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Eduqas GCSE Geology (9-1) > 1.3 Sedimentary Rocks and their Fossil Content > Flashcards

1.3 Sedimentary Rocks and their Fossil Content Flashcards

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1
Q

What are processes carried out by?

A

Agents

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2
Q

What categories can the geological processes taking place on earth be divided into?

A
  • weathering
  • erosion
  • deposition
  • transportation
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3
Q

What is weathering?

A

The breakdown of rocks in situ

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4
Q

What are the three main types of weathering?

A
  • physical
  • chemical
  • biological
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5
Q

What is physical weathering?

A

The mechanical breakdown of rocks

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6
Q

What is chemical weathering?

A

The breakdown of rocks by chemical reactions

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7
Q

What is biological weathering?

A

The breakdown of rocks by organic processes

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8
Q

What type of weathering can form tors?

A

Chemical

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9
Q

What are tors?

A

Rock outcrops on the tops of hills

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10
Q

How are tors formed?

A

Chemical weathering:

  • granite contains feldspar - reacts with water
  • produces kaolin (clay)
  • forms outcrops on top of hills
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11
Q

What does orthoclase feldspar react with water to produce?

A

Potassium carbonate, kaolin (china clay) and silica

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12
Q

What is kaolin also known as?

A

China clay

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13
Q

What is the process that takes place when the feldspar in granite reacts with water?

A

Hydrolysis

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14
Q

What is physical weathering also known as?

A

Mechanical weathering

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15
Q

What type of weathering is freeze thaw?

A

Physical/mechanical

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16
Q

How does freeze thaw weathering occur?

A

Water fills cracks in rock, freezes and expands at night and thaws in the day. The pressure on the rocks breaks angular pieces off

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17
Q

What is formed from freeze thaw weathering?

A

Scree fans - where angular pieces of rock broken off by freeze thaw collect

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18
Q

What are scree fans?

A

Where the angular pieces of rock broken off by freeze thaw collect

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19
Q

What is limestone pavement?

A

Where flat layers of limestone are weathered along joints to form blocks (clints) surrounded by cracks (grykes)

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20
Q

What is a scarp?

A

Steep rock face

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21
Q

How does chemical weathering occur?

A
  • permeable rock (e.g. limestone) lets water pass along its joints and bedding planes
  • calcium carbonate of limestone is dissolved away by weak carbonic acid in rainwater
  • cave system dissolved out of limestone water
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22
Q

How does biological weathering occur?

A

Roots of trees grow down into cracks in rocks, widening them and breaking the rock up

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23
Q

Is clay impermeable?

A

Yes

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24
Q

Is shale impermeable?

A

Yes

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25
Q

How are limestone pavements formed?

A
  • limestone laid down - tropical shallow marine environment
  • layers of sedimentary rock above the marine environment removed by glaciers
  • exposes limestone at surface - limestone has joints and bedding planes
  • rain-stream water has slight acidity and flows down joints - widening them to grykes eventually → limestone pavement formed
  • swallow holes formed due to widening of bedding plane into an underground cavern
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26
Q

What type of weathering is exfoliation?

A

Mechanical

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27
Q

How does exfoliation occur?

A

Rocks warm in day and cools at night - forming an onion skin texture

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28
Q

What rocks could exfoliation occur to?

A

Granite and sandstone

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29
Q

How are some dry valleys eroded?

A
  • end of last ice age, ground was permanently frozen
  • nearby glaciers were melting, so a lot of melt water
  • melt water flows over surface as ground frozen
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30
Q

What is erosion?

A

The process where material is removed from the site of weathering by wearing it away and then transportation

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31
Q

What are the 5 main agents of erosion?

A
  • wind
  • rivers
  • gravity
  • sea
  • glaciers
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32
Q

What are the ways that erosion can take place?

A
  • corrasion
  • attrition
  • abrasion
  • hydraulic action
  • plucking
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33
Q

What is corrasion?

A

Where rock fragments erode the bedrock

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34
Q

What is attrition?

A

Where rock fragments hit against one another

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35
Q

What is abrasion?

A

A combination of corrasion and attrition

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36
Q

What is hydraulic action?

A

Where air is trapped and squeezed by water

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37
Q

What is plucking?

A

Where ice freezes to bedrock and plucks it away

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38
Q

What is transportation?

A

The process where eroded material is moved to another location

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39
Q

What is the eroded material called in transportation?

A

The load

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40
Q

What are the main processes of transportation?

A
  • solution
  • suspension
  • saltation
  • traction
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41
Q

What is solution?

A

Where the load is dissolved in water

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42
Q

What is suspension?

A

Where the load is carried in the main body of the water, or in the air by wind

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43
Q

What is saltation?

A

Where the load is bounced along the eroded surface

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44
Q

What is traction?

A

Where the load is rolled or dragged along the eroded surface by water or wind

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45
Q

How can clasts be described?

