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Intro to Earth Science > Surface Processes - Lec 9 > Flashcards

Surface Processes - Lec 9 Flashcards

1
Q

List the steps in order that causes igneous rocks to become sedimentary rocks (4)

A

Weathering of rocks at surface
Erosion and transport
Deposition of sediment
Burial and compaction

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2
Q

What is weathering?

A

The breakdown and alteration of rocks at Earth’s surface through physical and chemical reactions with
the atmosphere and the hydrosphere.
Decay and disintegration of rock ‘in
-situ’ at or near the Earth’s surface.
(reduce solid rock to sediment and dissolved products)

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3
Q

What is physical weathering?

A

The mechanical (breakdown) fragmentation of rocks from stress acting on them.

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4
Q

What is possibly the most important type of physical weathering?

A

Ice wedging

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5
Q

What is chemical weathering?

A

It involves chemical reactions with minerals that progressively decompose the solid rock

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6
Q

List the major types of chemical weathering. (4)

A

Dissolution (solution?)
Hydrolysis
Hydration
Oxidation

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7
Q

How do joints and fractures facilitate/help weathering?

A

They permit water and gases in the atmosphere to attack a rock body at considerable depth. They also greatly increase the surface area on which chemical reactions can occur

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8
Q

What are the major products of weathering?

A

Spheroidal rock forms, a blanket of regolith, eroded rock material and dissolved ions in solution

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9
Q

What is the upper part of regolith?

A

Soil

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10
Q

What is soil made of?

A

A mixture of clay minerals, weathered rock particles, and organic matter

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11
Q

What influences the type and rate of weathering?

A

Climate and rock type

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12
Q

What does weathering help control?

A

The amount of carbon dioxide in the atmosphere, and thus climate

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13
Q

What do the sedimentary components of the rock cycle entail?

A

The overlapping processes of weathering, erosion,

transportation, deposition, burial, and diagenesis

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14
Q

What do weathering and erosion produce?

A

The clastic particles and dissolved ions that compose sediments

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15
Q

What causes sediment to travel downhill (gravity)?

A

Water, wind and ice

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16
Q

What convert sediments to sedimentary rocks an how?

A

Burial and diagenesis

Via pressure, heat and chemical reactions

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17
Q

What are the 3 major types of sediments?

A

Clastic, chemical/biochemical and organic

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18
Q

What are clastic sediments formed from?

A

Rock particles (lithics) and mineral fragments

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19
Q

What forms chemical and biochemical sediments?

A

Ions dissolved in water (chemical and biochemical reactions precipitate these dissolved ions in solution)

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20
Q

What does diagenesis do?

A

Transforms sediment into sedimentary rock

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21
Q

How does burial help sediments transform into sedimentary rocks?

A

Subjects sediments to increased heat and pressure

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22
Q

How are sedimentary and clastic rocks classified?

A

Based on their grain size (Udden-Wentworth grain scale), the degree of their roundness for sandstone (sphericity and angularity) and the degree of sorting

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23
Q

How are chemical/biochemical sedimentary rocks named?

A

Based on their composition

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24
Q

How can the composition of sandstones be used?

A

To classify types of sandstone and offer insights in the environments and processes of formation

