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ES2001 > Sediments And Stratigraphy > Flashcards

Sediments And Stratigraphy Flashcards

1
Q

Where was the concept of deep time observed?

A

Siccar Point, between Berwick and Dunbar

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2
Q

What is Huttons Unconformity?

A

Vertical Silurian rocks overlain by gently dipping denovian rocks

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3
Q

Provide examples of sedimentary layers with different dips

A

Siccar Point
Mt Sharp, Mars
Stainmore Fm, Northumberland

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4
Q

What is Shaler Outcrop, Mars, an example of?

A

Cross bedding

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5
Q

Define sedimentary facies

A

A distinct set of lithological and fossil characteristics of a given sedimentologic unit, typically defined at the bed scale

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6
Q

What are the seven characteristics of sedimentary facies?

A

Composition
Texture
Sedimentary Structures
Bedding Geometry, Style and Thickness
Nature of Bedding Contacts
Fossils
Colour

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7
Q

What is the purpose of sedimentary facies?

A

Provide a guide for interpreting the environmental setting of sedimentary deposits

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8
Q

What are you looking for when describing composition?

A

The mineralogical constituents and their percentages
Quartz, Lithics, Feldspar

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9
Q

How do you describe texture?

A

Grain size
Shape
Sorting
Matrix supported vs clast supported

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10
Q

How do you describe the sedimentary structures?

A

Types of bedforms and scale
Cross bedding _______ vs trough cross bedding _/

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11
Q

How do you describe bedding geometry, style and thickness?

A

Shape (lenticular, wedge shaped etc)
Orientation
Lateral Continuity

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12
Q

How do you describe the nature of bedding contacts?

A

Sharp vs gradational
wavy, flat

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13
Q

How do you describe fossils?

A

Species type - body vs trace vs plant
Abundance
Life position vs disarticulated

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14
Q

What is the issue with describing colour?

A

May be primary, but can also be diagenetic, reflecting chemistry of pore fluids
Ie liesegang rings

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15
Q

What’s the difference between planar cross bedding and trough cross bedding?

A

Planar cross bedding bounding surfaces are planar and parallel
Trough cross bedding bounding surfaces are curve-planar and non-parallel

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16
Q

What could turn rocks red?

A

Ferric iron (Fe3+) in oxidising conditions
Hematite

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17
Q

What could make rocks yellow/brown/tan colours?

A

Hydrated forms of ferric oxide ie goethite and limonite

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18
Q

What could be a possible cause for greenish rocks?

A

Ferrous iron (Fe2+) present in reducing conditions
Glauconite, chlorite

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19
Q

What could give rocks a greyish black colour?

A

Organic Matter
Anoxic to oxic conditions
Pyrite

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20
Q

What should individual facies be?

A

Distinct
Exhaustive
Reproducible
Usable

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21
Q

What are we trying to reconstruct from facies?

A

Provenance (source areas)
Transport History
Place of deposition
Alteration since deposition

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22
Q

Facies Association is?

A

Groups of genetically related facies in terms of a depositional environment

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23
Q

What is facies succession?

A

Facies that change progressively either vertically or laterally

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24
Q

What can associated facies be used for?

A

To determine a depositional environment

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25
Q

What can facies models be used for?

A

A standard to compare real examples
A predictor for lateral and vertical changes
A framework and guide for observations
A basis for interpretation

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26
Q

What does a sharp contact in bedding suggest?

A

A sudden change in the energy of an environment

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27
Q

What is rheology?

A

The behaviour and properties of fluids and solids

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28
Q

What is the equation for force (and the units)?

A

F=ma
Newtons or kgms-1

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29
Q

What is the value for gravity?

A

9.81ms-2

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30
Q

What is stress, and what’s its equation?

A

Stress is force per unit area
Normal stress = pressure = force acting normal to an area
Shear stress = t wiggly = force acting tangential to an area
o = F/A (Nm-2)

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31
Q

What is Newton’s first law?

A

Inertia - an object will remain at rest or in uniform motion unless acted on by an external force

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32
Q

What is Newton’s second law?

A

F=ma

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33
Q

What is archimedes principle of levers and torque? (Formula)

A

Work = force x length of lever arm = FL

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34
Q

What is it called when grains start to move?

A

Sediment entrainment

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35
Q

What are the two types of loads in sediment transport?

A

Bed load and suspended load

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36
Q

What are the types of bedload?

