The document provides a comprehensive overview of structural geology, focusing on the characteristics and classifications of geological structures such as folds, faults, joints, and their origins. It details various types of dips, folds, and faults, explaining how they form and the processes that lead to their development. Additionally, it categorizes joints based on spatial relationships, geometry, and origin, emphasizing the significance of these structural features in geologic studies.

4. Introduction
Dip and Strike
Folds
Faults
Joints

6. Structural geology is the study of the factors such as origin,
occurrence, classification, type and effects of various
secondary structures like folds, faults, joints, rock
cleavage etc. and are different from those primary
structures such as bedding and vesicular structure, which
develop in rocks at the time of their formation.

7.  It means slope or inclination.
 The angle of inclination of a
bedding plane with horizontal
plane is called amount of dip.
 The direction along which the
inclination of the bedding plane
occurs, is called dip direction.
 So dip is expressed both as
amount and direction.
 The direction angle is measured
with clinometers.
 The direction is measured with a
compass.

8.  It’s defined as the direction of a line
formed by the intersection of a
bedding plane and a horizontal
plane.
 It’s always at right angle with the
true dip direction.
 It is a horizontal line on a surface of
rock beds.

9. Dip
According to
Direction
True Dip
Apparent
Dip
Local &
Regional
Dip
Primary
Dip
Secondary
Dip

10. According to Direction :-
When the dip of layer is measured in a direction that is
essentially at right angle (90) to the strike of that particular layer.True Dip
When the dip of layer is measured in any other direction, which
is not at right angle (90) to its strike direction.
Apparent
Dip

11. According to Deposition :-
When sedimentary rocks are deposited in an originally sloping basin they
(SR) are also inclined in the same fashion. Thus, if the original slope of the
basin of deposition is anything between 5-10 degrees the sedimentary
formations accumulating over there in the period of time, will also have
same direction, such dips are called Primary Dip or Depositional
Gradient.
Primary
Dip
Local dips are inclinations of the rocks exposed in a limited area of
observation. They may primary or secondary or may not show any
appreciable variation laterally or with depth.
Regional dips is an averaged general inclination of a series of formation
exposed over a wide area. These rocks may show varying local dips, both
in respect of degree and directions of inclination. Regional dips are prevail
over many hundreds km range.
Local &
Regional
Dip
Secondary dip is inclination induced in the strata after its deposition due
to the Tectonic Force. Secondary dip may range in value up to vertical (90).
Most folded mountain ranges of the world strata exhibit Secondary Dip.
Secondary
Dip

12. When a set of horizontal rock layers are subjected
to compressive force, undulation or bends
curvatures developed in the rock layers. These bends
are called folds.

14.  Hinge: It is the area of maximum curvature. It is
closure of fold sometimes.
 • Hinge line: It is line of maximum curvature. The
hinge line may be horizontal, inclined or vertical.
 • Limb: These are the areas between the hinges or in
other words these are sides of the fold.

15.  Axial plane: The imaginary plane which is equidistant from each
limb of a fold.
The axial plane actually cuts the hinge zone of the fold along a
line, which is termed as fold axis or axis.
 Plunge: The attitude of the fold axis is measured as the angle
between the axis and horizontal.
 Crest & Trough: The line running through the highest points in an
up arched fold defines its Crest. A corresponding line through the
lowest p0int in a down arched folds makes its Trough.

16. Based on outer surface profile
Based on upward and downward bending
Based on position of the axial plane
Based on degree of compression
Based on mode of occurrence
Based on plunge of the folds
Based on behavior with width
Based on Relative Curvature of outer & inner arcs
Based on different principles, it can be classified as :-
Miscellaneous folds

17. 1 Based on upward and downward bending, It can be classified as:-
1 2
When the beds are bent upwards, the
resulting fold is called anticline. This fold
is convex upwards. Naturally, in such a
fold, the older beds occur towards the
concave side, In a simple case, the limbs
of anticline slope in opposite directions
with reference to its axial plane.
Syncline is just opposite to anticline in
its nature, i.e. when the beds are bent
downwards the resulting fold is called
syncline. This fold is convex downwards.
In this the younger beds occur towards
the concave side and, in a simple type of
syncline, its limbs dip towards each other
with reference to the axial plane.

18. 2 Based On Position of the axial plane, It can be classified as:
:-
When the axial plane
divides a fold into
two equal halves
(half) in such a way
that one half is the
mirror image, then
the fold is called as
symmetrical fold.

19. If the compressive forces
responsible for folding are not
of the same magnitude,
asymmetrical folds are formed.
2 Based On Position of the axial plane, It can be classified as:
Overturned Fold
An overturned fold is an inclined
(asymmetric) fold in which both
limbs dip in the same direction but
with different angles.

