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Winter 2022 > EARTH 238 > Flashcards

EARTH 238 Flashcards

(127 cards)

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1
Q

What are younging indicators?

A

Primary structures which indicate the relative ages of different sedimentary beds

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2
Q

What is graded bedding?

A

Systematic variation in grain size within a bed - coarser at the bottom (heavier), finer at the top (lighter)

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3
Q

What is sliding?

A

Entire sedimentary layer/unit remains intact while ‘sliding’ down a slope

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4
Q

What is slumping?

A

Sedimentary layer/unit breaks up into smaller pieces while sliding down a slope

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5
Q

What is flow?

A

Sedimentary layer/unit breaks up into fine sediments, causing a turbidity current when met with water

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6
Q

What is shelf-edge failure?

A

Transition from slump to turbidity current

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7
Q

How do turbidites form?

A

Deposition of sediments carried by turbidity current

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8
Q

What are cross beds?

A

Surfaces within a thicker, master bed that are oblique to overall bounding surfaces of the master bed

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9
Q

How is the younging indicator determined from cross beds?

A

Cross-cutting relationship gives younging direction when erosion occurs as new bedding forms - asymptotic relationship

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10
Q

What are flute casts?

A

Asymmetric troughs formed by vortices (mini-tornadoes) within the fluid that dig into the unconsolidated substrate.

Deeper at upstream end (stronger vortex), gets shallower and wider at downstream end (weaker vortex)

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11
Q

What are ripple marks?

A

Ridges and valleys on the surface of a bed formed due to fluid flow.

If current flows back and forth - symmetric ripples; if current flows one direction - asymmetric ripples

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12
Q

How do load structures form

A

Occur at contact between sand layer and mud layer - sand ‘sinks’ into mud layer as it is heavier, mud injected up into the sand (forms a flame shape).

Sand may detach, forming a pillow structure isolated from original plane

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13
Q

What are dewatering structures?

A

Sediments oversaturated with water and under pressure. When disturbed by an event, the water wants to ‘get out’

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14
Q

What are sand volcanoes?

A

Dewatering structure where water is trapped under a lot of pressure, but rises up, bringing sand with it. Creates a small mound where water comes out

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15
Q

What are clastic dykes?

A

Dykes formed between two sedimentary rock layers because faults between a rock layer may allow water to pass through (bringing sediment with it)

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16
Q

What is a depositional contact?

A

Younger sedimentary rocks laid above older rocks, upwards younging direction

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17
Q

What is a fault contact?

A

Contact between two rock units is a fault

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18
Q

What is an intrusive contact?

A

Magma intrudes into an existing body of rock

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19
Q

What is an angular unconformity?

A

Strata below unconformity have a different attitude than strata above unconformity

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20
Q

What is a disconformity?

A

Beds of rock sequence above and below unconformity are roughly parallel, but there is a measurable age difference between the two sequences

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21
Q

What is a nonconformity?

A

Unconformity at which beds are deposited on a foundation of older crystalline rocks (either plutonic or metamorphic)

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22
Q

What is diagenesis?

A

All changes in texture, composition, and properties occurring in a sedimentary rock after being deposited as a sediment up until the time it is examined

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23
Q

What are ‘pinch and swell’ structures and how do they form?

A

Structures observed where sedimentary beds vary in thickness due to differential compaction

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24
Q

What is pressure solution?

A

Process where soluble grains preferentially dissolve along faces at which stress is highest

