Folds                                Faults

 


 

-Stage 2.1-

 

Folds

 

There are many types of fold that a geologist could study. These include:

 

An Anticline

 

A Syncline

 

Plunging Folds

 

and Nonsymmetrical Folds.

 

You should also be aware of how to name folds,

 

but before going into those, you need to understand some basic geologic map skills.

 


Geologic Rock Units

Geology Legend

 

The list on the left is a representative of a geologic map legend

 

Rocks on maps are listed in age order

 

The rocks on the top of the list are the youngest

 

The one's on the bottom are the oldest

 

This resembles real-life where rocks are deposited then the "younger rocks" are deposited later on top of them

 

These rock units will be used in the proceeding pictures

 

 

 

 

 

 


Anticline

Anticline

A fold in the rocks resulting in a "A" shape (A for Anticline)

 

The top side of the box on the left represents the Earth's surface

 

The front of the box shows the type of fold

 

The dotted line represents the "fold axis"

 

The resulting fold has the oldest rocks in the center

 

Then rocks repeat on both side of the center symmetrically

 

The width of the units on the surface are equal on both sides of the center unit

 

 


Syncline

Syncline

A fold in the rocks resulting in a "U" shape

 

The top side of the box on the left represents the Earth's surface

 

The front of the box shows the type of fold

 

The dotted line represents the "fold axis"

 

The resulting fold has the youngest rocks in the center

 

Then rocks repeat on both side of the center symmetrically

 

The width of the units on the surface are equal on both sides of the center unit

 

 

 


Plunging Folds

Plunging Sycline and Plunging Anticline

Plunging Syncline                                                    Plunging Anticline 

 

The direction of plunge is visible along the side of the blocks

 

This changes the symmetrical pattern seen along the surface

 

The new pattern is giant curves on the earths surface

 

The "arrow" pattern points in the direction of plunge in an anticline

 

The "arrow" points in the opposite direction in a syncline

 


Nonsymmetrical Folds

Non-symmetrical Anticline

 

Nonsymmetrical folds cause the same rock units to be different widths on either side of the center unit

 

Synclines and Anticlines will both have the unequal unit widths

 

The thinner side of the unit widths overly the steeper portion of the fold

 

 

 

 

 

 

 

    Non-Symmetrical Anticline

 


Identifying Folds

 

When identifying folds there are 3 types of descriptions that must be used for a complete description:

 

Anticline or Syncline

Symmetrical or Nonsymmetrical

Plunging or Non-plunging

(typically you don't say "non-plunging", you would just leave off that term)

 

Examples:

Plunging Symmetrical Anticline

Nonsymmetrical Syncline