A

Traction transport - rolling, sliding, impact and creep
Uninterrupted saltation - perfect curve
Interrupted saltation - grain collision

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37
Q

What is Fg?

A

Gravity force
= mg
= density x volume x g

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38
Q

What is the true equation for gravity force (Fg)?

A

Fg = (ps - pf) 1/6 pi D^3 g
Density of sediment minus density of fluid x 1/6 pi x diameter cubed x g

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39
Q

What is the point when a grain starts moving called?

A

Critical entrainment

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40
Q

What are the forces acting on a grain?

A

Fl - lift force l^
Ff - fluid force /
Fd- drag forces -
Fg - gravity force lv

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41
Q

What is Bernoullis principle and what force does it correspond to?

A

Pressure is inversely related to velocity
Lift force - consequence of Newton’s third law

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42
Q

What is Ff?

A

Fluid force
Vectorial sum of lift force and drag force
l^ + - = /

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43
Q

How do you calculate Fluid Force

A

Ff = wiggly t x pi x D^2
Shear stress times surface area

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44
Q

How do you define fluid force?

A

The shear stress operating over the grains surface area

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45
Q

What is Shields Criterion?

A

Ff / Fg = o (o with an h)(theta)

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46
Q

What is the fully formed equation for Shields Criterion?

A

wiggly t / (ps - pf) gD = o (theta)

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47
Q

What does Hjulströms curve show?

A

The critical velocity for movement if quartz grains on a plane bed at water depth 1m.

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48
Q

What are the units for Shields Criterion?

A

Dimensionless

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49
Q

Using shields criterion, how can theta be increased?

A
  • increased shear stress
  • increased fluid velocity
  • decreased grain density
  • decreased grain diameter
  • decreased g (i.e on Mars)
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50
Q

What happens to shear stress in entrainment of mixed grain sizes?

A

Coarser sizes will move at lower shear stress, and smaller grain sizes will require larger shear stresses, than in a uniformly sized sediment.

-tennis ball over marbles vs marble over marbles

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51
Q

Why do large grains move easier over small grains than small grains?

A

Larger grains have longer lever arms so the torque is greater.

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52
Q

What is the angle of internal friction?

A

a
The angle between the pivot points of two spheres

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53
Q

Give an example of entrainment of big and little grains

A

Placers

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54
Q

When does entrainment occur?

A

When gravity force is less than fluid firce

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55
Q

What is the value of theta in shields criterion just before motion begins?

A

1

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56
Q

In Hjulströms curve, why do clay and slit require the same velocity as boulders?

A

Clay and slit are mud so they stick together and require more force to get into suspension

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57
Q

What are the conditions of Hjulströms curve and what does this mean?

A

Conditions : quartz grains, depth 1m, flat bed
Therefore limited application

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58
Q

What are the three controls of sediment settling?

A

Fb - buoyant force
Fg - gravity force
Fd - drag force

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59
Q

What is sediment settling through a fluid affected by?

A

Grain size (D)
Grain Density (Ps)
Fluid viscosity (u)
Fluid density (Pf)
Gravity (g)
Velocity (U)

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60
Q

What is the equation for buoyant force?

A

Fb = pi/6 x D^3 x pf x g

A sixth of pi x grain size cubed x density of the fluid x gravity

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61
Q

In what circumstances would a grain sink?

A

If the density of the grain is greater than the density of the fluid
If there is a net force between gravity and buoyancy

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62
Q

What happens at constant settling velocity?

A

Drag on the grain balances fge net force between gravity and buoyancy

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63
Q

How do you calculate the net force on a grain?

A

F g-b = pi/6 x (ps-pf) x g xD^3

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64
Q

How do you calculate the net force on a grain?

A

Fd = F g-b = pi/6 x (ps-pf) x g xD^3
Or
Fd = 3pi x D x u x U

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65
Q

What is the drag force exhibited on a grain related to?

A

Viscosity of the fluid
Size of the grain
Grain velocity through the fluid

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66
Q

What is stokes law?

A

U = (ps-pf) x g xD^2
——————————
Qi u

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67
Q

What is the purpose of stokes law?

A

Describing the resisting force in on a particle moving through a viscous fluid and showing that a maximum velocity is reached in such cases

68
Q

What is terminal velocity?

A

The highest velocity attainable by an object as it falls through a fluid.

69
Q

When does terminal velocity occur?

