Geologic units in Marshall county, Alabama

Additional scientific data in this geographic area

Pottsville Formation (Pennsylvanian) at surface, covers 46 % 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.

Pottsville Formation (lower part) (Pennsylvanian) at surface, covers 18 % 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. The Boyles Sandstone Member is a formally named unit in the lower part of the formation. Top of unit is mapped at the Black Creek coal.

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

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

Pennington Formation (Mississippian) at surface, covers 5 % 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.

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

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

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

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.

Nashville and Stones River Groups undifferentiated (Ordovician) at surface, covers 2 % of this area

Medium to dark-gray fossiliferous limestone, argillaceous in part; yellowish-gray laminated silty limestone in upper part. Contains one or more thin beds of bentonite and bentonitic shale.

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

Leipers Limestone -- medium to dark-gray thin to medium-bedded fossiliferous limestone containing interbeds of thin argillaceous limestone. Mapped in Sequatchie Valley. Inman Formation -- interbedded greenish-gray or moderate to dusky-red shale and light-gray peloidal limestone. Mapped in Sequatchie Valley.

Red Mountain Formation (Silurian) at surface, covers 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.

Bangor Limestone (Mississippian) at surface, covers 1 % of this area

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

Sequatchie Formation (Ordovician) at surface, covers 1.0 % 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. In Jackson County, includes the Leipers Limestone and Inman Formation.

Fort Payne Chert (Mississippian) at surface, covers 0.6 % 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.

Inman Formation (Ordovician) at surface, covers 0.5 % of this area

Interbedded greenish-gray or moderate to dusky-red shale and light-gray peloidal limestone. Mapped in Sequatchie Valley.

Tuscumbia Limestone (Mississippian) at surface, covers 0.5 % of this area

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

Hartselle Sandstone (Mississippian) at surface, covers 0.4 % of this area

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

Hartselle Sandstone (Mississippian) at surface, covers 0.2 % of this area

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

Pride Mountain Formation (Mississippian) at surface, covers 0.1 % 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.

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

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

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.

Tuscumbia Limestone (Mississippian) at surface, covers < 0.1 % 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.

Parkwood and Pennington Formations undifferentiated (Pennsylvanian-Mississippian) at surface, covers < 0.1 % 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.