GEOL 325: Stratigraphy

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GEOL 325 Stratigraphy Sedimentary
BasinsUniversity of South CarolinaSpring 2005
An Overview of Carbonates
Professor Chris Kendall EWS 304 kendall_at_sc.edu
777.2410
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Precipitated Sediments Sedimentary Rocks

• An Epitaph to
• Limestones Dolomites

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Lecture Series Overview

• sediment production
• types of sediment and sedimentary rocks
• sediment transport and deposition
• depositional systems
• stratigraphic architecture and basins
• chrono-, bio-, chemo-, and sequence stratigraphy
• Earth history

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Sedimentary rocks are the product of the
creation, transport, deposition, and diagenesis
of detritus and solutes derived from pre-existing
rocks.
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Sedimentary rocks are the product of the
creation, transport, deposition, and diagenesis
of detritus and solutes derived from pre-existing
rocks.
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Sedimentary Rocks

• Detrital/Siliciclastic Sedimentary Rocks
• conglomerates breccias
• sandstones
• mudstones
• Carbonate Sedimentary Rocks
• carbonates
• Other Sedimentary Rocks
• evaporites
• phosphates
• organic-rich sedimentary rocks
• cherts
• volcaniclastic rocks

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Lecture Outline

• How photosynthesis, warm temperatures low
  pressures in shallow water control carbonate
  distribution
• How carbonate sediment types is tied to
  depositional setting
• How most mud lime mud has a bio-physico-chemical
  origin
• Origins of bio-physico-chemical grains- ooids,
  intraclasts, pellets, pisoids
• Separation of bioclastic grains- forams,
  brachs, bryozoan, echinoids, red calc algae,
  corals, green calc algae, and molluscs by
  mineralogy fabric
• How CCD controls deepwater carbonate ooze
  distribution
• How Folk Dunhams classifications are used for
  carbonate sediments
• How most diagenesis, dolomitization,
  cementation of carbonates takes place in near
  surface trace elements are used in this
  determination
• How Stylolites develop through burial
  solution/compaction

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Limestones Form - Where?

• Shallow Marine Late Proterozoic to Modern
• Deep Marine Rare in Ancient commoner in
  Modern
• Cave Travertine and Spring Tufa both Ancient
  Modern
• Lakes Ancient to Modern

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CO2 - Temperature Pressure Effect!

• High temperatures, low pressure breaking waves
  favor carbonate precipitation
• CO2 3H2O HCO3-1 H3O1 H2O CO3-2
  2H3O1
• Carbon dioxide solubility decreases in shallow
  water and with rising in temperature
• At lower pressure CO2 is released at higher
  pressure dissolves
• HCO3-1 and CO3-2 are less stable at lower
  pressure but more stable at higher pressure
• HCO3-1 and CO3-2 have lower concentration in warm
  waters but higher concentrations in colder waters

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Calcium Carbonate - Solubilty

• Note calcium carbonate dissociation CaCO3 Ca2
  CO3-2
• CaCO3 is less soluble in warm waters than cool
  waters
• CaCO3 precipitates in warm shallow waters but is
  increasingly soluble at depth in colder waters
• CO2 in solution buffers concentration of
  carbonate ion (CO3-2)
• Increasing pressure elevates concentrations of
  HCO3-1 CO3-2 (products of solubility reaction)
  in sea water
• CaCO3 more soluble at higher pressures with
  decreasing temperature

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Controls on Carbonate Accumulation

• Temperature (climate) -Tropics temperate
  regions favor carbonate production true of
  ancient too!
• Light Photosynthesis drives carbonate
  production
• Pressure CCD dissolution increases with depth
• Agitation of waves - Oxygen source remove CO2
• Organic activity - CaCO3 factories nutrient
  deserts
• Sea Level Yield high at SL that constantly
  changes
• Sediment masking - Fallacious!

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Limestones Chemical or Bochemical
Distinction between biochemical
physico-chemical blurred by ubiquitous
cyanobacteria of biosphere!

