Geological Oceanography Section II Lecture 11

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Geological Oceanography Section II Lecture 11

• Geologic History of Florida
• 25 March 2008

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Geologic History of Florida
Florida has been described as Land from the Sea
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Goal of Lecture

• Provide an example of geologic history as it
  relates to Florida
• Provides an example of how geology influences
  daily lives
• Where people live and why?
• What about the future?

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Geology of FloridaCondensed Version

• Proto-Florida was a piece of Gondwana
  (Mid-Paleozoic)
• The Iapetus Ocean (Proto-Atlantic) closed (Late
  Paleozoic)
• The continents rifted apart, leaving a sliver of
  Gondwana as an offshore bank of SE North America
  (Early-Mid Mesozoic)
• The continental margin began to thermally subside
  (Jurassic)
• Carbonate sedimentation proceeded (Late Jurassic
  - mid Oligocene)
• What is now penninsular Florida was an offshore
  bank
• The Appalachians rejuvenated (Oligocene)
• Terrigenous clastic sediments filled the Suwanee
  Straits, then covered Florida
• Closing of Panama Seaway accelerated Gulf Stream
  (Miocene)
• Upwelling and phosphorite deposition over much of
  Florida
• Sea level rose and fell (Miocene to Recent)
• Well-sorted quartz sands frost the surface with
  dunes and beach deposits
• Paleoshorelines and dune ridges
• Some heavy metal beach placer deposits in north
  Florida
• Limestone erosion produced karst topography
  (sinkholes, springs
• Florida aquifer corresponding to Eocene
  limestones is major water resource
• Shell deposits on shoals and shelf margins
• Coral reefs, oolite shoals and bryozoan-rich
  limestones in south Florida

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FloridaAn Exotic Terrane?
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Mid - Late Ordovician
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Postulated position for the Tallahassee-Suwannee
terrane in the Siluro-Devonian (Channell et al.
1992)
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Closure of the Iapetus Ocean

• Hercynian Orogeny formed Appalachian Mountains
• Suturing of Gondwana to Laurasia formed Pangea
• Fragment that became Florida attached to North
  America
• Timing Late Paleozoic

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Break-up of Pangea/Opening of the Atlantic

• Florida basement rocks left behind as a fragment
• Characteristics provide evidence
• Osceola Granite has equivalent in N. Africa
• Paleozoic sediments of Suwanee Basin also have
  North African equivalents
• Triassic and Jurassic volcanics produced by
  rifting

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Atlantic Rift Zone
Africa
Bahama Fracture Zone
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• Osceola
• Granite

BFZ
Florida Straits Block was not in this position
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Proto- Florida
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Proto- Florida
Paleozoic sediments
Equivalents in North Africa
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Proto- Florida
Paleozoic sediments
Osceola Granite
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The Peninsular Arch

• Basement rocks on top of which shallow water
  carbonates began to accumulate
• Carbonate sedimentation initiated in Jurassic

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Geologic Cross Section of Florida Northwest to
Southeast
Paleozoic sedimentary rocks
Cenozoic sediments/sed. rocks
Cretaceous sedimentary rocks
Osceola (Cambrian) Granite
Precambrian metamorphics
Triassic/Jurassic igneous
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Major Geologic Eventsof the Jurassic (200-144 Ma)

• Spreading centers/transform faults propagate
  around peninsular Florida
• Seafloor spreading begins in Gulf of Mexico
• Widespread evaporite (salt) deposits in the Gulf
  of Mexico rift basins
• Florida Straits Block migrates in from west
• Carbonate platform initiates on top of Paleozoic
  basement and Early Mesozoic volcanics on Florida
  pennisula

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Major Geologic EventsEarly Jurassic

• Spreading centers/transform faults propagate
  around peninsular Florida
• Seafloor spreading begins in Gulf of Mexico

Note The source of 3 color interpretations that
follow is Explorer (2000) J. PINDELL, L. KENNAN,
S. BARRETT http//www.aapg.org/explorer/geophys
ical_corner/2000/gpc10.cfm
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Florida
Florida Straits Block
185 Ma
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Major Geologic Eventsof the Mid-Late Jurassic

• Seafloor spreading continues in Gulf of Mexico
• Widespread evaporite (salt) deposits in the rift
  basins
• Florida Straits Block continues to move eastward
• Carbonate platform develops on top of Paleozoic
  basement and Early Mesozoic volcanics on Florida
  pennisula
• Bahamas-Grand Banks gigaplatform develops on
  continental margin of eastern North America

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Middle Jurassic (170 Ma) Paleogeography of the
Gulf of Mexico
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Late Jurassic
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Late Jurassic -- Bahama-Grand Bank Gigaplatform
Florida
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Florida
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Major Geologic EventsEarliest Cretaceous (140
Ma)

• Seafloor spreading ends in Gulf of Mexico (1)
• Florida Straits Block in place, forming southern
  portion of peninsular Florida (2)
• Demise of carbonate sedimentation along upper
  North American continental margin (Bahamas-Grand
  Banks gigaplatform) (3)
• Early opening of the Caribbean (4)

