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Carbonates overview

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Carbonates overview

  1. 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. 2. Precipitated Sediments & Sedimentary Rocks An Epitaph to Limestones & Dolomites
  3. 3. Lecture Series Overview <ul><li>sediment production </li></ul><ul><li>types of sediment and sedimentary rocks </li></ul><ul><li>sediment transport and deposition </li></ul><ul><li>depositional systems </li></ul><ul><li>stratigraphic architecture and basins </li></ul><ul><li>chrono-, bio-, chemo-, and sequence stratigraphy </li></ul><ul><li>Earth history </li></ul>
  4. 4. Sedimentary rocks are the product of the creation, transport, deposition, and diagenesis of detritus and solutes derived from pre-existing rocks.
  5. 5. Sedimentary rocks are the product of the creation, transport, deposition, and diagenesis of detritus and solutes derived from pre-existing rocks.
  6. 6. Sedimentary Rocks <ul><li>Detrital/Siliciclastic Sedimentary Rocks </li></ul><ul><ul><li>conglomerates & breccias </li></ul></ul><ul><ul><li>sandstones </li></ul></ul><ul><ul><li>mudstones </li></ul></ul><ul><li>Carbonate Sedimentary Rocks </li></ul><ul><ul><li>carbonates </li></ul></ul><ul><li>Other Sedimentary Rocks </li></ul><ul><ul><li>evaporites </li></ul></ul><ul><ul><li>phosphates </li></ul></ul><ul><ul><li>organic-rich sedimentary rocks </li></ul></ul><ul><ul><li>cherts </li></ul></ul><ul><ul><li>volcaniclastic rocks </li></ul></ul>
  7. 7. Lecture Outline <ul><li>How photosynthesis, warm temperatures & low pressures in shallow water control carbonate distribution </li></ul><ul><li>How carbonate sediment types is tied to depositional setting </li></ul><ul><li>How most mud lime mud has a bio-physico-chemical origin </li></ul><ul><li>Origins of bio-physico-chemical grains:- ooids, intraclasts, pellets, pisoids </li></ul><ul><li>Separation of bioclastic grains:- foram’s, brach’s, bryozoan, echinoids, red calc’ algae, corals, green calc’ algae, and molluscs by mineralogy & fabric </li></ul><ul><li>How CCD controls deepwater carbonate ooze distribution </li></ul><ul><li>How Folk & Dunham’s classifications are used for carbonate sediments </li></ul><ul><li>How most diagenesis, dolomitization, & cementation of carbonates takes place in near surface & trace elements are used in this determination </li></ul><ul><li>How Stylolites develop through burial & solution/compaction </li></ul>
  8. 9. Limestones Form - Where? <ul><li>Shallow Marine – Late Proterozoic to Modern </li></ul><ul><li>Deep Marine – Rare in Ancient & commoner in Modern </li></ul><ul><li>Cave Travertine and Spring Tufa – both Ancient & Modern </li></ul><ul><li>Lakes – Ancient to Modern </li></ul>
  9. 10. CO 2 - Temperature & Pressure Effect! <ul><li>High temperatures , low pressure & breaking waves favor carbonate precipitation </li></ul><ul><li>CO 2 + 3H 2 O = HCO 3 -1 + H 3 O +1 + H 2 O = CO 3 -2 + 2H 3 O +1 </li></ul><ul><li>Carbon dioxide solubility decreases in shallow water and with rising in temperature </li></ul><ul><li>At lower pressure CO 2 is released & at higher pressure dissolves </li></ul><ul><li>HCO 3 -1 and CO 3 -2 are less stable at lower pressure but more stable at higher pressure </li></ul><ul><li>HCO 3 -1 and CO 3 -2 have lower concentration in warm waters but higher concentrations in colder waters </li></ul>