• Shallow sea water is commonly saturated with
  respect to calcium carbonate
• Dissolved ions expected to be precipitated as sea
  water warms, loses CO2 evaporates
• Organisms generate shells skeletons from
  dissolved ions
• Metabolism of organisms cause carbonate
  precipitation

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Biological Carbon Pump

• Carbon from CO2 incorporated in organisms through
  photosynthesis, heterotrophy secretion of
  shells
• gt 99 of atmospheric CO2 from volcanism removed
  by biological pump is deposited as calcium
  carbonate organic matter
• 5.3 gigatons of CO2 added to atmosphere a year
  but only 2.1 gigatons/year remains the rest is
  believed sequestered as aragonite calcite

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Carbonate Mineralogy

• Aragonite high temperature mineral
• Calcite stable in sea water near surface
  crust
• Low Magnesium Calcite
• High Magnesium Calcite
• Imperforate foraminifera
• Echinoidea
• Dolomite stable in sea water near surface
• Carbonate mineralogy of oceans changes with time!

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TROPICS
TEMPERATE OCEANS
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Basin
Ramp
Open Shelf
Restricted Shelf
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Basin
Open Shelf
Rim
Restricted Shelf
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Carbonate Components The Key

• Interpretation of depositional setting of
  carbonates is based on
• Grain types
• Grain packing or fabric
• Sedimentary structures
• Early diagenetic changes
• Identification of grain types commonly used in
  subsurface studies of depositional setting
  because, unlike particles in siliciclastic rocks,
  carbonate grains generally formed within basin of
  deposition
• NB This rule of thumb doesnt always apply

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Carbonate Particles

• Subdivided into micrite (lime mud) sand-sized
  grains
• These grains are separated on basis of shape
  internal structure
• They are subdivided into skeletal non-skeletal
  (bio-physico-chemical grains)

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Lime Mud or Micrite
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Lime Mud or Micrite
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WHITING
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Three Creeks Tidal Flats
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Lime Mud - Ordovician Kentucky
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Carbonate Bio-physico-chemical Grains

• Ooids
• Grapestones and other intraclasts
• Pellets
• Pisolites and Oncolites

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Ooids
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Aragonitic Ooids
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After Scholle, 2003
Aragonitic Ooids
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Calcitic Aragonitic Ooids Great Salt Lake
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Grapestones
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Grapestones
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Pellets
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Pellets
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After Scholle
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Skeletal Particles - Mineralogy

• Calcite commonly containing less than 4 mole
  magnesium
• Some foraminifera, brachiopods, bryozoans,
  trilobites, ostracodes, calcareous nannoplankton,
  tintinnids
• Magnesian calcite, with 4-20 mole magnesium
• Echinoderms, most foraminifera, red algae
• Aragonite tests
• Corals, stromatoporoids, most molluscs, green
  algae, blue-green algae.
• Opaline silica
• sponge spicules radiolarians

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Foraminifera
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After Scholle
Foraminifera
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Brachiopod
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Brachiopods
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Brachiopod
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Bryozoan
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Bryozoan
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Trilobite Remains
Ostracod Remains
Calcispheres
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Trilobite Carapice
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Syntaxial cement
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Red Calcareous Algae
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Surface Water Organic Productivity

• Marine algae cyanobacteria base of marine food
  chain
• Fed by available nitrogen and phosphorus
• Supplied in surface waters by deep water
  upwelling
• Vertical upwelling drives high biological
  productivity at
• Equator
• Western continental margins
• Southern Ocean around Antarctica
• Produce biogenous oozes

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Deep Water Carbonate Deposits

• Deep water pelagic sediments accumulate slowly
  (0.1-1 cm per thousand years) far from land, and
  include
• abyssal clay from continents cover most of deeper
  ocean floor
• carried by winds
• ocean currents
• Oozes from organisms' bodies not present on
  continental margins where rate of supply of
  terriginous sediment too high organically
  derived material less than 30 of sediment

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Carbonate Compensation Depth - CCD