A
  • size
  • sorting
  • roundness
  • sphericity
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46
Q

How is the size of a clast found?

A

By measuring the length of its long axis, or if too small, by sieving

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47
Q

How are clasts named according to their size?

A

Using the Wentworth scale

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48
Q

In most cases, if a clast is smaller, what does this mean for the distance it has been transported?

A

Smaller clast, greater distance it has been transported

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49
Q

In most cases, if a clast is smaller, what does this mean for its hardness?

A

It is less hard

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50
Q

What factors can have an effect on the size of a clast?

A
  • distance it has been transported

* the hardness of mineral or rock

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51
Q

What is sorting?

A

The nearness of the clasts in a sediment come to being the same size

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52
Q

How will the clasts be in a well sorted sediment?

A

Similar in size (may be described as mature)

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53
Q

How will the clasts be in a poorly sorted sediment?

A

Different sized clasts (may be described as immature)

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54
Q

How will the degree of sorting be represented?

A

Using a histogram or cumulative frequency curve

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55
Q

What does roundness describe?

A

How angular the edges of and corners of clasts are

56
Q

What does it mean, in terms of erosion, when a clast is more rounded?

A

Greater degree of erosion and transportation

57
Q

What factors will affect a clasts roundness?

A
  • hardness of rock or mineral

* degree of erosion and transportation

58
Q

How is roundness measured?

A

A visual roundness chart

59
Q

What does sphericity describe?

A

How near clasts come to being spheres

60
Q

What type of processes does deposition include?

A

Physical and chemical

61
Q

When will clasts be carried by a current?

A

If it has a high enough velocity, and in turn enough energy

62
Q

Why might the current of water fall?

A
  • change in angle - alluvial fan - steep slope, fast moving but then at bottom its slow (still going fast at top)
  • change in speed of movement - fast river to slow moving sea
63
Q

What are clastic rocks?

A

Sedimentary rocks formed by the deposition of clasts

64
Q

When are sediments called organic?

A

When they have a high percentage of animal and plant fossils that have been deposited like clasts

65
Q

Example of a clastic sedimentary rock?

A

Conglomerate

66
Q

How does precipitation occur?

A

If water is saturated or oversaturated with a certain compound, then these compounds can be precipitated out as a crystalline substance

67
Q

When is precipitation more likely?

A

If the water is agitated (swirled around)

68
Q

Example of precipitation?

A

Precipitation of calcite from warm tropical sea water, resulting in formation of limestones due to CO2 being released

69
Q

What are chemical precipitates?

A

Rocks formed by precipitation

70
Q

Why does a solution often become saturated?

A

Due to heat from the sun

71
Q

How is halite formed?

A

When temperature rise evaporates away much of the water in seas or salt lakes

72
Q

Example of a chemical precipitate?

A

Carboniferous limestone

73
Q

What type of weathering is scree usually formed by?

A

Freeze thaw

74
Q

What do sedimentary rocks form from?

A

Compaction of soft sediment into hard rock

75
Q

What type of clasts are more easily compacted?

A

Fine clasts (as oppose to large ones)

76
Q

If sediments have clasts, how will they stick together?

A

Cemented

77
Q

What natural cements can stick together clasts in sedimentary rocks?

A
  • silica
  • calcite
  • iron oxide
78
Q

What will it mean if sediments are crystalline, in terms of how they are formed?

A

They will have precipitated directly from water

79
Q

Do crystalline sediments need cement?

A

No

80
Q

Types of sedimentary environments?

A
  • warm shallow marine
  • cold shallow marine
  • deep marine
  • rivers and deltas
  • deserts
81
Q

Types of depositional environment?

A
  • screes
  • rivers
  • shallow/deep seas
  • wind-formed dunes
82
Q

What do porosity and permeablility of sedimentary rock depend upon?

A
  • characteristics of original sediment

* degree of compaction and cementation

83
Q

Examples of sedimentary rocks?

A
  • breccia
  • conglomerate
  • shale
  • sandstone
  • evaporites
  • limestone
84
Q

Example of warm shallow marine environment?

A

the Bahamas

85
Q

What environment does limestone form in?

A

Warm shallow marine

86
Q

What are ooliths?

A

Spheres of calcite made of concentric layers

87
Q

How are ooliths formed?

A

When calcite has been precipitated around a nucleus of a sand grain or piece of shell

88
Q

What are cocoliths?

A

Remains of the minute skeletons of simple sea creatures

89
Q

How is shale formed?

A

Flood plain of meandering river - deposited when river channel overflows

90
Q

How is reef limestone formed?

A

Warm clear shallow oxygenated, turbulent tropical marine conditions by build up of organic matter on a reef

91
Q

How is chalk formed?

A

Clear, warm, shallow tropical marine conditions (low energy) coccoliths create skeletons of calcite = very pure rock

92
Q

How is chemical limestone formed?