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3
1
2
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Early Cretaceous (140 Ma)
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Carbonate sedimentation continued over
Florida-Bahamas region
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Approximate location of Suwanee Straits
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The Carbonate Cover
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Geologic Cross Section of Florida Northwest to
Southeast
Paleozoic sedimentary rocks
Cenozoic sediments/sed. rocks
Cretaceous sedimentary rocks
Osceola (Cambrian) Granite
Precambrian metamorphics
Triassic/Jurassic igneous
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Mid Mesozoic to Cenozoic Sedimentationcross
section west to east
Cenozoic
Cretaceous
Jurassic
Cenozoic
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Cretaceous Carbonate Sediments

• More than 3,000 m thick in south Florida
• Nearly 2,000 m thick in north Florida
• Thinner over Pennisular Arch
• Origin
• Skeletal and non-skeletal carbonates
• Dolomites
• Extensive evaporites
• Dolomitization of calcium carbonate commonly
  occurs in association with evaporites
• Minor shales, possibly of eolian origin

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Early Cretaceous deposition Primarily limestone,
dolomite, and associated evaporites
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Lower Cretaceous Limestones

• Platform carbonates characterized by rudistid
  bivalves in carbonate muds
• Carbonate muds likely produced by widespread
  whiting-type events

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Analogy Lower Cretaceous Boquillas Limestone,
Big Bend National Park, TX
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Carbonate mud production by microbial activity
Whiting over Cay Sal Bank, Bahamas
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CO2 IN THE GEOLOGIC RECORD
(Berner 1994)
GEOCARB 2
Mesozoic
Cenozoic
Paleozoic
RCO2
Time (million years)
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Calcite-aragonite cycles in the geologic record

• Sandberg (1983) model
• pCO2 controls aragonite/calcite cycles
• Hardie (1996)
• Mg/Ca controls aragonite/calcite cycles
• Based on evaporite minerals which are independent
  of pCO2

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Note very high Ca
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Some possible consequences of high atmospheric
pCO2 combined with high Ca2 concentrations in
seawater

• Calcium is toxic intracellularly
• More rapid transport out of cell was required
• Calcification is a mechanism for cells to
  eliminate calcium
• E.g., coccolithophorids produced more massive
  coccoliths
• Long-term, high atmospheric CO2 meant very high
  alkalinity in seawater
• Active photosynthesis probably triggered
  supersaturation and whiting production

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West Florida Margin

• Defined by West Florida Escarpment
• Situated on top of structural high formed by
  oceanic crust/rifted crust boundary.
• Limestone platform built vertically on top of the
  basement high.
• West Florida Escarpment oversteepened by erosion,
  6 km retreat.

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West Florida Margin
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Mid-Cretaceous ( 90-80 Ma) Widespread Drowning
of Carbonate Platforms

• Terminating carbonate platforms worldwide
• Including west Florida
• Associated with Oceanic Anoxic Events
• Ocean Plateaus Mantle Plumes
• High CO2, Greenhouse Earth
• Very high sea levels brought uppermost
  thermocline waters onto platforms
• Nutrient rich, low O2
• Origin of Straits of Florida

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Upper Cretaceous Sedimentation

• Shallow platform sedimentation continued in some
  areas
• Open shelf pelagic sedimentation was widespread
• Chalks produced by coccolithophorids and planktic
  foraminifera

0.1 mm
http//www.unifr.ch/geoscience/geology/Research/mi
rcopaleontology.html
http//www.mnr.manston.net/geology.htm
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Cenozoic Terminology

• Two sets of terminology - can be confusing
• Tertiary/Quaternary
• Tertiary refers to Paleocene through Pliocene
• Quaternary referes to Pleistocene and Holocene
• Paleogene/Neogene
• Paleogene refers to Paleocene through Oligocene
• Neogene refers to Miocene through Holocene

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Cenozoic History of Florida

• Paleogene continued carbonate sedimentation
• Oligocene uplift of Appalachians
• Terrigenous clastic sediments filled Suwanee
  Straits
• Miocene
• Terrigenous sediments carried south
• Sea level fluctuations resulted in upwelling and
  phosphorite deposition
• Pliocene through Holocene
• Sea level fluctuations
• Working of siliciclastics (mostly quartz sands)
• Shell deposits (coastal) and reefs (south Florida)

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Correlations of Cenozoic formations southeastern
U.S.
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Collision between Greater Antilles (Cuba) and
Fl/Bahamas

• Antillean Orogeny 56-50 Ma (Lower Eocene)
• Southern portion of Florida Platform uplifted to
  form limestone mountains in western Cuba
• Contributed to formation of Straits of Florida

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Paleocene-Eocene Paleogeography

• Pennisular Florida remained an offshore platform
• Suwanee Channel (Straits) prevented
  siliciclastics from reaching pennisula
• Structural low formed as a result of failed
  rifting
• Shallow-water carbonate sedimentation
• Coralline algae, bryozoans, larger benthic
  foraminifera predominated
• Corals and calcareous green algae present but
  less important

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Paleogeographic map of Paleocene deposition
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Suwannee Straits (Seaway)
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Paleogeographic map of Early Eocene deposition
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Paleogeographic map of Middle Eocene deposition
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Paleogeographic map of Late Eocene deposition
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Paleocene-Eocene

