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Geology > Sedimentary Geology > Flashcards

Sedimentary Geology Flashcards

1
Q

Define weathering

A

The in situ chemical alteration and mechanical breakdown of rocks by exposure to the atmosphere, water and/or organic matter

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2
Q

Give two examples of chemical weathering

A

Carbonation and hydrolysis

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3
Q

What do all chemical weathering reactions involve?

A

Water

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4
Q

What do chemical weathering reactions all produce?

A

Ions that are removed in solution leaving an insoluble residue

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5
Q

What type of minerals make up the remaining insoluble residue during chemical weathering?

A

Clay minerals

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6
Q

What two common mineral types do carbonation and hydrolysis affect?

A

Calcite and feldspar

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7
Q

How does carbonation occur? (4)

A

Carbon dioxide gas in the atmosphere reacts with rainwater and pore water in the soil to form carbonic acid which reacts with calcite.

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8
Q

Why is groundwater more acidic than rainwater?

A

Pore spaces in the soul are rich in carbon dioxide due to decomposing plant litter, which forms carbonic acid with water

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9
Q

What is the equation for carbonation?

A

CaCO3 +H2CO3 —> Ca2+ + 2HCO3-
calcite + carbonic acid —> calcium + hydrogen carbonate ions in solution

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10
Q

What rock is most affected by carbonation?

A

Limestones

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11
Q

What happens to insoluble impurities in limestone during carbonation?

A

They are left as insoluble residues

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12
Q

What type of minerals are most affected by hydrolysis?

A

Silicate minerals, especially feldspars

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13
Q

How does hydrolysis occur? (3)

A

Water reacts with silicate minerals. Hydrogen ions from the water or from carbonic acid react with ions in the minerals producing residual clay mineral, silica, carbonate or bicarbonate (K, Na or Ca) in solution

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14
Q

What factor speeds up the rate of hydrolysis?

A

The presence of carbonic acid in the water

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15
Q

What are the products of hydrolysis?

A

Residual clay mineral, silica, carbonate or bicarbonate in solution

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16
Q

Name three examples of mechanical weathering

A

Exfoliation, frost shattering (freeze-thaw weathering), pressure release

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17
Q

What is the alternate name for exfoliation

A

Onion skin weathering

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18
Q

What happens during exfoliation?

A

Curved sheets of rock peel off from rocks due to fluctuations in temperature. In hot deserts, hot daytime and cold nights cause minerals to expand and contract by different amounts during heating and cooling, causing the rock to disintegrate.

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19
Q

What happens during frost shattering?

A

Water enters cracks, joints and bedding planes. Temps fluctuate around 0°C. Water freezes and expands by 9%. Exerts pressure on rocks leading to eventual failure and production of scree.

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20
Q

What is scree and how is it produced?

A

Angular fragmental residue formed during frost shattering.

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21
Q

What happens during pressure release?

A

Atmospheric pressure at Earth’s surface lower than pressures within earth. Rocks above eroded and pressure released from lower rocks, causing them to expand and produce fractures. Fractures more widely spaced the further they are from the surface.

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22
Q

Which rocks are less likely to be affected by pressure release?

A

Well jointed or rocks w many bedding planes

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23
Q

What is the most stable mineral?

A

Quartz

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24
Q

Define a clast

A

A fragment of broken rock produced by mechanical weathering and erosion

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25
Q

Two examples of biological weathering?

A

Root action and burrowing

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26
Q

What pattern on rocks does exfoliation cause?

A

Concentric layers (like when u cut into an onion)

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27
Q

What does oxidation look like in a rock?

A

Orange, yellow or red discolouration

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28
Q

What happens during root action?

A

Tree roots grow along bedding planes or joints and force them apart mechanically. They keep surfaces open so water can penetrate and chemically weather. Trees swaying in the wind can prise open fractures in rock.

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29
Q

What happens during burrowing?

A

Invertebrate and vertebrate animals mixed and brings rocks and soil particles up to the surface, allowing weathering at greater depth by providing access for atmospheric gases and water

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30
Q

What type of weathering is most prevalent in Arctic climates? (2)

A

Mechanical (mostly frost shattering)

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31
Q

What type of weathering is most prevalent in temperate climates? (7)

A

Mechanical, chemical, biological (frost shattering, carbonation, hydrolysis, root action)

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32
Q

What type of weathering is most prevalent in warm arid climates? (2)

A

Mechanical (exfoliation)

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33
Q

What type of weathering is most prevalent in humid tropical climates? (6)

A

Intense chemical, some biological with greatest amount of residue (carbonation, hydrolysis, root action)

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34
Q

What is Bowens reaction series order?

