The St. Marks Formation is a Miocene geologic formation in the eastern Florida Panhandle.
Age Period: Neogene Epoch: Miocene ~23.03 to 5.33 mya, calculates to a period of Faunal stage: Arikareean through Hemphillian
Location The St. Marks Formation is exposed in Wakulla, southern Leon and southern Jefferson County, Florida on the northwestern flank of the Ocala Platform and along with Suwannee Limestone and Ocala Limestone makes up the upper part of the Floridan Aquifer in the eastern panhandle.USGS Florida Geology, Open File Report 80
Composition The St. Marks Formation consists of a white to yellowish gray, poorly to moderately hard, sandy, fossil bearing rock in molds and casts within packstone to wackestone.
Fossils The fossils are in molds and casts and include: Mollusks
References
Florida Carbonate "Formations" and Conflicting Interpretations of Injection Well Regulations Finch, J., Geological essay on the Tertiary formation in America: American Journal of Science, v. 7, p. 31-43, 1823.