  10. 11. Calcium Carbonate - Solubilty <ul><li>Note calcium carbonate dissociation: CaCO 3 = Ca +2 + CO 3 -2 </li></ul><ul><li>CaCO 3 is less soluble in warm waters than cool waters </li></ul><ul><li>CaCO 3 precipitates in warm shallow waters but is increasingly soluble at depth in colder waters </li></ul><ul><li>CO 2 in solution buffers concentration of carbonate ion (CO 3 -2 ) </li></ul><ul><li>Increasing pressure elevates concentrations of HCO 3 -1 & CO 3 -2 (products of solubility reaction) in sea water </li></ul><ul><li>CaCO 3 more soluble at higher pressures & with decreasing temperature </li></ul>
  11. 12. Controls on Carbonate Accumulation <ul><li>Temperature (climate) - Tropics & temperate regions favor carbonate production: true of ancient too! </li></ul><ul><li>Light – Photosynthesis drives carbonate production </li></ul><ul><li>Pressure – “CCD” dissolution increases with depth </li></ul><ul><li>Agitation of waves - Oxygen source & remove CO 2 </li></ul><ul><li>Organic activity - CaCO 3 factories nutrient deserts </li></ul><ul><li>Sea Level – Yield high at SL that constantly changes </li></ul><ul><li>Sediment masking - Fallacious ! </li></ul>
  12. 13. Limestones – Chemical or Bochemical <ul><li>Shallow sea water is commonly saturated with respect to calcium carbonate </li></ul><ul><li>Dissolved ions expected to be precipitated as sea water warms, loses CO 2 & evaporates </li></ul><ul><li>Organisms generate shells & skeletons from dissolved ions </li></ul><ul><li>Metabolism of organisms cause carbonate precipitation </li></ul>Distinction between biochemical & physico-chemical blurred by ubiquitous cyanobacteria of biosphere!
  13. 17. Biological Carbon Pump <ul><li>Carbon from CO 2 incorporated in organisms through photosynthesis, heterotrophy & secretion of shells </li></ul><ul><li>> 99% of atmospheric CO 2 from volcanism removed by biological pump is deposited as calcium carbonate & organic matter </li></ul><ul><li>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 </li></ul>
  14. 18. Carbonate Mineralogy <ul><li>Aragonite – high temperature mineral </li></ul><ul><li>Calcite – stable in sea water & near surface crust </li></ul><ul><ul><li>Low Magnesium Calcite </li></ul></ul><ul><ul><li>High Magnesium Calcite </li></ul></ul><ul><ul><ul><li>Imperforate foraminifera </li></ul></ul></ul><ul><ul><ul><li>Echinoidea </li></ul></ul></ul><ul><li>Dolomite – stable in sea water & near surface </li></ul><ul><li>Carbonate mineralogy of oceans changes with time! </li></ul>
  15. 20. TROPICS TEMPERATE OCEANS
  16. 22. Basin Ramp Restricted Shelf Open Shelf
  17. 23. Basin Rim Restricted Shelf Open Shelf
  18. 24. Carbonate Components – The Key <ul><li>Interpretation of depositional setting of carbonates is based on </li></ul><ul><ul><li>Grain types </li></ul></ul><ul><ul><li>Grain packing or fabric </li></ul></ul><ul><ul><li>Sedimentary structures </li></ul></ul><ul><ul><li>Early diagenetic changes </li></ul></ul><ul><li>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 </li></ul><ul><li>NB : This rule of thumb doesn’t always apply </li></ul>
  19. 25. Carbonate Particles <ul><li>Subdivided into micrite (lime mud) & sand-sized grains </li></ul><ul><li>These grains are separated on basis of shape & internal structure </li></ul><ul><li>They are subdivided into: skeletal & non-skeletal (bio-physico-chemical grains) </li></ul>
  20. 26. Lime Mud or Micrite
  21. 27. Lime Mud or Micrite
  22. 28. WHITING LIME MUD ACCUMULATES ON BANK, OFF BANK & TIDAL FLATS
  23. 29. Three Creeks Tidal Flats
