Carbonates overview

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  • 1. GEOL 325: Stratigraphy & Sedimentary Basins University of South Carolina Spring 2005 Professor Chris Kendall EWS 304 kendall@sc.edu 777.2410 An Overview of 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
  • 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. 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
  • 7. 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
  • 8.  
  • 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
  • 10. CO 2 - Temperature & Pressure Effect!
    • High temperatures , low pressure & breaking waves favor carbonate precipitation
    • CO 2 + 3H 2 O = HCO 3 -1 + H 3 O +1 + H 2 O = CO 3 -2 + 2H 3 O +1
    • Carbon dioxide solubility decreases in shallow water and with rising in temperature
    • At lower pressure CO 2 is released & at higher pressure dissolves
    • HCO 3 -1 and CO 3 -2 are less stable at lower pressure but more stable at higher pressure
    • HCO 3 -1 and CO 3 -2 have lower concentration in warm waters but higher concentrations in colder waters
  • 11. Calcium Carbonate - Solubilty
    • Note calcium carbonate dissociation: CaCO 3 = Ca +2 + CO 3 -2
    • CaCO 3 is less soluble in warm waters than cool waters
    • CaCO 3 precipitates in warm shallow waters but is increasingly soluble at depth in colder waters
    • CO 2 in solution buffers concentration of carbonate ion (CO 3 -2 )
    • Increasing pressure elevates concentrations of HCO 3 -1 & CO 3 -2 (products of solubility reaction) in sea water
    • CaCO 3 more soluble at higher pressures & with decreasing temperature
  • 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 CO 2
    • Organic activity - CaCO 3 factories nutrient deserts
    • Sea Level – Yield high at SL that constantly changes
    • Sediment masking - Fallacious !
  • 13. Limestones – Chemical or Bochemical
    • Shallow sea water is commonly saturated with respect to calcium carbonate
    • Dissolved ions expected to be precipitated as sea water warms, loses CO 2 & evaporates
    • Organisms generate shells & skeletons from dissolved ions
    • Metabolism of organisms cause carbonate precipitation
    Distinction between biochemical & physico-chemical blurred by ubiquitous cyanobacteria of biosphere!
  • 14.  
  • 15.  
  • 16.  
  • 17. Biological Carbon Pump
    • Carbon from CO 2 incorporated in organisms through photosynthesis, heterotrophy & secretion of shells
    • > 99% of atmospheric CO 2 from volcanism removed by biological pump is deposited as calcium carbonate & organic matter
    • 5.3 gigatons of CO 2 added to atmosphere a year but only 2.1 gigatons/year remains; the rest is believed sequestered as aragonite & calcite
  • 18. 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!
  • 19.  
  • 20. TROPICS TEMPERATE OCEANS
  • 21.  
  • 22. Basin Ramp Restricted Shelf Open Shelf
  • 23. Basin Rim Restricted Shelf Open Shelf
  • 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
  • 25. 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)
  • 26. Lime Mud or Micrite
  • 27. Lime Mud or Micrite
  • 28. WHITING LIME MUD ACCUMULATES ON BANK, OFF BANK & TIDAL FLATS
  • 29. Three Creeks Tidal Flats
  • 30. Lime Mud - Ordovician Kentucky
  • 31. Carbonate Bio-physico-chemical Grains
    • Ooids
    • Grapestones and other intraclasts
    • Pellets
    • Pisolites and Oncolites
  • 32.  
  • 33.  
  • 34.  
  • 35. Ooids
  • 36.  
  • 37. Aragonitic Ooids
  • 38. After Scholle, 2003 Aragonitic Ooids
  • 39. Calcitic & Aragonitic Ooids Great Salt Lake
  • 40. Grapestones
  • 41. Grapestones
  • 42. Pellets
  • 43. Pellets
  • 44.  
  • 45.  
  • 46.  
  • 47.  
  • 48. After Scholle
  • 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
  • 50. Drafted by Waite 99, after James 1984)
  • 51. Foraminifera
  • 52. After Scholle Foraminifera
  • 53. Brachiopod
  • 54. Brachiopods
  • 55. Brachiopod
  • 56. Bryozoan
  • 57. Bryozoan
  • 58. Trilobite Remains Ostracod Remains Calcispheres
  • 59. Trilobite Carapice
  • 60. Syntaxial cement Crinoid
  • 61. Red Calcareous Algae
  • 62.  
  • 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
  • 64.  
  • 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
  • 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 - 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
  • 67. After James, 1984
  • 68.  
  • 69. After James, 1984
  • 70.  
  • 71.  
  • 72.  
  • 73.  
  • 74.  
  • 75.  
  • 76.  
  • 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
  • 78.  
  • 79.  
  • 80.  
  • 81. Isopachus Marine Cement
  • 82.  
  • 83. Meniscus Cement
  • 84.  
  • 85.  
  • 86.  
  • 87.  
  • 88.  
  • 89.  
  • 90.  
  • 91.  
  • 92.  
  • 93.  
  • 94.  
  • 95.  
  • 96. Influx of Magnesium Rich Continental Ground Waters Influx of sea water Evaporation of mixed Waters 1. Aragonite 2. Gypsum 3. Anhydrite 4. Dolomite 5. Halite accumulate in this order
  • 97.  
  • 98.  
  • 99.  
  • 100.  
  • 101.  
  • 102.  
  • 103.  
  • 104.  
  • 105.  
  • 106.  
  • 107. Stylolites
    • 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 ) Two-dimensional cross-sectonal views of
  • 108. Stylolites
    • Tangential (A)
    • flattened (B)
    • concavo-convex (C)
    • sutured (D) ( after Bruce Railsback )
    Intergranular contacts as seen in thin section
  • 109. Stylolites After Bruce Railsback
  • 110. Stylolites After Bruce Railsback
  • 111. 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
  • 112. End of the Lecture Lets go for lunch!!!
  • 113. 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)
  • 114. 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) Phanerozoic Global Climate History
  • 115. Copied from Steven Wojtal of Oberlin College
  • 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
    • CO 2 + 3H 2 O = HCO 3 -1 + H 3 O +1 + H 2 O = CO 3 -2 + 2H 3 O +1
    • At higher pressure CO 2 dissolves & is released at lower pressures
    • HCO 3 -1 and CO 3 -2 are more stable at higher pressures but less stable at lower pressures
    • HCO 3 -1 and CO 3 -2 reach higher concentrations in colder waters but lower concentration at warm waters
  • 117. Copied from Steven Wojtal of Oberlin College
  • 118. Calcium Carbonate - Solubilty
    • Note behavior of calcium carbonate: CaCO 3 = Ca +2
    • Concentration of carbonate ion (CO 3 -2 ) is buffered by amount of CO 2 in solution
    • Increasing pressure elevates concentrations of HCO 3 -1 & CO 3 -2 (products of solubility reaction) in sea water
    • CaCO 3 is more soluble at higher pressures
    • Similar effect occurs with decreasing temperature
    • CaCO 3 is more soluble in cool waters than warm waters
    • CaCO 3 is increasingly soluble at depth in colder waters but precipitates in warm shallow waters
  • 119. Copied from Steven Wojtal of Oberlin College
  • 120. Copied from Suzanne O'Connell Wesleyan College
  • 121. Copied from Suzanne O'Connell Wesleyan College
  • 122.  
  • 123.  
  • 124.  
  • 125.  
  • 126.  
  • 127.  
  • 128.