GEO 101 Lecture Notes - Lecture 17: Syncline, Anticline, Structural Basin
23 Jun 2018
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Folding
A layered rock that exhibits bends is said to be folded. The layered rock was at one
time uniformly straight but was stressed to develop a series of arches and troughs. A
compressive stress compacts horizontal rock layers and forces them to bend vertically,
forming fold patterns.
Anticlines and synclines. An anticline is a fold that is arched upward to form a ridge;
a syncline is a fold that arches downward to form a trough. Anticlines and synclines
are usually made up of many rock units that are folded in the same pattern. The tip of a
fold is called the nose. The center axis of a fold is called the hinge line and lies in
the axial plane that separates the rocks on one side of the fold from the rocks on the
other side that dip in the opposite direction. Extensive folding is represented by a
repeated pattern of anticlines and synclines. Two anticlines are always separated by a
syncline, and two synclines are always separated by an anticline. One side of the fold is
called the limb; a side by side syncline and anticline share a limb. Frequently, an ‐ ‐
anticline or syncline can be identified only from the systematic change in the dips of the
sloping rock units from one direction to the other, identifying the hinge line of the fold
Plunging folds. Plunging folds have been tipped by tectonic forces and have a hinge
line not horizontal in the axial plane. The angle between the horizontal and the hinge
line is called the plunge and, like dip, varies from less than 1 degree to 90 degrees.
Plunging folds characteristically show a series of V patterns on a bedrock surface
Structural domes and basins. A structural dome, a variety of anticline, is a feature in
which the central area has been warped and uplifted and all the surrounding rock units
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Document Summary
A layered rock that exhibits bends is said to be folded. The layered rock was at one time uniformly straight but was stressed to develop a series of arches and troughs. A compressive stress compacts horizontal rock layers and forces them to bend vertically, forming fold patterns. An anticline is a fold that is arched upward to form a ridge; a syncline is a fold that arches downward to form a trough. Anticlines and synclines are usually made up of many rock units that are folded in the same pattern. The tip of a fold is called the nose. Extensive folding is represented by a repeated pattern of anticlines and synclines. Two anticlines are always separated by a syncline, and two synclines are always separated by an anticline. One side of the fold is called the limb; a side by side syncline and anticline share a limb.