20. 2 Based On Position of the axial plane, It can be classified as:
Usually the folds have inclined limbs, i.e. the
limbs will be mutually diverging or
converging with reference to axial planes.
But in some folds, the limbs will be
mutually parallel to a great extent. Such
folds are called isoclinals folds. These folds
may be vertical inclined or horizontal.
Box Fold
Box fold are special type of fold with
exceptionally flattened top and
steeply inclined limbs almost
forming 3 sides of a rectangle.

21. 2 Based On Position of the axial plane, It can be classified as:
Fan Folds
In Fan folds the anticline
tops are said to have
opened up unto a broad,
fan-shaped outline due
to intense compression
in the lower region.
Conjugate Folds
Conjugate folds are a pair
of folds that are
apparently related to
each other may have
mutually inclined
axial planes.
Recumbent Folds
Recumbent folds are extreme types of
overturned folds in which the axial
plane acquires on almost horizontal
attitude and limbs comes to lie
exactly under the other limb.

22. 3 Based On Degree of Compression, It can be classified as:
1 2
The folds in which thickened crests or
troughs and thinner limbs are found.
Open Fold
The folds in which the thickness of the
rocks is not affected during the
process.

23. 4 Based On Mode Of Occurrence, It can be classified as:
1 2
Synclinorium is the reverse of
anticlinorium & may defined as an
extensive system of folds having
clearly down-arched folding trend.
Anticlinorium
Anticlinorium is a system of exceptionally
large sized folds running often for
several hundred km in length &
several km in width and having up-
arched folding trend.

24. 4 Based On Mode Of Occurrence, It can be classified as:
2
Dome
Domes are a group of strata central
uplifted in such a way that they seen
from the top these dip away in all
direction
Basin are the reverse of the domes & may be defined
as a group of strata that are centrally depressed in
such a way that the involved layer dip towards a
common central point from all the sides.

25. 5 Based On Plunge Of the Folds, It can be classified as:
1 2
Plunging folds
Any fold in which fold axis is not
horizontal.
Non-Plunging folds
Any fold in which fold axis is
essentially horizontal.

26. 6 Based On outer surface profile, It can be classified as:
1
3
Conjugate folds
Conjugate folds are composite folds
characterised with 2-hinges & 3
planner limbs in which the central
limb is exceptionally flattened.
Cheveron folds
These are characterized with well-
defined, sharp hinge points & straight
planner limbs.
4
2

27. 6 Based On outer surface profile, It can be classified as:
Cylindrical folds
The cylindrical folds resemble sections of
pipes and have very well defined axes of
folds repeated parallel to each other.
In Non-Cylindrical folds repetition of
axes parallel to themselves is not
possible.
Cuspate folds
The limbs of the folds are not planner
they are quite clearly curved becoming
concave upward in the case of
Anticlines & concave downward in the
case of Synclines.

28. 7 Based On Behaviour with depth, It can be classified as:
1
3 Supertanuous folds
These showing differences in
thickness at crest and the
trough regions, not induced
by folding process but
essentially being due to
erosional & depositional
processes operating in the
folding regions.
Concentric folds
The strata in concentric or parallel
folds has reacted to the effecting
tangential compression in such a
way that the thickness of the
involved layer remained
uniform and constant even after
folding.
2
Similar folds
Those folds in which
the degree of
folding is observed
to be similar for
indefinite depths
are grouped as
similar folds.

29. 8 Based On Relative curvature of outer & inner arcs, It can be classified as:
1
3
Class 2 folds
All those folds in which the
degree of curvature in
the outer arc (o) of the
fold is equal to that of the
inner arc (i). {o = i}
Class 1 folds
All those folds in which the
degree of curvature in
the outer arc (o) of the
fold is less than that of
the inner arc (i).
{o < i}
2
Class 3 folds
All those folds in which the
degree of curvature in the
outer arc (o) of the fold is
greater than that of the
inner arc (i). {o > i}

30. 9 Miscellaneous :-

31.  Most of the important folds, as already pointed out, are due to tectonic
causes. But a few folds of a minor type are due to non-tectonic causes.
 Non-tectonic causes like landslides, creeping, differential compaction, and
glaciations too are responsible for some folds. These are minor in terms of
frequency of occurrence and magnitude.

32. A fault may be defined as a fracture surface along which
relative movement of adjacent blocks has taken place.
Faulting is entire process of development of fracture
& displacement of the blocks against each other.