A

Discontinuous, decreasing temperature: Olivine, pyroxene (augite), amphibole (hornblende), biotite mica

Continuous, decreasing temp: Ca rich —> Na-rich Plagioclase feldspar

At the bottom: K feldspar, Muscovite mica, Quartz (Kill Me Quick)

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35
Q

How is weathered material transported and in what sizes?

A

Gravity down slopes, wind for finer grained, rivers for all sizes, the sea for all sizes, ice for large amounts of rock debris

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36
Q

Define erosion

A

The wearing away of the land surface and removal of sediment by means of transport

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37
Q

Define abrasion

A

The wearing away of the earth’s surface by the action of wind, water or ice dragging sediment over or hurling it at a surface

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38
Q

Define attrition

A

The wearing down of sedimentary grains due to collisions with other grains during transport

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39
Q

Define mineralogical maturity

A

A measure of the extent to which minerals have been destroyed by weathering and attrition

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40
Q

Define solution

A

The transport of ions dissolved in water, particularly K, Ca and Na 

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41
Q

Define traction

A

The transport of material by rolling and sliding along a surface 

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42
Q

Define saltation

A

The transport of material by bouncing

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43
Q

Define suspension

A

The transport of material in water or air, without it touching the earth’s surface

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44
Q

Give three examples of where abrasion could occur. 

A

Sandblasting by wind blown sediments in a desert, grinding down by boulders rolling along a river bed; chipping by shingle carried by the sea when waves crash into cliffs

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45
Q

What is responsible for increased grain roundness?

A

Longer periods of attrition

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46
Q

Which types of minerals are more affected by attrition?

A

Soft minerals like mica

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47
Q

What type of minerals are less affected by attrition?

A

Hard minerals like quartz

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48
Q

Define the phrase mineralogically mature

A

Sediments that contain little or no variety of minerals, so example those that contain only quartz grains 

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49
Q

Which methods of transport are included in the suspended load? 

A

Suspension

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50
Q

Which method of transport are included in the bedload? 

A

Saltation and traction

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51
Q

How does the velocity of a current affect the size of grains carried?

A

With increasing velocity, grain size increases

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52
Q

Why do clay sized particles require high velocities for erosion?

A

They are flats and platy in shape and are cohesive so tend to stick together

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53
Q

Why do clay particles remain in suspension at very low current velocity?

A

They are small, have low mass and are buoyant

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54
Q

What does a Hjulstrom curve represent?

A

Hjulstrom curves represent the relationship between current velocity of water and sediment transport. The lower line represents the point below which deposition occurs. The upper line shows the points above which erosion occurs. Between these two lines, transportation occurs. Velocity (cm s-1) is marked on the y-axis and grain size (mm) is marked on the X axis



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55
Q

What affects the shape of grains? 

A

The type of rock or mineral from which they are made.

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56
Q

What are the four grain shapes?

A

Blade, rod, disc, sphere 

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57
Q

What are the classifications of roundness? 

A

Very angular, angular, subangular, sub rounded, rounded, well rounded

58
Q

What scale is used for the measurement and classification of the grain size of sediment?

A

The Wentworth-Udden Scale

59
Q

What scale is the diameter in millimetres converted to in the Wentworth-Udden scale

A

The phi scale

60
Q

Define textural maturity

A

A measure of the extent to which a sediment is well sorted and well rounded

61
Q

What type of scale is the phi scale?

A

Logarithmic. Values increase arithmetically as the grain size decreases geometrically

62
Q

Write out the Wentworth-Udden scale 

A

Diameter(mm);Phi;Sediment Name
>2;-2to-8;gravel,pebbles,cobbles,boulders
2;-1;Very coarse sand
1;0;Coarse sand
0.5;1;Medium Sand
0.25;2;Fine sand
0.125;3;very fine sand
0.0625;4;Silt
0.0039;8;Clay

63
Q

How would you describe a wide range of minerals from the source rock? 

A

Mineralogically immature

64
Q

How would you describe very angular and poorly sorted grains? 

A

Texturally immature

65
Q

How would you describe a smaller range of minerals?

A

Mineralogically sub mature

66
Q

How would you describe less angular and more uniform grain size? 

A

Texturally sub mature

67
Q

How would you describe one chemically stable mineral only?

