Geologic units in Gadsden county, Florida

Citronelle Formation (Pliocene) at surface, covers 52 % of this area

The Citronelle Formation is widespread in the Gulf Coastal Plain. The type section for the Citronelle Formation, named by Matson (1916), is near Citronelle, Alabama. The Citronelle Formation grades laterally, through a broad facies transition, into the Miccosukee Formation of the eastern Florida panhandle. Coe (1979) investigated the Citronelle Formation in portions of the western Florida panhandle. The Citronelle Formation is a siliciclastic, deltaic deposit that is lithologically similar to, and time equivalent with, the Cypresshead Formation and, at least in part, the Long Key Formation (Cunningham et al., 1998) of the peninsula. In the western panhandle, some of the sediments mapped as Citronelle Formation may be reworked Citronelle. The lithologies are the same and there are few fossils present to document a possible younger age. The Citronelle Formation consists of gray to orange, often mottled, unconsolidated to poorly consolidated, very fine to very coarse, poorly sorted, clean to clayey sands. It contains significant amounts of clay, silt and gravel which may occur as beds and lenses and may vary considerably over short distances. Limonite nodules and limonite-cemented beds are common. Marine fossils are rare but fossil pollen, plant remains and occasional vertebrates are found. Much of the Citronelle Formation is highly permeable. It forms the Sand and Gravel Aquifer of the surficial aquifer system.

Hawthorn Group, Torreya Formation (Miocene) at surface, covers 33 % of this area

The Torreya Formation is exposed or near the surface from western Gadsden County eastward to western-most Hamilton County. It is informally subdivided into a lower carbonate unit and an upper siliciclastic unit (Scott, 1988). The majority of Torreya Formation outcrops expose the siliciclastic part of the unit. The carbonate sediments are white to light olive gray, generally poorly indurated, variably sandy and clayey, fossiliferous (molds and casts) limestone (mudstone and wackestone). The limestones often grade into calcareous-cemented sands. Phosphate is present in the carbonate sediments, particularly in the Sopchoppy Member. The siliciclastics vary from white to light olive gray, unconsolidated to poorly indurated, slightly clayey sands with minor phosphate to light gray to bluish gray, poorly consolidated, variably silty clay (Dogtown Member). The siliciclastics are sporadically fossiliferous. The Torreya Formation overlies the FAS and forms part of the intermediate confining unit/aquifer system.

Miccosukee Formation (Pliocene) at surface, covers 14 % of this area

The Miccosukee Formation, named by Hendry and Yon (1967), is a siliciclastic unit with a limited distribution in the eastern panhandle. It occurs in the Tallahassee Hills from central Gadsden County to eastern Madison County, often capping hills. The Miccosukee Formation grades to the west, through a broad facies transition, in central Gadsden County into the Citronelle Formation. The Miccosukee Formation is a prodeltaic deposit. The Miccosukee Formation is composed of grayish orange to grayish red, mottled, poorly to moderately consolidated, interbedded clay, sand and gravel of varying coarseness and admixtures (Hendry and Yon, 1967). The unit is relatively impermeable but is considered a part of the surficial aquifer system (Southeastern Geological Society, 1986).

Residuum on Oligocene sediments (Oligocene) at surface, covers 1 % of this area

The undifferentiated Oligocene residuum, mapped on parts of the Chattahoochee "Anticline", characteristically consists of reddish brown, variably sandy clay with inclusions of variably fossiliferous, silicified limestone (Huddlestun, 1993). The residuum includes Lower and Upper Oligocene weathered sediments (Huddlestun, 1993).

Miccosukee Formation (Neogene) at surface, covers 0.2 % of this area

Miccosukee Formation

Hawthorn Formation (Miocene) at surface, covers 0.1 % of this area

Includes Marks Head Formation; Parachucia Beds (Sloan, 1905); and Alum Bluff Formation (Veatch and Stephenson, 1911).

Jackson Bluff Formation (Pliocene) at surface, covers < 0.1 % of this area

The Jackson Bluff Formation, named by Vernon and Puri (1964), occurs at or near the surface in a limited area of the panhandle in Leon, Liberty and Wakulla Counties. It has attracted much attention due to its abundant fossil molluscan fauna (Huddlestun, 1984; Schmidt, 1984). In the outcrop area, the Jackson Bluff Formation is described as a sandy, clayey shell bed (Schmidt, 1984). It is composed of tan to orange-brown to gray green, poorly consolidated, fossiliferous, sandy clays to clayey sands. Fossils present include abundant mollusks, corals, foraminifers and occasional vertebrate remains.

Chattahoochee Formation (Miocene) at surface, covers < 0.1 % of this area

The Chattahoochee Formation, originally named by Dall and Stanley-Brown (1894), is predominantly a yellowish gray, poorly to moderately indurated, fine-grained, often fossiliferous (molds and casts), silty to finely sandy dolostone (Huddlestun, 1988). Siliciclastic beds and limestones may be present. The Chattahoochee Formation is exposed in Jackson County, central panhandle, on the Chattahoochee "Anticline". It grades laterally across the Gulf Trough into the St. Marks Formation through a broad transition area (Scott, 1986). The Chattahoochee Formation forms the upper part of the FAS in the central panhandle.

Undifferentiated sediments (Pleistocene/Holocene) at surface, covers < 0.1 % of this area

Undifferentiated Quaternary Sediments - Much of Florida's surface is covered by a varying thickness of undifferentiated sediments consisting of siliciclastics, organics and freshwater carbonates. Where these sediments exceed 20 feet (6.1 meters) thick, they were mapped as discrete units. In an effort to subdivide the undifferentiated sediments, those sediments occurring in flood plains were mapped as alluvial and flood plain deposits (Qal). Sediments showing surficial expression of beach ridges and dunes were mapped separately (Qbd) as were the sediments composing Trail Ridge (Qtr). Terrace sands were not mapped (refer to Healy [1975] for a discussion of the terraces in Florida). The subdivisions of the Undifferentiated Quaternary Sediments (Qu) are not lithostratigraphic units but are utilized in order to facilitate a better understanding of the State's geology. The siliciclastics are light gray, tan, brown to black, unconsolidated to poorly consolidated, clean to clayey, silty, unfossiliferous, variably organic-bearing sands to blue green to olive green, poorly to moderately consolidated, sandy, silty clays. Gravel is occasionally present in the panhandle. Organics occur as plant debris, roots, disseminated organic matrix and beds of peat. Freshwater carbonates, often referred to as marls in the literature, are scattered over much of the State. In southern Florida, freshwater carbonates are nearly ubiquitous in the Everglades. These sediments are buff colored to tan, unconsolidated to poorly consolidated, fossiliferous carbonate muds. Sand, silt and clay may be present in limited quantities. These carbonates often contain organics. The dominant fossils in the freshwater carbonates are mollusks.