USGS Home
Contact USGS
Search USGS

Mineral Resources > Online Spatial Data > Geology > by state > Alabama Geology

Geologic units in Calhoun county, Alabama

[Additional scientific data in this geographic area]

Knox Group undifferentiated (Ordovician-Cambrian) at surface, covers 23 % of this area

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

Lithology: dolostone (dolomite); limestone; chert

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

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

Lithology: dolostone (dolomite); chert

Little Oak Limestone (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.

Lithology: limestone; chert; bentonite

Colvin Mountain Sandstone (Ordovician) at surface, covers 0.2 % of this area

Colvin Mountain Sandstone - light-gray quartzose sandstone, pebbly in part. Locally contains thin beds of bentonite in the upper part.

Lithology: sandstone; bentonite

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

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

Lithology: shale; mudstone; limestone; siltstone; sandstone

Tuscumbia Limestone and Fort Payne Chert undivided (Mississippian) at surface, covers 3 % of this area

Tuscumbia Limestone and Fort Payne Chert undivided - Tuscumbia Limestone -- light-gray partly oolitic limestone; very coarse bioclastic crinoidal limestone common; light-gray chert nodules and concretions locally abundant. Fort Payne Chert -- 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. Lenses of dark-gray siliceous shale occur locally at the base of the Fort Payne in Wills Valley. Commonly present below the Fort Payne is a ligh-olive-gray claystone or shale (Maury Formation) which is mapped with the Fort Payne. The Tuscumbia and Fort Payne are undifferentiated in Murphrees and Wills Valleys.

Lithology: limestone; chert; siltstone; shale; claystone

Pottsville Formation (upper part) (Pennsylvanian) at surface, covers < 0.1 % of this area

Pottsville Formation (upper part) - 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.

Lithology: shale; siltstone; sandstone; coal

Pottsville Formation (lower part) (Pennsylvanian) at surface, covers 0.1 % of this area

Pottsville Formation (lower part) - 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.

Lithology: sandstone; shale; siltstone; coal

Red Mountain Formation (Silurian) at surface, covers 0.4 % of this area

Red Mountain Formation - 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.

Lithology: sandstone; shale; siltstone; limestone

Chattanooga Shale and Frog Mountain Sandstone undifferentiated (Devonian) at surface, covers 0.1 % of this area

Chattanooga Shale and Frog Mountain Sandstone undifferentiated (In areas mapped as Dcfm one or both units may be locally absent) - Chattanooga Shale -- Brownish-black organic shale containing light to dark-gray sandstone and rare limestone interbeds near the base. Frog Mountain Sandstone -- 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.

Lithology: shale; sandstone; limestone; dolostone (dolomite); chert

Parkwood Formation and Floyd Shale undifferentiated (Pennsylvanian-Mississippian) at surface, covers 18 % of this area

Parkwood Formation and Floyd Shale undifferentiated - 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.

Lithology: shale; sandstone; mudstone; limestone; chert; mixed clastic/coal; clay or mud

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

Sequatchie Formation - Grayish-red, grayish-green, and yellowish-gray thin-bedded calcareous shale and calcareous mudstone containing interbedded fossiliferous limestone, and medium-gray to moderate-red partly sandy and glauconitic, medium to coarse-grained bioclastic limestone.

Lithology: shale; mudstone; limestone

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

Lay Dam Formation (Talladega Group) - 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).

Lithology: phyllite; metasedimentary rock; quartzite; slate; meta-conglomerate

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

Heflin Phyllite - 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.

Lithology: metasedimentary rock; quartzite; marble

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

Sequatchie Formation, Colvin Mountain Sandstone, Greensport Formation undifferentiated - 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).

Lithology: shale; mudstone; dolostone (dolomite); siltstone; sandstone

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

Little Oak and Newala Limestones undifferentiated - 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.

Lithology: limestone; chert; bentonite; dolostone (dolomite)

Weisner and Wilson Ridge Formations undifferentiated (Cambrian) at surface, covers 3 % of this area

Weisner and Wilson Ridge Formations undifferentiated -- interbedded quartzose to slightly feldspathic sandstone and laterally continous conglomerate in ledge-forming units separated by greenish-gray silty mudstone.

Lithology: sandstone; conglomerate; mudstone

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

Chilhowee Group undifferentiated - 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.

Lithology: conglomerate; mudstone; siltstone; sandstone

Frog Mountain Sandstone (Devonian) at surface, covers 0.5 % of this area

Frog Mountain Sandstone -- 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.

Lithology: sandstone; shale; mudstone; limestone; chert

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

Little Oak and Lenoir Limestones undifferentiated - 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 separated by a tongue of the Athens Shale.

Lithology: limestone; mudstone; chert

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

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

Lithology: mudstone; siltstone; sandstone

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

Paleozoic shale undifferentiated - 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.

Lithology: shale; mudstone; sandstone

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

Cochran Formation - 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.

Lithology: arkose; conglomerate; siltstone; mudstone

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

Newala Limestone - light to dark-gray thick-bedded micritic and peloidal limestone and minor dolomite.

Lithology: limestone; dolostone (dolomite)

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

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

Lithology: mudstone; shale; siltstone; sandstone; limestone; dolostone (dolomite)

Conasauga Formation, lower unnamed shale facies (Cambrian) at surface, covers 2 % of this area

Conasauga Formation, lower unnamed shale facies - 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.

Lithology: shale; limestone

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

Lithology: shale; sandstone; mudstone; limestone; clay or mud; mixed clastic/coal

Athens Shale (Ordovician) at surface, covers 1.0 % of this area

Athens Shale - black graptolitic shale, locally contains interbedded dark-gray limestone.

Lithology: black shale; limestone

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

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

Lithology: limestone; shale

Floyd Shale (Mississippian) at surface, covers 1 % of this area

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.

Lithology: shale; sandstone; limestone; chert