This document summarizes a seminar on Ramsay classification of folds and folding mechanisms. It introduces Ramsay fold classification, which divides folds into three classes based on criteria like dip isogon patterns and curvature. Class 1 folds have convergent dip isogons and greater inner curvature. Mechanisms of folding discussed include buckling, which can form Class 1b folds of constant thickness, and bending due to intrusion or between boudins. Applications of the classification include hydrocarbon and salt dome exploration.

1. A seminar on Ramsay classification of fold and
mechanism of folding
PRESENTED BY : DARSHAN MALVIYA
MASTER OF SCIENCE IN GEOLOGY (FIRST SEM.)
Krantiguru Shyamji Krishna Verma Kachchh University

2. TABLE OF CONTENT :
1. INTRODUCTION
2. WHAT ARE FOLDS?
3. TERMINOLOGIES IN RAMSAY CLASSIFICATION
4. RAMSAY FOLD CLASSIFICATION
5. FOLD INTERPRETATION
6. MECHANISM OF FOLDING
A.) BENDING
B.) BUCKLING
7. APPLICATION OF RAMSAY FOLD CLASSIFICATION
8. REFRENCES

3. INTRODUCTION :
Ramsay fold classification was given by British Geologist
Sir.John Ramsay .
A seperate book was published by him , on fold and
strain analysis.
Folds are best found in sedimentary strata.
 Folds are found from centimetres to hundreds of metres.

4. What are folds ?
 Wave like structure
 Folds are formed by process of ductile deformation.
The main thing about folds is that they vary in their geometric shape
depending upon the rock material.
Folds are formed in lithosphere inside earth where pressure and
temperature are quite high.
Folds do shortening of the layer.
Folds do not result from confining pressure.
Resulting from strain .

5. Terminologies in Ramsay classification:
Axial plane : imaginary plane passing from the hinge line dividing fold in two equal
parts.
Dip isogon : the line joining point of same dip on either side of layer
Orthogonal thickness : thickness of fold measured perpendicular to the axial plane.
Axial trace thickness : thickness of the fold measured parallel to the axial plane .
Inner curvature : bending of hinge area of inner layer
Outer curvature : bending of hinge area of outer layer
Interlimb angle : angle between line joining limbs of the fold.

7. Criteria for Ramsay classification :
1.Nature of dip isogon
2.Outer and inner curvature
3.Interlimb angle
4.Thickness of limbs
5.Thickness of hinge area

8. Ramsay fold classification :
Ramsay fold were divided into three parts viz.
• Class 1 fold
- In this type of fold the dip isogons are convergent
- Inner curvature is greater than outer curvature
- inter limb angle > 0
Further divided in class 1a, 1b, 1c
Class I a – limb thick , hinge thin
Class I b – equal thickness throughout the fold
Class I c – limbs thin , hinge thick

9. Class 2 fold
- Dip isogons are parallel to each other
- Inner curvature is equal to the outer curvature
- Interlimb angle = 0

10. Class 3 fold
- Dip isogons are divergent
- Inner curvature is less than outer curvature
- Interlimb angle < 0

11. Class 1b fold , I observed in Spiti valley
(same thickness throughout the fold)
• Formed from buckling.
• Scale – man standing in the left .
• Axial plane is represented by solid
black line.
• Dip isogons are indicated in yellow and
are just a interpretation , not
calculated
• Red lines are the limb of fold.

12. Folding mechanism
Buckling -
- Buckling is a fold process that can initiate when a layer is shortened parallel to the layering.
- thickness is constant , i.e class 1b fold
-

13. BENDING : - When forces act across the layers at a high angle,unlike buckle folds
where the main force acts parallel to a layer.

14. - may result from forceful intrusion of magma or salt diapairs.
- may result between boudins.

15. Passive folding :
- Passive folds are produced by accentuation of pre existing curvature of layers by more or less
homogenous strain.
- Result from shear stress.
- If you have straight bed , we cant produce passive folds , there must be a slight curvature

16. Application of Ramsay fold classification :
- To find presence of hydrocarbons
- To find presence of salt domes
- Any fold in the world doesn’t differ from the classification given by Ramsay.
- Widely accepted in the world.

17. Refrences :
- The techniques of modern structural geology by Ramsay
and Huber Martin , volume 1&2
- Principles of engineering geology by K.M.Bangar
- Structural Geology by Haakon Fosen
- NPTEL lecture by Prof.Santanu Misra