Main Types of Geological Folds

Main Types of Geological Folds

What is a fold?

• Folds are primarily caused by compressive stress.

• Folds form perpendicular to the direction of stress.

• Compression can form folds & faults.

Multiple Choice

Folds are mostly caused by ______ stress.

• shear

• tension

• compression

Main Types of Folds

• Anticline and Synclines often form together as part of a series of folds.

• For Anticlines, (shaped like A)the oldest rock is in the center.

• Where Synclines have the youngest rock in the center of the fold.

Multiple Choice

Identify this fold as either anticline or syncline.

• anticline

• syncline

Multiple Choice

In a syncline such as this one, the (youngest/oldest) layers are in the middle of the fold.

• youngest

• oldest

Domes and Basins

• Dome: circular uplifted anticline exposing older rock.

• Basin: single syncline forming a depression with younger layers surrounded by older layers.

Multiple Choice

This famouns feature in Yosemite NP is an example of a

• dome

• basin

Monocline

As the name implies (mono = one) monoclines have just a single fold such as this example named Waterpocket Fold

Multiple Choice

Monoclines have a single fold, seperating two areas of horizontal layers.

• True

• False

Geometry of Folds

• Hinge: sharpest point of curvature also called "fold axis"

• Limbs: each fold has two limbs on both sides of the hinge.

• If a hinge is not horizontal it is said to be "plunging"

Asymmetric & Overturned folds

• asymmetric fold is slightly inclined.

• overturned folds are inclined by more than 90 degrees

Multiple Choice

The sharpest part of the anticline fold is called the

• limb

• hinge

Multiple Choice

This photo shows a fold that (is / is not) plunging.

• is

• is not

Multiple Choice

Based on the axial surface, this fold is said to be ___

• asymmetrical

• overturned