A

When the sum of the drag force and the buoyancy is equal to the downward force of gravity acting on the object

70
Q

What are the four types of bedforms that evolve as flow increases?

A

Flat beds
Ripples
2-D dune
3-D dune

71
Q

What is the anatomy of a symmetrical bedform?

A

Water surface in phase with bed surface
Characteristic of alternating flow direction
Symmetrical

72
Q

What is the anatomy of an asymmetrical bedform?

A

Water surface out of phase with bed surface
Stoss slope, summit, crest, brink, lee slope, trough

73
Q

How to identify stoss vs lee slopes?

A

Stoss is a long gentle slope on the first side
Lee is short and highly angled on the second side
-stand in lee of building to avoid wind

74
Q

What do migrating bedforms lead to?

A

Lead to various sedimentary structures which are stable under certain conditions

75
Q

What is a bedform?

A

Features that form under certain flow conditions

76
Q

What are the characteristics of 2-D dunes?

A

Planar tabular or wedge shaped cross stratification
Flow ————>
Stoss then lee side
Stratification matches lee slope

77
Q

What is the characteristics of 3-D dunes?

A

Trough cross-stratification
Curved surfaces

78
Q

What are the seven types of upper plane beds?

A

Typical ripple pattern
Dunes with ripples superposed
Dunes
Washed out dunes
Plane bed
Antidune standing wave
Antidune breaking wave

79
Q

What are the characteristics of ripples?
(Length, height, ripple index, geometry, flow velocity, flow depth, sediment size)

A

Length - 0.1-0.2m
Height - few cms
Ripple index - relatively low
Geometry - strongly irregular/short crested
Velocity - low
Depth - less than a few cm
Sediment size - 0.03-0.6mm

80
Q

What are the characteristics of 2D dunes?
(Length, height, ripple index, geometry, flow velocity, flow depth, sediment size)

A

Length: 10s cm - 100s m
Height: cms - cm-10s of m
Ripple index: relatively high
Geometry: straight/ sinuous and long crested
Velocity: low/moderate
Depth: few dm
Sediment size: >0.3mm

81
Q

What is the Southard diagram?

A

Bedform stability diagram

82
Q

What happens to bed forms when velocity is low, and when it increases?

A

At low velocities grain sizes >0.7mm can form ripples
As it increases fine grains upper plane beds, grain sizes >0.2mm form dunes

83
Q

What are the parameters of Southards bedform stability diagrams?

A

Velocity and grain size based on hundreds of experiments in a lab
Water depth 0.25-0.4m

84
Q

What is Froudes number?

A

The energy state of a flow
Small u / V/gh
Flow speed divided by the square root of gravity times depth of flow

85
Q

What does the Froude number suggest?

A

Fr<1 : subcritical waves
Fr=1 : critical waves at the same speed of bulk fluid
Fr>1 : supercritical waves

86
Q

What are standing waves an example of?

A

Critical energy state

87
Q

What is Reynolds number?

A

Defines whether a flow is laminar or turbulent
(Density of fluid x flow speed x depth of flow)/viscosity

88
Q

What does the Reynolds number suggest?

A

Re<500 : laminar flow-flow is dominated by viscous forces
500<Re<2000 : transitional flow
Re>2000: turbulent flow-flow is dominated by inertial forces

89
Q

What does the mud line represent?

A

Where the system loses energy and fine sands are replaced with muds

90
Q

What is sediment transport and deposition controlled by?

A

Tides and waves

91
Q

When do fluvial systems influence coastal settings?

A

When water and sediment discharge are at large

92
Q

What is the difference between the fair weather wave base and the storm wave base?

A

Fair weather base is the average day
Storms have a deeper wave base

93
Q

How are tides controlled?

A

Gravitational forces set up by the alignment of the sun, earth and moon

94
Q

How are tides controlled?

A

Gravitational forces set up by the alignment of the sun, earth and moon

95
Q

What are, and why do, spring tides occur?

A

Highest high tide and lowest low tide
Sun and moon in alignment

96
Q

What is, and why do, spring tides occur?

A

Lowest high tide and highest low tide
When moon is 90 degrees from sun ie perpendicular

97
Q

What are the three bedforms under tides?

A

Herring bone cross stratification
Mud drapes on cross beds
Reactivation surfaces

98
Q

What are the four stages of bedforms under tides?

A
  1. Dominant current stage
  2. First slack water stage
  3. Subordinate current stage
  4. Second slack water stage
99
Q

What happens during the dominant current stage?

