The document discusses folds, their geometry, classification, and field study. It defines folds as bent rock layers caused by compressional forces. The geometry of folds includes limbs, hinge points, hinge lines, axial planes, axes, and other features. Folds are classified based on their shape, including anticlines, synclines, symmetrical, overturned, and others. Field study of folds involves direct observation of fold features and measuring the attitude of hinge lines and axial planes to characterize fold structures.

2. UNIVERSITYOF AZADJAMMUANDKASHMIR
MUZAFFARABAD
The Institute of Geology
Topic: Folds its geometry, nomenclature and their field study
Prepared by :
Abdur Rauf
Roll no: 125
presented To:
Dr. jahanzeb khan SB
And whole class

3. Topics
1) Folds
2) Geometry of folds
3) Classification of folds
4) Field study of folds

4. 1) Fold
 The bending of rock strata of plastic nature due to
Compressional forces acting horizontally toward a common point
or plane from opposite directions is known as fold.
Or
 Folds may be defined as undulation, bending or curvatures in rocks
of the crust’s as a result of stresses.
 Folds are one of the most common geological structures found in
rocks.
 a set of horizontal layers are subjected to compressive forces,
they bend either upward or downward.

5. 2) Geometry of a fold

6. a) Limbs
 Limbs or a flank of the fold is sloping side from the crest to the
trough.
b) Hinge points
 The point of maximum curvature of a folded layer is located in the
center of the hinge zone and is called the hinge point.
c) Hinge line
 Hinge points are connected in three dimensions by a hinge line.
Or
 The line which connect all the hinge pints is called hinge line.

7. d) Axial plane
 The axial plane is the surface connecting all the hinge. It may be a
simple plane or a curved surface. It may be horizontal or vertical.
e) Axis of the fold
 It is a line parallel to the hinge line of a fold or it may be defined as
a line of interaction of a axial plane of a fold and with any bed of a
fold.
f) Inflection point
 The point where the convex change into concave.

8. g) Inflection line
 The line joining the inflection points is called inflection line.
h) Crest and trough
 The line running through the highest points in a uparch fold is called crust,
and if the line running through lowest point in a downarch fold is called
trough.
i) Wave length of a fold
 The distance between two adjacent crest or trough is known as wave length.
Interlimb angle
 The interlimb angle is define as the angle between the planes tangential to the fold
surface at the inflection line.

9. 3) Classification of folds
Anticline.
 The word anticline is a Greek word which means “opposite inclined”. it may be define as a
fold that is convex upward; it may also be defined
as a fold that has older rocks in the center and the younger are at limbs.
 In this type of fold,
the limbs are dip away from each other.
An anticline expose during road cut at new jercy USA

10. Syncline
 The word syncline is a Greek word which means “together
inclined”.
 It may be define as a fold that is convex downward.
 In this kind of folds the two limbs dip toward each other.
 So its means that the younger rocks are at the center and older are
at limbs.
This photo showing syncline

11. Symmetrical fold
 That type of fold in which the axial surface is essentially vertical.
 The term upright is also used.
 In symmetrical folds no limb is steeper then other.
This photo showing symmetrical
fold

12. Hormonic and disharmonic fold
 The type of folds in which the geometry ofdifferent layers
matches with each other is called hormonic fold. In this type,
folding is not uniform throughout the stratigraphic column. Folding
changes upwards or downwards.
 Conversely, when the geometry of different layers of a fold cant
match each other is called disharmonic fold.
This photo shows hormonic folding
This photo shows Dis
hormonic folding

13. Cylindrical and non cylindrical folds.
 If the surface of a fold can be translated with the help of a
strait line, the fold will called cylindrical.
 And if the surface of a fold can’t be translated with the help of
strait line, the fold will known as non cylindrical fold.
 The geometry of non cylindrical folds is like egg tray.
This photo shows cylindrical
folding
Non cylindrical
folding

14. Monocline fold
 That fold in which only one limb is dipping is termed as monoclonal
folds.
Overturned fold
 In the overturned fold the axial plane is inclined and both limbs dip in
the same direction, usually at different angles.
 The overturned, inverted, or reversed limb is the one that has been
rotated more than 90.
This photo showing overturned fold.
This photo showing monoclonal
folding

15. Recumbent fold
 A recumbent fold is one in which the axial plane is essentially horizontal.
 These types of folds are produce when the deformation is intense.
 And one fold lies on the top of next fold so that the axial plane become sub
horizontal.
 Such kind of fold can be found in alps mountains.
This photo shows recumbent
folding.

