Classification Of Fold By,

Trishnangini Deka

Dpt. Of Applied Geology

Trishnangini Deka Bangalore

University.

Classification Of Fold Is Classified On The Basis

Of-Position of axial planeDegree of

compressionBehavior of depth Position of axisProfile of the outer

surfaceMode of occurenceMiscellaneous type

Posi t ion Of Axial Plane

Symmetrical foldsAsymmetrical foldRecumbent fold

Isoclinal foldConjugate fold

Box folds

A.SYMMETRICAL FOLD

A Fo l d e d S u r f a c e Fo rm s A S y m m e t r i c a l Fo l d I f I n P ro fi l e T h e S h a p e O n O n e S i d e O f A Fo l d I s T h e M i r ro r I m a g e O f T h e S h a p e O n T h e O t h e r S i d e A n d I f T h e Ad j a c e n t L i m b s A re I d e n t i c a l I n Le n g t h . B a s i c a l l y I t M a y B e A n t i c l i n e O r S y n c l i n e A n d W h e n C l a s s i fi e d A s S y m m e t r i c a l A n t i c l i n e O r S y n c l i n e .

SYMMETRICAL FOLD

B. ASYMMETRICAL FOLD

Asymmetrical folds in profile have no mirror plane in symmetry and the limbs are unequal in length. In asymmetrical fold the axial plane is inclined.

B. ASYMMETRICAL FOLD

A s y m m e t r i c a l f o l d s i n p ro fi l e h a v e n o m i r ro r p l a n e i n s y m m e t r y a n d t h e l i m b s a re u n e q u a l i n l e n g t h . I n a s y m m e t r i c a l f o l d t h e a x i a l p l a n e i s i n c l i n e d .

C.Overturned FoldIt is an

asymmetrical fold with inclined axial plane in which both the limbs are dipping essentially in the same general direction usually at different angles. Eg- Overfolds of krol belt, The Himalaya. Andaman Ridge.

OVERTURNED FOLD

A s y m m e t r i c a l f o l d s i n p ro fi l e h a v e n o m i r ro r p l a n e i n s y m m e t r y a n d t h e l i m b s a re u n e q u a l i n l e n g t h . I n a s y m m e t r i c a l f o l d t h e

a x i a l p l a n e i s i n c l i n e d .

D. Recumbent Fold

This is the extreme types of overturned folds in which the axial plane becomes nearly horizontal. In such fold the upper limb is called normal limb and the lower limb is called inverted or reversed limb. Eg -Recumbent folds of the Alps.

D.Recumbent Fold

E. Isoclinal Fold

Folds having parallel limbs are called Isoclinal folds. In such fold, the limbs dip at same angle and same direction.

It is of 3 types- 1)Inclined Isoclinal fold2) Vertical Isoclinal fold3)Recumbent Isoclinal fold.

Isoclinal Fold

F. Conjugate Fold

In certain cases, a pair of folds that have apparent mutual inclined axial plane. Such folds are described as conjugate folds.

Conjugate Fold

G. Box Folds

In such type of folds the crest is broad and flat and two hinges are present.

Degree Of Compression

A)Open fold In such type the

folding is mild, limbs meet at the bends at an obtuse angle and the thickness of the rocks remains unchanged.

O PEN FOLD

CLOSE FOLD Thinning at the

flanks and thickening at the crest

Behaviour With DepthA)Parallel fold

In such type the folded layers are parallel and the curvature is greatest at the centre reduces upwards in case of upfold and downwards in case of downfold.

B) Similar fold

Curvature of the folded surface are similar and it is thickened at the hinge and thin along the limbs.

C) Suprataneous fold

A fold in which the beds are thinner at the crest and thicker at the trough and the folding is accompanied by erosion and deposition.

Position of axis

A) Plunging folds- when the axis makes an angle with the horizontal plane B) Non-plunging folds- When the fold axis is horizontal, then it is described as Non-plunging folds.

Profile Of The Outer Surface

A) Chevron fold- In this fold the hinges are sharp and angular. B) Fan fold- In this fold both the limbs are overturned.

Mode Of Occurence

A) Domes- It is an anticlinal structure which plunges in all directions.

B) Basin- It is an synclinal depression having controversial dip.

Miscellaneous TypeA) Monocline-It is due to the local steepening of belt whereby their occurs a sudden increase in the dip of the bed.

B. Homocline

This can be well said as tilted beds where all the beds have same amount of dip in the same direction.