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Sedimentology and Stratigraphy > (S11) Carbonates and Evaporites > Flashcards

(S11) Carbonates and Evaporites Flashcards

1
Q

What is the Chemical equation for Calcium Carbonate?

A

CaCO3

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2
Q

What is the difference between calcareous and carbonaceous?

A

Calcareous is rich in Calcium Carbonate, Carbonaceous is rich in Carbon

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3
Q

What common elements are found in carbonates?

A

Magnesium, Iron, Copper

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4
Q

Give two examples of copper carbonates?

A

Malachite, Azurite

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5
Q

What is a carbonate?

A

Sediments and rocks made up of ___ Carbonate, e.g. Mg- Fe- Cu-

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6
Q

What rock has the same minerals as carbonates but is not infact called a carbonate?

A

Marble

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7
Q

What is the name for the uncommon carbonate-rich lava?

A

Carbonatite

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8
Q

What is the Moh’s hardness of Calcite?

A

3

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9
Q

What colour does Calcite have in hand sample?

A

White, Colourless

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10
Q

What are the two ways to distinguish Calcite in hand sample?

A

Moh’s hardness, Reaction to HCl (10% dilute)

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11
Q

Where does most Calcite come from?

A

Biogenic origin

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12
Q

What two elements can substitute calcium in Calcite?

A

Magnesium, Strontium

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13
Q

What are the two grades of Magnesium Calcite?

A

Low and high grade

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14
Q

What defines a low grade Magnesium Calcite?

A

Less than 4% Mg

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15
Q

What defines a high grade Magnesium Calcite?

A

11% - 19% Mg

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16
Q

Give three examples of marine organisms which create high-Mg Calcite

A

Echinoderms, Barnacles, Foraminifers

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17
Q

Why is strontium useful in calcite?

A

Use for dating rocks

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18
Q

What quantity can strontium be found in calcite?

A

<1%

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19
Q

How does the mineral form of Aragonite differ from Calcite?

A

Calcite is trigonal and aragonite is orthorhombic

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20
Q

Which is more dense, aragonite or calcite?

A

Aragonite

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21
Q

What is the density of aragonite and calcite respectively?

A

Aragonite = 2.95, Calcite = 2.72 - 2.94

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22
Q

What is the Moh’s hardness of Aragonite?

A

3.5 - 4

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23
Q

Give two examples of intvertebrets which use Aragonite to build their hard parts?

A

Bivalves and Corals

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24
Q

What is the chemical name and formula for Dolomite?

A

Calcium Magnesium Carbonate (CaMg(CO3)2)

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25
Q

What is the difference between Dolomite and Dolostone?

A

Dolostone is the rock which is made up of Dolomite

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26
Q

What is the distinguishing factor between Dolomite and Calcite/Aragonite?

A

Little or no reaction to the HCl acid test

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27
Q

How is Dolomite considered to be formed?

A

Diagenisis

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28
Q

What is the chemical name and formula for Siderite?

A

Iron Carbonate (FeCO3)

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29
Q

What impurities does Siderite often contain as a substitute for Iron?

A

Magnesium, Manganese

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30
Q

When does Siderite form?

A

As an early diagenic material in sediments

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31
Q

When do Molluscs date back to?

A

Cambrian

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32
Q

What do Molluscs usually create their form out of?

A

Calcareous

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33
Q

What does a Bivalve Molluscs shell layers look like?

A

Usually two or three layers of Calcite, Aragonite or both

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34
Q

What are most modern Molluscs made from?

A

Aragonite

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35
Q

Why are no pre-Jurassic bivalve shells preserved?

A

Instability of Aragonite compared to Calcite

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36
Q

What is the distinguishing difference between Gastopods and Cephalopods

A

Cephalopods are chambered

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37
Q

When were Ammonites most common?

A

Mesozoic

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38
Q

When were Brachiopods most common?

A

Palaeozoic and Mesozoic - Not seen modernly

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39
Q

What were the shells of Brachiopods made up of?

