Carbonates 1

Question 1

How do carbonates form?

Answer 1

They are generated by organisms that live in the marine environment which have calcium carbonate shells, shells accumulate as calcium carbonates when they die.

Question 2

Are carbonate sediments the same as carbonaceous sediments?

Answer 2

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

Question 3

Are carbonates autochthonous or allochthonous?

Answer 3

carbonates are autochthonous as they are generated locally in their environment.

Question 4

Why is most of the fossil record found in carbonates?

Answer 4

Because they are well preserved

Question 5

Why can CO2 be drawn down in the atmosphere?

Answer 5

Because carbon organisms draw it out.

Question 6

In the palaeozoic (late cambrian) what was the Co2 levels like and what organisms were present?

Answer 6

High CO2 levels. Brachiopods, Molluscs, echinoderms.

Question 7

What organisms were present in the Mesozoic

Answer 7

Brachiopods, Molluscs, echinoderms, corals

Question 8

what are the 5 controls on carbonate deposition

Answer 8

geotectonics, temperature and salinity, climate, water depth, water circulation & current regime.

Question 9

Where do corals, clean grainstones and lime mud (micrite) like to be on the marine platform?

Answer 9

Corals: at the front of platform where food is brought to them
clean grainstones: high energy areas
Lime mud: low energy areas

Question 10

Why is most accumulation and cement growth in the tropics?

Answer 10

saturation state for aragonite and CaCo3 in the tropics is very high so thats why most accumulation happens there

Question 11

Where is the carbonate factory?

Answer 11

At depths <15m

Question 12

What is the photic zone required for

Answer 12

It is required for corals and algae or any photosynthetic organisms.

Question 13

why will non-skeletal carbonates only be found in tropical areas? Name 2 types of non-skeletal carbonates.

Answer 13

Only found in the tropics because calcium carbonate saturation levels are very high in the sea. Examples include lime mud and ooids

Question 14

Fenestral pores indicate what type of environment?

Answer 14

Intertidal

Question 15

If an environment is intertidal, name 2 features youd expect to see

Answer 15

Fenestral pores and algal lamination

Question 16

what are fenestral pores?

Answer 16

They are gas bubbles which are created when carbon breaks down

Question 17

what is the difference between calcite and aragonite?

Answer 17

They have the same chemistry but different chemical structures, it is down to how the atoms are arranged in the crystals

Question 18

Name the different types of grain types and give examples.

Answer 18

Non-skeletal; ooids
Skeletal; bivalves, corals, foraminifera
Micrite (lime mud) constituent of most limestones except clean grainstones

Question 19

corals are in what category of the dunham classification and why.

Answer 19

Boundstone as they give a framework

Question 20

Dolomites are in what category of the dunham classification and why.

Answer 20

crystalline carbonates as you cant see their original sed structures of rock they were deposited in

Question 21

Name the differences between carbonates and clastics

Answer 21

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

Question 22

Name the other carbonate depositional systems and whether they are attached or detached.

Answer 22

Ramps (attached) 
Rimmed Shelves (attached) 
Escarpment Margins (attached) 
Isolated Platforms (detached)

Question 23

How are platforms built?

Answer 23

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.

Question 24

What kind of surface does rainwater create on a carbonate layer?

Answer 24

A carstified surface

Question 25

give an example of when and where carbonate sediments undergo transportation

Answer 25

During times of over-production on the shallow shelf, carbonates are re-sedimented into the basin.