Flashcards in Chapter 7 add on - Biogenic Sediments and Sedimentary Rocks Deck (28):
define coral reef
-ridge of rock in sea formed by growth and deposit of coral
What are the dangers our coral reef? Why is this happening?
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
How to get carbonate sediment to transform into limestone?
Lithification - physical compaction + breakage, cementation, thickness reduction, tighter grain packing, grain rotation, grain breakage, cementation
an organism or inorganic object or material that takes various forms.
What polymorphs does calcium carbonate have?
Largest coral reefs?
Near Australia, 2-3km long
Stages of reef growth, what is resultant?
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
Name 3 carbonates
Calcite (mineral), aragonite(mineral); CaCO3
(Calcite and aragonite make up Limestones)
Dolomite (mineral) - CaMg (CO3)2
(Dolomite makes up Dolostone)
What is kind of rock is limestone, and what is it made out of?
Sedimentary rock, made out of calcite, aragonite, which are different crystal forms of calcium carbonate.
-also made out of skeletons of coral reefs
What are the most common reef building organisms? Describe them. Talk about their microstructure.
-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
How are coral species similar to plants?
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
What is needed in the formation of most calcareous sediments? (sediments that contain calcium carbonate)
Shallow marine, warm environment
Evolution of coral reefs, 3 steps
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
What are some types of shallow marine limestones?
oolitic limestone - made up partly of ooids, which are spherical grains of calcium
Coquina - limestone made up of entirely broken shells
What is the point of looking at the porosity of a reef?
if high % porosity, you drill for oil in those spots, that's why we bother looking at a reef organism
How do you get from limestone to dolostone? What is the chemical equation? How does the process happen
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
What is dolomitization?
write the eqn (online info)
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+
Specifically describe how dolomite gets formed?
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
How can you tell the difference between limestone and dolostone?
Acid test. Fizzing gas from CO2, calcite(limestone) reacts, dolomite doesn't.
What are 2 the types of ooze?
Siliceous ooze - silica SiO2
Calcareous ooze - Calcium carbonate
What is a pelagic carbonate rock?
What is a pelagic siliceous rock?
What happens when calcareous ooze get piled up?
They make sedimentary rocks.
(compaction, lithification, thickness reduction, cementation)
pelagic carbonate rock - chalk
What happens when siliceous ooze get piled up?
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)
If you need magnesium, would u eat dolomite???
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)
Where do you find siliceous ooze? Where do you find Calcareous ooze?
Siliceous ooze - higher latitude, colder regions
Carbonate oozes - warmer regions
What is chalk?
Pelagic carbonate rock (CaCO3)