Carbonates Flashcards
1
Q
What are the three main types of carbonate minerals?
A
Calcite CaCO3
Aragonite CaCO3
Dolomite CaMg(CO3)2
2
Q
What are common substitutes for carbonate minerals?
A
Mg, Fe, Sr commonly substitute into crystal lattices
3
Q
What is the structure of dolomite?
A
Alternating layers of calcite CaCO3 and magnesite MgCO3
Rhombohedral
4
Q
What are the key concepts of modern carbonates?
A
Mostly primary meta-stable marine minerals
Aragonite
High Mg Calcite
5
Q
What are the key concepts of ancient carbonates?
A
Mostly secondary minerals
Dolomite CaMg(CO3)2
Low Mg Calcite
6
Q
What is the composition of seawater?
A
Water
NaCl
Sulphate
Magnesium
Bicarbonate
Calcium
Potassium
7
Q
What precipitates first out of seawater?
A
Water
Calcite
Gypsum
Halite
K and Mg salts
8
Q
What is biologically induced mineralisation?
A
Metabolic byproducts of algae and microbes interact with seawater to produce supersaturated conditions that promote precipitation
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)
10
Q
What is the modern reef window?
A
Salinity 25-35%
Temperature 25-29
Within the photic zone
Siliciclastic input is low
11
Q
Why are there no barrier reefs in India?
A
Abundant clastic input from erosion of Himalayas
12
Q
What is pelagic and benthic?
A
Pelagic - open sea/ surface
Benthic - seafloor
13
Q
What are the types of transport for the carbonate factory?
A
Shoreward transport
Basinward transport
Calcareous pelagic rain
14
Q
Where is carbonate mainly produced?
A
90% from biological origins
Around equator - production varies with species abundance, related to latitude
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
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
17
Q
What is the chemical formula for carbonate?
A
CO2- 3
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
19
Q
What is the average coral growth rate?
A
5-10mm/year
20
Q
What are two types of coral?
A
Framework Builders ie monastrea
Branching Corals ie stag horn
21
Q
What are possible reasons for aragonite needles on green algae?
A
Structure support against tides
Protection against predators
22
Q
What are reefs?
A
Biologically constructed reliefs which grow up from the sea floor
23
Q
What are the three types of reef?
A
Barrier
Fringing
Patch
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 /-\
25
What are the characteristics of a fringing reef?
Builds at the coastline
26
What are the characteristics of a patch reef/atoll?
Isolated offshore, ie on a seamount
27
What are the three environments of a reef setting?
Off reef open shelf
Reef core
Back reef lagoon
28
What are the four constitutes of the reef core?
Dish, branching, Masai e, reef crest
29
What causes bleached corals?
Low pH causes algae to leave, and the corals cannot build their skeletons without the symbiosis
30
Where are carbonate factories found?
Warm water protozoan systems:
- reefs
- ooid sand shoals
- open seafloor
- lagoons
31
What are the characteristics of a rimmed platform?
Highly differentiated facies
32
What direction is sediment swept in a carbonate system?
Swept landward
33
What are the different types of rimmed platforms?
Shoal rimmed
Continuous coral reef i.e. Belize
Segmented coral reef with tidal channels i.e. Exuma Island Chain, Bahamas
34
Give an example of an ooid shoal complex
Tongue of the ocean, Bahamas
35
What is the composition of Ooids?
Spherical particles of CaCO3
Smaller than 2mm in diameter
Nucleus ie sand grain, surrounded by concentric lamallae
36
What does a thin dark lamallae in ooids mean?
Organic matter
37
What are possible ooid origins?
Algal induced
Inorganic ppt
Mechanical aggregate
38
What are the three species of algae that grow aragonite needles?
Halimedia
Penicillus
Udotea
39
What aids the generation of carbonate grains?
Bioerosion by different macro and micro invertebrates, microbes and fish that break down carbonate substrates
Echinoids, worms, sponges, byrozoans, fish
40
What are the two types of non skeletal grains?
Peloids
Ooids
41
What are peloids?
Fecal pellets, non skeletal grains
42
What are the characteristics of peloids?
Spherical, elliptical or angular grains
Micritic composition
No internal structure
Feacal in origin i.e. from gastropods, crustaceans, polychaetes
Rich in organic matter
43
What are the lithologies of lagoons/subtidal facies?
Wackstone and packstones with bioturbation
44
What is the peritidal zone?
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
45
What are subtidal, intertidal, supratidal zones?
Subtidal - below low tide
Intertidal - below high tide
Supratidal - above high tide/below storm driven high tide
46
What is the importance of Andros Island, the Bahamas?
