Lecture 4 - Folding

Question 1

What is the vergence of a fold?

Answer 1

The direction in which the axial fold is tilting

Question 2

Describe box folds, kink folds and ptygmatic folds

Answer 2

a box fold is a special form of a kink fold, also forms in very anisotropic material kink-folds form in very anisotropic material (thin layers or cleavage) ptygmatic folds form in very soft material, similar to the mixing of two fluids (milk in coffee…)

Question 3

Different fold styles come with different fold mechanisms. What is the difference between parallel folds and similar folds?

Answer 3

Parallel folds beds stay constant thickness, bed shape changes Similar folds thickening at the hinge zone, top and base of beds identical

Question 4

What is a flexural flow?

Answer 4

Beds are sheared, most of the time these are soft (marbles, clay or silt layers). Thickness parallel to the axial surface of the fold remains constant.

Question 5

What is a flexural slip?

Answer 5

Beds slip past each other. Thickness of beds is not altered. Beds often show indicators of slip -> slickenlines or fibres.

Question 6

Where does cleavage form?

Answer 6

Parallel to the fold axial plane.

Question 7

What faults are compressional and extensional environments associated with?

Answer 7

extensional = normal Compresional = reverse

Question 8

Describe the formation of a salt dome

Answer 8

In the begining during sedimentation the salt has a higher density than the non-compacted rocks. Once the rocks compact they will become more dense than the salt and the salt wants to move upwards.