Geologic units in Calhoun county, Alabama

Additional scientific data in this geographic area

Knox Group undifferentiated in part (Ordovician-Cambrian) at surface, covers 23 % 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 18 % 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.

Conasauga Formation (Cambrian) at surface, covers 14 % 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.

Rome Formation (Cambrian) at surface, covers 10 % of this area

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

Chilhowee Group undifferentiated (Cambrian) at surface, covers 10 % of this area

Light to medium-gray arkose, arkosic conglomerate, and discontinous mudstone overlain by greenish-gray mudstone with minor siltstone and sandstone; dominantly light-gray pebbly quartzose sandstone in upper part.

Shady Dolomite (Cambrian) at surface, covers 5 % of this area

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

Tuscumbia Limestone and Fort Payne Chert undifferentiated (Mississippian) at surface, covers 3 % 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.

Weisner and Wilson Ridge Formations undifferentiated (Cambrian) at surface, covers 3 % 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, lower unnamed shale facies (Cambrian) at surface, covers 2 % 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.

Heflin Phyllite (Cambrian?) at surface, covers 2 % of this area

Grayish-green, medium-gray, and medium-bluish-gray calcareous sandy metasiltstone interbedded with minor greenish-gray fine to coarse-grained metasandstone and rare thin lenses of calcite and dolomite marble; an interval of greenish-gray to dark-gray phyllitic quartzite or quartz-pebble metaconglomerate is locally present near the base. The Heflin underlies the Lay Dam Formation and overlies the rocks tentatively identified as the Chilhowee Group undifferentiated.

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

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

Talladega Group; Lay Dam Formation (Silurian?-Devonian) at surface, covers 1 % of this area

Interbedded dark-green phyllite, medium-gray to light-brown and black metasiltstone, dark-green feldspathic metagraywacke, and light-gray and dark-gray medium to coarse-grained arkosic quartzite and metaconglomerate; graphitic phyllite common in upper part. In Cleburne and Calhoun Counties, rocks mapped as the Lay Dam include the Abel Gap Formation of Bearce (1973) and consist of interbedded greenish-gray metasiltstone and quartzite, black phyllitic metasiltstone, medium-gray to greenish-gray arkosic quartzite, and dark-gray pyritic quartzite. In Clay Chounty the upper part of the Lay Dam includes black graphitic sericite phyllite and slate reportedly containing plant fossils (Erin Slate Member).

Floyd Shale (Mississippian) at surface, covers 1 % 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.

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

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

Parkwood Formation (Pennsylvanian-Mississippian) at surface, covers 0.8 % 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.

Paleozoic shale undifferentiated (Mississippian) at surface, covers 0.7 % of this area

Dark-gray shale and mudstone, locally containing thin interbeds and lenses of dark-greenish-gray sandstone includes Athens Shale and probable Floyd Shale in the structural windows near Anniston, Calhoun County.

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

Massive to laminated greenish-gray and black micaceous mudstone containing minor interbeds of siltstone and very fine-grained sandstone.

Frog Mountain Sandstone (Devonian) at surface, covers 0.4 % of this area

Light to dark-gray sandstone with thin dark-gray shale interbeds, light-gray to black dolomudstone, glauconitic limestone, and fossiliferous chert locally in lower part.

Red Mountain Formation (Silurian) at surface, covers 0.4 % 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.

Little Oak Limestone (Ordovician) at surface, covers 0.4 % 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.

Little Oak and Newala Limestones undifferentiated (Ordovician) at surface, covers 0.3 % of this area

Little Oak Limestone -- dark-gray medium to thick-bedded fossiliferous, argillaceous to silty limestone containing chert nodules. Locally includes thin beds of bentonite in the upper part. Newala Limestone -- light to dark-gray thick-bedded micritic and peloidal limestone and minor dolomite.

Sequatchie Formation (Ordovician) at surface, covers 0.2 % 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 0.2 % of this area

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

Pottsville Formation (lower part) (Pennsylvanian) at surface, covers 0.1 % 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.

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

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

Little Oak and Lenoir Limestones undifferentiated (Ordovician) at surface, covers 0.1 % 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.

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 (Scraper Mountain) and in the structurally complex area at the east end of Dry Creek Mountain.

Pottsville Formation (upper part) (Pennsylvanian) at surface, covers < 0.1 % 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.

Cochran Formation (Cambrian) at surface, covers < 0.1 % of this area

Poorly sorted arkosic sandstone and conglomerate containing interbedded greenish-gray siltstone and mudstone. The Cochran Formation is exposed only in northeastern Calhoun and northwestern Cleburne Counties.

Paleozoic shale undifferentiated (Mississippian) at surface, covers < 0.1 % of this area

Dark-gray shale and mudstone, locally containing thin interbeds and lenses of dark-greenish-gray sandstone includes probable Floyd Shale in area east of Gadsden, Etowah County.