• Evaporites
• Widespread in Paleocene
• Progressively diminish through Eocene
• Siliciclastic influence in North Florida
• Diminished in Mid-Late Eocene

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Siliciclastic Invasion Begins Middle Oligocene
30 Ma

• Erosion of southern Appalachian Mountains is
  ultimate source of siliciclastics
• First, Suwannee Straits infilled
• Then quartz sand introduced onto carbonate
  Florida Platform
• Transported by rivers and longshore currents

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Siliciclastic sediments from the north filled
Suwanee Straits, then inundated the Florida
Platform
Eocene
Oligocene
Geologic map pre-Hawthorn
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Hawthorne Group (Miocene) over Ocala Group
(Eocene) and Suwanee Limestone (Oligocene
N
S
Ocala Group
Hawthorn Group
Oligocene
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Middle Miocene (10-15 Ma)
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Closure of Caribbean Gateway -- 15-2.6 Ma

• Tectonic formation of Isthmus of Panama
• Strengthened western boundary current
• Widespread erosion along margins of Florida
  Platform
• Topographically induced upwelling induced
  phosphatization events on Florida Platform

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Phosphates

• Primary nutrient in ocean
• Mineralizes on/within sediments in areas of
  upwelling--high organic matter loading
• P released during organic matter decomposition
• Primarily used in fertilizers
• Florida contains 30 worlds phosphate

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The Hawthorn Group

• Early Miocene through Early Pliocene in age
• Lower units carbonates interbedded with
  siliciclastics
• Upper units siliclastics with some interbedded
  carbonates
• Economic importance characterized by occurrence
  of an unusual suite of minerals
• Apatite (phosphate grains) mined for fertilizer
• Palygorskite, sepiolite (Mg-silicate clay
  minerals) absorbant clays (e.g., kitty
  litter)
• Dolomite

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Thickness of Hawthorn sediments
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Areas of significant phosphate resources
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Florida phosphate mine
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What is Karst?

• Karst is best described as a region characterized
  by sinkholes, underground streams, and caverns
• These underground conduits are typically formed
  by acidic rain water dissolving soluble bedrock
  (typically limestones or dolomites) over
  thousands to millions of years
• Karst areas are typically devoid of surface water
  as all the water is diverted through underground
  channels
• The main theme in karst regions is underground
  drainage

http//www.karstconservancy.org/karst/photos-of-ka
rst.asp
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Karst topography
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http//www.karstconservancy.org/karst/photos-of-ka
rst.asp
Briar Cave, Florida
Karst Spring
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Karstification

• Karstification process of dissolution that forms
  karst topography
• Occurs whenever limestone is exposed to
  dissolution by rainwater or groundwater
• Extensive karstification during sea-level
  lowstands at 30 Ma and 12 Ma
• Continued during subsequent lowstands
• Rocks break along trends called joints
• Water can act along these breaks
• Large-scale dissolution has formed many features
  of the Florida landscape
• Okeechobee, Tampa Bay, Charlotte Harbor basins
• Linear groups of smaller lakes
• Linear trends to many Florida rivers

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• Karst features
• Some linear features
• Lines of lakes
• Straight rivers
• Large dissolution features
• Lake Okeechobee
• Tampa Bay
• Charlotte Harbor

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Notice how straight Florida rivers tend to run
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Seismic evidence for karstification
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Tampa Bay
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Seismic evidence for karstification Tampa Bay
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Late Stage Siliciclastic Transport -- 5.6-2.0 Ma

• Quartz-rich sediments infilled basins in south
  Florida
• May have been transported by large rivers
• Evidence of river deltas on Florida Platform

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Sea level interpretations for the Long Key
Formation
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Carbonates in South Florida
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Reef Development
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Sea Level and Isotope Stages
Key Largo Limestone
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Elbow Reef and underlying Key Largo Limestone
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Miami Oolite
Key Largo Limestone
Miami Oolite
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Sea Level and Isotope Stages
Last Glacial Retreat
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Modern Reefs
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Present Features
Barrier Islands
Barrier Islands
Marsh Coastline
Barrier Islands
Barrier Islands
Mangrove and Marsh
Coral Reefs
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Physiography
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Environmental Geology
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Modern shorelines are quartz rich
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Where do people live and why? 1990 population
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Even small differences in topography are important
Miami
Everglades
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Floridas Water Supplies

• Floridan Aquifer
• Paleogene limestones
• Underlies entire state but not always potable
• Shallow Hawthorne aquifers
• Local and intermittent
• Biscayne aquifer
• Surficial aquifer
• People live in their water supply
• Relatively high rates of waterborne viral
  diseases

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The future?
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Civilization exists by geological consent (Mark
Twain)
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Study Questions

• Summarize the geologic history of Florida from
  late Paleozoic to Recent
• Discuss ten aspects of marine geology that you
  have learned in previous lectures for which
  Florida geology provides examples
• What are three major types of coastlines of
  Florida and what factors control predominant
  sedimentary features?
• Why have sea level changes been (and undoubtedly
  will be) important to human history in Florida