A graphical method and workflow for the generation of structure contours for horizontal cylindrical folds

Abstract

A graphical method developed for the construction of structure contours for inclined planar surfaces has been extended to curved or folded surfaces with cylindrical geometries and horizontal axes. These structure contours can be used to constrain the outcrop trace of a folded contact on a geological map. The extended method requires, as a minimum, a field of orientation data and the map position of a single elevation on the contact under investigation. The method utilises orientation data collected on and around a partially mapped trace of a folded contact to constrain the outcrop trace throughout a geological map. The method uses a vertical cross-section that is parallel to the profile plane of any folds present. Crest, trough and hinge points identified in the cross-section can be projected on to the geological map in their correct positions and elevations. Similarly, structure contours on fold axial surfaces can be projected on to the geological map and the contours used to locate the axial traces of cylindrical folds with horizontal axes.