GEOLOGY OF FLORIDA

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MIOCENE TO HOLOCENE
CHAPTER 5


 






I. Introduction
     A. Paleogene
        1. Paleocene-Early Eocene
           a. shallow carbonate deposits
           b. rich marine faunas with North African and Paris Basin (Tethyan Sea) affinities
      2. Middle to Late Eocene
           a. land plants leaves in the Avon Park
           b. carbonate deposition
           c. marine faunas with non-Tethyan affinities
      3. Oligocene
           a. Sea level drops
           b. Clastic deposits from Applachian increase
           c. Suwannee Straight deepens for the last time
      4. Late Oligocene to Early Miocene
           a. Ocala Platform is active
           b. Peninsula emerges
           c. First land vertebrates
     B. Neogene-begins about 23 My ago
        1. Early Miocene
          a. Carbonates over most of the state
          b. Becoming intermixed with increasing percentages of clastics
          c. At the end of the Early Miocene, carbonate deposition only in southern peninusular Florida
        2. Middle to Late Miocene
           a. Dominated by siliciclastic deposition that continued until Late Miocene
           b. Chattahoochee Formation
            (1) fossiliferous, silty to sandy dolostone
            (2) occurs in a limited area west of the  axis of the Gulf Trough
            (3) grades laterally into basal Hawthorn Group
          c. St Marks Formation
            (1) quiet water deltaic and estuarine deposits
            (2) can grade into  Chattahoochee Fm
          d. Hawthorn Group
            (1) complex series of phosphate and clay bearing sediments
            (2) unusual mineralogy
            (3) dolostone is the main carbonate present
            (4) sediments may cover Ocala Platform in a thin layer, later eroded
            (5) Northern Section-interbedded  phosphates and siliciclastics; locally important aquiclude and/or intermediate aquifer
                 (a) Coosawhatchie-Statenville
                 (b) Marks Head
                 (c) Penney Farms
            (6) Southern Section
                 (a) lower phosphatic-carbonate section
                 (b) upper phosphatic -siliciclastic  section
                 (c) Divisions
                      i) Peace River
                      ii) Arcadia-Tampa Formation
                          a) Arcadia Fm consisting of the Tampa-Nocatee members representing a mixture of clastic and carbonate       sedimentation

II. Lithologies

    A. Unique charcteristics of Hawthorn Fm
      1. high phosphate content
      2. unusual clay minerals
      3. variable sedimentology (sand content; Gulf province vs Atlantic province sandier)
      4. weathering effects
     B. Phosphate occurrence types; the basis for     dividing these sediments
      1. marine-most abundant; makes up part of the economic deposit
      2. reworked-occurrences in scour channels; some economic deposits
      3. residual-areas of enrichment; "leached zone ore" in central Florida; high in uranium; Fe and Al may be to high for             conventional economic use
  4. Alachua Fm-restricted to phosphatic   sediments outside  the Hawthorn Fm; originally defined in north Florida (can be  seen near the top of the Devil's Mill Hopper)

