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ES2001 > Carbonates > Flashcards

Carbonates Flashcards

1
Q

What are the three main types of carbonate minerals?

A

Calcite CaCO3
Aragonite CaCO3
Dolomite CaMg(CO3)2

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2
Q

What are common substitutes for carbonate minerals?

A

Mg, Fe, Sr commonly substitute into crystal lattices

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3
Q

What is the structure of dolomite?

A

Alternating layers of calcite CaCO3 and magnesite MgCO3
Rhombohedral

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4
Q

What are the key concepts of modern carbonates?

A

Mostly primary meta-stable marine minerals
Aragonite
High Mg Calcite

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5
Q

What are the key concepts of ancient carbonates?

A

Mostly secondary minerals
Dolomite CaMg(CO3)2
Low Mg Calcite

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6
Q

What is the composition of seawater?

A

Water
NaCl
Sulphate
Magnesium
Bicarbonate
Calcium
Potassium

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7
Q

What precipitates first out of seawater?

A

Water
Calcite
Gypsum
Halite
K and Mg salts

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8
Q

What is biologically induced mineralisation?

A

Metabolic byproducts of algae and microbes interact with seawater to produce supersaturated conditions that promote precipitation

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9
Q

What is biologically controlled mineralisation?

A

CaCO3 locked in skeletons of animals and plants that directly control precipitation
(Aragonite - gastropods + corals)
(High Mg calcite - benthic forams)
(Low Mg calcite - brachs)

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10
Q

What is the modern reef window?

A

Salinity 25-35%
Temperature 25-29
Within the photic zone
Siliciclastic input is low

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11
Q

Why are there no barrier reefs in India?

A

Abundant clastic input from erosion of Himalayas

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12
Q

What is pelagic and benthic?

A

Pelagic - open sea/ surface
Benthic - seafloor

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13
Q

What are the types of transport for the carbonate factory?

A

Shoreward transport
Basinward transport
Calcareous pelagic rain

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14
Q

Where is carbonate mainly produced?

A

90% from biological origins
Around equator - production varies with species abundance, related to latitude

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15
Q

What is the reaction to make carbonate ions?

A

CO2 (g) dissolves in water to form CO2 (aq)
CO2 (g) <-> CO2 (aq)

CO2 is hydrated to make carbonic acid
CO2 (aq) + H2O <-> H2CO3

From here, carbonic acid can form bicarbonate ion
HCO- 3

Or carbonate ion
CO 2- 3

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16
Q

What happens to mineralisation as pH decreases?

A

CO2 becomes H2CO3 carbonic acid, meaning there is less carbonate available for mineralisation, and therefore mineralisation decreases

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17
Q

What is the chemical formula for carbonate?

A

CO2- 3

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18
Q

What is the relationship between algae and coral?

A

Symbiosis
Algae photosynthesises, producing sugars and O2
Corals use sugars to build CaCO3 skeleton

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19
Q

What is the average coral growth rate?

A

5-10mm/year

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20
Q

What are two types of coral?

A

Framework Builders ie monastrea
Branching Corals ie stag horn

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21
Q

What are possible reasons for aragonite needles on green algae?

A

Structure support against tides
Protection against predators

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22
Q

What are reefs?

A

Biologically constructed reliefs which grow up from the sea floor

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23
Q

What are the three types of reef?

A

Barrier
Fringing
Patch

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24
Q

What is the characteristic of a barrier reef?

A

Forms offshore on the shelf and protects a lagoon behind them

Ie gently slope then /-\

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25
Q

What are the characteristics of a fringing reef?

A

Builds at the coastline

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26
Q

What are the characteristics of a patch reef/atoll?

A

Isolated offshore, ie on a seamount

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27
Q

What are the three environments of a reef setting?

A

Off reef open shelf
Reef core
Back reef lagoon

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28
Q

What are the four constitutes of the reef core?

A

Dish, branching, Masai e, reef crest

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29
Q

What causes bleached corals?

A

Low pH causes algae to leave, and the corals cannot build their skeletons without the symbiosis

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30
Q

Where are carbonate factories found?

A

Warm water protozoan systems:
- reefs
- ooid sand shoals
- open seafloor
- lagoons

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31
Q

What are the characteristics of a rimmed platform?

A

Highly differentiated facies

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32
Q

What direction is sediment swept in a carbonate system?

A

Swept landward

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33
Q

What are the different types of rimmed platforms?

