Geologic units in Madison county, Alabama

Fort Payne Chert (Mississippian) at surface, covers 35 % 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.

Tuscumbia Limestone (Mississippian) at surface, covers 28 % 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.

Monteagle Limestone (Mississippian) at surface, covers 15 % of this area

Light-gray oolitic limestone containing interbedded argillaceous, bioclastic, or dolomitic limestone, dolomite, and medium-gray shale.

Tuscumbia Limestone (Mississippian) at surface, covers 8 % of this area

Light-gray partly oolitic limestone; very coarse bioclastic crinoidal limestone common; light-gray chert nodules and concretions locally abundant.

Bangor Limestone (Mississippian) at surface, covers 5 % of this area

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

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

Light-gray oolitic limestone containing interbedded argillaceous, bioclastic, or dolomitic limestone, dolomite, and medium-gray shale.

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.

Pennington Formation (Mississippian) at surface, covers 2 % of this area

Medium-gray shale, containing interbedded limestone, dolomite, argillaceous sandstone, dusky-red and grayish-olive mudstone, and minor shaly coal. Mainly restricted to northeastern AL and part of the Sequatchie anticline. Where less than 100 feet thick the formation is included in the Bangor Limestone.

Bangor Limestone (Mississippian) at surface, covers 0.6 % of this area

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

Hartselle Sandstone (Mississippian) at surface, covers 0.6 % of this area

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

Silurian System undivided (Includes Wayne Group and Brassfield Limestone) (Silurian) at surface, covers 0.3 % of this area

Wayne Group - medium-gray, greenish-gray, and moderate-red argillaceous limestone; moderate-red and greenish-gray shale; and grayish-green fossiliferous limestone with scattered pink calcite crystals. Brassfield Limestone - greenish-gray to light-brownish-gray argillaceous, dolomitic, cherty, sandy, glauconitic limestone.

Chattanooga Shale (Devonian) at surface, covers 0.2 % of this area

Brownish-black organic shale containing light to dark-gray sandstone and rare limestone interbeds near the base.

Ordovician System undivided in part (Includes Sequatchie Formation, Elkmont Formation, Leipers Limestone, Inman Formation, Nashville Group, and Stones River Group) (Ordovician) at surface, covers 0.2 % of this area

Sequatchie Formation -- grayish-red and yellowish-gray calcareous shale containing interbedded fossiliferous limestone. Elkmont Formation -- medium to dark-gray phosphatic limestone with interbeds of light to medium-gray and black shale. Leipers Limestone -- medium to dark-gray thin to medium-bedded fossiliferous limestone containing interbeds of argillaceous limestone. Inman Formation -- interbedded greenish-gray or moderate to dusky-red shale and light-gray peloidal limestone. Nashville Group undifferentiated -- medium to dark-gray argillaceous and fossiliferous limestone overlain by yellowish-gray laminated silty limestone. Stones River Group -- medium to dark-gray thick to thin-bedded limestone, argillaceous in part, locally very fossiliferous.

Pennington Formation (Mississippian) at surface, covers < 0.1 % of this area

Medium-gray shale, containing interbedded limestone, dolomite, argillaceous sandstone, dusky-red and grayish-olive mudstone, and minor shaly coal. Mainly restricted to eastern part of Interior Low Plateaus province and where less than 100 feet thick the formation is included in the Bangor Limestone.

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

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.

Fort Payne Formation and Chattanooga Shale (Mississippian) at surface, covers < 0.1 % of this area

Fort Payne Formation - Bedded chert; calcareous and dolomitic silicastone; minor limestone and shale; scattered lenses of crinoidal limestone. Thin green shale (Maury) at base. Average thickness about 250 feet (475 in Wells Creek area); and Chattanooga Shale - Black carbonaceous shale, fissile. Thickness 0 to 70 feet; average about 20 feet. (Mapped as MDc on East-Central and East sheets)

Pennington Formation (Mississippian) at surface, covers < 0.1 % of this area

Reddish and greenish shale and siltstone; fine-grained dolomite; and minor fragmental and oolitic limestone. Thickness 240 to 360 feet.

Monteagle Limestone (Mississippian) at surface, covers < 0.1 % of this area

Mainly fragmental and oolitic, light-gray limestone; blocky bryozoan chert weathers from base. Thickness 180 to 300 feet.

Bangor Limestone and Hartselle Formation (Mississippian) at surface, covers < 0.1 % of this area

Bangor Limestone - Dark brownish-gray limestone, thick-bedded. Thickness 100 to 250 feet; and Hartselle Formation - Thin-bedded, fine-grained sandstone and greenish-gray shale interbedded with coarse limestone. Thickness 0 to 60 feet.