Deformation: Unconformities, Folds and Faults

Question 1

Define Stress

Answer 1

Forces applied to a rock

Question 2

Define Strain

Answer 2

The deformation caused by the stress

Question 3

Define Elastic Deformation

Answer 3

No permanent deformation, will recover after stress is removed

Question 4

Define Plastic (Ductile) Deformation

Answer 4

Permanent change in shape

Question 5

Define Fracture Point

Answer 5

When the rock starts to break

Question 6

Define Elastic Limit

Answer 6

Marks the start of permanent deformation

Question 7

Define Brittle Response

Answer 7

Yield strength of the material has been exceeded and the material fails in a brittle way

Question 8

What are four factor affecting stress and strain?

Answer 8

Temperature, Composition of rock/strength, Confining pressure, Strain rate

Question 9

Define Strike

Answer 9

Angle/direction of no dip

Question 10

Define True Dip

Answer 10

The maximum angle of dip a rock can have

Question 11

Define Dip Direction

Answer 11

The direction in which the rock is tilted

Question 12

Define Apparent Dip Direction

Answer 12

Any angle between 0 and maximum tilt

Question 13

Define Unconformity

Answer 13

A boundary that marks a break in deposition, a period of erosion

Question 14

What are five features providing evidence for the presence of an unconformity?

Answer 14

Erosional surface between two layers, Changes in dip amount and direction wither side of the U/C, Cross cutting relationships, Gap in fossil ages either side of U/C, Conglomerate above U/C

Question 15

What are the four types of unconformity?

Answer 15

Angular, Nonconformity, Paraconformity, Disconformity

Question 16

Define Nonconformity

Answer 16

Igneous/metamorphic underlying

Question 17

Define Paraconformity

Answer 17

Looks like no break in deposition but sequential fossils are missing

Question 18

Define Disconformity

Answer 18

Horizontal on either side with erosion surface

Question 19

Define Folding

Answer 19

Occurs when the compressional stresses exceed the yield strength of the rock, causing rock layers to change their attitude or dip

Question 20

What are the two main shapes of a fold?

Answer 20

Synform, Antiform

Question 21

Define Anticline

Answer 21

Upwards closing fold with the oldest rocks in the centre

Question 22

Define Synform

Answer 22

downward closing fold with the youngest rocks in the centre

Question 23

Define Fold Limb

Answer 23

Section of the fold between crest and trough

Question 24

Define Hinge

Answer 24

Line at which there is a change in dip direction, the most curved part of the fold

Question 25

Define Crest

Answer 25

Highest point on a fold

Question 26

Define Trough

Answer 26

Lowest point on a fold

Question 27

Define Axial Plane

Answer 27

A plane that joins all the hinges of all the beds

Question 28

Define Axial Planar Trace (APT)

Answer 28

Outcrop of the axial plane at the Earth’s surface

Question 29

What are the four attitudes of a fold?

Answer 29

Upright (70-90), Inclined (10-70), Overturned, Recumbent (0-10)

Question 30

What are the four types of interlimb angles?

Answer 30

Open (135-90), Tight (40-1), Isoclinal (0)

Question 31

Define Fault

Answer 31

A fracture in a rock along which there has been observable displacement

Question 32

Define Fault Plane

Answer 32

Plane where movement takes place

Question 33

Define Hanging Wall

Answer 33

Block above the fault plane

Question 34

Define Footwall

Answer 34

Block below the fault plane

Question 35

Define Throw

Answer 35

Vertical displacement

Question 36

Define Heave

Answer 36

Horizontal displacement

Question 37

Define Dip-Slip Fault

Answer 37

A fault that moves vertically

Question 38

Define Strike-Slip Fault

Answer 38

A fault that moves horizontally

Question 39

What are the three types of dip-slip fault?

Answer 39

Normal (tensional stress), Reverse (compressional stress), Thrust (compressional stress, less than 30 degrees)

Question 40

What are the two types of strike-slip fault?

Answer 40

Sinistral (move to left), Dextral (move to right)

Question 41

What stress is associated with strike-slip faults?

Answer 41

Shear stress

Question 42

What dip do faults usually have with a straight outcrop pattern?

Answer 42

90 degree

Question 43

The youngest rocks are…

Answer 43

Always on the downthrown side

Question 44

What does SWAN stand for?

Answer 44

Synclines are Wider on the downthrown side and Anticlines are Narrower