Odenville Formation

Geologic formation in Alabama, United States

Odenville Limestone
Stratigraphic range: Ordovician
Type	Formation
Underlies	post-Knox formations
Overlies	Newala Limestone
Thickness	0-366 feet
Location
Region	Alabama
Country	United States
Type section
Named for	Odenville, Alabama
Named by	Charles Butts

The Odenville Limestone is a geologic formation in Alabama. It preserves fossils dating from the early Ordovician Period.

As first described by geologist Charles Butts in a 1926 report on Alabama’s geology, the Odenville consisted of “impure argillaceous and siliceous dark fine-grained cherty limestone,” about fifty feet in thickness.^[1]

Butts’ original type exposure could not be located by subsequent mappers, so the Odenville nomenclature was dropped and the formation was considered a locally-occurring facies of the underlying Newala Limestone.^[2]

Keith Roberson in 1988,^[3] and Ed Osborne in 1992,^[4] demonstrated the Odenville is indeed a distinctive, mappable lithologic unit, and the term was restored to the Ordovician nomenclature used by the Geological Survey of Alabama in the Appalachian fold-and-thrust belt.^[5]

As defined today, the Odenville Limestone is described as a dark gray, primarily dolomitic, stylonodular limestone^[6] whose fossil assemblage includes brachiopods and sponges. It is the uppermost member of the Knox Group, a related suite of carbonate rocks deposited at the end of the Cambrian and beginning of the Ordovician.^[7]

The Odenville Limestone occupies a narrow outcrop belt within the Cahaba Valley. Its extent along strike reaches from the overlap of Coastal Plain sediments in northwestern Chilton County^[8] to a point just northeast of its type locality, where it appears to pinch out in central St. Clair County.^[9] The formation does not crop out among Ordovician units exposed in the Coosa Deformed Belt.^[10] The Odenville may be present among Knox Group units in the Coosa Valley, but lack of exposures and intense weathering have precluded definitive identification of the Odenville in Knox-underlain areas between Pell City and Talladega.^[11]

References

^ "Geology of Alabama" (PDF). Geological Survey of Alabama. p. 99. Retrieved November 13, 2022.
^ Osborne, W. Edward; Irvin, G. Daniel (2002). Geology of the Odenville 7.5-Minute Quadrangle, St. Clair County, Alabama. Geological Survey of Alabama.
^ Roberson, Keith (1988). The post–Knox unconformity and its relationship to bounding stratigraphy, Alabama Appalachians. Master's thesis, University of Alabama.
^ Osborne, W. Edward (1992). Bedrock geology of the Cahaba Valley area between Helena and Lake Purdy, Shelby and Jefferson Counties, Alabama. Geological Survey of Alabama.
^ "National Geologic Map Database - Geolex". U.S. Geological Survey. Retrieved November 13, 2022.
^ Osborne, W. Edward; Irvin, G. Daniel (2002). "Cross Section A-A' and Explanation for the Geologic Map of the Odenville 7.5-Minute Quadrangle, St. Clair County, Alabama" (PDF). Geological Survey of Alabama. Retrieved November 13, 2022.
^ Lacefield, Jim (2013). Lost Worlds in Alabama Rocks (second edition). Alabama Museum of Natural History. pp. 94–95.
^ Osborne, W. Edward; Irvin, G. Daniel (2002). "Geologic Map of the Montevallo 7.5-Minute Quadrangle, Chilton and Shelby counties, Alabama" (PDF). Geological Survey of Alabama. Retrieved August 9, 2024.
^ Osborne, W. Edward; Garry, W. Brent; Thomas, William A. (2019). "Geologic Map and Cross Sections of the Ashville 7.5-Minute Quadrangle, St. Clair and Blount counties, Alabama" (PDF). Geological Survey of Alabama. Retrieved August 9, 2024.
^ Thomas, William A.; Drahovzal, James A.; Ward, Willard E. (2013). "Geologic Map and Cross Sections of the Pell City 7.5-Minute Quadrangle, St. Clair and Talladega counties, Alabama" (PDF). Geological Survey of Alabama. Retrieved August 9, 2024.
^ Irvin, G.D.; Thomas, W.A.; Osborne, W.E.; Drahovzal, J.D.; Ward, W.E. (2005). Geology of the Vincent 7.5-Minute Quadrangle, Shelby, St. Clair and Talldega counties, Alabama. Geological Survey of Alabama.