A

Shoal rimmed
Continuous coral reef i.e. Belize
Segmented coral reef with tidal channels i.e. Exuma Island Chain, Bahamas

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34
Q

Give an example of an ooid shoal complex

A

Tongue of the ocean, Bahamas

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35
Q

What is the composition of Ooids?

A

Spherical particles of CaCO3
Smaller than 2mm in diameter
Nucleus ie sand grain, surrounded by concentric lamallae

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36
Q

What does a thin dark lamallae in ooids mean?

A

Organic matter

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37
Q

What are possible ooid origins?

A

Algal induced
Inorganic ppt
Mechanical aggregate

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38
Q

What are the three species of algae that grow aragonite needles?

A

Halimedia
Penicillus
Udotea

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39
Q

What aids the generation of carbonate grains?

A

Bioerosion by different macro and micro invertebrates, microbes and fish that break down carbonate substrates
Echinoids, worms, sponges, byrozoans, fish

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40
Q

What are the two types of non skeletal grains?

A

Peloids
Ooids

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41
Q

What are peloids?

A

Fecal pellets, non skeletal grains

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42
Q

What are the characteristics of peloids?

A

Spherical, elliptical or angular grains
Micritic composition
No internal structure
Feacal in origin i.e. from gastropods, crustaceans, polychaetes
Rich in organic matter

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43
Q

What are the lithologies of lagoons/subtidal facies?

A

Wackstone and packstones with bioturbation

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44
Q

What is the peritidal zone?

A

Zone extending from above the level of the highest tide to below that exposed at the lowest tide, and thus somewhat wider than the intertidal zone

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45
Q

What are subtidal, intertidal, supratidal zones?

A

Subtidal - below low tide
Intertidal - below high tide
Supratidal - above high tide/below storm driven high tide

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46
Q

What is the importance of Andros Island, the Bahamas?

A

Producing carbonate since Triassic
6km in thickness
1000’s km2

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47
Q

What are the characteristics of humid tidal flat sub environments?

A

Supratidal marsh
Pond and channel belt - tidal channels, intertidal flat
Subtidal marine

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48
Q

Give an example of a tidal flat sub environment

A

Triple goose creek, bahamas

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49
Q

What is the intertidal zone?

A

Between normal low and high tide levels
Complex topography featuring tidal channels, brackish or saline ponds

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50
Q

What is the subtidal zone?

A

Permanently submerged
Low energy lagoon, high energy shoals
May be exposed during neap tides

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51
Q

What are intertidal facies?

A

Sediment deposited between normal high tide and normal low tide
Exposed twice a day

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52
Q

What is the lithologies of intertidal facies?

A

Burrowed to laminated mudstones to wackstones
Algal bound stones with algal heads
Thin cross bedded grain stones
Rare storm deposits

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53
Q

What sedimentary structures are found in supratidal facies?

A

Mud cracks, fine laminations, algal mats and domes, fenestrae structures, desiccation cracks
Fuggy texture
Plant , animal and insect burrows
Intraclasts and dolomite crusts

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54
Q

Give an example of arid tidal flats

A

Trucial coast, united arab emirates

55
Q

What causes teepee structure?

A

Salt precipitation

56
Q

What are allochem textures influenced by?

A

Given environmental and time controls, influenced by wave energy

57
Q

Name the progression of allochem textures in order of increasing grain size and decreased mud.

A

Mudstone, wackstone, packstone, grainstone, boundstone
Crystalline

58
Q

Where are clastic sediments found?

A

Not climatically constrained
Both terrestrial and marine
Unconsolidated in the depositional environment

59
Q

Where are carbonate sediments found?

A

Shallow, warm water environments
Mostly marine
Cemented to seafloor

60
Q

What does grain size and mud indicate in clastic sediments?

A

Grain size reflects hydraulic energy of the environment
Mud indicates settling from suspension

61
Q

What does grain size and mud indicate in carbonate sediments?

A

Grain size reflects the size of skeletons and precipitated grains
Mud commonly indicates prolific growth of organisms that produce tiny crystals

62
Q

What are environmental changes induced by for clastic sediments?

A

Induced by widespread changes in hydraulic regime

63
Q

What are environmental changes induced by for carbonate sediments?

A

Induced by localised buildup of carbonate, without change in hydraulic regime

64
Q

What is the energy of an open unrimmed platform?

A

High energy conditions prevail across the shallows

65
Q

How do Ooids form?

