The folds “folds” are one of the forms of secondary geological structures that occur in rock masses as a result of their exposure to a number of geological forces, where the pressure resulting from ground movements causes the appearance of folds or wrinkles within the rocks, especially sedimentary and metamorphic, called sedimentary and metamorphic rocks. These wrinkles folds. And the convex fold: in which its wings are tilted outward,
Concave fold: The wings are inclined inward. As shown in the following figure.
Parts of the Fold
1- Wings of the fold: are The oblique rocky parts that are on its sides, when it tilts outward, the fold is convex, and when it leans inward, the fold is concave. 2- The axial plane: is that plane that bisects the angle between Wings of the fold.
3- The fold axis: is that line that arises from the intersection of the axial plane with the body of the fold. 4- The Summit: It is the highest part of the convex fold.
2018 5- Bottom: It is the lowest part of the concave fold.
Types of folds
1- The fold of the body
The axial plane of the symmetrical fold is vertical so that the layers on its sides are inclined to the same degree, in addition to that the axis of The fold is horizontal.
2- The fold is asymmetrical
The axial plane of the asymmetric fold is slightly inclined from the vertical with the fixed position of the axis so that it is horizontal as the previous type.
3- Inverted fold
The axial plane of the inverted fold is inclined so that the two ends are tilted in the same direction with the position of the axis fixed horizontally.
4- The recumbent fold
It is almost the axial plane of the recumbent fold Likewise, the axis is in a horizontal position or closer to the horizontal.
5- Submersible fold
In the preceding kinds, the fold axis was horizontal, but in the sinking fold, it becomes inclined.
6- Dome and Basin
When a person is exposed to a total of The inclination of the stone units, such as the sedimentary layers of horizontal pressure pressures in all directions, becomes outward, and folding occurs in all directions, resulting in the creation of a convexity with a centre and a lazy axis. If the rock units are subjected to tectonic movements and the slope of the strata is reversed towards a central bottom, another geological structure known as a basin emerges. On structural geological maps, the symbol represents the basin, whereas the sign represents the dome.