The Florida Platform lies on the south-central part of the North American Plant, extending to the southeast from the North American continent separating the Gulf of Mexico from the Atlantic Ocean. The Florida Platform, as measured about the 300 foot (91 meter) isobath, spans more than 350 miles (565 kilometers) at its greatest width and extends southward more than 450 miles (725 kilometers) at its greatest length. The modern Florida peninsula is the exposed part of the platform and lies predominately east of the axis of the platform. Most of the State of Florida lies on the Florida Platform; the western panhandle is part of the Gulf Coastal Plain.

The basement rocks of the Florida Platform include Precambrian-Cambrian igneous rocks, Ordovician-Devonian Sedimentary rocks, and Triassic-Jurassic volcanic rocks (Arthur, 1988). Florida's igneous and sedimentary foundation separated from what is now the African Plat when the super-continent Pangea rifted apart in the Triassic (pre-Middle Jurassic?) and sutured to the North American craton (Smith, 1982).

A thick sequence of mid-Jurassic to Holocence sediments (unlithified to well lithified) lies unconformably upon the eroded surface of the basement rocks. Carbonate sedimentation predominate from mid-Jurassic until at least mid-Oligocene on most of the Florida platform. In response to renewed uplift and erosion in the Appalachian highlands to the north and sea-level fluctuations, siliciclastic sediments began to encroach upon the carbonate-depositing environments of the Florida Platform. Deposition of siliciclastic-bearing carbonates and siliciclastic sediments predominated from mid-Oligocene to the Holocene over much of the platform. Numerous disconformities that formed in response to nondeposition and erosion resulting from sea-level fluctuations occur within the stratigraphic section.

The oldest sediments exposed at the modern land surface are Middle Eocene carbonates of the Avon Park Formation which crop out on the crest of the Ocala Platform in west-central Florida. The pattern of exposures of younger sediments is obvious on the geologic map. Much of the state is blanketed by Pliocene to Holocene siliciclastic-bearing sediments that were deposited in response to late Tertiary and Quaternary sea-level fluctuations .

The characteristic landscape of Florida is relatively to extremely flat. There are few large, natural exposures and limited smaller exposures that geologists can investigate. The result is that geologists must rely primarily on de-watered or dry pits and quarries for exposures and must make use of subsurface data in studying the geology of Florida. Subsurface data, in the form of well cuttings and cores, were utilized extensively in the development of this map. Formational tops recognized in the subsurface have been extrapolated to the surface where exposures are limited.

Previously published geological maps of Florida include Smith (1881), Dall and Harris (1892), Matson et al. (1909), Sellards, Gunter and Cooke (1922), Cooke and Mossom (1929), Cooke (1945), Vernon (1951), Vernon and Puri (1964) and Brooks (1982).

Groundwork for a new geologic map of Florida began in the 1980s with a county-level mapping effort as part of a statewide radon investigation. The county maps created for the radon project were merged and modified to produce a new State map. The geologists from the Florida Geological Survey (FGS) involved in the project included Jon Arthur, Ken Campbell, Joel Duncan, Frank Rupert, and Tom Scott. Tom Missimer, Missimer International, Ft. Myers, Florida was part of the mapping team for Charlotte and Lee Counties. Previous mapping provided a basis for this project. Geologists involved in the preliminary mapping included Paulette Bond, Richard Johnson, Ed Lane, Walt Schmidt and Bill Yon.

Much of Florida is covered by a blanket of Pliocene to Holocene, undifferentiated siliciclastics that range in thickness from less than one foot to greater than 100 feet. As a result, in developing the criteria for producing this map, FGS geologists decided to map the first recognizable lithostratigraphic unit occurring within 20 feet (6.1 meters) of the land surface. In areas where highly karstic limestones underlie the undifferentiated siliciclastics, paleosinkholes may be infilled with significantly thicker sequences of siliciclastics. If the shallowest occurrences of the karstic carbonates were 20 feet (6.1 meters) or less below land surface, the carbonate lithostratigraphic unit was mapped. If the carbonates lie more than 20 feet (6.1 meters) below land surface, an undifferentiated siliciclastic unit was mapped.

Undifferentiated siliciclastic sediments occur in significant thickness (>20 feet [6.1 meters]) over much of the Gulf Coastal Lowlands (White, 1970; Scott, in preparation) and the eastern part of the Florida peninsula. Where these sediments were mapped, efforts were made to determine if beach-ridge or dune topography was present in order to subdivide the siliciclastic sediments.

Lithostratigraphic terminology applied in this mapping effort followed, with limited changes, the lithostratigraphic framework delineated for the Gulf Coast Region chart from the Correlation of Stratigraphic Units of North America Project (COSUNA) (Braunstein et al., 1988). Although some of the units depicted on the COSUNA chart have a significant biostratigraphic basis, the COSUNA chart represents the best effort to date to provide an accurate stratigraphic framework for the Florida Platform and surrounding regions.

Figure 1. Stratigraphic column showing the lithostratigraphic units used on the map. [larger image]

A peer review of the geologic map and this text by members of the geologic community outside the FGS was done by S. Upchurch, R. Portell, T. Missimer, J. Bryan, J. Vecchioli, A. Tihansky, K. Cunningham, G. L. Barr and R. Spechler. The FGS greatly appreciates the efforts of these geologists.

FGS cartographers Jim Jones and Ted Kiper worked on the initial phase of this project. CAD analyst Amy Graves assisted in the map preparation. Lou Cross and Peter Krafft from Florida Resources and Environmental Analysis Center, Florida State University, finalized the map in preparation for publication.

Lithostratigraphic units expressed on the State geological map range from Middle Eocene to Holocene. The stratigraphic column showing the lithostratigraphic units utilized on the map delineates only the formations occurring at or near the surface (Figure 1). Table 1 lists the stratigraphic units and provides a brief lithologic components list. Cross sections (Figures 2 and 3) were constructed utilizing cores and well cuttings from the FGS well cuttings and core repository. By necessity, the cross sections show some lithostratigraphic units that do not crop out. These include the Pensacola Clay, Coarse Clastics, Bruce Creek Limestone, and the Long Key Formation. Table 2 lists information for the wells used in the cross sections.

Figure 2. Geological cross section locations. [larger image]

The geologic structures (Figure 4) that have affected shallow Tertiary and Quaternary sediments of the Florida Platform have been defined by numerous authors (Puri and Vernon, 1964; Miller, 1986; Scott, 1988; Scott, 1991). The majority of the structures recognized as influencing the deposition, erosion and alteration of the Cenozoic sediments in Florida do not appear to have had a significant effect on the surface expression of the lithostratigraphic units. These geologic structures include the Gulf Basin, Jacksonville Basin, St. Johns Platform, Sanford High, Brevard Platform, Osceola Low and the Okeechobee Basin (Scott, 1992). Those structural features that exerted an influence on the surficial or very near surface distribution of the Cenozoic sediments, or mark areas of significant facies changes, include the Gulf Trough/Apalachicola Embayment, Chattahoochee "Anticline" and the Ocala Platform. Eocene sediments crop out on the Chattahoochee Anticline and the Ocala Platform. The Gulf Trough/ Apalachicola Embayment formed an important bathymetric and environmental barrier from the latest Eocene or earliest Oligocene into the Miocene. As a result, the Oligocene carbonate facies east and south of the Gulf Trough/Apalachicola Embayment are distinctly different from those occurring to the west and north (see Schmidt [1984] and Bryan [1991] for discussion).