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Geology > Dynamic Surface L6 > Flashcards

Dynamic Surface L6 Flashcards

1
Q

What is a reef?

A

A biologically influenced carbonate accumulation which possessed topographic relief during its growth.

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2
Q

Are all reefs built by corals - how do we know this?

A

No - corals are absent from many pre Caenozoic examples

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3
Q

What is the geological time scale of tabulate and rugose corals and what did they secrete?

A

Ordovician-Permian range
Calcite

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4
Q

What order to modern corals belong to?

A

Scleractinia

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5
Q

What do modern corals secrete?

A

Aragonite

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6
Q

When did modern corals arise?

A

The Mid Triassic

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7
Q

What do shallow water Scleractinia contain as a part of a symbiotic relationship and what do they need to survive?

A

Xooxanthellae - photosynthetic dinoflagellates
Need light to survive (the photic zone)

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8
Q

What type of modern corals are vulnerable to ocean acidification and why?

A

Deep, cold water corals are more vulnerable to ocean acidification than tropical corals as deep ocean water has a lower pH

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9
Q

When did the stromatolites first appear?

A

The Archean

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10
Q

How did stromatolites form reefs?

A

Stromatolites form algal mats that colonise sediment surfaces which can build up large structures

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11
Q

When do rugose and tabulate corals first appear?

A

Ordovician

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12
Q

When do stromatoporoids first appear?

A

Ordovician

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13
Q

What do stromatoporoids secrete?

A

Calcite

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14
Q

When did the stromatoporoids become extinct?

A

Devonian

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15
Q

When do rudists first appear and what order to they belong to?

A

Rudists are bivalves and first appear in the Cretaceous

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16
Q

What are skeletal/framework reefs?

A

Living colonies that form topographic highs, usually forming at the edge of continental margins and isolated platforms

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17
Q

What are 4 types of skeletal/framework reefs?

A

Fringing reef
Barrier reef
Submerged shelf-edge reef
Atoll reef

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18
Q

Where are fringing reefs found?

A

Fringing reefs are attached to continents and exist in the intertidal zone

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19
Q

Where are barrier reefs found?

A

Barrier reefs are separated from land by an area of shallow water

20
Q

Where are submerged shelf-edge reefs found?

A

Found on continental shelf edges

21
Q

What is an atoll reef?

A

A reef located on sea mounts and isolated platforms

22
Q

What is the difference between a reef mound and a skeletal reef?

A

Reef mounds don’t have a living framework unlike skeletal reefs

23
Q

How is a reef mound formed?

A

Calcareous material (algal remains, coral remains etc) is swept together by currents and tides into heaps which are held together by algal mats.

24
Q

When have reef mounds been frequent in geological history?

A

At times of high sea level

25
Q

What organisms have dominated frame-built reefs throughout Earth’s history?

A

Corals
Stromatolites
Stromatoporoids
Algaes

26
Q

What organisms primarily form reef mounds?

A

Bryozoans
Sponges
Crinoids

27
Q

What type of organisms form mud mounds?

A

Microbial mats

28
Q

What do rugose corals secrete?

A

Calcite

29
Q

Are rugose corals colonial or solitary

A

Solitary

30
Q

Are tabulate corals colonial or solitary?

A

Colonial

31
Q

What to tabulate corals secrete?

A

Calcite

32
Q

Why are stromatoporoid reefs able to deflect wave energy so effectively?

A

Due to their rounded dome structure

33
Q

Why does the back reef area contain more delicate organisms not found elsewhere on the reef?

A

The reef front protects the back reef against wave action

34
Q

What are 5 destructive processes that affect reefs?

A

Physical
Biological
Sedimentation
Cementation
Rising temperature

35
Q

How do physical processes damage reefs?

A

Wave action breaks off pieces of the reef and carries them to environments where growth is not possible e.g. tsunamis

36
Q

How do biological processes damage reefs?

A

Invasive species such as starfish and sea urchins destroy reefs by extracting coral polyps destroying huge areas of reef rapidly

37
Q

How do rising sea temperatures destroy reefs?

A

Warm water causes corals to spew out zooxanthellae causing coral bleaching

38
Q

How does sedimentation destroy reefs?

A

Flash flooding can wash terrestrial clastic sediment down onto reef communities causing corals to die due to indigestion

39
Q

How is cementation essential to reefs?

A

Modern reefs are strengthened and stuck together by chemical precipitates forming in areas of high rate of evaporation, concentration of sea water and safe spaces where micrite can precipitate.

40
Q

What is the growth rate of modern scleractinians in m/yr?

A

9-15m/1000years

41
Q

What water depth do modern scleractinians live in?

A

<100m

42
Q

What is the optimum temperature for modern scleractinians?

A

25-29 degrees Celsius

43
Q

What is the optimum salinity for modern scleractinians?

A

36 parts per thousand

44
Q

Why is an excess of nutrients hazardous to modern scleractinians?

A

An excess of nutrients increases the planktonic population rapidly, causing light from the sun to be blocked.

45
Q

What are some characteristics of corals found at the reef front?

A

Robust
Large surface area

Geology (17 decks)

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