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Geology > Chapter 8 - Structural Geology > Flashcards

Chapter 8 - Structural Geology Flashcards

1
Q

What is a bed?

A

A unit of sedimentation which can vary considerably in thickness

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2
Q

What is a bedding plane?

A

Marks a break between beds. They represent a break in sedimentation, a change in the composition or grain size, or a change in colour of sediments

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3
Q

What is dip?

A

The maximum inclination of a bed measured from the horizontal using a clinometer

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4
Q

What is true dip?

A

The actual angle dip measured at right angles to the strike

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5
Q

What is apparent dip?

A

A dip that is measured to be less than the maximum inclination

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6
Q

What is strike?

A

The horizontal line on a bedding plane, measured as a bearing from north using a compass. It is at right angles to the dip.

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7
Q

What is a stratigraphic method?

A

A study of strata or layers of rock

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8
Q

What are the 6 laws of stratigraphy?

A
  • Law of superposition
  • Law of original horizontality
  • Law of cross-cutting relationships
  • Law of lateral continuity
  • Law of inclusion
  • Law of faunal sucession
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9
Q

What does the law of superposition mean?

A

Younger layers of rock sit atop older layers

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10
Q

What does the law of original horizontality mean?

A
  • Most sedimentary rocks are laid down horizontally
    —-> presumed if tilted moved from original horizontal position ( older )
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11
Q

What does the law of cross-cutting relationships mean?

A

Features which cut through rocks must be younger than the rocks they cut through

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12
Q

What does the law of lateral continuity mean?

A

Layers of rock are continous until they encounter other solid bodies that block their deposition or until they are acted upon by agents that appeared after deposition took place
——-> valleys

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13
Q

What does the law of inclusion mean?

A

Oldest rocks are inside younger rock
e.g Xenoliths/fossils

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14
Q

What does the law of faunal succession mean?

A

If fossils go extinct they cant be found in younger rocks

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15
Q

How can beds be different to eachother?

A
  • Colour
  • Grain size
  • Grain shape
  • Sorting
  • Composition
  • Thickness
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16
Q

How can colour vary in beds?

A
  • Major changes —-> red/green
  • Subtle changes —-> grey/brown
17
Q

How can grain size differ in beds?

A
  • Major changes —> fine clay/coarse pebbles
  • Minor changes —> fine/medium sand
18
Q

How can grain shape differ in beds?

A

-Angular/rounded

19
Q

How can sorting differ in beds?

A
  • Well/poorly sorted
20
Q

How can composition differ in beds?

A

Each bed will contIn different amounts of minerals and the cement/matrix will vary

21
Q

How can bed thickness differ in beds?

A

Thin = lamination
Thick = massive

22
Q

What is a fault?

A

Brittle fracture where there is displacement

23
Q

Characteristics of faults:

A

-Horizontal, vertical or combination
-Very common structures
-Areas of weakness where EQ takes place when stored stress is released
-cm—> km in length

24
Q

What are faults formed by?

A

Tension, compression or shear forces

25
Q

What direction are dip-slip faults?

A

Vertical

26
Q

What are the 4 dip-slip faults?

A
  • Normal faults
  • Gaben and horst
  • Reverse faults
  • Thrust fault
27
Q

Normal faults:

A
  • Dip-slip fault
  • Earth’s crust is being stretched
  • Crust lengthening
  • Clear gap in beds
  • Principle stress is vertical due to weight of overlying rocks
28
Q

Graben and horst:

A
  • Two normal faults face each other —> graben or rift valley is formed
  • Centre of the MOR and form the East African Rift Valley
  • Two normal faults fave away from each other —> horst is formed
29
Q

Reverse faults:

A
  • Compressional faults
  • Shortening of the Earth’s crust
  • Overlap in beds
  • Principal stress direction is horizontal
  • Near surface sue to less overlying rock
30
Q

Thrust fault:

A
  • Fault dip <45 degrees
  • Compressional forces
  • Associated with major fold mountain systems
  • Displacement measured in km
31
Q

What direction are strike slip faults?

A

Horizontal

32
Q

Strike-slip faults:

A
  • Vertical fault plane
  • Horizontal movement along fault (parallel to strike of fault plane)
  • Large scale structures —> large displacement
33
Q

3 types of strike-slip faults:

A
  • Tear
  • Dextral and sinistral
  • Transform
34
Q

Tear fault:

A
  • Result of shearing forces
    Example: Great Glen Fault, Highlands of Scotland
    —> 100km displacement from Caledonian Orogeny
35
Q

What direction does sinistral mean?

A

left

36
Q

What direction does dextral mean?

A

Right

Geology (4 decks)

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