Chapter 7 add on - Biogenic Sediments and Sedimentary Rocks

Question 1

define coral reef

Answer 1

-ridge of rock in sea formed by growth and deposit of coral

Question 2

What are the dangers our coral reef? Why is this happening?

Answer 2

Massive mortality of coral reefs
~30% of worlds coral reefs have died about 1970
~60% expected to be lost by 2030
-This is due to increase of acidification and temperature increase

Question 3

How to get carbonate sediment to transform into limestone?

Answer 3

Lithification - physical compaction + breakage, cementation, thickness reduction, tighter grain packing, grain rotation, grain breakage, cementation

Question 4

define polymorph

Answer 4

an organism or inorganic object or material that takes various forms.

Question 5

What polymorphs does calcium carbonate have?

Answer 5

Calcite

Aragonite

Question 6

Largest coral reefs?

Answer 6

Near Australia, 2-3km long

Question 7

Stages of reef growth, what is resultant?

Answer 7

One settles, then more settles, then the reef dies, gets buried. Then you have a buried city of dead corals, which then become a reservoir

Question 8

Name 3 carbonates

Answer 8

Calcite (mineral), aragonite(mineral); CaCO3
(Calcite and aragonite make up Limestones)

Dolomite (mineral) - CaMg (CO3)2
(Dolomite makes up Dolostone)

Question 9

What is kind of rock is limestone, and what is it made out of?

Answer 9

Sedimentary rock, made out of calcite, aragonite, which are different crystal forms of calcium carbonate.
-also made out of skeletons of coral reefs

Question 10

What are the most common reef building organisms? Describe them. Talk about their microstructure.

Answer 10

Corals

• corals are filter feeders, animals, that live on outside of skeletal structure
• microstructure of coral is species specific, so the microstructure tells u what kind of coral it is
• macrostructure depends on environment, so the outside of the same coral could be different for the same species, or the same for the different species

Question 11

How are coral species similar to plants?

Answer 11

The same coral species has a different growth form under different conditions.
Equivalent to what many plants do.. Pine trees could grow differently in different climate in response to different water conditions or temperature

Question 12

What is needed in the formation of most calcareous sediments? (sediments that contain calcium carbonate)

Answer 12

Shallow marine, warm environment

Question 13

Evolution of coral reefs, 3 steps

Answer 13

1) fringing reef forms around an island in tropics
2) island sinks as oceanic plate on which it rides moves away from spreading ridge. Island sinks slower than coral grows upwards.
3) Island eventually disappears beneath the surface, but coral remains at surface

Question 14

What are some types of shallow marine limestones?

Answer 14

oolitic limestone - made up partly of ooids, which are spherical grains of calcium
Coquina - limestone made up of entirely broken shells

Question 15

What is the point of looking at the porosity of a reef?

Answer 15

if high % porosity, you drill for oil in those spots, that’s why we bother looking at a reef organism

Question 16

How do you get from limestone to dolostone? What is the chemical equation? How does the process happen

Answer 16

Via dolomitization
2CaCO3 + Mg2+ --> CaMg(CO3)2 + Ca2+
A) evaporation from sediment
B)evaporation from standing water
-in order to get dolomitization, you need a source of magnesium to conduct

Question 17

What is dolomitization?

write the eqn (online info)

Answer 17

process by which limestone is altered into dolomite; when limestone comes into contact with magnesium-rich water, the mineral dolomite, calcium and magnesium carbonate, CaMg(CO 3) 2, replaces the calcite (calcium carbonate, CaCO 3) in the rock, volume for volume.
2CaCO3 + Mg2+ —> CaMg(CO3)2 + Ca2+

Question 18

Specifically describe how dolomite gets formed?

Answer 18

In hot climate, some some of water evaporates

• remained water gets very saline, makes it heavier
• seawater has a density for 1.1g/cm^3
• when we evaporate, it gets more dense
• this allows it to seep into sediments
• if there is a source of magnesium, it will convect through the calcium carbonate limestone and turn it into dolomite with a convection tide

Question 19

How can you tell the difference between limestone and dolostone?

Answer 19

Acid test. Fizzing gas from CO2, calcite(limestone) reacts, dolomite doesn’t.

Question 20

What are 2 the types of ooze?

Answer 20

Siliceous ooze - silica SiO2

Calcareous ooze - Calcium carbonate

Question 21

What is a pelagic carbonate rock?

Answer 21

chalk

Question 22

What is a pelagic siliceous rock?

Answer 22

chert (flinstone)

Question 23

What happens when calcareous ooze get piled up?

Answer 23

They make sedimentary rocks.
(compaction, lithification, thickness reduction, cementation)
pelagic carbonate rock - chalk

Question 24

What happens when siliceous ooze get piled up?

Answer 24

Same as calcareous, They make sedimentary rocks.
(compaction, lithification, thickness reduction, cementation), but they also go under recrystallization. These crystals are opal (glass)
-by the time its rock, the opal has recrystallized into quartz
-quartz was used long ago cuz it was so hard (in stone ages)
Also, Pelagic siliceous rock make chert (flinstone)

Question 25

If you need magnesium, would u eat dolomite???

Answer 25

NO, even though they sell the pills, you cant just injest magnesium through dolomite b/c you humans can’t digest it unless they stay in our stomach for a very long time (we just poop it out and barely take in anything)

Question 26

Where do you find siliceous ooze? Where do you find Calcareous ooze?

Answer 26

pelagic environments
Siliceous ooze - higher latitude, colder regions
Carbonate oozes - warmer regions

Question 27

What is chalk?

Answer 27

Pelagic carbonate rock (CaCO3)

Question 28

What is chert?

Answer 28

Pelagic siliceous rock (Silica)