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Carbonate sediments and depositional environments

Carbonate sediments and depositional environments. http://smu.edu/earthsciences/academics/courses/geol3472/. Carbonates tropical climates dominantly shallow marine sediment produced in situ lime mud not indicative of hydrodynamic conditions. Siliciclastics all climates worldwide

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Carbonate sediments and depositional environments

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  1. Carbonate sediments and depositional environments http://smu.edu/earthsciences/academics/courses/geol3472/

  2. Carbonates • tropical climates • dominantly shallow marine • sediment produced in situ • lime mud not indicative of • hydrodynamic conditions • Siliciclastics • all climates worldwide • all depths, continental • sediment transported • mud particles = • suspension settling

  3. Carbonates • grain size/texture reflects • organism skeletal size & • bioerosion • buildups & reefs • sediments cement early • exposure: dissolution & • karstification • Siliciclastics • grain size/texture reflects • source, hydraulic regime, • weathering • shallow sand bodies • sediments remain • unlithified for long time • exposure: erosion

  4. CaCO3 High-Mg Calcite Low-Mg Calcite Aragonite

  5. Low-Mg calcite High-Mg calcite Ca2+ + 2HCO3 ------> CaCO3 + H2CO3

  6. Erosion: Mechanical erosion – by waves, currents   Chemical erosion – dissolution   Bioerosion – boring, etching or rasping organisms Carbonate precipitation modes andcarbonate factories (Schlager, 2005)

  7. Foramol - association of bryozoa, foraminifera, coralline red algae & molluscs that inhabit seas in higher latitudes Chlorozoan - association of calcareous green algae, hermatypic corals, & molluscs that live in low latitudes

  8. Most carbonate sediments are organic in origin biomineralization - bioclastic grains

  9. Coral reefs-hyperproductive carbonate production

  10. ‘whitings’ of lime mud - inorganic precipitation Bahama Bank

  11. micrite - lime mud <4mm • bioerosion • algal or • bacterial • inorganic

  12. Ooids - inorganic precipitation in agitated water

  13. Calcite cement - inorganic

  14. Production of the tropical factory from terrestrial elevation to subphotic depth Erosion: Mechanical erosion – by waves, currents   Chemical erosion – dissolution   Bioerosion – boring, etching or rasping organisms The depth windows of carbonate production

  15. Carbonate ‘factory’ - base of photic zone ~ 70-100 m

  16. On a healthy carbonate platform (like the Bahama Banks) sediment is produced in the shallow subtidal regions and exported to tidal flats (by tidal currents and storms) and to the deeper platform (by currents and storms)

  17. Modern carbonate producing areas

  18. During lowstand, the carbonate factory is shut down, or confined to a small fringing shelf on the slope. During transgression and highstand, shelves are flooded and shallow water habitat is at a maximum. Because of the ability of carbonate producing organisms to grow quickly under these conditions, carbonate sediments have a tendency to aggrade, creating a carbonate platform.

  19. Cretaceous shallow-water carbonates

  20. Castle Mountain, Banff NP, southern Canadian Rockies

  21. Biomineralized constituents of limestones: - skeletal debris (molluscs, brachiopods, corals, foraminifera)

  22. Coral patch reef, Bahamas Dendrogyra sp.

  23. Pleistocene coralline limestone, south Florida

  24. Fusulinid (Permian foram) limestone (thin section)

  25. Foraminiferal tests - producers of today’s majority of carbonates on the deep seafloor

  26. Halimeda calcareous algae - sand size plates

  27. Calcifying green algae Halimeda Penicillus Udotea Rhipocephalus

  28. Coralline red algae - Goniolithon

  29. photosynthetic cyanobacteria

  30. intertidal stromatolites western Australia

  31. mm-scale laminations in ancient stromatolites

  32. subtidal stromatolites - 6 m water depths in tidal channel, Bahamas

  33. subtidal stromatolites, Bahamas

  34. domal stromatolites, Archean, South Africa

  35. Proterozoic stromatolites, Canada

  36. Cambrian stromatolite bioherms, Nevada

  37. Cambrian thrombolite, Providence Mtns.,Calif.

  38. Classification of Carbonate Rocks Based on relative importance of (1) Mud-sized material (micrite <4mm) (2) Ooids/pisoids/Oncolites/Intraclasts - Grains (3) Pellets (4) Cement There are “Allochems” and “Orthochems”

  39. micrite - lime mud <4mm • bioerosion • algal or • bacterial • inorganic

  40. Micrite - mud sized calcite crystals from ~1-5mm

  41. Peloids - Silt to very find sand 0.03-1.0 mm Internally massive Calcite and/or aragonite POOP

  42. Ooids - Oolites Sand-sized allochems

  43. Pisoids - Pisolites Sand-sized allochems

  44. Oncolites - Big Ooids

  45. Intraclasts

  46. Cement

  47. Matrix Grains

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