A

Sand is deposited on Lee slope
Megaripple/ sand wave migration

100
Q

What happens during slack water stages?

A

Mud is deposited on Lee slope, creating a mud drape

101
Q

What happens during subordinate current stage?

A

Water goes backwards, creating a reactivation surface and rippled sand

102
Q

What are bedforms affected by?

A

Tidal range
Tidal current velocities
Sand/mud ratios

103
Q

What are the five types of bedform organisation from high velocity and sand availability to low?

A

Flaser
Wavy
Lenticular
Wavy
Pinstripe

104
Q

What do surface waves control?

A

Erosion
Sediment transport and deposition

105
Q

What are the characteristics of a wave?

A

wave Length
wave Height
wave Celerity (speed)

106
Q

What is the period of a wave?

A

T = L/C
the time (s) it takes for one wavelength to pass a point on the water surface

107
Q

What are the most important type of waves?

A

Wind generated waves

108
Q

What does wind speed control (waves)?

A

Size and energy of the waves, positively correlated with wave height, length and period

109
Q

What is a wave orbital?

A

The fluid beneath a rising and falling wave that follows a circular path

110
Q

What is the diameter of a wave orbital dependant on?

A

Height and length of the waves
Depth below water surface

111
Q

What is deep water?

A

When h > L/2
When the orbitals are small enough that fluid motion is negligable

112
Q

What is the wave base?

A

Depth h >L/2
The depth below the surface where waves no longer affect the water column

113
Q

What is effective wave base?

A

The depth below the surface at which the fluid motion due to waves is not sufficient to move sediment on the bed

114
Q

What are transitional waves?

A

When L/20 < h < L/2
Orbitals become flatter as the approach the bed, and at the bottom the orbitals are flat and the motion of the water is back and forth (oscillating)

115
Q

What are the three types of wave?

A

Deep water
Transitional
Shallow

116
Q

What are the characteristics of classical wave ripples?

A

Oscillation
Symmetrical profile
Peaked crests
Broad troughs
Straight, bifurcating crests

117
Q

What can we do with wave ripples?

A

Wavelengths reflect orbital diameter, therefore water depth
Ripple crests are parallel to wave crests, so are aligned parallel to shoreline at time of formation - palaeoshoreline

118
Q

What can the appearance/direction of ripples be affected by?

A

Ebb tidal current

119
Q

What causes combined flows?

A

Storms with onshore winds
Also called riptides

120
Q

What types of cross stratification are formed in combined flows?

A

Hummocky x-strat
Swaley x-strat

121
Q

What are the characteristics of a combined flow cross stratification?

A

Convex upward (hummocky) and concave upward (swales) laminae
Low angles
Internal laminae approx parallel to lower bounding surfaces
Best developed in coarse slit and fine sand

122
Q

What are the three causes of waves?

A

Gravitational waves
Marine landslides ie seismicity
Wind - Shear stress

123
Q

What is a Newtonian fluid?

A

A fluid that has no strength and does not undergo a change in viscosity as the shear rate increase
Ie plain wtaer

124
Q

What is an eddy?

A

Highly turbulent water masses

125
Q

What does the Hjulström curve show?

A

The flow velocity required to move sediment of different grain sizes

126
Q

What is the basic mechanism behind the phenomenon of sediment transport?

A

Drag force in the direction of the flow

127
Q

True or False:
Facies successions are facies and/or facies associations that change progressively either vertically or laterally

A

True

128
Q

True or False:
Facies successions are facies and/or facies associations that change progressively either vertically or laterally

A

True

129
Q

True or false:
Retro gradation is the landward change in position of the front of a delta with time. Retro gradation is most common during periods of sea level fall.

A

False

130
Q

Hummocky cross stratification is characterised by:

A

Convex upward lamination that is typically low angle dipping

131
Q

What would typify the deposit of a. Idealised sediment gravity flow in which the mechanism for grain suspension was turbulence?

A

A bed that showed coarse tail reverse grading

132
Q

Which sandstone types is most likely to form by the mechanical and intense chemical weathering of a granite?

A

Quartz arenite

133
Q

What is the facies model for a storm dominated shallow marine environment?

A

From top to bottom:
- coastal plain
- coal
- breaker zone (ridge and runnel rip channels)
- shore face (swaley cross stratification)
- lower shore face (Hummocky cross stratification)
- mid shelf (bioturbated sandy siltstone)
- outershelf (bioturbated mudstone)

134
Q

Give an example of a shallow marine, storm dominated succession.

