Odenville Formation
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| 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]