III. Hawthorn Group
 A. Found in most of Florida except on the crestal  area of the Ocala uplift.
 B. First described in 1887 by L. C. Johnson in a USGS paper that called it the Waldo Formation
 C. In 1892, Dall first used the "Hawthorne beds" for sediments "being quarried and ground  up as fertilizer near Hawthorne,"    Fla; the pits of C. A. Simmons may be the "type section;" includes the Waldo Formation
 D. Matson and Clapp (1909) accepted Dall's ideas  and raised the sediments to Hawthorne Formation; first to use this name
 E. Matson and Sanford dropped the "e" in 1913 claiming that the town name was originally misspelled
 F. Bishop (1956) included the "Citronelle" sands in the Hawthorn as a "non-marine, continental facies
 G. 1950s and early 60s, a lot of USGS interest in  the Hawthorn of Central and North Florida;  Altschuler (1964) described the intensive weathering of the Hawthorn
 H. Puri and Vernon (1964) did not accept Dall's interpretation of the "type section" (the concept really didn't exist in Dall's time) and adopted;  preferred Johnson's sketches included in Dall; suggested that the sections at the Devils Mill Hopper or Brooks Sink were the type sections   (cotype locality); this is not valid under today's  Strat Nomen Code
 I. In 1988, Huddleston raised Hawthorn to Group in Georgia with the Grove Park as the type section; included 9 formations: Scott extended the idea into Florida (What is a formation?)
 J. Formation Names and Lithologies
  1. North Florida-thickness varies from zero along positive features to 800 feet in the  Jacksonville Basin
   a.  Formations
    (1) Statenville/ Coosawhatchie   (Charlton Member)
    (2) Marks Head
    (3) Penney Farms
   b. Lithologies
    (1) clays (quantity depends on    location)
    (2) sands (quantity depends on    location)
    (3) carbonates--mostly dolomite with calcite shells
    (4) phosphates (pebbles to very fine   sand sizes and below)
    (5) upper parts are similar to  sediments in Georgia, resulting in  the same terminology in both   states (also some similar stuff in  South Carolina)
  2. South Florida-thickness varies from near zero to 700 feet in the Okeechobee Basin
    a. new formation names required to support group concept and to  recognize the changes in lithologies
    (1) Peace River Formation (Bone Valley Member at top)
    (2) Arcadia Formation (Tampa/Nocatee  Members at bottom)
    b. Lithologies
    (1) same general sediment types as north Florida, but distribution is different
    (2) in the western half the lower unit is predominantly carbonate
    (3) eastern half, lower units are distinctly siliciclastic
    (4) generally becomes more siliciclastic and complex as you go eastward

IV. Problems with Dall's definition of Hawthorn Beds
 A. Dall neither designated nor referred  to type localities in general; not part of Dall's concept of stratigraphy
 B. In 1892, type sections were only rarely   mentioned in the geologic literature
 C. no stratigraphic code existed at that time to offer guidelines
 D. Overgrown by the time Cooke visited in 1913
 E. Controversy
  1. Vernon and later Brooks  believed that the  Hawthorn Fm covered the Ocala uplift and Sanford High
  2. others do not believe this
  3. evidence is conflicting and depends on interpretation of sediment distribution (laps up or is eroded)
  4. Hard rock phosphate (Dunnellon Fm) in north Central Florida is interpreted as derived from guano or altered and removed Hawthorn

V. Alachua Formation
 A. Originally "Alachua Clays" by Dall and Harris     (1892)
  1. based and sand and clay fillings in sinkholes
  2. stream fillings
 B. Sellards included the Hardrock Phosphates  from around Dunnellon in the formation  (Dunnellon Fm)
 C. Vernon (1951) and later Vernon and Puri (1964) used "an interbedded, irregular deposit of clay, sand, and sandy clay with diverse  characteristics"
 D. Origins
  1. Cooke (1945) residual, in-sit accumulation
  2. Vernon and Puri (1964) thought it was terrestial and in part lacustrine and fluvial
  3. Brooks (1966) estuarine sediments  containing some Hawthorn and covered by  Plio sediments and karstic fills
  4. Scott (1988) believes that it is reworked Hawthorn and is not part of the Hawthorn Grp
  5. Proposed dates range from middle Mio to Plio-Pleistocene
  6. Complex and needs more study

VI. Bone Valley Sediments (name based on vertebrate remains found in the central Florida phosphate mines)-demoted to member of the Peace River Fm in current usage
 A. Criteria for demotion (Scott, 1988)
  1. limited areal extent
  2. gradational boundaries
  3. lithologic similarities with Peace River Fm
  4. overlies the Arcadia in some areas, but overlies and often interfingers with the  Peace River Fm
 B. History
  1. proposed by Matson and Clapp (1909) from phosphate mines west of Bartow, but no type section was given (section constantly changes with mining)
  2. thus "type section" remains in the current pits; section may have expanded as deeper pits have been mined
 C. Lithology
  1. very important economic deposits; the main ore of the early phosphate district
  2. entirely a clastic unit
  3. pebble and gravel size phosphate  fragments and sand sized phosphate mixed  with quartz sand and clay; percentage of phases varies widely
  4. clays occur as discrete units of "bed clays" in the phosphate matrix; some consider to  be residuum  of agrillaceous carbonate rocks of the Hawthorn (Altschuler et al., 1964)
  5. beds often are graded and cross-bedded
  6. Upper Bone Valley may be so weathered  that the apatitic phosphate is removed and is replaced by Fe,Al phosphates (Leached Zone Ore, very high in uranium)
 D. Age
  1. original "type" sections contained   post-Messinian  (regression with an  unconformity) gravels and vertebrates; thus latest Messinian or Early Zanclian age (Latest Miocene or Earliest Pliocene)
  2. deeper mining pushed the oldest dates back to latest Early or early Middle Miocene