• Deep-ocean waters undersaturated with calcium
  carbonate opalline silica.
• Biogenic particles dissolve in water column and
  on sea floor
• Pronounced for carbonates
• Calcareous oozes absent below CCD depth
• CCD varies from ocean to ocean
• 4,000 m in Atlantic.
• 500 - 1,500 m in Pacific
• Siliceous particles dissolve more slowly as sink
  not so limited in distribution by depth
• Nutrient supply controls distribution of
  siliceous sediments

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After James, 1984
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After James, 1984
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Carbonate Cement Fabrics

• Crust or rims coat grains
• Syntaxial overgrowth optical continuity with
  skeletal fabric
• Echinoid single crystals
• Brachiopod multiple crystals
• Blocky equant - final void fill

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Isopachus Marine Cement
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Meniscus Cement
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Evaporation of mixed Waters
Influx of Magnesium Rich Continental Ground
Waters
Influx of sea water
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Stylolites
Two-dimensional cross-sectonal views of

• Dissolution seam(A),
• Stylolite (B),
• Highly serrate stylolite (C)
• Deformed stylolite (D).

A few grains are shown schematically to emphasize
the change in scale from the previous figure

(after Bruce Railsback)
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Stylolites
Intergranular contacts as seen in thin section

• Tangential (A)
• flattened (B)
• concavo-convex (C)
• sutured (D) (after
  Bruce Railsback)

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Stylolites
After Bruce Railsback
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Stylolites

• After Bruce Railsback

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Lecture Conclusions

• Photosynthesis, warm temperatures low pressures
  in shallow water control carbonate distribution
• Carbonate sediment types indicate depositional
  setting
• Most mud lime mud has a bio-physico-chemical
  origin
• Ooid, intraclast, pellet, and pisoid grains have
  bio-physico-chemical origin
• Mineralogy fabric separate forams, brachs,
  bryozoan, echinoids, red calc algae, corals,
  green calc algae, and molluscan skeleletal
  grains
• CCD controls deepwater ooze distribution
• Folk Dunham are best way to classify carbonates
• Most diagenesis, dolomitization, cementation of
  carbonates takes place in near surface crust
  trace elements can be used in this determination
• Stylolites develop through burial
  solution/compaction

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End of the Lecture

• Lets go for lunch!!!

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Global Climate Cycles
Global climatic cycles, referenced to geologic
periods (yellow), megasequences (light purple),
sea level cycles (blue), volcanic output (dark
purple).  (Redrawn modified L. Waite, 2002
after Fischer, 1984)
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Phanerozoic Global Climate History
Frakes et al. (1992) have alternating cold warm
states ("cool" "warm" modes) at comparable time
scales to Fischer (1984) cycles but propose older
portion of Mesozoic greenhouse (Middle Jurassic
to Early Cretaceous) has a cool climate,
presence of seasonal ice at higher latitudes
(after L. Waite, 2002)
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Copied from Steven Wojtal of Oberlin College
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CO2 - Temperature Pressure Effect!

• Carbonate precipitation favored by high
  temperatures, low pressure and breaking waves.
• Solubility of carbon dioxide increases with depth
  and drops in temperature
• CO2 3H2O HCO3-1 H3O1 H2O CO3-2
  2H3O1
• At higher pressure CO2 dissolves is released at
  lower pressures
• HCO3-1 and CO3-2 are more stable at higher
  pressures but less stable at lower pressures
• HCO3-1 and CO3-2 reach higher concentrations in
  colder waters but lower concentration at warm
  waters

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Copied from Steven Wojtal of Oberlin College
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Calcium Carbonate - Solubilty

• Note behavior of calcium carbonate CaCO3 Ca2
• Concentration of carbonate ion (CO3-2) is
  buffered by amount of CO2 in solution
• Increasing pressure elevates concentrations of
  HCO3-1 CO3-2 (products of solubility reaction)
  in sea water
• CaCO3 is more soluble at higher pressures
• Similar effect occurs with decreasing temperature
• CaCO3 is more soluble in cool waters than warm
  waters
• CaCO3 is increasingly soluble at depth in colder
  waters but precipitates in warm shallow waters

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Copied from Steven Wojtal of Oberlin College
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Copied from Suzanne O'Connell Wesleyan College
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Copied from Suzanne O'Connell Wesleyan College
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