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Carbonate sediments and rocks Introduction to sedimentary petrology
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Diagenesis and its Influence on
Petrophysical Properties of Carbonates
Diagenesis describes all physical and chemical
processes that affect a sediment after deposition
Carbonate DiagenesisSix major processes can be distinguished:
1. Cementation 2. Microbial micritization3. Neomorphism4. Dissolution 5. Compaction6. Dolomitization
Carbonate diagenesis mostly involves the carbonate minerals: aragonite, calcite, and dolomite; but other minerals such as quartz, feldspar, clays, phosphates, iron oxides and sulphides, and evaporitesalso may be involved. The diagenesis of carbonate begins at the sea floor; in fact depositional and diagenetic processes may be going on at the same time.As a reef is growing or carbonate sand is being moved by the waves, cements may be precipitated within interskeletal cavities and grains altered by micritization.
Carbonate Diagensis
Carbonate DiagenesisSix major processes can be distinguished:
1. Cementation 2. Microbial micritization3. Neomorphism4. Dissolution 5. Compaction6. Dolomitization
Carbonate diagenesis mostly involves the carbonate minerals: aragonite, calcite, and dolomite; but other minerals such as quartz, feldspar, clays, phosphates, iron oxides and sulphides, and evaporitesalso may be involved. The diagenesis of carbonate begins at the sea floor; in fact depositional and diagenetic processes may be going on at the same time.As a reef is growing or carbonate sand is being moved by the waves, cements may be precipitated within interskeletal cavities and grains altered by micritization.
Carbonate Diagensis
Carbonate DiagenesisSix major processes can be distinguished:
1. Cementation 2. Microbial micritization3. Neomorphism4. Dissolution 5. Compaction6. Dolomitization
Carbonate diagenesis mostly involves the carbonate minerals: aragonite, calcite, and dolomite; but other minerals such as quartz, feldspar, clays, phosphates, iron oxides and sulphides, and evaporitesalso may be involved. The diagenesis of carbonate begins at the sea floor; in fact depositional and diagenetic processes may be going on at the same time.As a reef is growing or carbonate sand is being moved by the waves, cements may be precipitated within interskeletal cavities and grains altered by micritization.
Carbonate DiagenesisSix major processes can be distinguished:
1. Cementation 2. Microbial micritization3. Neomorphism4. Dissolution 5. Compaction6. Dolomitization
Carbonate diagenesis mostly involves the carbonate minerals: aragonite, calcite, and dolomite; but other minerals such as quartz, feldspar, clays, phosphates, iron oxides and sulphides, and evaporitesalso may be involved. The diagenesis of carbonate begins at the sea floor; in fact depositional and diagenetic processes may be going on at the same time.As a reef is growing or carbonate sand is being moved by the waves, cements may be precipitated within interskeletal cavities and grains altered by micritization.
Major Controls on Diagenesis of Carbonates
a. Original mineralogy of sedimentb. Pore fluid chemistry and flow rate c. Sea level history d. Burial history e. Time
Various diagenetic environments
Can CREATE or DESTROY porosity
Diagenesis early diagenesis on the seafloor or close to sediment surface; Meteoric Marine Deep marine bottom (rare) late (burial) diagenesis During burial
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diagenetic environments
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S. Cirilli: Petrografia del Sedimentario
S.Cirilli-SedPetr
Isopachus Marine Cement
S.Cirilli-SedPetr
Isopachus Marine Cement
Loose sediment cemented rock
S. Cirilli
Cements and cementation
Porosity decreases
DA FARE
• Crystals precipitated from solutions within a pore or void space.
• Major process involved in lithification of carbonate sediments.
• Can be syndepositional to late diagenetic.
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cement mineralogy
Crystal size partially dependent on
Crystal form
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Many: Small size (from 10 to less than 50-80 microns)
Few: larger size (from few mm to cm)
Availability of CaCO3 in the waters
Number of nuclei or seed crystals
Shape classified based on crystal relative length to width
ratio.
• Fibrous or acicular. • Bladed or prismatic. • Equant.
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