VII. Eastern Florida Panhandle--westward limit is the  Appalachicola River in Gadsden and    Liberty Counties (western edge of the Gulf Trough)
 A. Lithology
  1. decreased phosphate content throughout the section
  2. sandy clay or clayey sand in most areas;  commercial source of palygorskite mixed with sepiolite and smectite used in animal litters and commercial absorbents
  3. carbonates increase westward in the Gulf Trough area
 B. Formations
 1. Torreya Formation
  a. Dogtown Member (upper middle)

VIII. Hawthorn Group Mineralogy
 A. Phosphates--nearly ubiquitous
  1.  mostly sand sized
  2. economically very important
  3. mineralogically carbonate fluorapatite
  4. origin
   a. related to global sea level changes
   b. topograpicall induced upwelling
   c. preservation traps
  5. post-depositional modification
   a. results from groundwater migration that leaches phosphates (leached zone ores)
   b. supergene enrichment removing  carbonates
   c. processes also affect the clays
 B. Palygorskite and Sepiolite--often the dominant clays of the Hawthorn Group
  1. origins
   a. weathering
   b. altered volcanic ash
   c. transformation of existing clays
   d. neoformation (precipitation)
 C. Dolomite--rather enigmatic
  1. several types occur
  2. often associtated with palygorskite or sepiolite
  3. dolomitization has destroyed most of the original depositional structures
  4. often occur immediately overlying   undolomitized limestones
  5. often occur in fine particle sizes and are  referred to as dolosilts

IX. Problems
 A. Palogene is dominated by carbonates
 B. Gulf Trough/Suwannee Channel closed at the  end of the Eocene
 C. No siliciclastic sediments are recognized until the Miocene (no Oligocene clastics)
 D. deposition doesn't exactly follow the sealevel curves of Vail et al.
 E. areal extent (Ocala Uplift and Sanford High)

X. Alum Bluff Group
  A. replaces the Hawthorn west of the Applachicola River
  B. no lithostratigraphic separation
  C. formations are based on molluskan faunas
  D. Other units
   1. Pensacola Clay
   2. Intracoastal Formation

XI. Introduction to Pliocene
 A. Surficial cover of the State ranges in age from Miocene to Holocene
 B. Exposures limited to rivers and streams valleys and a few sinkholes
 C. Represents environments with fluvial,   freshwater, and aeolian deposits
 D. Thicknesses range from a few feet in Panhandle and west central Peninsula to more than 1000 feet in southern Florida
 E. Source of commercial sands, clays, shells, and heavy minerals

XII. Stratigraphic Problems
 A. Use of biostratigraphy to identify "formational" units; Tamiami, Alum Bluff, Caloosahatchee based on faunas, not lithology
 B. Limited number of exposures
 C. Complex facies relationships
 D. Diagenetic alteration has obliterated many fossil assemblages
 E. Incomplete understanding of sea level     changes

XIII. Neogene Transition
 A. Renewed uplift of the Blue Ridge portion of the  Appalachians provided siliciclastics to replace carbonates
 B. Siliciclastics covered the entire State by the    end of the Miocene; reached a maximum in    Early Pliocene
 C. Later in Pliocene and into the Pleistocene carbonate sedimentation once more became established in southernmost portion of Florida platform (Anastasia Fm, south Fla LS, and Keys)
 D. Most of this deposition took place around the margins of the Peninsula
 E. Paleogene structures provided the pattern for Neogene deposition Apalachicola Embayment, SE Georgia Embayment, Jax Basin, Okeechobee Basin were depocenters
 F. Positive areas existed on the Ocala Platform,  Brevard and St Johns Platforms,    Chattahoochee "Arch"
 G. Post Miocene erosion removed sediment from the crest of the Ocala Platform and Sanford High to  expose the Avon Park; later Plio-Pleistocene deposition covered the Sanford High and parts of the Ocala Platform; these features have been extensively modified by erosion and karstification
 H. "Faults" identfied in these unconsolidated  sediments may be karst features with high relief
 I. Differential subsidence during the Cenozoic has resulted in positive and negative features
 J. SW trending South Florida Basin disappearing in Late Oligocene and replaced by SE trending  Okeechobee Basin; Petuch (1985) suggested
   this might be an astrobleme; more like a result of tectonic adjustment of the Florida Platform