A

Mineralogically mature

68
Q

How would you describe rounded grains of fairly uniform size?

A

Texturally mature

69
Q

What do angular grains suggest about their environment?

A

Rapid deposition with little transport

70
Q

What are the degrees of sorting?

A

Very well sorted, well sorted, moderately sorted, poorly sorted, very poorly sorted

71
Q

Why do you desert streams deposit sediment very quickly?

A

They dry rapidly due to infiltration or high temperatures

72
Q

How are sand and gravel size sediments analysed?

A

Using a sieve bank. A stack of sieves is arranged so that the biggest holes are at the top (4mm or 2 phi) and the smallest (0.0625mm or 4phi) are at the bottom. Sediment is poured in the top and the sides are rotated and shaken. A digital balance is used to measure the mass of the sediment within each sieve.

73
Q

How are results from a sieve bank plotted?

A

Using a histogram. This allows the comparison of grain size distribution. Grain size data is posted as cumulative frequency curves.

74
Q

What do cumulative frequency curves show from a sieve bank? 

A

The total percentage of sediment that fails to get through a given sieve size

75
Q

What would the curve look like for a well sorted sediment?

A

Almost vertical

76
Q

What does an increasingly horizontal curve show? 

A

Increasingly poorly sorted sediment

77
Q

How is the coefficient of sorting (p) measured from cumulative frequency graphs ? (Equation)

A

where the symbol for phi (a circle with a vertical line through the centre) is represented by Ø

p = Ø84 - Ø16/2

78
Q

What does Ø84 represent?

A

The cumulative mass of 84% of the sample

79
Q

In a sieve stack what does the pan collect?

A

Sediment finer than sand

80
Q

What are the coefficient of sorting values in relation to the degree of sorting? 

A

<0.50 = well sorted
0.5 - 1.00 = Moderately sorted
>1.00 = poorly sorted

81
Q

Identify the environment of deposition:
Fine to medium sand, composed of all quartz, sometimes red due to iron oxide, well rounded and very well sorted

A

A wind blown dune sand in a high energy environment

82
Q

Identify the environment of deposition: Variation from very coarse boulders to very fine clay, with a varied composition of any rock fragments and clay, angular to sub angular and very poorly sorted

A

Ice. Deposited as glacial till in a low energy environment

83
Q

Identify the environment of deposition: Coarse to find sand, maybe coarser nearer to source, quartz and mica with rock fragments, angular near to source but sun angular to sub rounded further away, poorly sorted near source, moderately sorted further away

A

River deposit of sand in channel. Usually high energy with fast current

84
Q

Identify the environment of deposition: medium sand, sometimes coarse (pebbles and gravel) close to shore and on beaches, nearly all quartz with some shell or rock fragments, sub rounded to rounded and moderately sorted with sediment mainly in a few sieves 

A

Beach or offshore bar in the sea. High energy

85
Q

Identify the environment of deposition: Varies from very coarse boulders in rockfalls to very fine in soil creep, varied composition of any rock fragments, angular to very angular and very poorly sorted with larger fragments sometimes found at the base of a slope

A

Gravity, low energy

86
Q

Draw a diagram showing how the observation of characteristic features can be used to identify siliciclastic rocks

A

Page 58

87
Q

draw diagrams and label:
breccia, conglomerate, orthoquartzite, desert sandstone, arkose and greywacke

A

Page 58

88
Q

Breccia
a) grain size
b) composition
c) roundness
d)matrix/cement
e) sorting
f) location/type of deposit
g) energy and length of transport

A

a) coarse (above 2mm)
b) siliciclastic
c)angular
d)matrix with coarse clasts mixed with finer grains
e) poorly sorted
f) scree, alluvial fans, wadi deposits, volcanic vents (when pyroclastic)
g) lost energy quickly, short length

89
Q

Conglomerate

a) grain size
b) composition
c) roundness
d)matrix/cement
e) sorting
f) location/type of deposit
g) energy and length of transport

A

a)coarse
b)siliciclastic
c) rounded
d) finer grained matrix with large clasts may contain mineral cement
e)poorly sorted
f) beach and river channel
g) longer than a breccia

90
Q

Sandstones

a) grain size
b) composition
c) roundness
d)matrix/cement
e) sorting
f) location/type of deposit
g) energy and length of transport