A

Warm, clear, shallow, tropical sea (low energy) by the precipitation of calcite from water rich in CaCO3

93
Q

What are turbidity currents?

A

Powerful, sediment charged underwater currents that flow down the continental slope

94
Q

How is sandstone (greywacke) formed?

A

Turbidity currents flowing off the shelf (high energy) down the continental slope and settling rapidly on the abyssal plain

95
Q

What is graded bedding?

A

Decreasing grain size upward through the bed - indicating deposition from a waning current

96
Q

When does graded bedding form?

A

As a result of a slowing turbidity flow

97
Q

How is sandstone (subgreywacke) formed?

A

As the point bar on the inside of a meandering river channel - sediment is deposited as the meander migrates laterally

98
Q

What are deltas?

A

Areas of deposition where rivers enter the sea or a lake

99
Q

How are canyons formed?

A

Upland areas are often cut by flash floods

100
Q

What environment do canyons form?

A

Hot desert

101
Q

What is a flash flood?

A

In hot desert environments - heavy rain produces rapid run-off

102
Q

How are desiccation cracks formed?

A

Hot deserts - water in lakes dry out - and then mud in bottom dries out also - contracting

103
Q

What are salt pans?

A

When water collected in a desert evaporates - dissolved salts precipitated out in layers

104
Q

How are barchan dunes formed?

A

When wind blows sand over an obstruction - dune grows and takes on a crescent shape

105
Q

What are moraines?

A

The deposits left by glaciers

106
Q

What do moraines consist of?

A

Poorly sorted rock debris that has fallen onto or into the ice

107
Q

How is desert sandstone formed?

A

As wind blows across a desert (high energy), with corrasion and attrition producing very well rounded and sorted grains deposited as dunes

108
Q

How is halite formed?

A

Intense evaporation of a shallow lake or sea in a desert environment - with mineral content of the waters precipitated out as salts

109
Q

How is quartz conglomerate formed?

A

On a beach (high energy) by continuous reworking of sediment - removing almost all minerals bar quartz

110
Q

Cement in quartz conglomerate?

A

Silica

111
Q

Examples of rocks that form in shallow marine environments?

A
  • limestone
  • sandstone
  • conglomerate
112
Q

Examples of rocks that form in deep marine environments?

A
  • turbidites

* black shale

113
Q

Examples of rocks that form from deposition in rivers and deltas?

A
  • shale
  • sandstone
  • conglomerate
  • coal
114
Q

Examples of rocks that form from deposition by wind and water in deserts?

A
  • breccia

* desert sandstone

115
Q

Examples of rocks that form from precipitation from saline water during evaporation?

A
  • evaporites
  • halite
  • gypsum
116
Q

Examples of rocks that form from deposition by ice?

A

Glacial till

117
Q

What is a bed?

A

A layer of rock separated from the layer above and below by a bedding plane

118
Q

What is a flag/flagstone?

A

Bed 2-5mm thick

119
Q

What is a bedding plane?

A

Defines the top or bottom of a bed - represents a change in the nature of sedimentation

120
Q

Difference between a bed and lamination?

A
  • lamination - layer of sediment < 1 cm thick

* bed - > 1 cm

121
Q

In graded bedding, where is the finer sediment?

A

At the top

122
Q

How might the fining upward sequence in graded bedding be produced?

A

Turbidity currents

123
Q

How do turbidity currents form the fining upward sequence in graded bedding?

A

In comparatively calm bodies of water - larger denser fragments sink first, followed by small silt and clay particles

124
Q

How is a graded bed with an erosional base formed?

A

When the layer above was laid down, the layer underneath was damaged

125
Q

What does a graded bed with an erosional base represent?

A

An abrupt change from the much finer grained sediment underneath

126
Q

What can cross bedding be left by?

A

Wind and rivers

127
Q

How is cross bedding formed?

A

By uni-directional current of wind or water moving sediment as a series of asymmetrical ripples of dunes

128
Q

If cross bedding is on a very large scale, what is it called?

A

Dune bedding

129
Q

If cross bedding is on a very small scale, what is it called?

A

Cross lamination

130
Q

How are rain pits formed?

A

By impact of rain drops on an exposed sediment surface

131
Q

What does it show, if ripple marks are symmetrical?

A

The beach used to be horizontal

132
Q

What does it show, if ripple marks are unsymmetrical?

A

Formed by uni-directional current - downstream/downwind side will have the steeper face

133
Q

What do reef building corals indicate the past environment was like?

A

Marine, shallow, warm

134
Q

What do trilobites indicate the past environment was like?

A

Marine

135
Q

What do ammonites indicate the past environment was like?

A

Marine

136
Q

What do plants indicate the past environment was like?

A

Terrestrial, indicating past climate

137
Q

What do trace fossils indicate the past environment was like?

A

Tracks indicating terrestrial, burrows indicating shallow water

Eduqas GCSE Geology (9-1) (13 decks)

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