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Geology > Sedimentary Rocks and Processes > Flashcards

Sedimentary Rocks and Processes Flashcards

1
Q

Define Weathering

A

The physical breaking up of rock into smaller pieces

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2
Q

Define Erosion

A

The removal of material

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3
Q

What are three physical weathering processes?

A

Freeze-thaw, Insolation, Pressure release

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4
Q

What is a biological weathering process?

A

Root growth

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5
Q

What are four chemical weathering processes?

A

Carbonation, Oxidation, Hydrolysis, Solution

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6
Q

Define Carbonation

A

Rainwater containing carbon dioxide from the air and soil reacts with carbonates to form soluble hydrogen carbonates

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7
Q

Define Freeze-Thaw

A

Water expands by 9% upon freezing so fractures filled with water are prized further apart

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8
Q

Define Insolation

A

Heating and cooling of rocks in desert regions causes minerals to expand and contract at different rates until the rock fractures

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9
Q

Define Oxidation

A

The addition of oxygen to the atomic structures of minerals or a similar chemical change

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10
Q

Define Hydrolysis

A

The addition of water molecules to the atomic structures of minerals

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11
Q

Define Root Growth

A

Plant roots growing in fractures

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12
Q

Define Solution

A

Soluble minerals dissolve and are carried away in solution

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13
Q

Define Pressure Release

A

Deeply buried rocks are compressed by the pressure of the rocks above. When the overburden is removed, the rock expands to produce stress release fractures

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14
Q

What are the three agents of erosion?

A

Wind, Water, Ice

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15
Q

Define Agent of Erosion

A

Things that move material

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16
Q

What does the Hjulstrom Curve help geologists to determine?

A

What velocity is required to erode, transport and deposit different sized clasts

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17
Q

What is the Hjulstrom Curve based on?

A

The results from an experiment with flowing water (1m depth) over flat-lying, unconsolidated sediment

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18
Q

What are three positives of the Hjulstrom Curve?

A

Uses a logarithmic scale to show a wide range of clast sizes and velocities, Describes the relationship between velocity and grain size, Uniformitarianism - present is the key to the past

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19
Q

What are three negatives of the Hjulstrom Curve?

A

Only applies to rivers 1m deep, Loose sediment on the bottom of the river only, Doesn’t take density, shape or angularity of sediment into consideration

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20
Q

What are two erosional processes that modify shape during transportation?

A

Abrasion and Attrition

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21
Q

Define Abrasion

A

Particles grind down the bedrock

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22
Q

Define Attrition

A

The particles grind against each other

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23
Q

What are the five processes of transportation?

A

Suspension, Solution, Saltation, Traction, Sliding

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24
Q

What are three ways sediment can change as it moves downhill?

A

Size, Shape, Composition

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25
Q

Relating to size, the further a grain moves from its source…

A

The smaller it becomes

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26
Q

What scale can size be categorised by?

A

Wentworth Scale

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27
Q

Relating to shape, the further a grain moves from its source…

A

The more rounded it becomes

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28
Q

What is roundness described by?

A

Using six different classes from very angular to well rounded

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29
Q

What is shape influenced by?

A

The planes of weakness within the rock

30
Q

What are the four categories on the Zingg Analysis?

A

Blade, Disc, Rod, Sphere

31
Q

Relating to composition, the further a sediment moves from its source…

A

The more compositionally mature it becomes

32
Q

Define Bowen’s Reaction Series

A

Helps geologists to predict the stability of a mineral and therefore how likely it is to weather

33
Q

The higher the temperature at which a mineral forms…

A

The more likely it is to be weathered

34
Q

Using Bowen’s Reaction Series, what are the four least stable minerals?

A

Olivine, Pyroxene (Augite), Amphibole (Hornblende), Feldspar

35
Q

Using Bowen’s Reaction Series, what are the two most stable minerals?

A

Quarts and Muscovite

36
Q

What happens to the feldspars when granite is weathered?

A

They undergo hydrolysis to form clay

37
Q

What happens to the biotite when granite is weathered?

A

Undergo hydrolysis to form clay and oxidation to form iron oxides

38
Q

What happens to the quartz when granite is weathered?

A

It remains as residual minerals due to their chemical weathering resistance

39
Q

Define Sorting

A

The size range exhibited by a sediment

40
Q

What can a grain size analysis help geologists decide?

A

What the main method of transportation was

41
Q

Mean Grain Size =

A

(∅75+∅50+∅25)/3

42
Q

Skewness =

A

(∅84-∅50)/(∅84-∅16) - (∅50-∅5)/(∅95-∅5)

43
Q

Sorting Coefficient =

A

(∅84-∅16)/2

44
Q

Define Matrix

A

Fine grained sediment holding clasts together

45
Q

Define Cement

A

A crystalline material (calcite or quartz usually) which holds grains together

46
Q

Define Monomictic

A

One clast composition

47
Q

Define Polymictic

A

Variety of clast compositions

48
Q

Define Clast Supported

A

Clasts touch each other

49
Q

Define Matrix Supported

A

Clasts are not touching

50
Q

What are thirteen sedimentary structures which can be used as a way up indicator?

A

Cross bedding, Graded bedding, Ripple marks, Desiccation cracks, Flute casts, Prod marks, Roots, Burrows, Geopetal structures, Fossils in life assemblage, Included fragments, Channels, Load casts and flame structures

51
Q

What are six sedimentary structures which can be used as a paleocurrent indicator?

A

Cross bedding, Imbricate structures, Ripple marks (if asymmetrical), Flute casts, Prod marks (trend), Channels (trend)

52
Q

What are the four facies in a desert?

A

Scree slopes, Alluvial fan, Aeolian sand dunes, Playa lake

53
Q

What are the four facies in a fluvial system?

A

Channel, Point bar, Flood plain, Ox-bow lake

54
Q

Define Delta

A

Where river carry sediment into deeper relatively still water, forming the mouth of a river

55
Q

What are five sedimentary structures found in the top set of a deltaic sequence?

A

Channel, Cross bedding, Laminations, Ripples, Roots

56
Q

What are two sedimentary structures found in the foreset of a deltaic sequence?

A

Cross bedding, Ripples

57
Q

What are three sedimentary structures found in the bottom set of a deltaic sequence?

A

Laminations, Burrows, Fossils

58
Q

What are the four facies in a marine environment?

A

Beach, Tropical, Deep marine, Turbidites

59
Q

What are four conditions required for limestone formation?

A

Marine water, Shallow water depth, Warm water temperature, Clear water

60
Q

What type of limestone was formed in the Cretaceous?

61
Q

What type of limestone was formed in the Jurassic?

62
Q

What type of limestone was formed in the Carboniferous?

A

Bioclastic

63
Q

Define Turbidites

A

Underwater avalanche moving downhill (density driven) made from greywacke and mudstone, triggered by mass movement or an earthquake

64
Q

Define Diagenesis

A

The group of processes which change a sediment into a rock, at low temperatures and pressures near the Earth’s surface

65
Q

What are the two main processes of diagenesis?

A

Compaction and Cementation

66
Q

Define Compaction

A

Sediment is squeezed by the pressure of overlying sediment

67
Q

What happens during compaction?

A

Water is lost as porosity and permeability are reduced

68
Q

Define Cementation

A

Minerals crystallise in pore spaces, cementing the grains together

69
Q

What happens to permeability during cementation?

A

Decreases as the grains are bound together

70
Q

What are three minerals commonly acting as cement?

A

Quartz, Calcite, Iron minerals e.g. haematite

Geology (16 decks)

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