Producing carbonate since Triassic
6km in thickness
1000’s km2
47
What are the characteristics of humid tidal flat sub environments?
Supratidal marsh
Pond and channel belt - tidal channels, intertidal flat
Subtidal marine
48
Give an example of a tidal flat sub environment
Triple goose creek, bahamas
49
What is the intertidal zone?
Between normal low and high tide levels
Complex topography featuring tidal channels, brackish or saline ponds
50
What is the subtidal zone?
Permanently submerged
Low energy lagoon, high energy shoals
May be exposed during neap tides
51
What are intertidal facies?
Sediment deposited between normal high tide and normal low tide
Exposed twice a day
52
What is the lithologies of intertidal facies?
Burrowed to laminated mudstones to wackstones
Algal bound stones with algal heads
Thin cross bedded grain stones
Rare storm deposits
53
What sedimentary structures are found in supratidal facies?
Mud cracks, fine laminations, algal mats and domes, fenestrae structures, desiccation cracks
Fuggy texture
Plant , animal and insect burrows
Intraclasts and dolomite crusts
54
Give an example of arid tidal flats
Trucial coast, united arab emirates
55
What causes teepee structure?
Salt precipitation
56
What are allochem textures influenced by?
Given environmental and time controls, influenced by wave energy
57
Name the progression of allochem textures in order of increasing grain size and decreased mud.
Mudstone, wackstone, packstone, grainstone, boundstone
Crystalline
58
Where are clastic sediments found?
Not climatically constrained
Both terrestrial and marine
Unconsolidated in the depositional environment
59
Where are carbonate sediments found?
Shallow, warm water environments
Mostly marine
Cemented to seafloor
60
What does grain size and mud indicate in clastic sediments?
Grain size reflects hydraulic energy of the environment
Mud indicates settling from suspension
61
What does grain size and mud indicate in carbonate sediments?
Grain size reflects the size of skeletons and precipitated grains
Mud commonly indicates prolific growth of organisms that produce tiny crystals
62
What are environmental changes induced by for clastic sediments?
Induced by widespread changes in hydraulic regime
63
What are environmental changes induced by for carbonate sediments?
Induced by localised buildup of carbonate, without change in hydraulic regime
64
What is the energy of an open unrimmed platform?
High energy conditions prevail across the shallows
65
How do Ooids form?
Continuous wave agitation rolls the grain, accumulating CaCO3 around nucleus in even coats, forming even coats of concentric laminae in a cross section
66
What are the characteristics of lagoonal/subtidal facies?
Protected from waves so lower energy
Lots of mud
Less biologically diverse
67
What are the characteristics of tidal channels?
Fixed ie dont migrate much
Limited sediment transport
68
Where are cold water corals found?
Temperature 4-12 degrees C
Shallow waters (50-1000metres) at high latitudes
Deep water (<4000m) beneath warm water masses
69
What influences the placement of deep water carbonates?
Ocean gyres, especially the Gulf Stream
70
What species are present in deep water reefs?
Bryozoan
Crinoid
Gastropods
71
What corals are common in deep water reefs
?
Framework corals
Lophelia pertusa
Madrepora oculata
72
What is the name of corals that lack symbiotic dinoflagellates?
Azooxanthellate corals
73
How do framework corals provide a structural habitat for other species?
Feed from suspended sediments, dissolved organic matter, bacteria, protozoans, and (zoo)(phyto)plankton
74
How do corals develop?
As a coral grows polyps in older portions die, and the skeleton becomes increasingly vulnerable to bioeroders and mechanical breakage
75
Name two solitary cold water corals
Desmophyllum cristagalli
Caryophyllia sp
76
What is the structure of reef mounds?
Flanking sediments
Cap of encrusting biota
Muddy Core with small invertebrate skeletons
Basal lime grainstone to wackestone pile
77
What kind of coral communities do you find in cold water?
Stony corals - scleractinia
Soft corals - octocorallia, gorgonian sea fans
Black corals - antipatharia
Hydrocorals - stylasteridae
78
What is porcupine mound?
Up to 300m high mounds in the Irish margin, colonising 2.5 Ma Miocene deposits
79
What are the five stages of the biogenic reef crest cycle?
Early interglacial
Interglacial
Interglacial
Glacial
New interglacial
80
How do we know there has been continuous cold water coral growth over the last 50,000years?
Uranium.thorium dating
81
Where are heterotroph reefs found?
Not constrained by light therefore can grow into deeper water than mixotroph counterparts
82
What threats are present to cold water corals?
Trawling for fish
83
What is the characteristic of carbonate slop sedimentation?
Long periods of boredom alternating with short periods of terror
84
What is a olistolith?