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25
What are stylolites?
Serrate surfaces at which minerals have been removed by pressure dissolution, decreasing the total volume of rock. Identified due to insoluble minerals like clays, pyrite, and oxides.
26
What are penecontemporaneous folds and faults?
Re-sedimentation of loosely held sediments that slump, fold, and fault intraformationally/chaotically
27
What are batholiths?
Huge bloblike intrusions; usually a composite of many plutons
28
What are dykes?
Sheet intrusions, crosscut stratification in a stratified sequence, or roughly vertical in a unstratified sequence
29
What is a hypabyssal?
Intrusion formed in upper few km of Earth's crust that cools relatively quickly and so is fine-grained
30
What is a laccolith?
A type of hypabyssal intrusion concordant with strata at its base, bows up overlying strata into a dome or arch
31
What is a pluton?
A moderate-sized bloblike intrusion (several km in diameter) sometimes used to generally refer to any intrusion regardness of shape or size
32
What is a sill?
Sheet intrusion that parallels pre-existing stratification in a stratified sequence (or roughly sub-horizontal in an unstratified sequence)
33
What is a stock?
A small bloblike intrusion (few km in diameter)
34
What is the difference between homogeneous and heterogeneous deformation?
Homogeneous - straight lines remain straight, parallel lines remain parallel, circles become ellipses, spheres become ellipsoids Heterogeneous - not all straight lines remain straight, not all parallel lines remain parallel
35
What is strain?
Concerned with a change in shape of a body and simply described the final shape in terms of the initial shape
36
What is general strain in terms of sigma?
S1 > S2 > S3
37
What is axial symmetrical extension in terms of sigma?
S1 > S2 = S3
38
What is axial symmetrical shortening in terms of sigma?
S1 = S2 > S3
39
What is plane strain in terms of sigma?
S2 = 1
40
What is simple shortening in terms of sigma?
S1 = S2 = 1
41
What is pure shear?
General or plane strain in which lines of particles that are parallel to principal axes have the same orientation throughout deformation Same as coaxial deformation
42
What is simple shear?
Plane strain in which a single family of parallel material planes remain undistorted and parallel to the family of planes throughout deformation. Involves strain and rotation Is non-coaxial deformation (but not all non-coaxial deformation is simple shear)
43
What are body forces?
Result from action of a field at every point within a body
44
What are surface forces?
Act only on surfaces, operate across contact area between adjacent parts of a body
45
What is stress?
Force per unit area Stress = F/A
46
How to calculate mean stress?
(S1+S2+S3)/3
47
How to calculate deviatoric stress?
Total stress - mean stress
48
What is isotropic material
Material that has the same mechanical properties in all directions, so reacts to stress identically regardless of directions
49
What is elastic strain behavior?
Strain takes place instantaneously once stress is applied or removed - response instantaneous and strain is recoverable
50
What is anelastic strain behavior?
Strain is recoverable, response is not instantaneous
51
What is viscous strain behavior?
Strain is permanent and not recoverable
52
What is plastic behavior?
Does not deform if stress is below a critical value, cannot maintain stress above a critical value (above which it will permanently deform)
53
What is brittle behavior?
Rocks deform by developing marked discontinuities across which there is often a break in cohesion
54
What is ductile behavior?
Rocks deform by distributing the strain in a smoothly varying manner throughout the deforming mass
55
Which factors affect brittle or ductile behavior?
Temperature, confining pressure, material, pore-fluid pressure, strain rate
56
What is homologous temperature?
The ratio of a material's temperature to its melting temperature (on a Kelvin scale)
57
What is competence?
Describes contrast in strength (relative) - more competent materials can support a higher deviatoric stress
58
What is cataclasis?
Fracture and crushing of grains, coupled with frictional sliding along grain contacts and grain rotation
59
What is the difference between veins and dykes/sills?
Veins are fractures filled with minerals, dykes/sills are fractures filled with magmatic rocks
60
What is a mode I fracture?
"Opening mode" Tensile stress, normal to plane of crack
61
What is a mode II fracture?
"Sliding mode" Shear stress acts parallel to plane of crack and perpendicular to crack front
62
What is a mode III fracture?
"Tearing mode" Shear stress acts parallel to plane of crack and parallel to crack front
63
What are joints?
Relatively planar fractures, form when tensile strength of stressed rocks is exceeded. Form parallel to S1 and S2, perpendicular to S3
64
What are systematic joints?
Planar, parallel, and evenly spaced - obvious spatial relationship
65
What are non-systematic joints?
Irregular in form, spacing, and orientation - no obvious spatial relationship
66
What is a joint set?
Group of systematic joints of common origin, often approximately parallel and equally spaced
67
What is a joint system?
Two or more sets of joints appearing together and usually intersecting from a joint system
68
What is an orthogonal joint system?
Two sets of joints that are perpendicular to each other
69
What is a conjugate joint system?
Two sets of joints with a dihedral angle of significantly less than 90 degrees (i.e., 30-60)
70
What is a plumose/plume structure?
Feather-like feature on the surface of some joints
71
How do columnar joints form?
Joints split rocks into hexagonal columns due to cooling and contraction
72
How do sheeting/exfoliation joints form?
Form due to erosional unloading on isotropic rocks such as sets of flat-lying joints in granitic rocks
73
How do pinnate fractures form?
Occur in vicinity of a fault plane and intersect the fault in an acute angle pointing in the direction of relative movement of the block containing the pinnate fractures
74
How do veins form?
Minerals (i.e., quartz and calcite) are precipitated from solution and fill a fracture
75
