Review
Definitions
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
FOLD CLASSIFICATION
Folds are classified according to various schemes which later permit interpretation.
TIGHTNESS: gentle, open, tight, isoclinal//based on interlimb angles
SIZE
SYMMETRY: asymmetrical folds have limbs of different lengths.
LAYER THICKNESS: concentric ore parallel folds: individual layers
maintain a constant thickness similar folds display significant thickening
in the hinge and significant thinning on the limbs