GEOL 325: Stratigraphy & Sedimentary Basins University of South Carolina Spring 2005 - PowerPoint PPT Presentation

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GEOL 325: Stratigraphy & Sedimentary Basins University of South Carolina Spring 2005
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GEOL 325: Stratigraphy & Sedimentary Basins University of South Carolina Spring 2005

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  1. GEOL 325: Stratigraphy & Sedimentary BasinsUniversity of South CarolinaSpring 2005 An Overview of Carbonates Professor Chris Kendall EWS 304 kendall@sc.edu 777.2410 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. 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. 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 = CO3-2 + 2H3O+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

  14. GEOL 325 Lecture 4: Carbonates

  15. GEOL 325 Lecture 4: Carbonates

  16. GEOL 325 Lecture 4: Carbonates

  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. 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

  19. GEOL 325 Lecture 4: Carbonates

  20. TROPICS TEMPERATE OCEANS GEOL 325 Lecture 4: Carbonates

  21. GEOL 325 Lecture 4: Carbonates

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

  23. 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. 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

  26. Lime Mud or Micrite GEOL 325 Lecture 4: Carbonates

  27. Lime Mud or Micrite GEOL 325 Lecture 4: Carbonates

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

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

  30. 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

  32. GEOL 325 Lecture 4: Carbonates

  33. GEOL 325 Lecture 4: Carbonates

  34. GEOL 325 Lecture 4: Carbonates

  35. Ooids GEOL 325 Lecture 4: Carbonates

  36. GEOL 325 Lecture 4: Carbonates

  37. Aragonitic Ooids GEOL 325 Lecture 4: Carbonates

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

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

  40. Grapestones GEOL 325 Lecture 4: Carbonates

  41. Grapestones GEOL 325 Lecture 4: Carbonates

  42. Pellets GEOL 325 Lecture 4: Carbonates

  43. Pellets GEOL 325 Lecture 4: Carbonates

  44. GEOL 325 Lecture 4: Carbonates

  45. GEOL 325 Lecture 4: Carbonates

  46. GEOL 325 Lecture 4: Carbonates

  47. GEOL 325 Lecture 4: Carbonates

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