  24. 30. Lime Mud - Ordovician Kentucky
  25. 31. Carbonate Bio-physico-chemical Grains <ul><li>Ooids </li></ul><ul><li>Grapestones and other intraclasts </li></ul><ul><li>Pellets </li></ul><ul><li>Pisolites and Oncolites </li></ul>
  26. 35. Ooids
  27. 37. Aragonitic Ooids
  28. 38. After Scholle, 2003 Aragonitic Ooids
  29. 39. Calcitic & Aragonitic Ooids Great Salt Lake
  30. 40. Grapestones
  31. 41. Grapestones
  32. 42. Pellets
  33. 43. Pellets
  34. 48. After Scholle
  35. 49. Skeletal Particles - Mineralogy <ul><li>Calcite commonly containing less than 4 mole % magnesium </li></ul><ul><ul><li>Some foraminifera, brachiopods, bryozoans, trilobites, ostracodes, calcareous nannoplankton, & tintinnids </li></ul></ul><ul><li>Magnesian calcite, with 4-20 mole % magnesium </li></ul><ul><ul><li>Echinoderms, most foraminifera, & red algae </li></ul></ul><ul><li>Aragonite tests </li></ul><ul><ul><li>Corals, stromatoporoids, most molluscs, green algae, & blue-green algae. </li></ul></ul><ul><li>Opaline silica </li></ul><ul><ul><li>sponge spicules & radiolarians </li></ul></ul>
  36. 50. Drafted by Waite 99, after James 1984)
  37. 51. Foraminifera
  38. 52. After Scholle Foraminifera
  39. 53. Brachiopod
  40. 54. Brachiopods
  41. 55. Brachiopod
  42. 56. Bryozoan
  43. 57. Bryozoan
  44. 58. Trilobite Remains Ostracod Remains Calcispheres
  45. 59. Trilobite Carapice
  46. 60. Syntaxial cement Crinoid
  47. 61. Red Calcareous Algae
  48. 63. Surface Water Organic Productivity <ul><li>Marine algae & cyanobacteria base of marine food chain </li></ul><ul><li>Fed by available nitrogen and phosphorus </li></ul><ul><li>Supplied in surface waters by deep water upwelling </li></ul><ul><li>Vertical upwelling drives high biological productivity at: </li></ul><ul><ul><li>Equator </li></ul></ul><ul><ul><li>Western continental margins </li></ul></ul><ul><ul><li>Southern Ocean around Antarctica </li></ul></ul><ul><li>Produce biogenous oozes </li></ul>
  49. 65. Deep Water Carbonate Deposits <ul><li>Deep water pelagic sediments accumulate slowly (0.1-1 cm per thousand years) far from land, and include: </li></ul><ul><ul><li>abyssal clay from continents cover most of deeper ocean floor </li></ul></ul><ul><ul><ul><li>carried by winds </li></ul></ul></ul><ul><ul><ul><li>ocean currents </li></ul></ul></ul><ul><ul><li>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 </li></ul></ul>
  50. 66. Carbonate Compensation Depth - CCD <ul><li>Deep-ocean waters undersaturated with calcium carbonate & opalline silica. </li></ul><ul><li>Biogenic particles dissolve in water column and on sea floor </li></ul><ul><li>Pronounced for carbonates </li></ul><ul><li>Calcareous oozes absent below CCD depth </li></ul><ul><li>CCD varies from ocean to ocean </li></ul><ul><ul><li>4,000 m in Atlantic. </li></ul></ul><ul><ul><li>500 - 1,500 m in Pacific </li></ul></ul><ul><li>Siliceous particles dissolve more slowly as sink & not so limited in distribution by depth </li></ul><ul><li>Nutrient supply controls distribution of siliceous sediments </li></ul>
  51. 67. After James, 1984
  52. 69. After James, 1984
  53. 77. Carbonate Cement Fabrics <ul><li>Crust or rims coat grains </li></ul><ul><li>Syntaxial overgrowth – optical continuity with skeletal fabric </li></ul><ul><ul><li>Echinoid single crystals </li></ul></ul><ul><ul><li>Brachiopod multiple crystals </li></ul></ul><ul><li>Blocky equant - final void fill </li></ul>
  54. 81. Isopachus Marine Cement
