What are the Geological Folds and its Type and components?

What are the Geological Folds?

A fold is a structural feature that is formed when planar surfaces are bent or curved. Geological folds are the curvatures in rocks or strata containing them. Stratified rocks were originally formed from sediments that were deposited in flat horizontal sheets, but in a number of places the strata are no longer horizontal but have been warped. 

Sometimes the warping is so gentle that the inclination of the strata is barely perceptible, or the warping may be so pronounced that the strata of the two flanks may be essentially parallel or lie nearly flat (as in the case of a recumbent fold). 

Folds vary widely in size; some are several kilometres or even hundreds of kilometres across, and others measure just a few centimetres or less. The tops of large folds are commonly eroded away on Earth’s surface, exposing the cross sections of the inclined strata

According to Wikipedia,

“A geological fold occurs when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. sedimentary folds are those due to slumping of sedimentary material before it is lithified. Folds in rocks vary in size from microscopic crinkles to mountain-sized folds.”

Major Types of Fold:

Anticline: Anticlines are a common fold type found in the Earth’s crust.In structural geology, an anticline is a type of fold that is an arch-like shape and has its oldest beds at its core, whereas a syncline is the inverse of a anticline.

An anticline is a structural trap formed by the folding of rock strata into an arch-like shape. The rock layers in an anticlinal trap were originally laid down horizontally and then earth movement caused it to fold into an arch-like shape called an  Anticlinal shape.

 Syncline: Synclines are also a common fold type that often forms together with anticlines during compression. In structural geology, a syncline is a fold with younger layers closer to the center of the structure.

When upright, synclines are trough shaped with beds dipping toward the axial surface. Like an antiform, the term synform is used to describe any structure with this general geometry. 

The more specific term syncline, however, indicates that layers get younger toward the axial surface. It is important to specify antiform from anticline and synform from syncline as folds can be rotated so that overturned synclines become antiforms and overturned anticlines become synforms. 

Monocline: A monocline is a simple bend in the rock layers so that they are no longer horizontal but are inclined . In a monocline, the oldest rocks are at the bottom and the youngest are at the top.

Major Component of a fold:

Axis- The line of intersection of the axial plane with the upper and lower surface of any of the constituent beds.

Limb– The Stretch of the rock beds lying between any crest and any of the adjacent troughs on either side is known as limb of the fold.

Axial Plane– It is an imaginary line which divides the fold as symmetrical as possible is described as its axial plane. It is the surface connecting all the hinges. It may be a simple plane or a curved surface.

Crest And Trough-  the line joining through the highest points in the uparched side of the fold is called Crest. Similarly line joining through the lowest points in the down-arched side of fold is called Trough.

Hinge- The point of maximum curvature that separates the two fold limbs. If maximum curvature is better represented by an area than a point, then this area is referred to as the hinge zone. In three dimensions, the fold hinge can be represented as a line that follows the central axis of the fold.