XIV. Sea Level Stands
 A. Early and Middle Miocene 50 to nearly 150 meters higher than present
 B. Late Miocene dropped well below current levels
 C. Early Pliocene nearly 100 meters higher than  present
 D. Late Pliocene and Pleistocene were in the  20 meter range

XV. Lithostratigraphic Framework
 A. Area is quite large (500 km X 800 km) so  significant local variations should be expected
XV. Pliocene
 A. Poorly exposed
 B. Mostly subsurface occurrence
 C. Paucity of diagnostic macro- and   microfossils
 D. Known from pits and quarries and some   subsurface work
  5. Units previously thought to be Miocene are  now considered Pliocene
   a. Tamiami Fm and Calossahatchee Fm      (Late Pliocene) originally assigned as     Pliocene by Cooke (1945)
   b. Jakcson Bluff in the Panhandle thought to be the equivalent of the Tamiami Fm
  6. Citronelle and Miccosukee Fms in the   Panhandle
  7. Cypresshead in the Peninsula
  8. Nashua Fm of North Fla is Late Pliocene to Early Pleistocene (Huddleston, 1988)
  9. Peace River in Upper Hawthorn Group is  Pliocene (Scott, 1992)Reworking of Miocene results in phosphate grains in Pliocene units of central and southern Florida; includes some commercial deposits
  10. Ft Thompson Fm of interbedded shells and limestone; freshwater, brackish, to marine
  11. Lake Wales Ridge coarse clastics of sand and clay along the center of the Peninsula
  12. Undifferentiated coarse clastics (Grandin  Sands?)

XVI. Pleistocene Units
 A. Exposures and limitations basically the same as in the Pliocene
 B. Undifferentiated Pleistocene Sediment  includes "terrace" deposits; peats, eolian sand dunes, fluvial deposits, and fresh water carbonates in   springs and in the Everglades
 C. Locally important in the surficial aquifer; up to 300 feet thick as paleokarst infilling.
 D. Trail Ridge of SE Georgia and NE Florida
 E. Anastasia Fm of interbedded qtz sand and  coquinoid LS; forms the Atlantic Coastal ridge along most of its exposure; grades southward into the Miami LS; part of the Biscayne and  Surficial Aquifer systems
 F. Miami LS contains oolites and bryozoans;  gradational between the Anastasia and Key Largo LSs; part of the Biscayne and surficial aquifer
 G. Key Largo is a coralline LS; lateral equivalent of  the Miami LS (oolitic) which conformably overlies much of the Key Largo

XVII. Effects of Sea Level Changes
 A. rate of change is the important variable
 B. rapid change--leaves things pretty much the    same.
 C. slow change--will build a succession of beaches and or dunes; not easy to identify the steps or stages
 D. lower terraces have much better chance of being preserved; older ones can be eroded, karstified, and eolian affected
 E. Identified Terraces
  1. Silver Bluff--8 foot; well seen in south  Florida near Cocanut Grove; some areas of this may be questionable and represents on   local hurricane surge tides
  2. Pamlico-25 foot; pretty common (San  Mateo, Vero Beach); fringing areas protected these features
  3. Talbot--40 to 45 foot; this surface is quite   clear in some areas
  4. Penholoway--70 foot pretty clear in DeSoto  County
  5. Wicomico--100 foot; fairly well developed   and widespread
  6. Higher terraces are restricted to Central Peninsula and Panhandle

XVIII. Miocene to Holocene Problems
 a. Hawthorn cover on Ocala Platform (Y/N)
 b. Citronelle Fm areal extent      (Citronelle-Miccosukee-Cypresshead-Nashua  Fms)
 c. Identification of Hawthorn Group formation in the field
 
 








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