Fold systems

Abstract

Anticlines and synclines can take on many different geometries. They can be either open tight, or isoclinal in shape. The tighter the folds, the more intense the stress (compression) that caused folding. Folds can also be symmetric or asymmetric, upright or overturned, curved or cornered. A fold “knocked” on its side is called recumbent. Folds don‛t have to be perfectly horizontal, often folds are not, because of twisting and tilting, and they can plunge into the Earth at an angle. Folds occur on all scales. Some are small enough to be contained in a hand-held rock specimen. Others cover large areas, so large that they can be seen from miles away. When we slice into a fold at a “road slopecut” for a highway, fold types are often easily identified by the distorted marker horizons. The fold patterns observed along the surface are also clues to the existence and type of fold that may be beneath the surface.