A

a) 0.0625 to 2mm
b)quartz and minerals low on Bowen’s reaction series such as Muscovite and K feldspar
c) well rounded
d) well cemented (low porosity) to poorly cemented (high porosity)
e) very well sorted
f) almost all sedimentary environments
g) mostly quartz so longer transport and slower deposition

91
Q

Why are sandstones useful? (3)

A

They are the main oil reservoir rocks, aquifers for water supply, they are building stones

92
Q

Orthoquartzite

a) grain size
b) composition
c) roundness
d)matrix/cement
e) sorting
f) location/type of deposit
g) energy and length of transport

A

a) 0.0625-2mm
b) only quartz grains, white or grey in colour (>90%)
c) well rounded
d) quartz cement
e)well sorted
f)beach and shallow marine deposits
g) long period of transport, extensive weathering

93
Q

Desert sandstone

a) grain size
b) composition
c) roundness
d)matrix/cement
e) sorting
f) location/type of deposit
g) energy and length of transport
h) alternate name due to…
i) ________ appearance

A

a) around 1mm, coarse sand
b)quartz coated with red iron oxide
c) very well rounded
d) silica or iron mineral cement
e) very well sorted
f) arid environments as wind blown sands
g) high energy, long transport
h) millet seed sand due to high sphericity
i) frosted appearance

94
Q

arkose

a) grain size
b) composition
c) roundness
d)matrix/cement
e) sorting
f) location/type of deposit
g) energy and length of transport

A

a) medium to coarse
b)25%+ feldspar (pink colour) and quartz, rock fragments, mica
c) subangular to sub rounded
d) unknown
e) moderately sorted
f) alluvial fan environments in arid areas
g) short transport time

95
Q

Greywacke

a) grain size
b) composition
c) roundness
d)matrix/cement
e) sorting
f) location/type of deposit
g) energy and length of transport
h) ______ bedding

A

a) fine to coarse
b) rock fragments (lithic clasts), quartz and K feldspar, dark colour
c) angular to subangular
d) 15% clay matrix
e) poorly sorted
f) turbidity deposits
g) rapid deposition, quick loss of energy
h) graded bedding

96
Q

How abundant are argillaceous siliclastic rocks?

A

They make up 75% of all sedimentary rocks

97
Q

What may argillaceous siliciclastic rocks contain?

A

Fossils

98
Q

Give three examples of argillaceous siliciclastic rocks

A

Clay, mudstone, shale

99
Q

Where are clay mudstone and shale deposited

A

Low energy, commonly marine environments, flood plains of rivers and lakes

100
Q

Do clay, shale or mudstones contain cement

A

No significant amount

101
Q

Clay

a) grain size
b) composition
c) roundness
d)matrix/cement
e) sorting
f) location/type of deposit
g) energy and length of transport
h) layering?
i) plasticity?

A

a) clay size (up to 0.0039 mm)
b) clay minerals (can be dark brown, red, green depending on carbon/iron content, darker with more organic content
c) ??
d) no significant amount
e) very well sorted
f) marine, floodplains, lakes
g) low energy, long time
h) yes, distinct bedding planes
i) yes, can be moulded

102
Q

Mudstone

a) grain size
b) composition
c) roundness
d)matrix/cement
e) sorting
f) location/type of deposit
g) energy and length of transport
h) layering?
i) plasticity?

A

a) <0.0625
b) clay minerals, mica and quartz but unidentifiable even w hand lens
c) ???
d) no significant amount
e) very well sorted
f) marine, floodplains, lakes
g) low, long transport
h) no, minerals have no preferred alignment
i) no

103
Q

Shale

a) grain size
b) composition
c) roundness
d)matrix/cement
e) sorting
f) location/type of deposit
g) energy and length of transport
h) layering?
i) plasticity?

A

a) fine grained <0.0625
b) Clay minerals, dark coloured, mica, quartz
c) ???
d) no significant amount
e) very well sorted
f) marine, floodplains, lakes
g) low energy, long transport
h) yes, distinctive due to parallel alignment of flat and platy clay minerals to beds at 90° to pressure from overlying rock mass. easily splits along layers/laminations (fissile)
i) no. hard, brittle, impermeable

104
Q

Define mechanically formed

A

Sedimentary rocks resulting from the processes of erosion, transport and deposition of clasts

105
Q

Define siliciclastic rocks

A

Rocks from sediments composted of silicate minerals and rock fragments

106
Q

Define matrix

A

The background material of small grains in which larger grains occur

107
Q

Clay minerals

A

A group of submicroscopic platy aluminium silicates related to mica

108
Q

Define plasticity

A

Ability of a material to permanently change shape without fracturing

109
Q

Define fissile

A

Tendency of a rock to split into thin layers

110
Q

Define rudaceous

A

Sedimentary rocks where grain size of clasts >2mm

111
Q

Arenaceous

A

Grain size of clasts 0.0625-2mm

112
Q

Argillaceous

A

Grain size of clasts <0.0625mm

113
Q

What makes up texture?