33.  Faults occur when brittle
rocks fracture and there
is an offset along the
fracture.
 When the offset is small, the
displacement can be easily
measured, but sometimes the
displacement is so large that it is
difficult to measure.

34. Fault plane:- It is the planar surface of fracture along which relative
displacement of the blocks takes place during the process of faulting.
When it is not planar, the same surface is simply described as Fault Surface.
Fault line:- It is the line of intersection between the fault plane.
1- Hanging Walls 2- Foot Walls
Hanging Walls:- Fault blocks above the fault place .
Foot Walls:- Fault block below the fault plane.
Fault line

35. Faults are classified on the basis of :-

36. 1
3
1- Normal Faults:-
In normal faults hanging wall has apparently
moved down with respect to foot wall.
2
1 Based On Apparent movement of fault blocks, It can be classified as:-
Horst
Vertical
Fault
Garben
4
Normal Faults

37. 3- Strike-slip Faults:-
In this faulted blocks have
been moved against each
other in an essentially
horizontal direction. I is
found in large scale like in
oceanic ridge.
2- Reverse Faults:-
In this hanging wall appears
to have moved up with
respect to the foot wall.
4- Hinge Faults:-
Hinge faults are characterised
by a movement of the
disrupted faults along a
medial point . The
movement is therefore
rotational .

38. 1 32
2 Based On Attitude of fault plane, It can be classified as:-
2- Dip Faults:-
Dip faults develop parallel
to the dip of the strata.
1- Strike Faults:-
These are the faults that
develop parallel to the
strike of the strata.
3- Oblique Faults:-
Oblique faults strike make an
oblique angle with the
strike of the rocks in which it
has it has caused the
displacement.

39. 1
3
1- Parallel Faults:-
A group of faults occurring in close proximity, having
their faults planes striking essentially in the same
direction & having parallel & equal dips from what
are commonly called parallel faults.
2
3 Based On Mode of occurrence, It can be classified as:-
4
2- Enechelon Faults:-
A group of small sized faults that
overlap each other in the
region of their occurrence.

40. 3 Based On Mode of occurrence, It can be classified as:-
4- Radial Faults:-
A group of faults appear emerging
outward from a common central
region are classed as radial faults.
3- Peripheral Faults:-
When in any given region the majority
of faults are concentrated along
the border or margin of the area.

41. 1 32
4 Based On slip, It can be classified as:-
2- Dip-slip Faults:-
All those faults in which the
net slip has taken place
parallel to the dip of the
faults, also called Normal-
dip-faults.
1- Strike –slip Faults:-
In which net slip is
essentially parallel to
the strike of the faults,
the slip along the dip
being almost absent.
3- Oblique –slip Faults:-
In which the direction of net
slip is neither parallel to the
dip of the faults nor to the
strike of the fault but is
inclined to both these
direction.

42. Faulting change in the elevation of the ground.
Omission of some strata where they are normally expected.
Repetition of some strata in a given direction against the normal order of super-position.
Displacement & shifts in the continuity of the same rocks in the certain regions.
Kashmir Himalayas Garhwal HimalayasShimla Thrust
Example of faults-

43. Joints are defined as divisional planes or fractures along which
there has been no relative displacement.
Or Any fracture, without any movement is called as joint.
Nature of
Joints:-
1. Open joints
2. Close joints
3. Smooth joints
4. Rough joints
5. Small joints
6. Master joints

44. Joints are
classified
on the
basis of :-

45. Joints are classified on the basis of :-
Spatial
Relationship
1 Geometry2 Origin3
Regular or
Systematic
Joints
Irregular or
Non-
Systematic
Joints
Tension
Joints
Shear
Joints
Compression
Joints
Strike
Joint
Dip Joint
Oblique
Joint
Bedding Joint

46. 1. On the basis of Spatial Relationship:-
Regular or Systematic
Joints
Irregular or Non-
Systematic Joints
These shows a distinct regularity in their
occurrence, which Can be measured &
mapped easily. Such joints occur in
parallel or sub-parallel joints sets that
are repeated in the rocks of regular
intervals.
As the name implies, these joints do
not possess any regularity in their
occurrence & distribution. They
appear at random in the rocks &
may have incompletely defined
surfaces.

47. 2. On the basis of Ge0metry:-
Dip Joint
When joints sets
strike, parallel to
the dip direction
of the rocks, they
are called Strike
Joints.
Oblique Joint
When strike of the joints
is at any angle
between the dip &
strike of the layers,
these are also called
Diagonal Joints

48. 3. On the basis of Origin:-
Shear Joint
Joints those are commonly
observed in the near of
faults planes & shear
zones where the
relationship with shearing
forces is clearly established.

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