A

Continuous wave agitation rolls the grain, accumulating CaCO3 around nucleus in even coats, forming even coats of concentric laminae in a cross section

66
Q

What are the characteristics of lagoonal/subtidal facies?

A

Protected from waves so lower energy
Lots of mud
Less biologically diverse

67
Q

What are the characteristics of tidal channels?

A

Fixed ie dont migrate much
Limited sediment transport

68
Q

Where are cold water corals found?

A

Temperature 4-12 degrees C
Shallow waters (50-1000metres) at high latitudes
Deep water (<4000m) beneath warm water masses

69
Q

What influences the placement of deep water carbonates?

A

Ocean gyres, especially the Gulf Stream

70
Q

What species are present in deep water reefs?

A

Bryozoan
Crinoid
Gastropods

71
Q

What corals are common in deep water reefs
?

A

Framework corals
Lophelia pertusa
Madrepora oculata

72
Q

What is the name of corals that lack symbiotic dinoflagellates?

A

Azooxanthellate corals

73
Q

How do framework corals provide a structural habitat for other species?

A

Feed from suspended sediments, dissolved organic matter, bacteria, protozoans, and (zoo)(phyto)plankton

74
Q

How do corals develop?

A

As a coral grows polyps in older portions die, and the skeleton becomes increasingly vulnerable to bioeroders and mechanical breakage

75
Q

Name two solitary cold water corals

A

Desmophyllum cristagalli
Caryophyllia sp

76
Q

What is the structure of reef mounds?

A

Flanking sediments
Cap of encrusting biota
Muddy Core with small invertebrate skeletons
Basal lime grainstone to wackestone pile

77
Q

What kind of coral communities do you find in cold water?

A

Stony corals - scleractinia
Soft corals - octocorallia, gorgonian sea fans
Black corals - antipatharia
Hydrocorals - stylasteridae

78
Q

What is porcupine mound?

A

Up to 300m high mounds in the Irish margin, colonising 2.5 Ma Miocene deposits

79
Q

What are the five stages of the biogenic reef crest cycle?

A

Early interglacial
Interglacial
Interglacial
Glacial
New interglacial

80
Q

How do we know there has been continuous cold water coral growth over the last 50,000years?

A

Uranium.thorium dating

81
Q

Where are heterotroph reefs found?

A

Not constrained by light therefore can grow into deeper water than mixotroph counterparts

82
Q

What threats are present to cold water corals?

A

Trawling for fish

83
Q

What is the characteristic of carbonate slop sedimentation?

A

Long periods of boredom alternating with short periods of terror

84
Q

What is a olistolith?

A

Sedimentary deposit of large homogenous sediment

85
Q

What does perennial mean?

A

Permanently filled

86
Q

What does ephemeral mean?

A

Periodically dry

87
Q

What kind of lacustrine settings are there?

A

Perennial or ephemeral lakes

88
Q

How do lacustrine settings differ from marine settings?

A

Lack tidal activity
Closed systems with smaller volumes of water and sediment
Relatively small size

89
Q

What does the relatively small size of lakes mean?

A

Water chemistry responds more rapidly to changes in local conditions and climate

90
Q

What is the littoral zone?

A

Encompasses shallow water around a lake margin.
Is often characterised by shallow water ‘bench’ or ‘terrace’

91
Q

What is the profundal zone?

A

Deep, aphotic region of the lake

92
Q

What is the sublittoral zone?

A

The transition region between littoral zone and deeper profundal zone

93
Q

What is the pelagic zone?

A

The water column above deep, aphotic region of the lake

94
Q

How does stratification develop in modern lakes?

A

Due to differential radiative heating

95
Q

What divides the warm water layer from the underlying cool water layer?

A

The thermocline

96
Q

What happens to water stratification during winter months?

A

Different layers mix following cooling and action of wind-induced currents
Once water in the epilimnion reaches four degrees it sinks

97
Q

When does meromixis develop?

A

When surface waters are consistently less dense than the deep waters

98
Q

What are the controls on lake sedimentation?

A

Abiogenic precipitation
Biologically induced precipitation
Biologically controlled precipitation
Extrinsic factors
Intrinsic factors

99
Q

What abiogenic precipitates are there
?

A

Aragonite, calcite, magnesite, hydromagnesite and dolomite

100
Q

What causes abiogenic precipitates?

A

Waters become supersaturated due to evaporation/cooling/CO2 degassing

101
Q

What biological communities control lake sedimentation?

A

Charophytes
Ostracod
Mollusks
Insects
Diatoms

102
Q

What are the extrinsic factors controls on lake sedimentation?

