Geoscience Ontology, Fold

A fold whose core contains the stratigraphically older rocks

A convex-upward, concave downward fold.

A fold with straight limbs and sharp hinges. Well developed, these folds develop repeated set of v-shaped beds. Inter-limb angles are generally 60 degrees or less. Chevron folding preferentially occurs in well bedded units where bedding regularly alternates between contrasting competences.

A curve or bend of a planar structure, such as rock strata, bedding planes, foliation or cleavage. A fold is usually the product of deformation, involving the compression of strata, but may include primary structures, as its definition is descriptive, not genetic. (Neuendorf et al., 2011).

the length of half the distance from the crest of a fold to the adjacent troughs.

Abstract surface that bisects the limbs of a fold or is the normal to a surface defined by the poles to the folded surface (typically visualized on a stereonet). The axial surface of a particular fold may be located based on observations of the folded geologic structure, but in general it has no direct physical manifestation. Contrast with hinge surface, which is defined as the surface containing a set of hinge lines in the stack of folded surfaces defining a fold structure. As a geologic surface, the axial surface has geometric properties, including orientation, which may be specified by observations at one or more locations, or generalized using terminology (upright, inclined, reclined, recumbent, overturned). (revised from GeoSciML 3.2)

the line linking points of maximum curvature on a folded surface (http://www.geosci.usyd.edu.au/users/prey/Teaching/Geos-2123/Folds/Sld22.html). A low-dimensional feature

Surface that contains the hinge lines in a stack of folded layers

The angle between adjacent limbs of a fold, normally determined by drawing tangents to the fold limbs at the inflection points.

The generally planar region of a fold which lies between two adjacent hinge lines and is confined between the zones of maximum curvature. A role played by some layered rock reated to the adjacent fold hinges. Not necessarily a feature

Straight vs curved limbs, eg kink, chevron, sinusoidal, box

linear distance between inflection points in a single fold (GeoSciML v3.2)

Concordance or discordance of bisecting surface and axial surface, or ratio of length of limbs. Folded surface may have asymmetry defined by limb length ratio if inflection points are defined. Definition based on bisecting surface/axial surface angle depends on having multiple surfaces defined such that the axial surface may be identified. (symmetric, assymetric)

A collection of congruent folds (axis and axial surface are parallel) produced by the same tectonic event. Sometimes referred to as a "Fold Train". (GeoSciML 4.0.1)

The distance between adjacent crest or trough of a single fold, or the average distance between adjacent crests or troughs in a fold system.

Variation in orientation of fold hinge along trend of fold, distinguish sheath from cylindrical folds. Specify with terminology eg sheath, dome, basin, cylindrical.

Rounded vs. angular hinge zones; has to do with the proportion of the wavelength that is considered part of hinge

boolean value, true if wavelength of folds in a fold system is approximately the same

step-like fold in rock strata consisting of a zone of steeper dip within an otherwise horizontal or gently-dipping sequence.

A fold which closes laterally and is therefore neither antiformal nor synformal.

Chaotic and highly sinuous fold typically in an isolated layer within a more homogeneous rock body. Typical of sedimentary slump folding and veins or dikes in medium to high-grade metamorphic rocks

Surface dips between 0 and 10 degrees; typically used to describe orientation of fold hing surface or axial surface, use equivalent term 'Horizontal inclination' for other geologic surfaces.

A fold that has an essentially horizontal axial plane.

A fold of which the core contains the stratigraphically younger rocks

A convex-downward, concave upward fold.

Surface dips between 80 and 90 degrees, used to describe orientation of fold hinge surface or axial surface; use equivalent term 'Vertical inclination' for other geologic surfaces.

A fold for which the fold axis is vertical and axial surface is upright.