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Dynamic Surface L4 Flashcards

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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?

24
Q

What are skeletal grains?

Study These Flashcards
A

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

25
What are 9 examples of skeletal grains?
Bivalves Gastropods Brachiopods Corals Crinoids Foraminifera Bryozoa Stromatoporoids Ostracods
26
What did bivalves secrete?
Most secrete aragonite
27
What did gastropods secrete?
Aragonite
28
What are brachiopod shells made of?
Calcite
29
What do corals secrete?
Calcite
30
What do crinoids secrete?
Calcite
31
What are foraminifera made of?
Calcite
32
What do bryozoa secrete?
Calcite
33
What do stromatoporoids secrete?
Calcite
34
What are ostracods a good indicator of?
Brackish water
35
What are crinoids a good indicator of?
Warm, gently agitated sea water
36
What do trilobites secrete?
Calcite
37
What are 3 examples of non-skeletal grains?
Ooids Intraclasts Peloids
38
Chronologically list the geological time periods starting from the Precambrian to the Cainozoic.
Precambrian Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Cainozoic
39
What is a distinctive feature of bivalves?
2 layered shell structure
40
When were foraminifera prevalent in the past?
Cambrian to the Cainozoic
41
When were corals prevalent in the past?
Late Ordovician to the Cainozoic
42
What are peloids?
Fine grained, oval shaped - often invertebrate faeces
43
What are intraclasts?
Fragments of recently cemented sediment that has been churned up by waves etc in their depositional environment.
44
What are peloids a good indicator for?
Quiet water, depositional conditions - allows easy preservation.
45
What are intraclasts a good indicator of?
High energy environments
46
What are ooids?
Round, sand-sized grains of calcium carbonate formed by the precipitation of minerals around a central nucleus.
47
What are ooids a good indicator of?
Tropical, shallow coastal waters
48
What are the 3 classification systems of limestone?
Carozzi Folk Dunham
49
How does the Carozzi limestone classification classify limestone?
By grain size only, no content or texture
50
What are the types of limestone in the Carozzi classification system?
>2mm calcirudite 0.62mm - 2mm calcarenite
51
What are the types of limestone in the Carozzi classification system?
>2mm calcirudite 0.62mm - 2mm calcarenite <0.62mm calcilutite
52
How does the Folk limestone classification classify limestone?
Folk reflects the content but not the size or texture
53
What do the prefixes of the Folk limestone classification indicate and what are the 4 groups?
The framework grains present: Bio - fossils (bioclasts) Pel - for peloids Oo - for ooids Intra - for intraclasts
54
What do the suffixes of the Folk limestone classification indicate and what are the 2 groups?
Indicate whether the interstitial calcite is sparry or micritic
55
What would a rock containing ooids with a sparry interstitial be named using the Folk limestone classification?
Oosparite
56
How does the Dunham limestone classification classify limestone?
Reflects texture but not content

Geology (17 decks)

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