Carbonate sediments and rocks

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Carbonate Mineralogy

Aragonite – high temperature mineral

Calcite – stable in sea water & near surface crust Low Magnesium Calcite

High Magnesium Calcite

Dolomite – stable in sea water & near surface

Carbonate rocks: > 50% of carbonate constituents

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S. Cirilli: Sedimentologia

Where?

S.Cirilli-Sedimentary Petrology

Depositional setting Type of deposit

Basin and slope Pelagic sediments. Turbidites and debris flows.

Platform margin Reefs and organic buildups. Sand shoals

Platform interior Epeiric sea, lagoon or bay, tidal flats

Terrestrial Dunes, lakes, cave deposits, solls, fanglomarate

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Skeletal & Non-Skeletal Settings in Bahamas S. Cirilli: Sedimentologia

Carbonate Components

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There are two main ways in which skeletal carbonates can be arranged. 1.  insitu organisms building a more or less rigid framework (e.g. coral reefs, stromatolite)

2. Loose particles (allochemical grains) lithified after diagenesis Once these carbonate particles are produced and deposited other biological organisms, such as grasses and microbes, act as sediment traps and stabilizers. In this way the entire carbonate factory is controlled by biota and evolves with the biology of its own system.

Carbonate Components

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S. Cirilli: Sedimentologia

Lime Mud or

Micrite

Carbonate Components

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S. Cirilli: Sedimentologia

Origin of mud in shallow waters

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precipitation CaCO3 Periplatform

ooze

Lime mud in

Deep basin

Planktonic skeletal

Origin of mud in deep waters

S.C

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S. Cirilli: Sedimentologia S.Cirilli-Sedimentary Petrology

Muddy rock (hand sample)

Mud-supported texture (thin section under microscpoe) 1mm 11

Carbonate particles

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Carbonate particles

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Carbonate grains

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Carbonate grains

Non skeletal skeletal

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Folk classification of carbonate rocks

Based on the presence of:

- micrite or sparite

- - kind of carbonate grains

Dunham classification of carbonate rocks:

• Texturally-based subdivision (loose particles): mudstone, wackestone,

packstone, grainstone, rudstone

• Organically bound framework during formation: boundstone

>10% grains > 2mm, grain or matrix supported (rudstone, floatstone)

Original components bound organically at deposition (framestone, bindstone,

bafflestone)

Classification of Carbonate rocks

Embry-Klovan classification of carbonate rock

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Folk classification

Based on the presence of:

- micrite or sparite

- - kind of carbonate grains

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Classificazione Rocce Carbonatiche di Dunham

• Texturally-based subdivision (loose particles): mudstone, wackestone, packstone, grainstone,

rudstone

• Organically bound framework during formation: boundstone S.Cirilli-Sedimentary Petrology 20

Embry-Klovan classification

S. Cirilli: Sedimentologia

S. Cirilli: Sedimentologia

Embry & Klovan classification a) >10% grains > 2mm; b) Original components bound organically at deposition

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