1. Professor Chris Kendall
GEOL 325: Stratigraphy & Sedimentary Basins University of South Carolina Spring 2005
An Overview of Carbonates
Professor Chris Kendall
EWS 304
GEOL 325 Lecture 4: Carbonates

2. Precipitated Sediments & Sedimentary Rocks
An Epitaph to
Limestones & Dolomites

3. 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
GEOL 325 Lecture 4: Carbonates

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

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

6. GEOL 325 Lecture 4: Carbonates
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
GEOL 325 Lecture 4: Carbonates

7. GEOL 325 Lecture 4: Carbonates
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:- foram’s, brach’s, bryozoan, echinoids, red calc’ algae, corals, green calc’ algae, and molluscs by mineralogy & fabric
How CCD controls deepwater carbonate ooze distribution
How Folk & Dunham’s 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
GEOL 325 Lecture 4: Carbonates

8. GEOL 325 Lecture 4: Carbonates

9. 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
GEOL 325 Lecture 4: Carbonates

10. CO2 - Temperature & Pressure Effect!
High temperatures, low pressure & breaking waves favor carbonate precipitation
CO2 + 3H2O = HCO3-1 + H3O+1 + H2O = CO H3O+1
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
GEOL 325 Lecture 4: Carbonates

11. Calcium Carbonate - Solubilty
Note calcium carbonate dissociation: CaCO3= Ca+2 + 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
GEOL 325 Lecture 4: Carbonates

12. 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!
GEOL 325 Lecture 4: Carbonates

13. 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
GEOL 325 Lecture 4: Carbonates

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17. Biological Carbon Pump
Carbon from CO2 incorporated in organisms through photosynthesis, heterotrophy & secretion of shells
> 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
GEOL 325 Lecture 4: Carbonates

18. GEOL 325 Lecture 4: Carbonates
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!
GEOL 325 Lecture 4: Carbonates

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TROPICS
TEMPERATE OCEANS
GEOL 325 Lecture 4: Carbonates

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Basin
Ramp
Open
Shelf
Restricted
Shelf
GEOL 325 Lecture 4: Carbonates

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Basin
Open
Shelf
Rim
Restricted
Shelf
GEOL 325 Lecture 4: Carbonates

24. 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 doesn’t always apply
GEOL 325 Lecture 4: Carbonates

25. GEOL 325 Lecture 4: Carbonates
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)
GEOL 325 Lecture 4: Carbonates

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Lime Mud or Micrite
GEOL 325 Lecture 4: Carbonates

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Lime Mud or Micrite
GEOL 325 Lecture 4: Carbonates

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WHITING
LIME MUD
ACCUMULATES
ON BANK, OFF BANK
& TIDAL FLATS
GEOL 325 Lecture 4: Carbonates

29. Three Creeks Tidal Flats
GEOL 325 Lecture 4: Carbonates

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Lime Mud -
Ordovician
Kentucky
GEOL 325 Lecture 4: Carbonates

31. Carbonate Bio-physico-chemical Grains
Ooids
Grapestones and other intraclasts
Pellets
Pisolites and Oncolites
GEOL 325 Lecture 4: Carbonates

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Ooids
GEOL 325 Lecture 4: Carbonates

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Aragonitic Ooids
GEOL 325 Lecture 4: Carbonates

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After Scholle, 2003
Aragonitic Ooids
GEOL 325 Lecture 4: Carbonates

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Calcitic &
Aragonitic
Ooids
Great
Salt
Lake
GEOL 325 Lecture 4: Carbonates

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Grapestones
GEOL 325 Lecture 4: Carbonates

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Grapestones
GEOL 325 Lecture 4: Carbonates

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Pellets
GEOL 325 Lecture 4: Carbonates

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Pellets
GEOL 325 Lecture 4: Carbonates

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After Scholle
GEOL 325 Lecture 4: Carbonates

49. 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
GEOL 325 Lecture 4: Carbonates