A

The interrelationship of grains including grain size, sorting, roundness, shape and packing

114
Q

Define fossil

A

The remains of an organism that lived more than 10,000 years ago including skeletons, tracks, impressions, trails, borings and casts

115
Q

What classifies carbonate rocks?

A

High percentages of calcite (CaCO3) or dolomite (CaMg(CO3)2)

116
Q

What is the other term for carbonate rocks?

A

Limestone or dolomitic limestone

117
Q

What are the two groups of limestones (based on formation, not mineral content)

A

Chemical - from the precipitation of CaCO3 from sea water
Biological - from organic remains like shell fragments

118
Q

What classifies a limestone?

A

Rock containing more than 50% calcium carbonate - but most contain over 90% on the form of calcite

119
Q

What is modern limestone composed of?

A

Aragonite, an unstable form of CaCO3 that breaks down into calcite over time

120
Q

How to identify calcite?

A

Reacts vigorously with dilute HCl
Has two cleavage directions not at right angles

121
Q

What are oolitic limestones?

A

Chemically formed limestones containing sub spherical sand sized grains about 1mm in diameter called ooliths.

122
Q

What do ooliths show in cross section?

A

Concentric layers of calcium carbonate surrounding a nucleus (a grain of sand, shell fragment or pellet)

123
Q

What are ooliths surrounded by in oolitic limestone?

A

Fine grained calcite mud matrix (mixture) or crystalline calcite cement (sparite)

124
Q

Where do oolitic limestones form?

A

Tropical or sub tropical seas in shallow water agitated by high energy waves

125
Q

What is fossiliferous limestone?

A

Biologically formed limestones composed of fossils or fossil fragments.

126
Q

How can fossilifierous limestone be bioclastic?

A

It can be made up of fossil fragments

127
Q

What matrix or cement may fossiliferous limestones have?

A

Micrite matrix or sparite cement

128
Q

What is a crinoid?

A

Crinoids are marine animals that make up the class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids

129
Q

What is crinoidal limestone?

A

Limestone made of stem sections or single ossicles with rare plates from the calyx or arms of a crinoid

130
Q

What do reef limestones contain? (3)

A

Coral fragments, brachiopod or bivalve shells

131
Q

What are shelly limestones made up of?

A

Bivalve or gastropod shells

132
Q

Where do fossil rich limestones form?

A

Range of environments; low energy freshwater lakes or lagoons or marine beds.

133
Q

What do whole fossils in a limestone suggest?

A

Low energy environment

134
Q

What do broken fossils in a limestone suggest?

A

High energy environment

135
Q

What is chalk?

A

A biological formed limestone composed of coccolithophores (coccoliths), the calcareous disc or oval shaped platelets that form part of the skeletons of single celled algae

136
Q

Why is chalk white?

A

It is pure calcium carbonate

137
Q

Where is chalk formed?

A

Low energy, deep water shelf environments

138
Q

How do you test for limestone?

A

Dilute HCl, fizzes

139
Q

What is the name for a turbidite sequence?

A

The Bouma sequence

140
Q

A-E in a turbidite graphic log:

A

A) Coarse bed of pebble to granule size, conglomerate in a sandy matrix (graded bedding, erosional base) - high velocity and energy
B) coarse then medium sandstone (greywacke) (parallel laminations, graded bedding) - decreasing energy and velocity
C) sandstone (greywacke) (cross bedding) - decreasing energy and velocity
D) fine sandstone then siltstone (ripples, cross bedding) - low energy and velocity
E) shale which may contain pelagic marine fossils such as grapolites (parallel laminations) - interturbidite

141
Q

Progression into ocean diagram relevant to turbines

A

Continental shelf —> continental slope —> continental rise (lower part of slope?) —> abyssal plain —-> ocean ridge —> abyssal plain —-> ocean trench

142
Q

What is the CCD? What occurs beneath it? What does this cause?

A

Carbon concentration depth
Carbonate material dissolves
Increased acidity and precipitation of silica.

Geology (8 decks)

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