(S11) Carbonates and Evaporites Flashcards
1
Q
What is the Chemical equation for Calcium Carbonate?
A
CaCO3
2
Q
What is the difference between calcareous and carbonaceous?
A
Calcareous is rich in Calcium Carbonate, Carbonaceous is rich in Carbon
3
Q
What common elements are found in carbonates?
A
Magnesium, Iron, Copper
4
Q
Give two examples of copper carbonates?
A
Malachite, Azurite
5
Q
What is a carbonate?
A
Sediments and rocks made up of ___ Carbonate, e.g. Mg- Fe- Cu-
6
Q
What rock has the same minerals as carbonates but is not infact called a carbonate?
A
Marble
7
Q
What is the name for the uncommon carbonate-rich lava?
A
Carbonatite
8
Q
What is the Moh’s hardness of Calcite?
A
3
9
Q
What colour does Calcite have in hand sample?
A
White, Colourless
10
Q
What are the two ways to distinguish Calcite in hand sample?
A
Moh’s hardness, Reaction to HCl (10% dilute)
11
Q
Where does most Calcite come from?
A
Biogenic origin
12
Q
What two elements can substitute calcium in Calcite?
A
Magnesium, Strontium
13
Q
What are the two grades of Magnesium Calcite?
A
Low and high grade
14
Q
What defines a low grade Magnesium Calcite?
A
Less than 4% Mg
15
Q
What defines a high grade Magnesium Calcite?
A
11% - 19% Mg
16
Q
Give three examples of marine organisms which create high-Mg Calcite
A
Echinoderms, Barnacles, Foraminifers
17
Q
Why is strontium useful in calcite?
A
Use for dating rocks
18
Q
What quantity can strontium be found in calcite?
A
<1%
19
Q
How does the mineral form of Aragonite differ from Calcite?
A
Calcite is trigonal and aragonite is orthorhombic
20
Q
Which is more dense, aragonite or calcite?
A
Aragonite
21
Q
What is the density of aragonite and calcite respectively?
A
Aragonite = 2.95, Calcite = 2.72 - 2.94
22
Q
What is the Moh’s hardness of Aragonite?
A
3.5 - 4
23
Q
Give two examples of intvertebrets which use Aragonite to build their hard parts?
A
Bivalves and Corals
24
Q
What is the chemical name and formula for Dolomite?
A
Calcium Magnesium Carbonate (CaMg(CO3)2)
25
What is the difference between Dolomite and Dolostone?
Dolostone is the rock which is made up of Dolomite
26
What is the distinguishing factor between Dolomite and Calcite/Aragonite?
Little or no reaction to the HCl acid test
27
How is Dolomite considered to be formed?
Diagenisis
28
What is the chemical name and formula for Siderite?
Iron Carbonate (FeCO3)
29
What impurities does Siderite often contain as a substitute for Iron?
Magnesium, Manganese
30
When does Siderite form?
As an early diagenic material in sediments
31
When do Molluscs date back to?
Cambrian
32
What do Molluscs usually create their form out of?
Calcareous
33
What does a Bivalve Molluscs shell layers look like?
Usually two or three layers of Calcite, Aragonite or both
34
What are most modern Molluscs made from?
Aragonite
35
Why are no pre-Jurassic bivalve shells preserved?
Instability of Aragonite compared to Calcite
36
What is the distinguishing difference between Gastopods and Cephalopods
Cephalopods are chambered
37
When were Ammonites most common?
Mesozoic
38
When were Brachiopods most common?
Palaeozoic and Mesozoic - Not seen modernly
39
What were the shells of Brachiopods made up of?
Low-Mg Calcite
40
What is the distinguishing feature of Echionoids and Crinoids?
Both create their bodies from entire calcite crystals
41
What are the two types of Forams?
Planktonic or Benthic
42
What is the main crystal form of Pre-Palaeozoic Corals?
Calcite
43
What is the main crystal form of Post-Palaeozoic Corals?
Aragonite
44
What is the name for a coral which has a symbiotic relationship with Algae, and exists in clear, warm, shallow marine environments?
Hermatypic Corals
45
What is the name for a coral which does not have a symbiotic relationship with Algae and exsit in colder, deeper waters?
Ahermatypic Corals
46
What is the name for a group of single-celled colonial organisms
Bryozoa
47
What are the three types of carbonate producing Algae?
Red Algae (Rhodophyta), Green Algae (Chlorophyta), Nanoplankton (Yellow-Green Algae)
48
What are Red Algae effective at doing, useful for the stratigraphic record?
Binding soft substrate
49
What do Green Algae contribute to the stratigraphic record?
Fine rods and grains
50
Name an example of a Nanoplankton?
Coccoliths
51
How do Cyanobacteria operate?
Create sheet like mats which trap fine grained carbonate, creating flat/dome structures
52
What is the name for the flat/dome structures created by Cyanobacteria?
Stromatolites
53
What are Thrombolites?
Cyanobacteria which create a irregular rathern than structured form
54
What are Ooids?
Spherical bodies of CaCO3, 2mm in diameter
55
What is the internal structure of an Ooid like?