50. GEOL 325 Lecture 4: Carbonates
Drafted by Waite 99, after James 1984)
GEOL 325 Lecture 4: Carbonates

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Foraminifera
GEOL 325 Lecture 4: Carbonates

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After Scholle
Foraminifera
GEOL 325 Lecture 4: Carbonates

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Brachiopod
GEOL 325 Lecture 4: Carbonates

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Brachiopods
GEOL 325 Lecture 4: Carbonates

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Brachiopod
GEOL 325 Lecture 4: Carbonates

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Bryozoan
GEOL 325 Lecture 4: Carbonates

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Bryozoan
GEOL 325 Lecture 4: Carbonates

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Trilobite Remains
Ostracod Remains
Calcispheres
GEOL 325 Lecture 4: Carbonates

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Trilobite Carapice
GEOL 325 Lecture 4: Carbonates

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Crinoid
Syntaxial
cement
GEOL 325 Lecture 4: Carbonates

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Red Calcareous Algae
GEOL 325 Lecture 4: Carbonates

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63. 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
GEOL 325 Lecture 4: Carbonates

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65. 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
GEOL 325 Lecture 4: Carbonates

66. 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 m in Pacific
Siliceous particles dissolve more slowly as sink & not so limited in distribution by depth
Nutrient supply controls distribution of siliceous sediments
GEOL 325 Lecture 4: Carbonates

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After James, 1984
GEOL 325 Lecture 4: Carbonates

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After James, 1984
GEOL 325 Lecture 4: Carbonates

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77. 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
GEOL 325 Lecture 4: Carbonates

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81. Isopachus Marine Cement
GEOL 325 Lecture 4: Carbonates

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Meniscus Cement
GEOL 325 Lecture 4: Carbonates

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Evaporation
of mixed
Waters
Influx of
Magnesium
Rich
Continental
Ground
Waters
Influx of
sea water
1. Aragonite
2. Gypsum
3. Anhydrite
4. Dolomite
5. Halite
accumulate
in this order
GEOL 325 Lecture 4: Carbonates

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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)
GEOL 325 Lecture 4: Carbonates

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Stylolites
Intergranular contacts as seen in thin section
Tangential (A)
flattened (B)
concavo-convex (C)
sutured (D) (after Bruce Railsback)
GEOL 325 Lecture 4: Carbonates

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Stylolites
After Bruce Railsback
GEOL 325 Lecture 4: Carbonates

110. Stylolites
After Bruce Railsback

111. GEOL 325 Lecture 4: Carbonates
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 foram’s, brach’s, 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
GEOL 325 Lecture 4: Carbonates

112. End of the Lecture
Lets go for lunch!!!

113. GEOL 325 Lecture 4: Carbonates
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)
GEOL 325 Lecture 4: Carbonates

114. GEOL 325 Lecture 4: Carbonates
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)
GEOL 325 Lecture 4: Carbonates

115. GEOL 325 Lecture 4: Carbonates
Copied from Steven Wojtal of Oberlin College
GEOL 325 Lecture 4: Carbonates

116. 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 + H3O+1 + H2O = CO H3O+1
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
GEOL 325 Lecture 4: Carbonates

117. GEOL 325 Lecture 4: Carbonates
Copied from Steven Wojtal of Oberlin College
GEOL 325 Lecture 4: Carbonates

118. Calcium Carbonate - Solubilty
Note behavior of calcium carbonate: CaCO3= Ca+2
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
GEOL 325 Lecture 4: Carbonates

119. GEOL 325 Lecture 4: Carbonates
Copied from Steven Wojtal of Oberlin College
GEOL 325 Lecture 4: Carbonates

120. GEOL 325 Lecture 4: Carbonates
Copied from Suzanne O'Connell Wesleyan College
GEOL 325 Lecture 4: Carbonates

121. GEOL 325 Lecture 4: Carbonates
Copied from Suzanne O'Connell Wesleyan College
GEOL 325 Lecture 4: Carbonates

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