Sedimentary deposit of large homogenous sediment
85
What does perennial mean?
Permanently filled
86
What does ephemeral mean?
Periodically dry
87
What kind of lacustrine settings are there?
Perennial or ephemeral lakes
88
How do lacustrine settings differ from marine settings?
Lack tidal activity
Closed systems with smaller volumes of water and sediment
Relatively small size
89
What does the relatively small size of lakes mean?
Water chemistry responds more rapidly to changes in local conditions and climate
90
What is the littoral zone?
Encompasses shallow water around a lake margin.
Is often characterised by shallow water ‘bench’ or ‘terrace’
91
What is the profundal zone?
Deep, aphotic region of the lake
92
What is the sublittoral zone?
The transition region between littoral zone and deeper profundal zone
93
What is the pelagic zone?
The water column above deep, aphotic region of the lake
94
How does stratification develop in modern lakes?
Due to differential radiative heating
95
What divides the warm water layer from the underlying cool water layer?
The thermocline
96
What happens to water stratification during winter months?
Different layers mix following cooling and action of wind-induced currents
Once water in the epilimnion reaches four degrees it sinks
97
When does meromixis develop?
When surface waters are consistently less dense than the deep waters
98
What are the controls on lake sedimentation?
Abiogenic precipitation
Biologically induced precipitation
Biologically controlled precipitation
Extrinsic factors
Intrinsic factors
99
What abiogenic precipitates are there
?
Aragonite, calcite, magnesite, hydromagnesite and dolomite
100
What causes abiogenic precipitates?
Waters become supersaturated due to evaporation/cooling/CO2 degassing
101
What biological communities control lake sedimentation?
Charophytes
Ostracod
Mollusks
Insects
Diatoms
102
What are the extrinsic factors controls on lake sedimentation?
Climate - not restricted by climatic zone, controls rainfall, water balance, biogenic activity
Tectonics
103
What are the intrinsic factors that control lake sedimentation?
Hydrology - controls flux of sediment
Lake stratification/mixing
Sediment sources
104
How does lake stratification and mixing affect lakes?
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
What are types of lacustrine deposits?
Shoreline facies
Lake centre/pelagic facies
106
What is a type of shoreline facies?
Marginal bench
107
What carbonate sediments do you find on marginal benches
?
Peloids
Oncoids
Stromatolites
108
What are microbialites ?
Limestones and dolomites formed by microbial activity that forms a biofilm, leading to calcite dolomite precipitation through extracting CO2 from water
Stromatolites
Thrombolites
109
What is the difference between stromatolites and thrombolites?
Stromatolites are laminated
Thrombolites are clotted
110
How are active springs defined?
Based on the highest temperature measured at the spring vent
111
What temperature are cool springs?
<20 degC
112
What are the temperature classifications of thermal springs?
Thermal >20 degrees
Warm 20-40 degrees
Mesothermal 40-75 degrees
Hyperthermal >75 degrees
113
What is tufa, where is it formed, and composition?
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
What is travertine and where is it formed?
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
What is crystal morphology related to?
CaCO3 supersaturation
116
What is barrage tufa formed of?
Vaucheria- green algae that forms overhangs and tongues a
117
Give six examples of tufa?
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
How does tufa form?
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
Give examples of tufa formation
Gordale, York’s, England
120
Give an example of a travertine formation
Pamukkale, turkey
Yellowstone
121
Give an example of tufa mounds
Mono lake California
Pyramid lake Nevada
122
Give an example of barrage tufa
Skriadin and plitvice, Croatia
123
What are important food sources for deep sea corals?
Resuspended material, bacteria and protozoans
Dissolved inorganic matter
Zooplankton and phytoplankton
124
What are important food sources for deep sea corals?
Resuspended material, bacteria and protozoans
Dissolved inorganic matter
Zooplankton and phytoplankton
125
What is an olistolith?
A large clast within slope deposits
126
True or false:
HMC is the dominant carbonate throughout the rock record
False
127
What do the horizontal growth bands in deep sea corals most likely represent?
Seasonal delivery of nutrients
128
What facies are most characteristic of arid carbonated tidal flat settings?
Microbialaminate
Teepee structures
Nodular anhydride
129
What role does Udotea play within carbonate settings?
Aragonite producing codiacean algae
130
True or false:
Carbonate sediment production is lowest in the shallowest, inner most areas of a platform>
True
131
True or false:
HMC is the dominant carbonate throughout the rock record
False
132
What is the rate of sediment production on Great Bahamas bank margins?
4 kg/m2/yr
133
In what carbonate setting is scytonema found?
Algal marsh
Peritidal zone
