Prepared byPrepared by

Azhar MahmoodAzhar MahmoodTopicTopic

Fold their geometry and Fold their geometry and classif icationclassif ication

Fold DefinitionFold Definition

►FoldsFolds are wave-like structures that result are wave-like structures that result from deformation of bedding, foliation, or from deformation of bedding, foliation, or other originally planar surfaces in rocks.other originally planar surfaces in rocks.

Geometry of FoldGeometry of Fold

► • • HingeHinge : points of maximum curvature within a single: points of maximum curvature within a single► folded surface.folded surface.► • • AxisAxis : a line when moved parallel to itself “sweeps out” a: a line when moved parallel to itself “sweeps out” a► folded surface. The fold axis and fold hinge line have thefolded surface. The fold axis and fold hinge line have the► same attitude.same attitude.► • • Axial Plane or SurfaceAxial Plane or Surface : the plane or surface defined by: the plane or surface defined by► connecting fold hinge lines in multiple folded surfacesconnecting fold hinge lines in multiple folded surfaces► • • Inf lect ion pointInf lect ion point : a point on a folded surface where the: a point on a folded surface where the► curvature changes direction. This is half the distancecurvature changes direction. This is half the distance► between hinge points.between hinge points.

Geometry of FoldsGeometry of Folds►CrestCrest – The highest point on the cross – The highest point on the cross

section of a foldsection of a fold►TroughTrough – The lowest point on the cross – The lowest point on the cross

section of a foldsection of a fold►LimbsLimbs – The straighter portion of the – The straighter portion of the

fold connecting the hinge zonesfold connecting the hinge zones►Hinge ZonesHinge Zones – Exhibit the greatest – Exhibit the greatest

curvature of a foldcurvature of a fold

Geometry of FoldsGeometry of Folds

Geometry of FoldsGeometry of Folds►Hinge LineHinge Line – The line joining points – The line joining points

of greatest curvature on a folded of greatest curvature on a folded surfacesurface

►Axial SurfaceAxial Surface – When many hinge – When many hinge lines (from multiple folded lines (from multiple folded surfaces) connect forming a planesurfaces) connect forming a plane

►PlungePlunge – When the fold hinge is – When the fold hinge is inclined to the horizontalinclined to the horizontal

Geometry of FoldsGeometry of Folds►WavelengthWavelength – The distance between – The distance between

subsequent crests or troughssubsequent crests or troughs►AmplitudeAmplitude – Half the distance from a – Half the distance from a

crest to the subsequent troughcrest to the subsequent trough►VergenceVergence – The direction of leaning of – The direction of leaning of

the axial surfacethe axial surface

Geometry of FoldsGeometry of Folds►First-Order FoldsFirst-Order Folds – The master (largest) – The master (largest)

foldfold►Second-Order FoldsSecond-Order Folds – Smaller folds on – Smaller folds on

the flanks of first-order foldsthe flanks of first-order folds►Enveloping SurfaceEnveloping Surface – Enables the – Enables the

relation of small to large scale foldsrelation of small to large scale folds

Fold ClassificationFold Classification

►General ClassificationGeneral Classification►Morphological ClassificationMorphological Classification►Geometric ClassificationGeometric Classification►Special ClassificationSpecial Classification

General ClassificationGeneral Classification

Kinds of FoldsKinds of Folds►AnticlineAnticline – A folds that is concave – A folds that is concave

towards older rocks in its centertowards older rocks in its center►AntiformAntiform – A fold that is concave – A fold that is concave

downwarddownward►SynclineSyncline – A folds that is concave – A folds that is concave

towards younger rocks in its centertowards younger rocks in its center►SynformSynform – A folds that is concave upward – A folds that is concave upward►DomeDome – An antiform where bedding dips – An antiform where bedding dips

away from the central pointaway from the central point►BasinBasin – A synform where bedding dips – A synform where bedding dips

towards a central pointtowards a central point

►Antiformal SynclineAntiformal SynclineHave a syncline character Have a syncline character Younger rock in core Younger rock in core Older rock on limbOlder rock on limbSyncformal AnticlineSyncformal AnticlineHave a anticline characterHave a anticline characterYounger rock on the limbYounger rock on the limbOlder rock in coreOlder rock in core

►DomesDomesHalf cut structure of circle Dip away from Half cut structure of circle Dip away from

center,convex upwardcenter,convex upwardExample. Salt forms,Doms structureExample. Salt forms,Doms structure►BasinBasinDip toward centerDip toward centerThese structure occur on regional These structure occur on regional

level,convex downwadlevel,convex downwad

Kinds of FoldsKinds of Folds

ClassificationClassification►SyntaxisSyntaxisIt is antiformal structure convex toward the It is antiformal structure convex toward the

interlad and concave toward the forelandinterlad and concave toward the forelandHomoclineHomocline Have uniformaly limbs which dip is same Have uniformaly limbs which dip is same

direction , regional folddirection , regional foldMonoclineMonocline Both limbs sometime parallal and some Both limbs sometime parallal and some

time gental to steeptime gental to steep

Overturned FoldsOverturned Folds

►• • Overturned folds possess an overturned Overturned folds possess an overturned limb- the limb must belimb- the limb must be

► rotated more than 90° to bring it back to its rotated more than 90° to bring it back to its original positionoriginal position

►• • Note that the overturned limb dips steeper Note that the overturned limb dips steeper than the axial planarthan the axial planar

►cleavagecleavage

Recumbent FoldRecumbent Fold► This type of fold is This type of fold is

compressed so much that compressed so much that it is no longer vertical. it is no longer vertical.

