Carbonates 1 Flashcards
How do carbonates form?
They are generated by organisms that live in the marine environment which have calcium carbonate shells, shells accumulate as calcium carbonates when they die.
Are carbonate sediments the same as carbonaceous sediments?
No, they are two different things, carbonaceous sediments have carbon in them and tend to be black in colour. Carbonates tend to be white or grey and have organic carbon within them
Are carbonates autochthonous or allochthonous?
carbonates are autochthonous as they are generated locally in their environment.
Why is most of the fossil record found in carbonates?
Because they are well preserved
Why can CO2 be drawn down in the atmosphere?
Because carbon organisms draw it out.
In the palaeozoic (late cambrian) what was the Co2 levels like and what organisms were present?
High CO2 levels. Brachiopods, Molluscs, echinoderms.
What organisms were present in the Mesozoic
Brachiopods, Molluscs, echinoderms, corals
what are the 5 controls on carbonate deposition
geotectonics, temperature and salinity, climate, water depth, water circulation & current regime.
Where do corals, clean grainstones and lime mud (micrite) like to be on the marine platform?
Corals: at the front of platform where food is brought to them
clean grainstones: high energy areas
Lime mud: low energy areas
Why is most accumulation and cement growth in the tropics?
saturation state for aragonite and CaCo3 in the tropics is very high so thats why most accumulation happens there
Where is the carbonate factory?
At depths <15m
What is the photic zone required for
It is required for corals and algae or any photosynthetic organisms.
why will non-skeletal carbonates only be found in tropical areas? Name 2 types of non-skeletal carbonates.
Only found in the tropics because calcium carbonate saturation levels are very high in the sea. Examples include lime mud and ooids
Fenestral pores indicate what type of environment?
Intertidal
If an environment is intertidal, name 2 features youd expect to see
Fenestral pores and algal lamination
what are fenestral pores?
They are gas bubbles which are created when carbon breaks down
what is the difference between calcite and aragonite?
They have the same chemistry but different chemical structures, it is down to how the atoms are arranged in the crystals
Name the different types of grain types and give examples.
Non-skeletal; ooids
Skeletal; bivalves, corals, foraminifera
Micrite (lime mud) constituent of most limestones except clean grainstones
corals are in what category of the dunham classification and why.
Boundstone as they give a framework
Dolomites are in what category of the dunham classification and why.
crystalline carbonates as you cant see their original sed structures of rock they were deposited in
Name the differences between carbonates and clastics
Carbonates are autochthonous whereas clastics are allochthonous. Clastics are transported whereas carbonates are not.
Clastics show a wide range of sedimentary structures unlike carbonates.
Sea level and environmental change strongly influence carbonate accumulation
Name the other carbonate depositional systems and whether they are attached or detached.
Ramps (attached) Rimmed Shelves (attached) Escarpment Margins (attached) Isolated Platforms (detached)
How are platforms built?
If they are in a carbonate happy environment they START UP, they then are in CATCH UP where they keep up with sea level rise. Get AGGRADATION until at peak of MFS. Then get PROGRADATION when it sheds sides of platform into deeper water.
What kind of surface does rainwater create on a carbonate layer?
A carstified surface
give an example of when and where carbonate sediments undergo transportation
During times of over-production on the shallow shelf, carbonates are re-sedimented into the basin.
