conasauga Formation (Cambrian) at surface, covers 13 % of this area

Medium-bluish-gray fine-grained, thin-bedded argillaceous limestone and interbedded dark-gray shale in varying proportions.

Knox Group undifferentiated in part (Ordovician-Cambrian) at surface, covers 13 % of this area

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

Parkwood Formation and Floyd Shale undifferentiated (Pennsylvanian-Mississippian) at surface, covers 8 % 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 (lower part) (Pennsylvanian) at surface, covers 6 % 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.

Floyd Shale (Mississippian) at surface, covers 4 % 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 4 % of this area

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

Pottsville Formation (Pennsylvanian) at surface, covers 3 % of this area

Light-gray thin to thick-bedded quartzose sandstone and conglomerate containing interbedded dark-gray shale, siltstone, and coal. Mapped on Lookout Mountain, Blount and Chandler Mountains, and Sand Mountain northeats of Blount County, and on the mountains of Jackson, Marshall and Madison Counties north and west of the TN river.

Bangor Limestone (Mississippian) at surface, covers 3 % of this area

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

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

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

Chepultepec and Copper Ridge Dolomites undifferentiated (Ordovician-Cambrian) at surface, covers 3 % of this area

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

Newala Limestone (Ordovician) at surface, covers 2 % of this area

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

Parkwood Formation (Pennsylvanian-Mississippian) at surface, covers 2 % 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.

Parkwood and Pennington Formations (Pennsylvanian-Mississippian) at surface, covers 2 % of this area

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

Red Mountain Formation (Silurian) at surface, covers 2 % of this area

Dark-reddish-brown to olive-gray partly fossiliferous, mostly fine-grained sandstone interbedded with siltstone and shale; minor amounts of bioclastic limestone and conglomerate sandstone; includes hematitic beds and beds of ferruginous sandstone, outcrops in northeastern AL are finer grained and include more limestone.

Pride Mountain Formation (Mississippian) at surface, covers 2 % 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.

Little Oak and Lenoir Limestones undifferentiated (Ordovician) at surface, covers 1 % 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.

Tuscumbia Limestone and Fort Payne Chert undifferentiated (Mississippian) at surface, covers 1 % of this area

Tuscumbia Limestone -- light to dark-gray fossiliferous and oolitic partly argillaceous and cherty limestone, absent locally and too thin to map seperately. 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.

Longview Limestone (Ordovician) at surface, covers 0.9 % of this area

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

Chickamauga Limestone (Ordovician) at surface, covers 0.6 % of this area

Medium to dark-gray thick to thin-bedded partly argillaceous, locally fossiliferous limestone. Restricted to the western part of the Valley and Ridge province and Murphrees Valley and Wills Valley anticlines. Locally includes a thin interval of Attalla Chert Conglomerate Member at base. Attalla Chert Conglomerate - conglomerate of pebbles, cobbles, and boulders of chert and rare dolomite and quartzite in a sand-sized matrix; thin beds of gray-green or dusky-red shale common at base.

Rome Formation (Cambrian) at surface, covers 0.6 % of this area

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

Little Oak Limestone (Ordovician) at surface, covers 0.6 % 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.

Greensport Formation (Ordovician) at surface, covers 0.4 % of this area

Variegated dusky-red and dark-yellowish-orange shale, calcareous mudstone, limestone, siltstone, and minor sandstone.

Sequatchie Formation (Ordovician) at surface, covers 0.3 % of this area

Dusky-red to light-olive-gray siltstone, sandstone, shale, and dolomite, regular but uneven bedding.

Colvin Mountain Sandstone (Ordovician) at surface, covers 0.3 % of this area

Light-gray quartzose sandstone, pebbly in part. Locally contains thin beds of bentonite in the upper part.

Conasauga Formation, lower unnamed shale facies (Cambrian) at surface, covers 0.1 % of this area

Lower unnamed shale facies in eastern Valley and Ridge consists of dark-green to pale-olive fossiliferous shale with a few dark-gray limestone interbeds.

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

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

Red Mountain Formation (Silurian) at surface, covers 0.1 % of this area

Interbedded yellowish-gray to moderate-red sandstone, siltstone and shale; greenish-gray to moderate-red fossiliferous partly silty and sandy limestone; few thin hematitic beds.

Sequatchie Formation, Colvin Mountain Sandstone, Greensport Formation undifferentiated (Ordovician) at surface, covers 0.1 % of this area

Variegated dusky-red and pale-yellowish-orange shale, calcareous mudstone, dolomite, siltstone, and minor sandstone. Mapped in areas of facies transition with the Chickamauga Limestone (Canoe Creek, Dunaway, and Hensley Mountains).

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.

Sequatchie Formation (Ordovician) at surface, covers < 0.1 % of this area

Light-olive-gray and dusky-red calcareous shale interbedded with light to dark-gray fine to coarse-grained partly bioclastic, argillaceous, locally glauconitic limestone.

Knox Group undifferentiated (Ordovician-Cambrian) at surface, covers < 0.1 % of this area

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

Attalla Chert Conglomerate Member of the Chickamauga Limestone (Ordovician) at surface, covers < 0.1 % of this area

Conglomerate of pebbles, cobbles, and boulders of chert and rare dolomite and quartzite in a sand-sized chert and quartz matrix; thin beds of gray-green or dusky-red shale common at base.

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

Medium to dark-gray thick to thin-bedded partly argillaceous, locally fossiliferous limestone. Restricted to the western part of the Valley and Ridge province and Murphrees Valley and Wills Valley anticlines. Locally includes a thin interval of Attalla Chert Conglomerate Member at base. Attalla Chert Conglomerate - conglomerate of pebbles, cobbles, and boulders of chert and rare dolomite and quartzite in a sand-sized matrix; thin beds of gray-green or dusky-red shale common at base.