Geology 3120 - Describing Folds

Geology 3120 - Geology 3120 - Describing FoldsDescribing Folds

OutlineOutline

• Terms For Describing Folds

• Parasitic Folds

• Vergence

Initial Layer CakeInitial Layer Cake

Direction of ClosingDirection of Closing

inflection point - change in curvature (i.e., concave to convex)

inflection point

Convexity and Age of Beds Convexity and Age of Beds

• Anticline - a fold that is convex in the direction of youngest bedsAnticline - a fold that is convex in the direction of youngest beds

• Syncline - a fold that is convex in the direction of oldest bedsSyncline - a fold that is convex in the direction of oldest beds

Determining the Fold Axial Determining the Fold Axial

SurfaceSurface

Determining the Fold Axial Determining the Fold Axial

SurfaceSurface

Profile Plane of a FoldProfile Plane of a Fold

Interlimb AngleInterlimb Angle

Five Categories:Five Categories:

Gentle Gentle

OpenOpen

CloseClose

TightTight

IsoclinalIsoclinal

Angularity of Interlimb Angularity of Interlimb

AngleAngle

Cylindrical or Non-Cylindrical Cylindrical or Non-Cylindrical

FoldsFolds

non-cylindrical foldnon-cylindrical fold

Attitude of Axial SurfaceAttitude of Axial Surface

Fold SymmetryFold Symmetry

Fold HarmonicsFold Harmonics

Parasitic FoldsParasitic Folds

Parasitic foldsParasitic folds

always vergealways verge

towards anticlinestowards anticlines

and away from and away from

synclinessynclines

Parasitic FoldsParasitic Folds

Parasitic folds verge towards anticlines and away from synclinesParasitic folds verge towards anticlines and away from synclines

Parasitic folds verge towards anticlines and away from synclinesParasitic folds verge towards anticlines and away from synclines

FacingFacing

VergenceVergence

VergenceVergence

ReferencesReferences

Most figures from:Most figures from:

http://earth.leeds.ac.uk/folds/describing/folddesc.htm