► There is a large extent of There is a large extent of overlapping and it can overlapping and it can take the form of an “s”.take the form of an “s”.

► To the right is a diagram To the right is a diagram that shows the process of that shows the process of recumbent folding.recumbent folding.

►Morphological ClassificationMorphological Classification

Chervan FoldChervan Fold

►ChevronChevron and and Kink FoldsKink Folds – Have straight – Have straight limbs and sharp angular hingeslimbs and sharp angular hinges

Hormonic FoldHormonic Fold

►Hormonic FoldHormonic Fold► A fold which maintains its geometric form, A fold which maintains its geometric form,

integral wavelength, and symmetry integral wavelength, and symmetry throughout a sequence of layersthroughout a sequence of layers

►Disharmonic FoldsDisharmonic Folds – Shape or wavelength – Shape or wavelength changes from one layer to anotherchanges from one layer to another

Box FoldBox Fold

►Crust flate Trough also flateCrust flate Trough also flate►Having two hingesHaving two hinges

Fan foldFan fold►Fan shape structureFan shape structure►Both limbs are over turnedBoth limbs are over turned►Having two FormsHaving two Forms►A.. Anticlinal Fan foldA.. Anticlinal Fan foldBoth limb over turn,older in core and younger Both limb over turn,older in core and younger

on limbson limbs►B.. Synclinal Fan foldB.. Synclinal Fan foldBoth limbs overturnd,younger in core older on Both limbs overturnd,younger in core older on

limbslimbs

Isoclined FoldIsoclined Fold

►Dip of limb is one either anti or syncline, Dip of limb is one either anti or syncline, axial plane is verticalaxial plane is vertical

TypesTypes Inclined Isoclined FoldInclined Isoclined Fold Horizental Isoclined fold Horizental Isoclined fold

Fold ClassificationFold Classification

Fold ClassificationFold Classification

Special ClassificationSpecial Classification

►Drag FoldDrag Fold►Fault Progated foldFault Progated fold►Fault bend foldFault bend fold►Detechment foldDetechment fold►Decollement foldDecollement fold

Drag FoldDrag Fold

►Related to faultRelated to fault►Z type fold are developed in thrust or Z type fold are developed in thrust or

reverse faultreverse fault►Z type shows thrusted, dip is north thrust or Z type shows thrusted, dip is north thrust or

reverse also called updip faultreverse also called updip fault

Fault Progated FoldFault Progated Fold

►Fold develop with faultFold develop with fault

Fault bend FoldFault bend Fold

►Formed as a result of the geometry of fault Formed as a result of the geometry of fault planeplane

Detechment FoldDetechment Fold

►Fold formed on the ramFold formed on the ram

Decollement FoldDecollement Fold

►Fold formed due to decollmaFold formed due to decollma

►Geometric FoldGeometric Fold

Symmetrical foldSymmetrical fold

► is a fold that is concave upward. An is a fold that is concave upward. An anticlinorium is a large anticline on which anticlinorium is a large anticline on which minor folds are superimposed, and a minor folds are superimposed, and a synclinorium is a large syncline on which synclinorium is a large syncline on which minor folds are superimposed. minor folds are superimposed. A A symmetrical foldsymmetrical fold  is one in which the  is one in which the axial plane is vertical. An aaxial plane is vertical. An asymmetrical symmetrical foldfold  is one in which the axial plane is  is one in which the axial plane is inclinedinclined

Asymmetrical foldAsymmetrical fold► .anticline on which minor folds are .anticline on which minor folds are

superimposed, and a synclinorium is a superimposed, and a synclinorium is a large syncline on which minor folds are large syncline on which minor folds are superimposed. A symmetrical fold is one superimposed. A symmetrical fold is one in which the axial plane is vertical. in which the axial plane is vertical. An An asymmetrical foldasymmetrical fold  is one in which  is one in which the axial plane is inclined. An overturned the axial plane is inclined. An overturned fold, or overfold, has the axial plane fold, or overfold, has the axial plane inclined to such an extent that the strata inclined to such an extent that the strata on one limb are overturnedon one limb are overturned

Asymmetrical foldAsymmetrical fold

UprightUpright Fold Fold

►Upright Upright folds (Have vertical, or nearly folds (Have vertical, or nearly vertical, axial surfacesvertical, axial surfaces