A

Climate - not restricted by climatic zone, controls rainfall, water balance, biogenic activity
Tectonics

103
Q

What are the intrinsic factors that control lake sedimentation?

A

Hydrology - controls flux of sediment
Lake stratification/mixing
Sediment sources

104
Q

How does lake stratification and mixing affect lakes?

A

Controlled by heating and cooling of surface waters, which promotes carbonate formation/biological activity
Recycling on nutrient elements that stimulates planktonic activity
Renewed oxygenation of bottom waves, leading to0 mineral precipitation and promote bioturbation

105
Q

What are types of lacustrine deposits?

A

Shoreline facies
Lake centre/pelagic facies

106
Q

What is a type of shoreline facies?

A

Marginal bench

107
Q

What carbonate sediments do you find on marginal benches
?

A

Peloids
Oncoids
Stromatolites

108
Q

What are microbialites ?

A

Limestones and dolomites formed by microbial activity that forms a biofilm, leading to calcite dolomite precipitation through extracting CO2 from water
Stromatolites
Thrombolites

109
Q

What is the difference between stromatolites and thrombolites?

A

Stromatolites are laminated
Thrombolites are clotted

110
Q

How are active springs defined?

A

Based on the highest temperature measured at the spring vent

111
Q

What temperature are cool springs?

A

<20 degC

112
Q

What are the temperature classifications of thermal springs?

A

Thermal >20 degrees
Warm 20-40 degrees
Mesothermal 40-75 degrees
Hyperthermal >75 degrees

113
Q

What is tufa, where is it formed, and composition?

A

Tufa= limestone formed in freshwater settings ie streams, lakes, springs, marshes
Formed at ambient temperatures, in water derived from rain/surface runoff/near surface ground water from limestone areas
Composed of calcite

114
Q

What is travertine and where is it formed?

A

Calcareous deposits precipitated from thermal springs
Water may be derived from from the deep subsurface
Minerals such as silica , aragonite and stevensite may be present

115
Q

What is crystal morphology related to?

A

CaCO3 supersaturation

116
Q

What is barrage tufa formed of?

A

Vaucheria- green algae that forms overhangs and tongues a

117
Q

Give six examples of tufa?

A

Vaucheria tufa - green algae - tongues, dams, pools
Moss tufa - springs
Vacuolar tufa - coated twigs, leaves, many holes
Dark ‘heavy’ rough nodular / pustular and black tufa
Laminated stromatolitic tufa
Oncoidal tufa
Tufa with chironomids

118
Q

How does tufa form?

A

Chemical precipitation of calcite through CO2 degassing and biochemical precipitation through photosynthetic activities of Cyanobacteria, mosses, bryophytes, green algae and diatoms
Microbes and EPS attract Ca2+ ions and creating a micro environment for calcite precipitation

119
Q

Give examples of tufa formation

A

Gordale, York’s, England

120
Q

Give an example of a travertine formation

A

Pamukkale, turkey
Yellowstone

121
Q

Give an example of tufa mounds

A

Mono lake California
Pyramid lake Nevada

122
Q

Give an example of barrage tufa

A

Skriadin and plitvice, Croatia

123
Q

What are important food sources for deep sea corals?

A

Resuspended material, bacteria and protozoans
Dissolved inorganic matter
Zooplankton and phytoplankton

124
Q

What are important food sources for deep sea corals?

A

Resuspended material, bacteria and protozoans
Dissolved inorganic matter
Zooplankton and phytoplankton

125
Q

What is an olistolith?

A

A large clast within slope deposits

126
Q

True or false:
HMC is the dominant carbonate throughout the rock record

A

False

127
Q

What do the horizontal growth bands in deep sea corals most likely represent?

A

Seasonal delivery of nutrients

128
Q

What facies are most characteristic of arid carbonated tidal flat settings?

A

Microbialaminate
Teepee structures
Nodular anhydride

129
Q

What role does Udotea play within carbonate settings?

A

Aragonite producing codiacean algae

130
Q

True or false:
Carbonate sediment production is lowest in the shallowest, inner most areas of a platform>

A

True

131
Q

True or false:
HMC is the dominant carbonate throughout the rock record

A

False

132
Q

What is the rate of sediment production on Great Bahamas bank margins?

A

4 kg/m2/yr

133
Q

In what carbonate setting is scytonema found?

A

Algal marsh
Peritidal zone

ES2001 (9 decks)

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