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Carbonate Diagenesis
From soft sediment to hard rockM.Geo.136b: Beckenanalyse 2
A Presentation by: Falko MalisStephan SarnerMaximilian SchaidtJohannes Sucke
25.04.2018
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
25.04.2018 Flügel, 2004
25.04.2018 Scholle, 2003
Carbonate classification after Folk
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
25.04.2018
Carbonate classification after Dunham
Scholle, 2003
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
25.04.2018Scholle, 2003
Carbonate classification after Dunham
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
• Diagenetic factors:
• Dolomitization
• Physical compaction
• Chemical processes• Cementation• Chemical compaction• Dissolution• Inversion• Recrystallization
25.04.2018
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Flügel, 2004
25.04.2018
Two basic models for dolomitization are discussed:
•Primary production of dolomite:• Microrganisms break down MgSO4, dolomite is produced• Only produces small amounts of dolomite
•Secondary transformation of calcite or aragonite:• Calcite or aragonite comes in contact with Mg‐rich fluids and reacts with them• Applies to most of global dolomites• 6 (or more) different types can be distiguished
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Dolomitization
25.04.2018
Models for secondary poduction:
• Coroong lagoon‐type:
• Lagoons are filled with marine water and Mg‐rich groundwaters• Water in the lagoons evaporates• The Mg‐rich brine seeps through the porous carbonates and reacts with them
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Flügel, 2004
25.04.2018
Models for secondary poduction:
• Sabkha‐evaporation‐type:
• The areas behind the shore lines become hit by storms
• The marine water is evaporated and a brine is formed
• The brine reacts with the upper layers of the carbonates
• Associated with saltflats
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Flügel, 2004
25.04.2018
Models for secondary poduction:
• Seepage‐ reflux‐type:
• Tides fill up lagoons behind the shore line
• This water is evaporated and poduces a brine that seeps back to the ocean
• Associated with evaporites
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Flügel, 2004
25.04.2018
Models for secondary poduction:
• Burial compaction‐type:
• Some carbonates are compacted and by this can loose some of their porewater
• Clayminerals transform and Mg is expulsed
• Porewater is rich in Mg and reacts with carbonates in higher areas
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Flügel, 2004
25.04.2018
Models for secondary poduction:
Mixing formation‐type:
•Marine water and fresh water are mixed in the underground
•Can be located more landward than the other forms of dolomitization
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Flügel, 2004
25.04.2018
Models for secondary poduction:
Seawater dolomitization‐type:
•Ocean current and Tides press seawater into the underground
•Geothermal heat warms up the water and makes it rise
•The warm water produces dolomite
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Flügel, 2004
25.04.2018
Physical Compaction
Two phases:
1. Deposition of sediments, change of packing density, dewatering
• Reduction to about 75% of original porosity
• Often happens within the burial depth of just one meter
2. Deformation of grains• Reduction to 50% of porosity at several 100m
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Flügel, 2004
No contact point contact tangential contact sutured +concave‐convex contact
Dynamic factors:
•Overburden•Temperature•Pressure•Duration of burial stress•Pore pressure•Pore‐water chemistry
• Inheritited factors
• Sedimentary fabric• Skeletal architecture and mineralogy
• Clay content• Grain size, sorting, shape• Cementation• Preburial dolomitization
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CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Chemical compaction
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• Result of rock‐fluid interaction
• Most important process:• Pressure solution
• Driving force:• Porespace fluid pressure
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Choquette, James; 19
Pressure solution
• „Riekesche Prinzip“
• Dissolution of minerals at contact
• Diffusion towards pore space
• Precipitation at less‐stressed faces of the grains
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Pressure solution process
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
wikipedia.org
25.04.2018
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Flügel, 2004
Stylolites
• Dissoluted mineral material from pressure solution
• Typically alongside layer surfaces (vertical by tectonic avtivity)
• Insoluble minerals (clays, pyrite and oxides)remain within the stylolites and make them visible
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Chemical dissolution/ formation of stylolites
Pressure solution forms
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Scholle, 2003Scholle, 2003
Stylolite classification
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stylolitized ooids
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Scholle, 2003
Flügel, 2004
Diagenetic changes
• Example of physical and chemical processeson an octacoral
• A – D: cementation of vugs inside the coral
• E & F: deep burial compaction resulting in grain breakage
• G: refilling with clasts and cementation
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CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Flügel, 2004
25.04.2018
Types of diagenesis
•1) Meteoric
•2) Marine
•3) Burial
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Flügel, 2004
25.04.2018
1) Meteoric vadose environment
•Above water table•Pores filled with freshwater & air•Two processes:
• a) extensive dissolution of unstable minerals (aragonite & high Mg‐calcite)• b) reprecipitation of stable carbonate (low Mg‐calcite)
•Strong effect on permeability•Cement fabrics reflect selective dissolution of water environment•Karstic features (sinkholes, caves, collapse breccias)
steady state
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Flügel, 2004
25.04.2018
Dissolution of ooids & meniscus fabric
Microstalactitic cement
Low‐Mg„needle
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Scholle, 2003Scholle, 2003
25.04.2018
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Flügel, 2004
25.04.2018
1) Meteoric phreatic environmentIsopachous low‐Mg calcite cementation
Complete filling ofprimary porosity &high dissolution of
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Scholle, 2003
Scholle, 2003
25.04.2018
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Flügel, 2004
25.04.2018
2) Marine phreatic environmentEarly stage cementamicrocrystalline gra
Thick micrite enve& aragonitic need
Botryocemen
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Scholle, 2003
Scholle, 2003
25.04.2018
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Flügel, 2004
3) Burial environment
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Physical compaction & reorientation of grains
Brittle defo
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Scholle, 2003
Scholle, 2003
3) Burial environment
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Chemical dissolution/ formation of stylolites
Physicacompa
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
Scholle, 2003
Scholle, 2003
Hydrocarbon in carbonates
• Carbonates are typical reservoir rocks• large porespace and high fissuringespecially Dolomite (highly stable)
• ~50% of world‘s oil and gas are stored in carbonate rocks
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CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
https://sofia.usgs.gov/
• Fluid migration from source rock due tolower density of hydrocarbon (0,5‐1,2 g/cm³)
• Accumulation of hydrocarbons under impermeabel caprock (seal)
25.04.2018
CarbonatesCarbonates – Diagenetic Mechanisms – Environments – Hydrocarbon
sepmstrata.or
Thank you for your attention!
References
• Flügel, E.: Microfacies of Carbonate Rocks; Berlin, Heidelberg; 2004
• Scholle, S.; Ulmer‐Scholle, D.: A Color Guide to the Petrography of Carbonate Rocks; Tulsa; 2003
25.04.2018