A

Low-Mg Calcite

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40
Q

What is the distinguishing feature of Echionoids and Crinoids?

A

Both create their bodies from entire calcite crystals

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41
Q

What are the two types of Forams?

A

Planktonic or Benthic

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42
Q

What is the main crystal form of Pre-Palaeozoic Corals?

A

Calcite

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43
Q

What is the main crystal form of Post-Palaeozoic Corals?

A

Aragonite

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44
Q

What is the name for a coral which has a symbiotic relationship with Algae, and exists in clear, warm, shallow marine environments?

A

Hermatypic Corals

45
Q

What is the name for a coral which does not have a symbiotic relationship with Algae and exsit in colder, deeper waters?

A

Ahermatypic Corals

46
Q

What is the name for a group of single-celled colonial organisms

A

Bryozoa

47
Q

What are the three types of carbonate producing Algae?

A

Red Algae (Rhodophyta), Green Algae (Chlorophyta), Nanoplankton (Yellow-Green Algae)

48
Q

What are Red Algae effective at doing, useful for the stratigraphic record?

A

Binding soft substrate

49
Q

What do Green Algae contribute to the stratigraphic record?

A

Fine rods and grains

50
Q

Name an example of a Nanoplankton?

A

Coccoliths

51
Q

How do Cyanobacteria operate?

A

Create sheet like mats which trap fine grained carbonate, creating flat/dome structures

52
Q

What is the name for the flat/dome structures created by Cyanobacteria?

A

Stromatolites

53
Q

What are Thrombolites?

A

Cyanobacteria which create a irregular rathern than structured form

54
Q

What are Ooids?

A

Spherical bodies of CaCO3, 2mm in diameter

55
Q

What is the internal structure of an Ooid like?

A

Precipitate layers of CaCO3, may have precipitated around a small fragment of another material

56
Q

What does accumulations of Ooids form?

A

Shoals

57
Q

Ooids are components of limestone throughout what time?

A

Phanerozoic

58
Q

What is a rock called which is made up of carbonate ooids?

A

Oolitic Limestone

59
Q

What is thought to be the origin of Ooids?

A

Chemical precipitation of agitated water which is saturated in CaCO3 in warm waters

60
Q

What is thought to have a role in the process of Ooid formation in less agitated waters?

A

Bacteria

61
Q

What is a pisoid?

A

A concentrically layered carbonate particle over 2mm in diameter

62
Q

What is a peloid and what is it’s origin?

A

Calcium carbonate particle which does not have a concentric structure - thought to be faecal pellets

63
Q

What is the name for fragments of CaCO3 which has been partly lithified, broken up, reworked to form a clast?

A

Intraclasts

64
Q

Where do intracalsts usually occur? (2 Exmaples)

A

When lime mud dries out by subaerial exposure, is reworked by a current, OR associated with reefs which have been broken up by wave/storm action and redeposited

65
Q

What is the name for a carbonate grain which contains several fagments cemented together?

A

Aggregate grains

66
Q

What is the name for a carbonate grain which contains several rounded grains?

A

Grapestones

67
Q

What are the three names given to a CaCO3 particle <4 microns diameter?

A

Lime mud, Carbonate mud or Micrite

68
Q

What are the three processes which form Lime Mud?

A

Chemical precipitation from water, Breakdwon of Skeletal Fragments, Algal/Bacterial Origin

69
Q

Why is it difficult to determine the source of Lime Mud?

A

Grains are too small

70
Q

What is the name for the classification scheme used in Limestones?

A

Dunham Classification

71
Q

What is the first and second stages to the classification used in the Dunham scheme?

A

First is to determine texture, second is to determine nature of the grains in the material

72
Q

What is the name for a limestone with less than 10% clasts?

A

Carbonate Mudstone

73
Q

What is the name for a limestone with more than 10% clasts?

A

Wackestone

74
Q

What is the name for a clast supported limestone with presence of mud?

