Lecture : Overview of the Geology of Florida (Tom Scott, FGS OFR 50)
Florida Geological Survey Homepage
Overview of Geology
I. Introduction Florida State Information Resource USGS Geologic Information about Florida
A. Location FGDL DATA PREVIEW
1. Most occurs on the Florida Platform
2. Panhandle is in Gulf Coastal Plain
3. Roughly 400 mi X 400 mi
4. More than half is under water with a narrow peninsula extending from the mainland
5. Geology
a. Mid-Mesozoic to Recent sediments
b. Mostly carbonates (through the Paleocene; 2000 to 5000 ft thick) capped by a thin siliciclastic sequence
c. Aquifers mostly in Paleocene to Late Pleistocene; Floridan one of the world's most prolific, regional units; upper Floridan confining unit and intermediate aquifer mostly in Neogene (Miocene to Recent) siliciclastic, clay and carbonate units; surficial aquifer occurs in Plio-Pleistocene units
d. Deposition influenced by changing sea levels and subaerial exposure
II. Geologic History Fossils, Minerals and Geology Internet sites - Florida.
A. Basement-Early Jurassic (>200 my); may be African in origin, separated at plate margin; base for Florida and Bahama Platform (Smith, 1982)
B. Florida Straits-separated Florida and Bahama Platforms by Late Cretaceous
C. Carbonates dominated southern and central Florida from mid-Mesozoic (145 My); northern and eastern panhandle from earliest Cenozoic (62 My); some evaporites in Mesozoic and Paleogene and below the Floridan aquifer due to local restricted environments
D. Gulf Trough (Suwanee Straits) intercepted low amount of clastics from low lying, eroded Appalachians, from Florida Platform resulting in thick, pure Paleogene carbonates
E. Siliciclastic sediments occur in central and western Panhandle during the Paleocene; carbonates formed with a decline in clastics during the late Eocene and continued through Late Oligocene (28 My)
F. Late Oligocene-Early Miocene-renewed uplift of Appalachians, siliciclastics flood the SEUS filling the Gulf Trough and encroaching on the Florida Platform; form the aquiclude over the Floridan aquifer; breaching in Early Pleistocene led to development of karst features and aquifer systems; some karst during the latest Oligocene (maybe Paleocene)
III. Structure
A. Pre-Middle Jurassic-erosional surface that includes the Peninsular Arch, the South Florida Basin, Southeast Georgia Embayment, Suwanee Straits, and the Southwest Georgia Embayment (Apalachicola Embayment); affected deposition of Mesozoic and Cenozoic sediments.
B. Post-Paleogene Structures-somewhat different; include Ocala Platform (Ocala Arch), Sanford High, Chattahoochee Anticline, Apalachicola Embayment, Gulf Trough, Jacksonville Basin (part of SE Georgia Embayment), Osceola Low, and the Okeechobee Basin
C. Positive (poorly confined) and negative (well confined) areas affect the Floridan aquifer system; intermediate is absent from positive areas; surficial reflects local conditions
IV. Geomorphology
A. Physical setting
1. Relatively flat with low relief
2. Result of complex depositional and erosional processes
3. Sea level fluctuations during the Cenozoic were a dominant feature; relict shorelines throughout the State
4. Karst feature large and small scale; original feature may be hard to know
B. Geomorphic Divisions (White, 1970, FGS Bull 51)
1. northern or proximal zone
2. central or mid-peninusular zone
3. southern or distal zone
4. Specific landscape types
a. Northern Highlands-typically well drained; area of recharge; karst features
b. Central Highlands-also well drained; recharge area; karst features
c. Coastal Lowlands-poorly drained, swampy areas; few recharge areas
C. Vernon and Puri as well as White used a hierachical classification scheme
1. Detailed classification of features reported in tabular form
2. Criticized because these features were basically described by the processes that formed them and not the geological materials that occurred in the areas.
D. Brooks' physiographic map created a number of new subdivisions that are largely based on surface flora that were interpreted to represent the near surface geology. Not widely accepted because it lacked peer-review.
E. Walt Schmidt, the State Geologist, has undertaken to remedy this shortcoming with the descriptions and maps that are in the Geology of Florida text.
