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Classification of folds

Short answer

Based on convexity: anticline (arches upward), syncline (trough), monocline (step). Based on axial plane: symmetrical (vertical), asymmetrical, overturned (both limbs dip same way), recumbent (horizontal), isoclinal (parallel limbs).

Describe the classification of folds (on the basis of convexity / position of axial plane).

Folds are classified on several bases. The two bases mentioned are explained here.

On the basis of convexity (upward or downward)

  1. Anticline - an upward arch; limbs dip away from the axis and older beds are in the core.
  2. Syncline - a downward trough; limbs dip towards the axis and younger beds are in the core.
  3. Monocline - a local steepening in otherwise gently dipping beds, a single step.

On the basis of position of the axial plane

FoldAxial planeLimbs
Symmetrical (upright)VerticalDip at equal angles in opposite directions
AsymmetricalInclinedDip at unequal angles
OverturnedInclined stronglyBoth limbs dip in the same direction, one limb inverted
RecumbentHorizontal (or nearly)Limbs lie horizontal, one above the other
IsoclinalAnyLimbs parallel to each other
 Symmetrical   Asymmetrical   Overturned   Recumbent
    /\             /\           /\          ____
   /  \           /  \         /  \_       /____\_
  /    \         /    \       /  /  /      \_____/
 vertical axial  inclined    both limbs     horizontal
 plane           axial       dip same way   axial plane

Other bases: plunge (plunging, non-plunging), shape (chevron, box, conical).

✓ Answer checked by Claude Opus 5.5 (high effort)

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