A

Packstone

75
Q

What is the name for a clast supported limestone without presence of mud?

A

Grainstone

76
Q

What is the name for a limestone which has an organic framework such as a ocral colony?

A

Boundstone

77
Q

What are the three sub-divisions of a Boundstone in the Dunham Classification scheme?

A

Bafflestone, Bindstone, Framestone

78
Q

What is the name for a limestone which has more than 10% grains and is matrix supported?

A

Floatstone

79
Q

What is the name for a limestone which has more than 10% grains and is clast supported?

A

Rudstone

80
Q

What is the difference between a conglomerate made up of limestone from older bedrock and a floatstone/rudstone?

A

Floatstone/Rudstones are deposited in the same or adjacent environment, where as a Limestone Conglomerate may be deposited in a completely different environment

81
Q

Describe a “oolitic grainstone”

A

A clast supported (no matrix) rock made of ooids.

82
Q

Describe a “bioclastic packstone”

A

Up to 90% shelly fragments in matrix of carbonate mud

83
Q

What is the most commonly encountered evaporite mineral?

A

Calcium Sulphate

84
Q

What are the two most common forms of Calcium Sulphate (minerals)?

A

Gypsum, Anhydrite

85
Q

When is Calcium Sulphate precipitated from sea water?

A

Once evaporation has concentrated water to 19% of its original volume

86
Q

What is the chemical formumla of Gypsum?

A

CaSO4.2H2O

87
Q

Where does Gypsum precipitate?

A

At the surface under all but the most arid of conditions

88
Q

What happens when Gypsum becomes dehydrated on burial?

A

Forms Anhydrite (CaSO4)

89
Q

Aside from Gypsum dehydration, when does Anyhdrite form?

A

Direct precipitation in arid conditions

90
Q

What happens to Anyhdrite with the introduction of water?

A

Hydrated to Gypsum

91
Q

What form does Gypsum take from primary preiciptation out of water?

A

Elongate Selenite crystals

92
Q

If Gypsum forms from a rehydration of Anhydrite, what form does it take?

A

Fine crystalline form in nodules of Alabaster

93
Q

What are the two ways to distinguish Gypsum from Calcite in hand sample?

A

Softer (Moh’s hardness of 2), Does not react with HCl

94
Q

How can we distinguish Gypsum from Halite?

A

Does not taste salty

95
Q

What is the difference between Gypsum and Anhydrite in hand sample? (1)

A

Anhydrite is harder (Moh’s of 3.5)

96
Q

When does Halite become precipitated out of seawater?

A

When it has been concentrated to 9.5% of its original volume

97
Q

What is distinctive about Halite crystals?

A

Cubic

98
Q

What is a Hopper Crystal?

A

A crystal which has a stepped crystal face, e.g. Halite

99
Q

When is Halite preserved?

A

When thre is an absence of dilute groundwater

100
Q

What is the name for naturally occuring Halite?

A

Rock salt

101
Q

What is the Moh’s hardness of Halite?

A

2.5

102
Q

What is the mineral name for Potassium Chloride?

A

Sylvite (KCl)

103
Q

What is the economic importance of Sylivte?

A

Industrial Potash

104
Q

Why is the lack of modern Sylvite precipitation important?

A

Chemical composition of the sea water has not been constant with time

105
Q

What are the suggested reasons for variations in chemical composition of sea water with time?

A

Variations in relative impotance of Runoff and Hydrothermal Waters

106
Q

What group of minerals does Saline lakes most often precipitate?

A

Sulphates

107
Q

What is the importance of limestone classification to hydrocarbon exploration?

A

Limestones can act as a reservoir with the same properties of limestone - hence it is important that classification schemes are consistant

108
Q

What is the importance of evaporites in hydrocarbon exploration?

A

Act as seals to migration of hydrocarbons, including diapir formations

109
Q

What is a diapir?

A

Subsurface movement of Halite

Sedimentology and Stratigraphy (19 decks)

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