FOLDS, FAULTS AND JOINTS

1. GOVERNMENT POLYTECHNIC PEN
STRUCTURAL GEOLOGY- FOLDS, FAULTS & JOINTS
CIVIL ENGINEERING DEPARTMENT
GUIDED BY: PRESENTED BY:
S.N. CHOURE PREETI SANTOSH PATIL

2. CONTENTS
 INTRODUCTION
 IMPORTANCE OF STRUCTURAL GEOLOGY
 TYPES OF GEOLOGIC STRUCTURES
 FACTORS AFFECTING HOW A ROCK DEFORM
 OUTCROP
 DIP & STRIKE
 FOLDS - DESCRIPTION OF FOLD
- TYPES OF FOLDS
 FAULT - COMPONENTS OF FAULT
- TYPES OF FAULTS
 JOINTS - TYPES OF JOINTS
 CONCLUSION

3. INTRODUCTION
Structural geology is the study of the three dimensional distribution of rock units
with respect to their deformational histories. The primary goal of structural geology is to
use measurements of present day rock geometries to uncover information about the
history of deformation in the rock.
Structural geology , scientific discipline that is concerned with rock deformation
on both a large and a small scale. Its scope of study is vast, ranging from submicroscopic
lattice defects in crystals to fault structures and fold system of the earth’s crust.

4. IMPORTANCE OF STRUCTURAL GEOLOGY
The study of structural geology has a primary importance in economic
geology, both petroleum geology and mining geology. An essential importance of
structural geology is know areas that contain folds and faults because they can form
traps in which the accumulation and concentration of fluids such as oil and natural gas
occur.
Environmental geologist and hydrologists need to understand structural
geology because structures are sites of groundwater flow and penetration which may
have an effect an leakage of toxic materials from waste dumps or leakage of salty
water into aquifers.

5. TYPES OF GEOLOGICS STRUCTURES

6. FACTORS AFFECTING HOW A ROCK DEFORM
 DEPTH
 TIME
 FLUIDS

7. OUTCROP
Outcrop is simply defined as an exposure of a solid rock on the
surface of the earth.
solid rocks are not exposed everywhere on the surface of the earth,
these are mostly covered with a thick or a thin layer of loose deposits called as
alluvium or in most common language called as soil.

8. DIP & STRIKE
 Strike is the direction of the line produced by the intersection of the inclined
plane with the horizontal plane. It is expressed as the angle of the line from
the north.
 Dip is the angle between the inclined plane and the horizontal plane.
 Strike and dip directions are always mutually perpendicular.

9. FOLDS
Folds are bends or flexures in the earth’s crust, and can therefore be
identified by a change in the amount and /or direction of dip of rock units. Most
folds resulted from the ductile deformation of the rocks when subjected to
compressional or shear stress.

10. DESCRIPTION OF FOLD

11. DESCRIPTIONS OF TERMS OF FOLD
 Hinge line is the line of maximum curvature on a folded surface.
 The axial plane is an imaginary plane dividing the fold into two equal parts known as limbs.
 Limb is the sloping side of the fold.
 The crest is the highest point of the folded surface.
 Trough is the lowest point of the folded surface.
 The Inter-limb angle is the angle between two limbs of same fold.
 The median surface is the surface that passes through the points where the fold limb changes its
curvature from concave to convex.
 The amplitude is the vertical distance between the meridian surface and the fold hinge, both taken
on the same surface of the same folded unit.
 The angle of plunge is the angle between the fold axis and the horizontal plane measured in
vertical plane.
 The wavelength is the distance between two consecutive crests or trough taken on the same
folded surface.

12. TYPES OF FOLDS
 anticline: upfolds or arches of rock layers
 syncline: downfolds or troughs of rock layers.
 monocline: only one direction of dip prevails in a fold system.
 symmetrical fold: the axial plane is vertical with the limbs dipping
symmetrically from the axis
 asymmetrical fold: the axial plane is inclined from the vertical with one limb
dipping more steeply than the other.
 overturned fold: one limb is inclined beyond the vertical
 recumbent fold: this is an overturned fold "lying on its side" so that the axial
plane is nearly horizontal.

13. TYPES OF FOLDS
Recumbent fold

14. FAULT
A fault is a fracture in the earth’s rock unit along which there has been
an observable amount of movement and displacement. Unlike folds which are
formed predominantly by compressive stress, faults are formed from either tension,
compression or shear.

15. The names of hanging wall and footwall came from miners mining
along fault zones, who hung their lanterns on the hanging wall
and walked on the footwall. (Tarbuck and Lutgents)

16. COMPONENTS OF FAULT
 Hanging wall: if the fault plane is not vertical, then the block lying on the top of the
fault plane is known as hanging wall.
 Footwall: whereas the block lying below the fault plane is known as footwall.
 Fault plane: is the plane of fracture along which displacement occurs.
 The down-thrown and up-thrown block: the block that has moved down is down-
thrown whereas the block that has moved up is up-thrown block.
 The dip of the fault plane is the angle of inclination of fault plane measured from
horizontal plane perpendicular to its strike.
 Fault throw: is the vertical displacement of a fault.
 Dip slip and Strike slip: the amount of displacement measured on the fault plane in
the direction of its dip is known as dip slip whereas in the direction of its strike is
known as strike slip.

17. TYPES OF FAULTS
 Normal fault
 Reversed fault
 Thrust fault
 (Dip slip fault: normal fault, reversed fault, thrust fault)
 Strike slip fault: left lateral, right lateral
 Oblique slip fault: has both strike-slip and dip-slip component. Note: The
textbook calls it "translation fault", which is rarely used.

18.  Normal fault is the fault in which hanging wall has moved downward relative to
the footwall.
 Reversed fault is the fault in which hanging wall has moved upward relative to
the footwall.
 Thrust fault is a reversed fault in which the fault plane is dipping at low angles
(<45’).

19.  Strike slip fault is the fault in which the movement is horizontal along the strike of the
fault plane.
 Oblique slip fault is the fault in which displacement was both in the strike and dip
directions.

20. JOINTS
Joints are the fractures in the rocks characterized by no movement along their
surfaces. Although most joints are secondary structures , some are primary forming at the
time of formation of rocks.

21. TYPES OF JOINTS
 Columnar joints : These joints are formed in the basalt rock, when the basaltic lava cools,
it contracts giving rise to hexagonal shaped column.
 Mud cracks: These are the joints formed in mud. As the mud loses its water, it contracts
and cracks.
COLUMNAR JOINT MUD CRACKS

22.  Secondary joint: these joints are formed in the rocks as a result of their subjection
to any form of stress.
 Sheet joint: these joints are formed in granitic rocks in the deserts causing them to
break into thin parallel sheets.
Secondary joint Sheet joint

23. CONCLUSION
Structural geology is obviously one of the most important subjects for
geoscientists working in petroleum as they can identify the locations that may have
traps such as folds, faults and joints which are good for the accumulation of oil and
natural gas.
The study of structural geology is important for the geologists to acquire
knowledge and data about the deformation caused in rock such as folds, faults and
joints due to subjected tension, compression or shear stresses.
The folds are the bends or flexure on the earth’s surface. A fault is a fracture
in the earth’s rock unit. Joints are the fractures in the rocks characterized by no
movement along their surfaces.

24. THANK YOU!