What is the difference between planar systematic veins and stockwork veins?
Planar systematic veins are planar, mutually parallel, regularly spaced, and spatially controlled by a systematic joint set Stockwork veins are irregular veins that occur in a pervasively fractured rock.
76
What is the difference between dilational and non-dilational veins
In dilational veins, the crack opens as a direct result of the formation of the vein causing a volume change. In non-dilational veins, the vein material replaces the existing material that was in the crack beforehand (no volume change)
77
How do veins form in pure shear?
Straight veins, stretched so that they remain straight
78
How do veins form in simple shear?
Veins form oblique to overall orientation, rotate due to simple shear, continue to form sigmoidally (en echelon veins)
79
What is the difference between blocky and fibrous veins?
In blocky veins, crystals are roughly equant, growing in an open cavity. In fibrous veins, crystals are very long relative to width
80
What is the crack-seal mechanism of fibrous vein formation?
Rock contains pore fluids (which contain dissolved minerals) Crack develops, fills with fluids Fluid pressure in crack is less than pores in surrounding rock Minerals precipitate, forming mineral fibres
81
What is the difference between syntaxial and antitaxial veins
Syntaxial veins have a vein fill the same composition as wall rock, vein fibres nucleate on surface of grains in the wall rock and grow inwards to meet at the median line Antitaxial veins have a vein fill that is a different composition as the wall rock, increments of cracking at contact between vein and wall rock
82
What is a hanging wall?
Block above non-vertical fault
83
What is a foot wall?
Block below nonvertical fault
84
What is a fault zone?
Tabular region containing many parallel faults - brittle
85
What is a shear zone?
Zone across which blocks of rock have been displaced in a fault-like manner but without development of visible faults - ductile
86
What is a listric fault?
Dip decreasing. progressively with depth
87
What is a strike-slip fault?
Net slip vector approximately parallel to strike of fault
88
What is a dip-slip fault?
Net slip vector approximately parallels the dip line of the fault
89
What is an oblique slip fault?
Has both strike and dip-slip components
90
What is a transcurrent/wrench fault?
Strike-slip fault with very steep to vertical dips
91
What is a thrust fault?
Low angle reverse fault
92
What is a thrust sheet?
Regional package of rocks above a thrust that has moved along the thrust
93
What is a nappe?
A thrust sheet that has moved more than 10 km relative to the footwall
94
What is an allochthon?
A regional thrust sheet that has moved a great distance
95
What is an autochthon?
Rocks (below a regional thrust sheet) that retain their original location
96
What is a window (fenster)?
Area of autochthonous rocks surrounded by allochthonous rocks
97
What is a klippe?
Isolated allochthonous rocks
98
What is a restraining bed?
Due to curvature of fault, walls are pushed against each other
99
What is a releasing bed?
Due to curvature of fault, the walls are pushed away from each other leaving a void. Can form a basin on a large scale, or veins on a small scale
100
What is an extensional fault?
Fault that results in lengthening of a layer
101
What is a contractional fault?
Fault that results in the shortening of a layer
102
At what depth in the Earth is breccia/gouge formed?
0-5 km deep
103
At what depth in the Earth is cataclastite formed?
5-10 km deep
104
At what depth in the Earth is mylonite formed?
10-15 km deep (brittle-ductile transition)
105
What are slickensides?
Smooth or shiny shear surfaces in rocks, commonly display striations
106
What are striations?
Scratches/grooves parallel to movement directions, or form by brittle-ductile transitional processes
107
What is slickenfiber
Mineral fibres growing during fault movement, showing direction of displacement
108
What is the difference between a cylindrical and a non-cylindrical fold?
Fold axis is straight in a cylindrical fold, is not in a non-cylindrical fold
109
What environment is a sheath fold characteristic of
High strain shearing
110
What is the difference between antiform and synform?
Antiform - curving down (n) shape | Synform - curving up (u) shape
111
What is the difference between anti/synform and anti/syncline?
Anti/synform only refers to shape, anti/syncline also refers to age relationship
112
What is the fold profile plane?
A frame of reference perpendicular to the fold
113
What is the interlimb angle of an isoclinal fold?
0-30 degrees
114
What is the interlimb angle of a tight fold?
70-30 degrees
115
What is the interlimb angle of an open fold?
120-70 degrees
116
What is the interlimb angle of a gentle fold?
180-120 degrees
117
What is the difference between kink folds and chevron folds?
Kink folds have one limb that is particularly longer/shorter than the other; chevron folds have limbs that are approximately the same length but very angular
118
What is the difference between harmonic and disharmonic folds?
Harmonic folds have approximately the same interlimb angle for each fold layer, disharmonic folds do not
119
What is the difference between parallel and similar folds?
Parallel folds have a true thickness equivalent throughout the layer in the fold; similar folds have an apparent thickness parallel to axial plane that is the same throughout the layer in the fold
120
What are dip isogons?
Lines joining points of equal dip on the upper and lower boundary of a folded layer
121
What fold class are convergent dip isogons associated with?
Class 1
122
What fold class are parallel dip isogons associated with?
Class 2
123
What fold class are divergent dip isogons associated with?
Class 3
124
What are parasitic folds?
Smaller folds occurring on the limb or in the fold closure of larger folds
125
What fold geometry is associated with type 1 fold interface pattern?
Dome and basin
126
What fold geometry is associated with type 2 fold interface pattern?
Mushroom
127
What fold geometry is associated with type 3 fold interface pattern?
Refolded

Winter 2022 (3 decks)

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