Geology Reference
In-Depth Information
Fig. 1.19.
Cylindrical folds.
a
Non-plunging.
b
Plunging
Fig. 1.20.
Fold classification based on orientation of the axis and axial surface.
a
Horizontal upright:
horizontal axis and vertical axial surface.
b
Vertical:
vertical axis and vertical axial surface.
c
Reclined:
inclined axis and axial surface.
d
Recumbent:
horizontal axis and axial surface. (After Fleuty 1964)
The complete orientation of a fold requires the specification of the orientation of both
the fold axis and the axial surface (Fig. 1.20). In the case of a conical fold, the orientation
can be specified by the orientation of the axial surface and the orientation of the crestal
line on a particular horizon. Common map symbols for folds are given in Fig. 1.21.
