Folds

Question 1

Cylindrical folds:

Answer 1

progressive curvature, hinge zone would wrap around a cylinder

Question 2

Kink/chevron folds:

Answer 2

sharp hinge zones, localized, planar limbs

Question 3

Symmetrical folds:

Answer 3

limbs of same length and dip

Question 4

Asymmetrical folds:

Answer 4

limbs of different lengths and dips

Question 5

Fold vergence:

Answer 5

Direction fold is leaning, or direction of short, steep limb. Needs to be evaluated in fold profile plane

Question 6

Parallel folds

Answer 6

folds marked by uniform thickness

Question 7

Similar folds

Answer 7

thicker near hinge, thinner towards limbs, same geometry between bedding

Question 8

Synforms:

Answer 8

a fold that is concave up

Question 9

Antiforms:

Answer 9

a fold that is convex up

Question 10

Monoclines:

Answer 10

relatively flat lower layer, steep incline over a short distance, into a flat upper layer (2 hinges, 1 anticline and 1 syncline) connected by middle limb, extensive trend (150km+ in length), Colorado Plateau

Question 11

Hinge lines:

Answer 11

like a crease down the middle, or points on the surface of the fold with maximum curvature, measured by trend and plunge

Question 12

Hinge zones:

Answer 12

location on a fold with maximum curvature

Question 13

Limbs:

Answer 13

flanks of a fold

Question 14

Axial planes:

Answer 14

an axial surface that is planar

Question 15

Axial surfaces:

Answer 15

passes through all points of maximum curvature in all stacked layers, irregularly curved fold, described in terms of strike and dip

Question 16

Axial traces:

Answer 16

line that passes through successive hinge points in stacked folded surfaces, OR GENERALLY a line of intersection of the plane with any other surface

Question 17

Fold profile planes:

Answer 17

plane perpendicular to hinge

Question 18

Name some types of folds

Answer 18

chevron, circular, cuspate, elliptical, box, teardrop

Question 19

Inter-limb angle:

Answer 19

describes the fold tightness of a limb (internal angle between limbs)

Question 20

Gentle inter limb angle

Answer 20

• Gentle 170–90°

Question 21

open inter limb angle

Answer 21

• Open 90–30°

Question 22

tight inter limb angle

Answer 22

• Tight 30–10°

Question 23

isoclinal

Answer 23

• Isoclinal 10–0°

Question 24

Class 1A

Answer 24

Parallel, inner arc curve > outer arc curve, layer thickness of hinge > layer thickness of limbs

Question 25

Class 1B

Answer 25

Parallel, inner arc curve > outer arc curve, uniform layer thickness

Question 26

Class 1C

Answer 26

between parallel and similar folds

Question 27

Class 2

Answer 27

similar fold, inner arc curve = outer arc curve

Question 28

Class 3

Answer 28

similar folds, outer arc curve > inner arc curve