Sedimentary 3 Carbonate minerals and rocks Flashcards
What canCO2 be injected into to capture and store it?
Depleted oil and gas reservoirs, coal seams that cannot be mined, saline aquifers
Why is CO2 injected as a supercritical fluid?
It moves through pores better than a gas or a liquid
How is CO2 trapped? (three ways)
Structural trapping - held in rock pores
Solubility trapping - dissolved in saline water
Mineral trapping - precipitates as minerals, e.g. calcite
What is meant by mineral carbonation?
Fixing of CO2 in minerals such as calcite, magnesite, siderite and dolomite
What is in situ mineral carbonation?
The injection of CO2 rich solutions into rocks rich in divalent cations
What are the best rocks for in situ carbonation and why?
Peridotite and basalt
- Contain high concentrations of Mg, Ca and Fe
- Elements hosted in soluble material e.g. olivine, anorthite
What promotes precipitation of calcite and aragonite in a saturated solution?
Evaporation and degassing of CO2
Name four ways that CO2 can be lost
Photosynthesis
Temp increase (solubility of CO2 in seawater decreases as temp increases)
Turbulence
Movement of a volume of water from areas of high to low pCO2 (e.g. submarine caves)
What three varities of CaCO3 precipitate in sea water?
Low magnesium calcite,
High magnesium calcite (both low in strontium)
Aragonite (high in strontium)
Today most marine carbonates are formed organically, by weak and strong biogenic effects. What do these entail?
Weak biogenic effect = photosynthetic marine organisms (algae) induce biomineralisation by removal of CO2 from seawater
Strong biogenic effect = Metabolic activity of an organism to form skeletal carbonates (bivalves, gastropods)
Why are carbonates good palaeoclimate indicators?
- Aragonite and calcite form at or close to surface so similar to conditions in air.
- Carbonate minerals undergo little transportation so represent environment where they were formed
In what three ways has carbonate rock deposition changed in the last 600 million years?
Skeletal constituents are different
Volume of limestones formed
Original, mineralogy, chemical and isotopic composition have all changed.
What are marine algae shells composed of?
Aragonite
What do organisms with a strong control on mineralisation compose their shell of?
LMC e.g. brachiopods or LMC + aragonite e.g. bivalves
How did Sandberg (1983) first know that the mineralogy of the sea had changed over the last 600 million years?
Examined fabrics of ooids and early marine sediments and sometimes composed of LMC and sometimes of HMC/aragonite