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25
How do plate tectonics play important roles in surface processes?
Uplift creates topography while denudations reduces it - without continued uplift the regolith would not be removed Sedimentary basins result from rifting, thermal sag, and flexure of the lithosphere (create topographic lows)
26
Is weathering self limiting? Why?
Yes, as for large sediment yields you need uplift as well as weathering
27
What is erosion?
Processes by which earth or rock materials are loosened and removed from the Earth's surface
28
What is denudation?
The lowering of land surface by weathering and erosion
29
Explain ice wedging (freeze thaw?)
Important where temps wise and fall below freezing Occurs when water seeps in fractures and expands as it freezes The expanding wedge forces the rock apart and produces loose, angular fragments that move downhill by gravity
30
What are talus cones/how do they form?
When the loose fragments from ice wedging accumulate at the bottom of the cliff
31
What are joints?
Natural cracks/fractures (no displacement)
32
How does jointing occur?
The expansion of rock undergoing exhumation (stress relaxation) Cooling and Contraction
33
How does joint-block separation occur?
When prominent fractures divide the rocks into smaller blocks
34
How does bedding-plane separation occur?
Occurs along a bedding zone of weakness in sedimentary rocks and causes the rock to break up into slabs
35
What is exfoliation/sheeting?
joints form roughly parallel to the outer surface (dominance of sub-horizontal joints)
36
Give an Irish example of jointing formed by uplift, unloading and erosion
The Burren
37
What is mineral wedging?
Minerals (eg salts and carbonates) precipitate along fractures
38
What is thermal expansion? And what is the name of the rock that breaks off as a result?
Heat causes rock to expand Rocks are poor conductors of heat Outer layer of rock expands and breaks off (spall)
39
List the associated processes with jointing (5)
``` Exfoliation/sheeting Mineral wedging Thermal Expansion Root Wedging Animal Activity ```
40
How does jointing lead to increased chemical weathering? (3)
Increases surface area as joint spacing decreases Increase in area available for chemical weathering Openings of fracture increase by dissolution
41
When do chemical reactions occur?
When surfaces come into contact with air or water
42
What are the major products of chemical weathering?
Dissolved ions
43
What happens in dissolution?
Minerals (salt and carbonates) pass completely into solution Minerals dissolve into constituent ions the pH of water is significant (acidic)(excess of hydrogen)
44
How does carbonic acid form??
Water + Carbon Dioxide = Carbonic Acid
45
What occurs in carbonate weathering?
Carbonic acid may react with calcite to form calcium and bicarbonate ions in solution
46
Where was an example of hydrolysis seen and what type of rock was it?
In Lower Egypt, granite rock
47
What happens in /what is hydrolysis?
Water chemically reacts with minerals to break them down | Solutions and solid products are produced
48
Kaolinised granite (china clay) is an example of what type of weathering?
Hydrolysis
49
Where can kaolinised granite be found?
St Austell, Cornwall
50
What do feldspars change to?
China clay (hence the kaolinised granite)
51
What is hydration?
The absorption of water into crystal structures of minerals
52
Give an example of hydration
Anhydrite (calcium sulphate) to gypsum (calcium sulphate dihydrate)
53
What happens to some clays/minerals as a result of hydration?
They expand
54
What is oxidation?
Elements combine with oxygen eg. oxidation (rusting) of iron
55
What minerals are often affected by oxidation?
Iron-bearing minerals
56
Give an example of oxidation
Pyrite (iron sulphide/fool's gold) alters to iron hydroxides and iron oxides
57
What is differential weathering a result of?
Differences in the rates of weathering
58
Is all soil regolith?
All soil is regolith but not all regolith is soil
59
What is the weathering of rocks influenced by?
Mineral Composition Rock Type + Texture Climate (precipitation, temperature, vegetation)
60
How does mineral composition influence weathering?
Controls relative susceptibility to weathering
61
How do rock type and texture influence weathering?
It influences the mode of breakdown | Bedded + foliated lithologies have pre-existing planes of weakness to separate across bedding and foliation planes
62
Why is climate the most important factor influencing weathering?
It determines the type and rate of weathering and it determines the characteristics of regolith and weathered rock surfaces
63
What climatic conditions strongly influence weathering conditions?
``` Amount of rainfall (most reactions need water) Average temperatures (increase of 10 degrees doubles reaction rate) ```
64
When is chemical weathering strongest?
When temperature and precipitation are high
65
When is physical weathering strongest?
Where the mean annual temperature is between -10 degrees and 10 degrees and precipitation is between 25 and 100 cm
66
When is weathering minimal?
When annual precipitation is <25cm
67
What mineral is found in arid/semi-arid conditions and turns to clay when broken down via hydrolysis?
Feldspar
68
What is the role of vegetation (still climatic) in weathering?
Streams draining off lava flows with vegetation produce approx. 5 times more solutes (dissolved material) than streams draining fresh lava
69
Where is weathering most pronounced and why?
In the tropics because rainfall, temperature and vegetation are at a maximum
70
Where is minimum weathering found and why?
In desert and polar regions as factors are at a minima
71
What is the importance of weathering? (4)
Helps create diverse range of sedimentary rocks Important to cycling of carbon between atmosphere and other reservoirs Differential weathering creates landscape Can lead to economic concentration of certain elements (Fe, Al, Si)
72
List the processes that form sedimentary rocks (6)
Weathering, Erosion, Transportation, Deposition (Sedimentation), Burial and Compaction, Diagenesis
73
How does transportation help form sedimentary rocks?
Particles carried by gravity, wind, streams, glaciers and move downhill
74
How does deposition/sedimentation helps form sedimentary rocks?
Occurs when particles settle or dissolved minerals prcipitate
75
How does burial help form sedimentary rocks?
Layers of sediment accumulate and compact previous layers (compaction + cementation)
76
How does diagenesis help form sedimentary rocks?
Lithifies the sediment to form sedimentary rocks
77
Signs of textural maturity
Small grain size, smaller and rounded, very well sorted
78
Signs of compositional maturity
Often only quartz grains (further from source), fewer variations - lithic clasts reduce to individual minerals
79
What are the 4 major compositional groups of sandstone in order?
Lithic sandstone (rock fragment rich - found in deltas) Arkose (feldspar rich - found in alluvial fans) Quartz Arenite (pure quartz - found on beaches) Graywacke (matrix rich - found in submarines fans - contians >15% mud grade material)
80
What is diagenesis?
All physical, chemical and biological changes that occur to a sediment after it is deposited
81
Where does disgenesis occur?
At shallow depths and temperatures between the surface and those that initiate metamorphism (~300 degrees)
82
What does compaction do?
Reduce space between particles
83
What does cementation do?
Precipitation of minerals as cement to 'link' particles
84
What are the 2 processes in lithification?
Compaction and cementation
85
What is porosity?
Indicates the void/empty spaces in rocks | The better the sorting, the better the porosity
86
What is permeability?
The ability for fluids to flow through a rock
87
Give and example of Eolian Sandstones
Permian Sandstones in the UK - 285mya
88
What are Eolian deposits?
Sand deposits

Intro to Earth Science (13 decks)

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