16. Isoclinal fold
 An isoclinal fold, from the Greek word meaning “equally inclined”,
refers to folds in which the tow limbs dip at equal angles in the same
direction.
Chevron fold
 chevron fold is one in which the hinges are sharp and angular.
Box fold
 A box fold is one in which the crest is broad and flat. Two hinges are
present, one on either side of the flat crest.

17. This photo shows chevron
folding
This photo shows box folding
This photo shows isoclinal folding

18. Fan fold
 A fan fold is one in which both limbs are overturned.
 In the anticlinal fan fold, the two limbs dip toward each other; in the
synclinal fan fold, the two limbs dip away from each other.
This diagram shows fan folding

19. Drag fold
 It forms when a competent bed slides past an incompetent bed.
 Such minor folds may form on the limbs of larger folds because
of the slipping of beds past each other, or they may develop
beneath overthrust blocks. Such structural features may form
during sedimentation, when a sheet of sediment slides over a
weaker bed.
This photo shows Drag folding

20. Dome and basin
 A dome is an anticlinal uplift that has no distinct trend. And a basin
is synclinal depression that has no distinct trend.
Anticlinorium and synclinorium
 A major anticline that is composed of many smaller folds is called
anticlinorium.
 The term is restricted to large folds that are least several miles
across. Similarly, a synclinorium is a large syncline composed of many
smaller folds it should be at least several miles across.

21. This photo shows dome This photo shows anticlinorium
This photo shows synclinorium
Sorbas basin in south-east Spain.

22. Geosyncline
 Literally it means an earth syncline but should not be used for
large syncline.
 It is a large depression, hundred of miles long and ten of miles
wides, in which many thousands or ten of thousands of feet of
sediments accumulate.

23. On the basis of interlimb angle the folds are classified as
following.
Interlimb angle Description of fold
180d – 120d Gentle
120d – 70d Open
70d – 30d close
30d – 0d Tight
0d Isoclinal
-angle Mushroom

24. Here we are using the following classification
Interlimb angle Folder description
Od - 10d Isoclinal fold
30d- 70d Close fold
70d- 120 Open fold
120d – 180d Gentle fold
10d – 30d Tight fold

25. 4) The field study of folds
Direct observation
 Fold may be recognized in many ways. The easiest and most
satisfactory method is to observe the fold, but this can be done in
comparatively few regions.
 Wherever small folds are observed in single outcrops, it is
desirable to record their attitude. To do this we must measure the
attitude of the hinges and the attitude of the axial plane.
 The pattern show The plane should also be recorded by minor folds
as it is of great use in conjunction with plunge of fold in deducing
large structures.

26. Plunge of axis
The plunge is measured by means of clinometer attached to the compass.
Attitude of axial plane
A note book or sheet of paper may be held parallel to the axial plane of a fold
in order to measure its attitude.
N
40 degree
The fold is anticline 40 degree west
The fold is syncline east west
horizontally
25 d AP
Axial plane, striking north & dipping 25d
west

27. Attitude of axis and axil plane
The symbol of axial plane and hinge will be combined to form the symbols shown
bellow.
35d
N
A fold plunging 35d east & a vertical axial plane striking east
51d
60d
An anticline plunging 51d NNW, with the axial plane striking N and dipping 60d W.

28. Inferred fold
 Fold large than an outcrop are based on inference moreover the part of
the fold that was above the present surface the earth has been removed
by erosion.
 One or more of the following pieces of information are commonly used to
deduced fold.
(1) Deference in attitude of some planer features at different localities.
(2) aerial map pattern
(3) Subsurface exploration by drilling and tunneling
(4) Subsurface studies by geophysical methods.

29. Any question!
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