Geometric and numerical model of progressive limb rotation in detachment folds

Abstract

A simple, area-balanced, geometric model of progressive limb rotation in detachment folds allows the quantification of displacement, uplift, and rotation and the assessment of their effect upon growth strata geometries. Translation of this geometric model into a velocity model of deformation allows the modeling of associated growth strata resulting from background sedimentation and local erosion, transport, and deposition. We show that with constant displacement and sedimentation rate, this model predicts a progressive unconformity, indicating the onlap and eventual overlap of the fold limb caused by a decreasing uplift rate. This decrease is a consequence of the kinematics of progressive limb rotation. Increases in displacement rate, with sedimentation rate kept constant, can lead to offlap and angular unconformities, although subsequent onlap does not necessarily reflect a return to a lower displacement rate. Modeled growth strata geometries exhibit many of the features reported from the literature.