Precipitate layers of CaCO3, may have precipitated around a small fragment of another material
56
What does accumulations of Ooids form?
Shoals
57
Ooids are components of limestone throughout what time?
Phanerozoic
58
What is a rock called which is made up of carbonate ooids?
Oolitic Limestone
59
What is thought to be the origin of Ooids?
Chemical precipitation of agitated water which is saturated in CaCO3 in warm waters
60
What is thought to have a role in the process of Ooid formation in less agitated waters?
Bacteria
61
What is a pisoid?
A concentrically layered carbonate particle over 2mm in diameter
62
What is a peloid and what is it's origin?
Calcium carbonate particle which does not have a concentric structure - thought to be faecal pellets
63
What is the name for fragments of CaCO3 which has been partly lithified, broken up, reworked to form a clast?
Intraclasts
64
Where do intracalsts usually occur? (2 Exmaples)
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
What is the name for a carbonate grain which contains several fagments cemented together?
Aggregate grains
66
What is the name for a carbonate grain which contains several rounded grains?
Grapestones
67
What are the three names given to a CaCO3 particle <4 microns diameter?
Lime mud, Carbonate mud or Micrite
68
What are the three processes which form Lime Mud?
Chemical precipitation from water, Breakdwon of Skeletal Fragments, Algal/Bacterial Origin
69
Why is it difficult to determine the source of Lime Mud?
Grains are too small
70
What is the name for the classification scheme used in Limestones?
Dunham Classification
71
What is the first and second stages to the classification used in the Dunham scheme?
First is to determine texture, second is to determine nature of the grains in the material
72
What is the name for a limestone with less than 10% clasts?
Carbonate Mudstone
73
What is the name for a limestone with more than 10% clasts?
Wackestone
74
What is the name for a clast supported limestone with presence of mud?
Packstone
75
What is the name for a clast supported limestone without presence of mud?
Grainstone
76
What is the name for a limestone which has an organic framework such as a ocral colony?
Boundstone
77
What are the three sub-divisions of a Boundstone in the Dunham Classification scheme?
Bafflestone, Bindstone, Framestone
78
What is the name for a limestone which has more than 10% grains and is matrix supported?
Floatstone
79
What is the name for a limestone which has more than 10% grains and is clast supported?
Rudstone
80
What is the difference between a conglomerate made up of limestone from older bedrock and a floatstone/rudstone?
Floatstone/Rudstones are deposited in the same or adjacent environment, where as a Limestone Conglomerate may be deposited in a completely different environment
81
Describe a "oolitic grainstone"
A clast supported (no matrix) rock made of ooids.
82
Describe a "bioclastic packstone"
Up to 90% shelly fragments in matrix of carbonate mud
83
What is the most commonly encountered evaporite mineral?
Calcium Sulphate
84
What are the two most common forms of Calcium Sulphate (minerals)?
Gypsum, Anhydrite
85
When is Calcium Sulphate precipitated from sea water?
Once evaporation has concentrated water to 19% of its original volume
86
What is the chemical formumla of Gypsum?
CaSO4.2H2O
87
Where does Gypsum precipitate?
At the surface under all but the most arid of conditions
88
What happens when Gypsum becomes dehydrated on burial?
Forms Anhydrite (CaSO4)
89
Aside from Gypsum dehydration, when does Anyhdrite form?
Direct precipitation in arid conditions
90
What happens to Anyhdrite with the introduction of water?
Hydrated to Gypsum
91
What form does Gypsum take from primary preiciptation out of water?
Elongate Selenite crystals
92
If Gypsum forms from a rehydration of Anhydrite, what form does it take?
Fine crystalline form in nodules of Alabaster
93
What are the two ways to distinguish Gypsum from Calcite in hand sample?
Softer (Moh's hardness of 2), Does not react with HCl
94
How can we distinguish Gypsum from Halite?
Does not taste salty
95
What is the difference between Gypsum and Anhydrite in hand sample? (1)
Anhydrite is harder (Moh's of 3.5)
96
When does Halite become precipitated out of seawater?
When it has been concentrated to 9.5% of its original volume
97
What is distinctive about Halite crystals?
Cubic
98
What is a Hopper Crystal?
A crystal which has a stepped crystal face, e.g. Halite
99
When is Halite preserved?
When thre is an absence of dilute groundwater
100
What is the name for naturally occuring Halite?
Rock salt
101
What is the Moh's hardness of Halite?
2.5
102
What is the mineral name for Potassium Chloride?
Sylvite (KCl)
103
What is the economic importance of Sylivte?
Industrial Potash
104
Why is the lack of modern Sylvite precipitation important?
Chemical composition of the sea water has not been constant with time
105
What are the suggested reasons for variations in chemical composition of sea water with time?
Variations in relative impotance of Runoff and Hydrothermal Waters
106
What group of minerals does Saline lakes most often precipitate?
Sulphates
107
What is the importance of limestone classification to hydrocarbon exploration?
Limestones can act as a reservoir with the same properties of limestone - hence it is important that classification schemes are consistant
108
What is the importance of evaporites in hydrocarbon exploration?
Act as seals to migration of hydrocarbons, including diapir formations
109
What is a diapir?
Subsurface movement of Halite
