Fold Classifications

Question 1

What are the common fold classifications

Answer 1

• Sense of curvature
• Symmetry and vergence
• Dip of axial surface and plunge of hinge line
• Interlimb angle

Question 2

fold classification according to the sense of curvature

Answer 2

Antiform and Synform

Question 3

Fold that limbs dip down and away from the hinge zone; convex upward.

Answer 3

Antiform

Question 4

Fold with a hinge zone is at the bottom (outlining a valley): convex downward.

Answer 4

Synform

Question 5

Megascopic, regional-scale forms of antifoms and synforms

Answer 5

Anticlinorium and synclinorium

Question 6

folds with rock layers that get younger away the core. (older rocks in core)

Answer 6

Anticline

Question 7

folds with rock layers that get younger towards from the core (younger rocks in core)

Answer 7

Syncline

Question 8

folds with rock layers that get younger away from the core BUT has the shape of a synform.

Answer 8

Synformal anticline

Question 9

Folds with rock layers get younger towards the core BUT has the shape of an antiform.

Answer 9

Antiformal anticline

Question 10

fold classification according to symmetry and vergence

Answer 10

• Symmetric folds
• Asymmetric folds
• Parasitic folds (Z, M, S Folds)

Question 11

the enveloping surface and axial
surface are perpendicular to each other.

Answer 11

Symmetric folds

Question 12

the enveloping surface and axial surface are not perpendicular to each other.

Answer 12

Asymmetric folds

Question 13

Large folds commonly have smaller-scale folds in their limbs and crest. They are referred to as _______?

Answer 13

Parasitic folds

Question 14

flexure of layered rock where slip occurs between rock layers

Answer 14

Flexural slip

Question 15

Parasitic fold with a clockwise vergence

Answer 15

Z-folds

Question 16

Parasitic fold with an anticlockwise vergence

Answer 16

S-folds

Question 17

What are special cases of folded or tilted beds

Answer 17

Monoclinal fold/ monoclines
Homoclinal fold/ homoclines

Question 18

A special case of fold structures with only one tilted limb; the beds on either side of the tilted limb are horizontal.

Answer 18

Monoclinal fold/ monoclines

Question 19

A special case of fold structures wherein the layers dip uniformly in a single direction having the same general inclination

Answer 19

Homoclinal fold/ homoclines

Question 20

Fold classification according to the dip of axial surface

Answer 20

1. Upright -70°- 90°
2. Inclined - 10°- 70°
3. Recumbent - 0°- 10°

Question 21

Fold classification according to the plunge of hinge line

Answer 21

1. Horizontal (to sub-horizontal) -0°-10°
2. Plunging - 10°-80°
3. Vertical (to sub-vertical) - 80°-90°

Question 22

angle enclosed by its two limbs.

Answer 22

Interlimb angle

Question 23

Fold classification according to its Interlimb angle

Answer 23

• Gentle (180-120°)
• Open (120-70°)
• Tight (70-30°)
• Isoclinal (30-0°)

Question 24

Th interlimb angle reflects the amount of strain involved during the folding. Hence, the smaller the interlimb angle = _____________?

Answer 24

greater intensity of folding.