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carbonate sedimentary rocks analysis.ppt
- 1. Chapter 6: CarbonateSedimentary Rocks
- 2. There are twomain categories of carbonate rocks: • Calcite (CaCO3) • Dolomite (CaMg(CO3)2) Both Calcite and Dolomite will contain varying amounts of Calcium and Magnesium. Other elements make up only trace amounts. Calcite Dolomite
- 4. Calcite Group Iceland SparCaCO3 Rhodochrosite MnCO3 Magnesite MgCO3 Siderite FeCO3 Smithsonite ZnCO3
- 5. Dolomite Group Dolomite CaMg(CO3)2 AnkeriteCa(Mg,Fe,Mn)(CO3)2
- 6. Aragonite Group Aragonite CaCO3 StrontianiteSrCO3 Cerussite PbCO3 Witherite BaCO3
- 7. Limestone (composed ofprimarily CaCO3) textures Carbonate Grains • Carbonate clasts (extraclasts & intraclasts--Lithoclasts) •Extraclast: derived from older limestone located outside the depositional environment. •Intraclast: derived from seafloor, adjacent tidal flats or a carbonate beach •Lithclast: a nonspecific term used when the distinction between extra & intraclast cannot be made. • Skeletal particles • Ooids • Peloids • Aggregate Grains Matrix cements: either sparry calcite or micrite
- 8. A: Rounded clasts cemented bysparry calcite. B: Angular clasts in micrite. C: Fossiliferous limestone with sparry cement. D: Normal ooids cemented with sparry. E: Radial ooids cemented with sparry & micrite. F: Pellets cemented with sparry.
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- 10. Microcrystalline calcite (Micrite)versus Sparry calcite
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- 12. Limestone classification basedon textures
- 13. Origin of CarbonateRocks Limestone: CO2 + H2O ↔ H2CO3 (carbonic acid) H2CO3 ↔ H+ + HCO3 - (bicarbonate ion) HCO3 - ↔ H+ + CO3 2- (carbonate ion) __________ H2O + CO2 + CaCO3 ↔ Ca2+ + 2HCO3 - (where the CaCO3 can be either Calcite or Aragonite)
- 14. Water condition Direction of change Directed effectEffect on CaCO3 solubility Kind of CaCO3 precipitated Temperature Increase Loss of CO2, increase in pH More likely to precipitate Micrite or ooids Pressure Decrease Loss of CO2, increase in pH More likely to precipitate Micrite or ooids Salinity Decrease Decrease in activity of “foreign cations” More likely to precipitate Micrite or ooids Principle factors that affect inorganic precipitation of CaCO3 in water (Table 6.4 pg. 175)
- 16. Organic activity andCaCO3 precipitation •Extraction of CaCO3 from water Growth of shells and tests •Photosynthesis Removes CO2 from water, thereby increasing pH. •Decay of soft tissue Increases pH of water •Feeding, sediment ingestion Reshapes sediment •Bacterial activity Promotes CaCO3 precipitation
- 17. Calcite versus Aragonite EraPeriod Dominate Carbonate Mineral Neogene-Quaternary A + HMC (Aragonite Sea) Ceno-zoic Paleogene Cretaceous Low-magnesian Calcite (LMC) (Calcite Sea) Jurassic Mesozoic Triassic Permian Pennsylvanian Aragonite (A) + High- magnesian Calcite (HMC) (Aragonite Sea) Mississippian Devonian Silurian Ordovician Paleozoic Cambrian Low-magnesian Calcite (LMC) (Calcite Sea)
- 18. Dolomite Classification andVariation
- 19. Dolomite formation: The Dolomiteproblem…. Scientists have not yet been successful in the laboratory in precipitation perfectly ordered Dolomite (50% Calcium and 50% Magnesium) at the normal temperatures and pressures of the Earth’s surface. Ca2+ (aq) + Mg2+ (aq) + 2CO3 2- (aq) = CaMg(CO3)2(solid) 2CaCO3(solid) + Mg2+ (aq) = CaMg(CO3)2(solid) + Ca2+ (aq)
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- 24. Stylolites: a pressure-solution featurecommon in carbonate rocks. These features are often associated with clay minerals and other fine-size non- carbonate minerals that accumulate as carbonate minerals dissolve.