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Dolomitization
Dolomitization is a geological process where magnesium ions replace calcium ions in the mineral calcite, resulting in the formation of dolomite.
Dolomitization conditions are present in Abu Dhabi, the Mediterranean Sea, and some Brazilian hypersaline lagoons (most notably Lagoa Vermelha Lagoon). The areas where dolomitization take place are limited, as modern seawater is less suited to dolomite formation. This is evident in the noticeable decrease in modern dolomite depositions compared to older depositions. Dolomitization involves substantial recrystallization which can be described by the following equation:
The conditions for dolomitization depend on several factors, including temperature, saturation state, Mg:Ca ratio, and the presence of inhibitors and microorganisms.Microorganisms allow the precipitation of preliminary dolomite stages through certain metabolic pathways. Dolomitization occurs in kinetic intermediate stages. First, a protodolomite is formed, then it is transformed to dolomite in a dissolution-recrystallization process.
Microorganisms allow the precipitation of dolomite by raising alkalinity and increasing pH buffering through metabolic pathways. Higher alkalinity leads to the transformation of HCO−3 to CO2−3, which allows for interruption of the magnesium hydrate to form dolomite. In most modern dolomitization sites, ‘microbial mats’ are present. Microbial mats are populations of microorganisms and their associated extracellular polymeric substances (EPS). EPS groups have been shown to be critical for the formation of stable nuclei in the early stages of dolomite formation, thus increasing dolomite saturation.
There are several key metabolic pathways for dolomite formation. These include microbial sulfate reduction, aerobic heterotrophy, chemotrophic sulfide oxidation, and the coupling of methanogenesis and anaerobic methane oxidation.
Microbial sulfate reduction reduces sulfate concentrations in seawaters, effectively removing one of the key inhibiting factors to dolomitization. This process also results in the production of sulfide ions, which promote Mg2+ dehydration.
Aerobic heterotrophy increases alkalinity by using nitrogenized organic matter as an electron acceptor.
In chemotrophic sulfide oxidation, organisms use sulfide for CO2 fixation, leading to seawater conditions that are thermodynamically favorable for dolomite formation.
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Dolomitization
Dolomitization is a geological process where magnesium ions replace calcium ions in the mineral calcite, resulting in the formation of dolomite.
Dolomitization conditions are present in Abu Dhabi, the Mediterranean Sea, and some Brazilian hypersaline lagoons (most notably Lagoa Vermelha Lagoon). The areas where dolomitization take place are limited, as modern seawater is less suited to dolomite formation. This is evident in the noticeable decrease in modern dolomite depositions compared to older depositions. Dolomitization involves substantial recrystallization which can be described by the following equation:
The conditions for dolomitization depend on several factors, including temperature, saturation state, Mg:Ca ratio, and the presence of inhibitors and microorganisms.Microorganisms allow the precipitation of preliminary dolomite stages through certain metabolic pathways. Dolomitization occurs in kinetic intermediate stages. First, a protodolomite is formed, then it is transformed to dolomite in a dissolution-recrystallization process.
Microorganisms allow the precipitation of dolomite by raising alkalinity and increasing pH buffering through metabolic pathways. Higher alkalinity leads to the transformation of HCO−3 to CO2−3, which allows for interruption of the magnesium hydrate to form dolomite. In most modern dolomitization sites, ‘microbial mats’ are present. Microbial mats are populations of microorganisms and their associated extracellular polymeric substances (EPS). EPS groups have been shown to be critical for the formation of stable nuclei in the early stages of dolomite formation, thus increasing dolomite saturation.
There are several key metabolic pathways for dolomite formation. These include microbial sulfate reduction, aerobic heterotrophy, chemotrophic sulfide oxidation, and the coupling of methanogenesis and anaerobic methane oxidation.
Microbial sulfate reduction reduces sulfate concentrations in seawaters, effectively removing one of the key inhibiting factors to dolomitization. This process also results in the production of sulfide ions, which promote Mg2+ dehydration.
Aerobic heterotrophy increases alkalinity by using nitrogenized organic matter as an electron acceptor.
In chemotrophic sulfide oxidation, organisms use sulfide for CO2 fixation, leading to seawater conditions that are thermodynamically favorable for dolomite formation.