Suwannee Limestone is found in the peninsula carbonate outcroppings on the northwestern, northeastern and southwestern flanks of the Ocala Platform. However, Suwannee Limestone is not present on an area known as Orange Island on the eastern side of the Ocala Platform due to erosion, nondeposition or both.[1] This limestone is present in southeastern Leon, Jefferson, Madison, Taylor, Lafayette counties as well as Hamilton along the upper Suwannee River basin, and southward into Suwannee County, Florida.
Early Oligocene Suwannee Limestone was recognized in the northwestern peninsula by P. F. Huddleston in 1993 as a triple subdivision of Suwannee Limestone, Ellaville Limestone, and Suwannacoochee Dolostone.[2] The Suwannacoochee Dolostone was later officially renamed as the Suwannacoochee Dolomite.[3]
Sedimentology
Suwannee Limestone consists of a white to cream, poorly to well hardened, fossil rich, vuggy to moldic grainstone and packstone. The dolomitized parts of the Suwannee Limestone are gray, tan, light brown to moderate brown, moderately to well indurated (hard), finely to coarsely crystalline, dolomite with limited occurrences of fossil-bearing beds. Limestone in silicate form is common in Suwannee Limestone.[4][5]
Stratigraphy
The Suwannee Limestone overlies the Ocala Limestone and forms part of the intermediate confining unit/aquifer system. (USGS)
Paleobiota
The Suwannee Limestone preserves numerous calcifying marine invertebrates, including foraminifers, echinoids, bryozoans and mollusks. Shark teeth belonging to Ginglymostoma and Carcharhinus are known from the Brooksville 2 site, which likely originate from the limestone formation rather than the fissure-fill fauna from the same locality.[6]
Fissure-fill fauna
Not long after the formation of the Suwannee Limestone, falling sea levels during the latter part of the Oligocene led to its exposure on land. Terrestrial vertebrates that inhabited this newly-exposed karstic landscape at the time sometimes became trapped within sinkholes that opened in the limestone, which filled up with sand and clay as fissure-fill deposits, fossilizing their remains. These deposits date to the latest Oligocene (late Chattian or Arikareean stage), and preserve numerous animals whose remains are otherwise rare in the region due to a lack of terrestrial deposits. Two major localities that preserve such fossils are Brooksville 2 in Hernando County and SB-lA/Live Oak in Suwanee County.[6][7]
^Bryan, J.R., 1991, Stratigraphic and paleontologic studies of Paleocene and Oligocene carbonate facies of the eastern Gulf Coastal Plain: unpublished Ph.D. dissertation, University of Tennessee, Knoxville, TN, 324 p.
^Huddleston, P.F., A revision of the lithostratigraphic units of the Coastal Plain of Georgia - The Oligocene: Georgia Geological Survey Bulletin 105, 152 p.
^Stamm, N., 2018, Geologic Unit: Suwannacoochee. National Geologic Map Database Geolex — Unit Summary, U.S. Department of the Interior, U.S. Geological Survey, Reston Virginia.
^Cooke, C. W., and Mansfield, W. C., 1936, Suwanne Limestone of Florida (abstract): Geological Society of America Proceedings, 1935, p. 71–72.
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