Dynamic Surface L4 Flashcards
How are non-clastic limestones produced?
By biogeochemical processes or direct precipitation
Where are limestones generally produced?
The basin where they are deposited
What is the reversible carbonate reaction?
CaCO3 + H2O + CO2 <–> Ca2+ + 2HCO3-
What is the name of the forward reaction in the reversible carbonate reaction?
Dissolution
What is the name of the backwards reaction in the reversible carbonate reaction?
Precipitation
In what conditions is the dissolution of carbonate favoured?
Low temperature
High hydrostatic pressure
In what conditions is the precipitation of carbonate favoured?
High temperature
Low hydrostatic pressure
Why does the rate of dissolution of carbonates increase at lower temperatures?
Warm water is more susceptible to evaporation
What is the main control on the reversible carbonate reaction?
The addition and removal of CO2
How does removing CO2 affect the reversible carbonate reaction?
Precipitation is favoured
How does adding CO2 affect the reversible carbonate reaction?
Dissolution is favoured
What are the 2 common polymorphs of CaCO3?
Calcite
Aragonite
What crystal system does calcite display?
Hexagonal
What crystal system does aragonite display?
Orthorhombic
What happens to aragonite when taken out of warm marine conditions?
It will transform into calcite
What concentration of magnesium does aragonite contain in ppm?
Less than 500ppm
Up to what concentration of Sr can aragonite contain in ppm?
Up to 10,000ppm of Sr substituting for Ca
What are the 4 components of limestones?
Skeletal grains
Non-skeletal grains
Micrite
Cements
What is an allochem?
A carbonate particle that was formed outside of the depositional environment and transported in
What is an orthochem?
Carbonate sediments that form within the depositional environment that represent the rock cement or matrix.
What are skeletal and non-skeletal grains known as in carbonate rocks?
Allochems
What is micrite?
A very fine grained component that often makes up the matrix of limestone
What are cements known as in carbonate rocks?
Orthochems
What are skeletal grains?
Grains of carbonate rock that are formed from organisms that were once alive.
What are 9 examples of skeletal grains?
Bivalves
Gastropods
Brachiopods
Corals
Crinoids
Foraminifera
Bryozoa
Stromatoporoids
Ostracods
What did bivalves secrete?
Most secrete aragonite
What did gastropods secrete?
Aragonite
What are brachiopod shells made of?
Calcite
What do corals secrete?
Calcite
What do crinoids secrete?
Calcite
What are foraminifera made of?
Calcite
What do bryozoa secrete?
Calcite
What do stromatoporoids secrete?
Calcite
What are ostracods a good indicator of?
Brackish water
What are crinoids a good indicator of?
Warm, gently agitated sea water
What do trilobites secrete?
Calcite
What are 3 examples of non-skeletal grains?
Ooids
Intraclasts
Peloids
Chronologically list the geological time periods starting from the Precambrian to the Cainozoic.
Precambrian
Cambrian
Ordovician
Silurian
Devonian
Carboniferous
Permian
Triassic
Jurassic
Cretaceous
Cainozoic
What is a distinctive feature of bivalves?
2 layered shell structure
When were foraminifera prevalent in the past?
Cambrian to the Cainozoic
When were corals prevalent in the past?
Late Ordovician to the Cainozoic
What are peloids?
Fine grained, oval shaped - often invertebrate faeces
What are intraclasts?
Fragments of recently cemented sediment that has been churned up by waves etc in their depositional environment.
What are peloids a good indicator for?
Quiet water, depositional conditions - allows easy preservation.
What are intraclasts a good indicator of?
High energy environments
What are ooids?
Round, sand-sized grains of calcium carbonate formed by the precipitation of minerals around a central nucleus.
What are ooids a good indicator of?
Tropical, shallow coastal waters
What are the 3 classification systems of limestone?
Carozzi
Folk
Dunham
How does the Carozzi limestone classification classify limestone?
By grain size only, no content or texture
What are the types of limestone in the Carozzi classification system?
> 2mm calcirudite
0.62mm - 2mm calcarenite
What are the types of limestone in the Carozzi classification system?
> 2mm calcirudite
0.62mm - 2mm calcarenite
<0.62mm calcilutite
How does the Folk limestone classification classify limestone?
Folk reflects the content but not the size or texture
What do the prefixes of the Folk limestone classification indicate and what are the 4 groups?
The framework grains present:
Bio - fossils (bioclasts)
Pel - for peloids
Oo - for ooids
Intra - for intraclasts
What do the suffixes of the Folk limestone classification indicate and what are the 2 groups?
Indicate whether the interstitial calcite is sparry or micritic
What would a rock containing ooids with a sparry interstitial be named using the Folk limestone classification?
Oosparite
How does the Dunham limestone classification classify limestone?
Reflects texture but not content
