Fold and its classification

Lab no: 03 Date:14-10-2019
 Title:
Folding and its classification.
 Aim:
To become familiar with folding , its types and formation in rocks.
 Theory back ground;
 Folds
Folds are one of the most common geological structures found in rocks. When a
set of horizontal layers are subjected to compressive forces, they bend eith upward or
downward. The bend noticed in rocks are called folds.
Fig:folds
 Parts of a Fold:
The various parts of a fold are briefly described below:
(i) Axis:
This is the median line about which the strata has folded. The axis of a fold may
be horizontal, inclined or vertical. If the axis of the fold is horizontal then it is parallel to
the strike of the fold.
(ii) Axial Plane:
This is a plane dividing the fold into two somewhat symmetrical parts. The axial
plane may be vertical, inclined or horizontal. The line of intersection of the axial plane
with any bedding plane is called the fold axis or the axial line.
(iii) Limbs of a Fold:
Two sides of a fold (on either side of the axial plane) are called the limbs of the
fold. In the usual cases the limbs are inclined. However in particular cases they may be

vertical or horizontal. The limbs may dip either way from each other or towards each
other. The angle between the limbs is called the inter-limb angle.
Fig:parts of folds
(IV) Hinge line:
Line connecting the points of maximum curvature on the fold profile
(v) Hinge zone:
The zone of maximum curvature on the fold profile
 Classification of Folds:
Folds are classified into two main types namely anticlines or up-folds and
synclines or down-folds.
1. Anticline Folds:
An anticline consists of beds bent upwards with limbs dipping away from each other.
2. Syncline Folds:
A syncline consists of beds bent downwards with limbs dipping towards each
other.

3. Symmetrical Fold and Asymmetrical Fold:
A symmetrical fold is a fold whose axial plane is vertical and the limbs dip equally. The
axial plane in this case divides the fold into two equal halves. If the two limbs dip at
different angles the fold is an Asymmetrical fold.
4. Monocline:
This is a fold in which only one limb is bent. This is a case when a rock-bed bends
abruptly and resumes the original attitude at the lower level.
5. Plunging Fold and non plunging Fold:
A fold whose axis is inclined at an angle (0<x<90) degree [ x= plunge of fold axis]
Said to be flunging and a fold whose axis is horizontal on the plunge of the fold axis is 0
degree.

6. Isocline or Carinate Fold:
This is a fold whose limbs dip at the same angle in the same direction. The two limbs
in this case are parallel. The axial plane may be vertical, inclined or horizontal.
Fig:isocline fold
7. Overturned Fold:
This is a fold whose limbs dip unequally in the same direction.

8. Recumbent Fold:
This is a fold whose limbs are bent back on themselves almost horizontally.
9. Zigzag Fold or Chevron Fold:
This is a fold having a sharp angular crest or trough.

10. Dome Fold or Quaquaversal Fold or Pericline:
Dome fold consists of a set of rock beds lifted centrally giving the feature of a dome.
The area of rock bed lifted may be circular or oval shaped. In a vertical section through
the summit, the fold exhibits an anticlinal feature. For this reason this fold is also called a
compound anticline. After the domes are eroded, the younger rocks appear surrounding
the older rocks.
11. Basin Fold or Centrocline:
Basin fold consists of a set of rock beds which are sunk down centrally giving the
feature of a basin. The area of the rock bed sunk may be circular or oval shaped. In a
vertical section taken centrally the fold exhibits a synclinal feature. For this reason this
fold is also called a compound syncline.
Refrences:
www.yourarticlelibrary.com>geology
Genral and engineering geology by K.M Bangar.
Signature of instructor:______________________

Subject: Structural Geology Lab
Submitted to: Engr Zahid Ur Rehman
 Submitted by: Ali khan
 Reg No: 17PWMIN0809
 Semester: 5th
 Dept: Mining Engg
 Lab : 03

Fold and its classification

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