  55. 83. Meniscus Cement
  56. 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
  57. 107. Stylolites <ul><li>Dissolution seam(A), </li></ul><ul><li>Stylolite (B), </li></ul><ul><li>Highly serrate stylolite (C) </li></ul><ul><li>Deformed stylolite (D). </li></ul>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
  58. 108. Stylolites <ul><li>Tangential (A) </li></ul><ul><li>flattened (B) </li></ul><ul><li>concavo-convex (C) </li></ul><ul><li>sutured (D) ( after Bruce Railsback ) </li></ul>Intergranular contacts as seen in thin section
  59. 109. Stylolites After Bruce Railsback
  60. 110. Stylolites After Bruce Railsback
  61. 111. Lecture Conclusions <ul><li>Photosynthesis, warm temperatures & low pressures in shallow water control carbonate distribution </li></ul><ul><li>Carbonate sediment types indicate depositional setting </li></ul><ul><li>Most mud lime mud has a bio-physico-chemical origin </li></ul><ul><li>Ooid, intraclast, pellet, and pisoid grains have bio-physico-chemical origin </li></ul><ul><li>Mineralogy & fabric separate foram’s, brach’s, bryozoan, echinoids, red calc’ algae, corals, green calc’ algae, and molluscan skeleletal grains </li></ul><ul><li>CCD controls deepwater ooze distribution </li></ul><ul><li>Folk & Dunham are best way to classify carbonates </li></ul><ul><li>Most diagenesis, dolomitization, & cementation of carbonates takes place in near surface crust & trace elements can be used in this determination </li></ul><ul><li>Stylolites develop through burial & solution/compaction </li></ul>
  62. 112. End of the Lecture Lets go for lunch!!!
  63. 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)
  64. 114. Frakes et al. (1992) have alternating cold & warm states (&quot;cool&quot; & &quot;warm&quot; 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
  65. 115. Copied from Steven Wojtal of Oberlin College
  66. 116. CO2 - Temperature & Pressure Effect! <ul><li>Carbonate precipitation favored by high temperatures, low pressure and breaking waves. </li></ul><ul><li>Solubility of carbon dioxide increases with depth and drops in temperature </li></ul><ul><li>CO 2 + 3H 2 O = HCO 3 -1 + H 3 O +1 + H 2 O = CO 3 -2 + 2H 3 O +1 </li></ul><ul><li>At higher pressure CO 2 dissolves & is released at lower pressures </li></ul><ul><li>HCO 3 -1 and CO 3 -2 are more stable at higher pressures but less stable at lower pressures </li></ul><ul><li>HCO 3 -1 and CO 3 -2 reach higher concentrations in colder waters but lower concentration at warm waters </li></ul>
  67. 117. Copied from Steven Wojtal of Oberlin College
  68. 118. Calcium Carbonate - Solubilty <ul><li>Note behavior of calcium carbonate: CaCO 3 = Ca +2 </li></ul><ul><li>Concentration of carbonate ion (CO 3 -2 ) is buffered by amount of CO 2 in solution </li></ul><ul><li>Increasing pressure elevates concentrations of HCO 3 -1 & CO 3 -2 (products of solubility reaction) in sea water </li></ul><ul><li>CaCO 3 is more soluble at higher pressures </li></ul><ul><li>Similar effect occurs with decreasing temperature </li></ul><ul><li>CaCO 3 is more soluble in cool waters than warm waters </li></ul><ul><li>CaCO 3 is increasingly soluble at depth in colder waters but precipitates in warm shallow waters </li></ul>
  69. 119. Copied from Steven Wojtal of Oberlin College
  70. 120. Copied from Suzanne O'Connell Wesleyan College
  71. 121. Copied from Suzanne O'Connell Wesleyan College

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