V. Lithostratigraphy
A. Paleozoic Era
1. Cambrian-Osceola Granite and high feldspar rocks(1-3 km below the northern peninsula); 600 MYBP
2. Lower Ordivician-Quartz sand with marine fauna, resembles NW Africa
3. Silurian-middle Devonian-dark shales and other marine sediments
4. Gondwanaland evidence-
a. flora and fauna are not North American
b. Paleomagnetic from Paleozoic sediments in Alachua county indicate 49, rather than the 28 expected for North America
c. Mineralogy of detrital sediments unlike any rocks known in Appalachians
d. Florida remained part of Gondwanaland though most of the Paleozoic
5. Pennsylvanian period-Florida and other terranes dispersed as Gondwanaland breaks up and the Atlantic Ocean forms
B. Mesozoic Era
1. Lower Triassic-Eagle Mills Formation, in the Panhandle, containing Red Beds and igneous rocks from rifting edge of Africa; Tallahassee Graben also originated with rifting
2. Upper Triassic-Florida sutured on to North America during the Alleghenian orogeny along a zone indicated by the Brunswick gravity anomaly in Georgia
3. Lower Jurassic-intrusive and extrusive rock activity from a center located near current Bahamas
4. Middle Jurassic-depocenter for shallow marine carbonates; northwest Florida and Gulf area underlain by Louann Evaporites due to restrictions and high salinities (doming of theses salt deposits produced oil traps in the overlying Smackover Formation of Late Jurassic limestone); peninsular carbonates interfinger with continental clays and sands from Appalachians in North Florida
5. Cretaceous-the Sunniland Limestone, north and west of the Everglades (an oil producing area) reach more than 3,000 m; Rebecca Shoals barrier reef forms along the SE margin of the Florid Platform; rhyolites extruded in south Florida adjacent to the newly opened Florida Straits
C. Cenozoic Erathem
1. Tertiary System-shallow marine conditions, fossiliferous limestones
a. Paleocene Series-faunas with affinities with North Africa and Paris Basin
(1) Cedar Keys Formation-dolostone and evaporites (gypsum and anhydrite) with minor limestone; forms the base of the Floridan over most on the State except NW Florida where the Oldsmar Formation forms the base
b. Eocene Series-begin with faunas similar to Paleocene (Tethys link-shells and bones in pyramids similar to Florida limestones); become Trans-Atlantic
(1) Lower to Middle Eocene Claiborne Group of NW Florida-glauconitic to clayey sand; usually about 100m below the surface with a thickness of 100m; unconformably overlain by the Ocala Limestone
(2) Oldsmar Formation-Lower to Middle Eocene in South and Peninsular Fla.; limestone with vuggy dolostone; bottom of the Floridan in some areas
(3) Avon Park Formation (Middle Eocene)-oldest outcropping rocks in Florida; fossiliferous ls with dolomite vugs; occurs throughout Panhandle and eastern peninsula; some land plant impressions indicating emergence; part of the Floridan aquifer; locally a confining bed (separates lower and upper Floridan)
(4) Ocala Limestone (Late Eocene)-two units differing textures (lower unit granular; upper muddy limestone); major component of Floridan aquifer; characteristic North American biota; surface and thickness highly irregular due to karst development
c. Oligocene Series-more clastic than earlier limestones due to Appalachian uplift; Ocala Platform active; first land vertebrates occur
(1) Suwanee Limestone-in Peninsular and part of the Panhandle, interbedded dolostone and limestone; absent in northern and central Peninsula due to erosion; scattered outliers; part of the Floridan where present
(2) Panhandle (central and western)-
(a) Bucatunna Clay-limited distribution in western Panhandle
(b) Marianna Limestone-lateral equivalent of the Suwanee
(c) Chickasawhay Formation-maybe Lower Miocene in age; limited to Western Panhandle
d. Miocene Series-change from carbonates to clastics in most of the Florida Platform; absent from the Ocala Platform
(1) Chattahoochee Formation-lower silty and sandy dolostone; occurs in central Panhandle; laterally gradational
(2) St Marks Formation-Moldic ls; occurs in Apalachicola Embayment
(3) Hawthorn(e) Group-Middle Miocene sand, silt, and clay; irregular karstic and erosional surface; aquitard for Upper Floridan; much more later
(4) Bruce Creek Limestone-Middle Miocene; occurs in the Apalachicola Embayment of west Fla.
(5) Alum Bluff Group-west of the Apalachicola River, Hawthorn replaced by Alum Bluff; clays, sands, and shell beds; locally in the intermediate aquifer
(6) Pensacola Clay-silty, sandy clays with plant remains
(7) Intracoastal Formation-sandy with abundant microfossils; Middle Miocene at the base to Late Pliocene at the top
2. Plio-Pleistocene Series-occur over most of the State; includes fossil barren sands to fossiliferous limestone.
a. "Coarse Clastics"-sands and gravels that occur in a variety of locations
b. Tamiami Formation-widespread in south Fla.; complex depositional history; part of the surficial aquifer
c. Citronelle Formation-fine to very coarse clastics; covers much of central and western Panhandle
d. Miccosukee Formation-grades laterally from Citronelle Fm; clayey unit occurring from Gadsden to Madison Counties
e. Cypresshead Formation-siliciclastic clayey sands; occurs in the Central Highlands to Highlands County; surficial aquifer in many places
f. Nashua Formation-calcareous to clayey sand; extent not well known; grades laterally to Cypresshead Fm; local aquifer
g. Caloosahatchee Formation-quartz sand and interbedded, freshwater ls; occurs along the west coast from Tampa to Lee County, then north along the east coast; undifferentiated from Ft Thompson as an aquifer
h. Fort Thompson-marine and freshwater limestone and shell beds
i. Key Largo Limestone-coralline limestone occurs from Miami to low Keys; grades laterally to Miami Ls
j. Miami Limestone-oolitic-bryozoan Ls; covers Dade and parts of Broward and Monroe Counties; grades laterally to Key Largo and Anastasia Fms; part of the Biscayne aquifer
k. Anastasia Formation-interbedded sands and coquinoid Ls; forms that Atlantic Coastal Ridge; outcrops from St Augustine to Boca Raton
l. Undifferentiated Pleistocene-Holocene Sediments-dunes, fluvial deposits. Aeolian deposits, carbonates, peats; locally important components of shallow aquifers
