Definitions

anticline - fold that is convex in the direction of the youngest beds

antiform- "a fold that is a fold that points up": convex upward

syncline- fold that is concave in the direction of the youngest beds

synform - "a fold that points down": concave upward

overturned folds: when one limb is overturned, i.e. younger rocks are underneath

fold limb: flank of a fold on either side of a fold

fold hinge: zone of maximum curvature

crest: highest point of a folded surface

crest line: collection of crests along on a common folded surface

inflection points: Location on a fold where curved limb segments of opposing convexity meet.

hingeline: collection of hinge points along a single folded surface

axial surface: surface that passes through the hingelines of various folded layers in a sequence (axial trace is the intersecting of the axial surface with any other surface, e.g. outcrop)

fold axis is a line that when moved parallel to itself orchestrates a fold

cylindrical folds are folds that possess fold axes; every part of the folded surface is oriented such that it contains a line whose orientation is identical to that of the hingeline

Readings

Ch. 7 Folds

Lecture

Folds are classified according to various schemes which permit later interpretation.

TIGHTNESS: gentle, open, tight, isoclinal//based on interlimb angles

SIZE

SYMMETRY: asymmetrical folds have limbs of different lengths.

LAYER THICKNESS: concentric or parallel folds: individual layers maintain a constant thickness similar folds display significant thickening in the hinge and significant thinning on the limbs

interlimb angle : For a given folded surface, this angle is the angle between the flanks

bisecting surface: Surface which splits the interlimb angle in half

p-diagram: stereographic plot of the poles of folded surfaces

b-diagram: stereographic plot of the great circles folded surfaces.