A

Mesaverde Fm, Wyoming

135
Q

What are the three types of shallow marine clastics?

A

Zoophycos - shallow water, bioturbated vertically
Cruziana
Skolithos - deep water. Bioturbated horizontally

136
Q

What is bioturbation?

A

Groups of trace fossils formed during feeding, dwelling, and escape behaviour of benthic organisms

137
Q

What is the importance of stratigraphy?

A

Archive earths history, which only sedimentary rocks archive

138
Q

What are the four types of sedimentary basin?

A

Foreland basin
Rift basin
Intercontinental basin
Passive margin basin

139
Q

What are the four types of sedimentary basin?

A

Foreland basin
Rift basin
Intercontinental basin
Passive margin basin

140
Q

How are foreland basins formed?

A

Weight of a mountain belt pushes down the crusts surface

141
Q

How are rift basins formed?

A

Downward slip on faults produces narrow troughs

142
Q

How are intercontinental basins formed?

A

Basin in the interior of a continent, perhaps over an old rift.

143
Q

How do passive margin basins form?

A

Subsidence occurs over thinned crust at the edge of an ocean basin

144
Q

What controls accommodation space?

A

Global sea level change
Sea floor (tectonic uplift/subsidence)
Changes in rate of sediment accumulation

145
Q

What is transgression?

A

Flooding due to sea level rise
Sediment belts shift landward, strata deepen upwards

146
Q

What is retrogradation?

A

Linked to transgression
Process of environment shifting backwards

147
Q

What is regression?

A

Exposure due to sea level fall
Depositional belts shift seaward, strata shallow upwards

148
Q

What is progradation?

A

Environments shifting seaward
Linked to regression

149
Q

What is Walther’s law?

A

Beds that occur in conformable vertical successions of strata were deposited in laterally adjacent environments

150
Q

What happens during uplift and subsidence in terms of erosion and deposition?

A

Uplift of mountains leads to downcutting of rivers and leads to lots of erosion
Subsidence leads to lots of deposition and leads to increased accommodation space

151
Q

What is a parasequence?

A

Small scale units resulting from a small amplitude, short term oscillation in the balance between sediment supply and accommodation space

152
Q

What is a flooding surface?

A

A transgression event marked by a distinct surface which caps the facies succession

153
Q

What is the facies model for a meandering river?

A

From top to bottom:
Floodplain - vertical accretion - caliche nodules, desiccation cracks, root traces
Point bar- lateral accretion - ripple cross lamination, trough cross lamination

154
Q

What is the facies model for braided river?

A

Coarser cross bedding ie pebbles
Point bar planar cross lamination
Characteristic of glaciation, or tectonically active areas

155
Q

What is the facies model of a delta?

A

Sandstone unit after sandstone unit with a coal horizon
Plant fragments may be present

156
Q

What is the facies model of a shoreline?

A

Hummocky and Swaley cross stratification
Storm deposits
2D planar cross bedding associated with beaches

157
Q

What is the facies model of a turbidite?

A

From top to bottom:
- pelagic and hemipelagic mud
- laminated silts
- cross laminated sands, ripples
- parallel laminated sands
- massive sand and granules, rapidly deposited under upper flow regime
- scoured base

158
Q

What is an aggradational sequence?

A

Where there is no change in the parasequence, vertical

159
Q

How do you identify flooding sequences?

A

Sharp contacts
Bioturbation

160
Q

What is chemostratigraphy?

A

Study of the chemical variations within sedimentary sequences to determine stratigraphic relationships

161
Q

What would typify the deposit of an idealised sediment gravity flow in which the mechanism for gran suspension was turbulence?

A

A decimetre thick graded bed

162
Q

In ppl, what is it called if you rotate the stage and the mineral changes colour?

A

Pleochroism

163
Q

What pleochroism is present in biotite mica?

A

Deep brown, straw yellow

164
Q

How do you describe relief?

A

High
Moderate
Low

165
Q

What is fracture?

A

Curved breaks or lines of weakness within mineral grains
Ie olivine and garnet

166
Q

What is cleavage?

A

Straight planar lines of weakness which relate to weakly bound directions

167
Q

What is the fancy word for angular crystals and rounded crystals, and in between?

A

Angular - euhederal
Middle - subhedral
Rounded p- anhedral

ES2001 (9 decks)

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