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Geology > Dynamic Surface L4 > Flashcards

Dynamic Surface L4 Flashcards

1
Q

How are non-clastic limestones produced?

A

By biogeochemical processes or direct precipitation

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2
Q

Where are limestones generally produced?

A

The basin where they are deposited

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3
Q

What is the reversible carbonate reaction?

A

CaCO3 + H2O + CO2 <–> Ca2+ + 2HCO3-

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4
Q

What is the name of the forward reaction in the reversible carbonate reaction?

A

Dissolution

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5
Q

What is the name of the backwards reaction in the reversible carbonate reaction?

A

Precipitation

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6
Q

In what conditions is the dissolution of carbonate favoured?

A

Low temperature
High hydrostatic pressure

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7
Q

In what conditions is the precipitation of carbonate favoured?

A

High temperature
Low hydrostatic pressure

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8
Q

Why does the rate of dissolution of carbonates increase at lower temperatures?

A

Warm water is more susceptible to evaporation

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9
Q

What is the main control on the reversible carbonate reaction?

A

The addition and removal of CO2

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10
Q

How does removing CO2 affect the reversible carbonate reaction?

A

Precipitation is favoured

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11
Q

How does adding CO2 affect the reversible carbonate reaction?

A

Dissolution is favoured

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12
Q

What are the 2 common polymorphs of CaCO3?

A

Calcite
Aragonite

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13
Q

What crystal system does calcite display?

A

Hexagonal

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14
Q

What crystal system does aragonite display?

A

Orthorhombic

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15
Q

What happens to aragonite when taken out of warm marine conditions?

A

It will transform into calcite

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16
Q

What concentration of magnesium does aragonite contain in ppm?

A

Less than 500ppm

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17
Q

Up to what concentration of Sr can aragonite contain in ppm?

A

Up to 10,000ppm of Sr substituting for Ca

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18
Q

What are the 4 components of limestones?

A

Skeletal grains
Non-skeletal grains
Micrite
Cements

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19
Q

What is an allochem?

A

A carbonate particle that was formed outside of the depositional environment and transported in

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20
Q

What is an orthochem?

A

Carbonate sediments that form within the depositional environment that represent the rock cement or matrix.

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21
Q

What are skeletal and non-skeletal grains known as in carbonate rocks?

A

Allochems

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22
Q

What is micrite?

A

A very fine grained component that often makes up the matrix of limestone

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23
Q

What are cements known as in carbonate rocks?

A

Orthochems

24
Q

What are skeletal grains?

A

Grains of carbonate rock that are formed from organisms that were once alive.

25
Q

What are 9 examples of skeletal grains?

A

Bivalves
Gastropods
Brachiopods
Corals
Crinoids
Foraminifera
Bryozoa
Stromatoporoids
Ostracods

26
Q

What did bivalves secrete?

A

Most secrete aragonite

27
Q

What did gastropods secrete?

A

Aragonite

28
Q

What are brachiopod shells made of?

A

Calcite

29
Q

What do corals secrete?

A

Calcite

30
Q

What do crinoids secrete?

A

Calcite

31
Q

What are foraminifera made of?

A

Calcite

32
Q

What do bryozoa secrete?

A

Calcite

33
Q

What do stromatoporoids secrete?

A

Calcite

34
Q

What are ostracods a good indicator of?

A

Brackish water

35
Q

What are crinoids a good indicator of?

A

Warm, gently agitated sea water

36
Q

What do trilobites secrete?

A

Calcite

37
Q

What are 3 examples of non-skeletal grains?

A

Ooids
Intraclasts
Peloids

38
Q

Chronologically list the geological time periods starting from the Precambrian to the Cainozoic.

A

Precambrian
Cambrian
Ordovician
Silurian
Devonian
Carboniferous
Permian
Triassic
Jurassic
Cretaceous
Cainozoic

39
Q

What is a distinctive feature of bivalves?

A

2 layered shell structure

40
Q

When were foraminifera prevalent in the past?

A

Cambrian to the Cainozoic

41
Q

When were corals prevalent in the past?

A

Late Ordovician to the Cainozoic

42
Q

What are peloids?

A

Fine grained, oval shaped - often invertebrate faeces

43
Q

What are intraclasts?

A

Fragments of recently cemented sediment that has been churned up by waves etc in their depositional environment.

44
Q

What are peloids a good indicator for?

A

Quiet water, depositional conditions - allows easy preservation.

45
Q

What are intraclasts a good indicator of?

A

High energy environments

46
Q

What are ooids?

A

Round, sand-sized grains of calcium carbonate formed by the precipitation of minerals around a central nucleus.

47
Q

What are ooids a good indicator of?

A

Tropical, shallow coastal waters

48
Q

What are the 3 classification systems of limestone?

A

Carozzi
Folk
Dunham

49
Q

How does the Carozzi limestone classification classify limestone?

A

By grain size only, no content or texture

50
Q

What are the types of limestone in the Carozzi classification system?

A

> 2mm calcirudite
0.62mm - 2mm calcarenite

51
Q

What are the types of limestone in the Carozzi classification system?

A

> 2mm calcirudite
0.62mm - 2mm calcarenite
<0.62mm calcilutite

52
Q

How does the Folk limestone classification classify limestone?

A

Folk reflects the content but not the size or texture

53
Q

What do the prefixes of the Folk limestone classification indicate and what are the 4 groups?

A

The framework grains present:
Bio - fossils (bioclasts)
Pel - for peloids
Oo - for ooids
Intra - for intraclasts

54
Q

What do the suffixes of the Folk limestone classification indicate and what are the 2 groups?

A

Indicate whether the interstitial calcite is sparry or micritic

55
Q

What would a rock containing ooids with a sparry interstitial be named using the Folk limestone classification?

A

Oosparite

56
Q

How does the Dunham limestone classification classify limestone?

A

Reflects texture but not content

Geology (17 decks)

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