Richard Lisle in Oviedo (Spain): Contributions to the analysis of folding – a review

The work carried out by Richard Lisle, stemming from his stay in Oviedo and his integration into the fold analysis group at the local university, addressed a wide range of topics concerning fold geometry and kinematics. Regarding 2D fold geometry, Richard led the development of a method to relate the various classification schemes based on fold fitting functions, using a parameter defined as the normalized area bounded by the folded surface profile. Non-cylindrical folds were analysed based on the properties of developable surfaces and curvature analysis. In the field of kinematics, special attention was given to the neutral surface folding, which led to the distinction between two modes: “parallel tangential longitudinal strain” and “equiareal tangential longitudinal strain”. A method was also developed to estimate the total bulk shortening associated with the formation of flattened parallel folds. The 2D kinematics of various fold types was explored through numerical simulations, based on the displacement laws governing different folding mechanisms. This methodology was applied to the study of chevron folds, folded oblique surfaces, asymmetric folds, recumbent folds, and similar folds. The investigation led to the resolution of certain problems related to rock deformation and resulted in the description of a new deformation mode: “rotation shear”. The study of these topics also involved the development of computational tools to automate and facilitate the strain calculations. The formation mechanisms of several structures associated with folding were likewise examined, including crenulation cleavage, so-called “saw-tooth structures”, curved veins related to folds, and cleavage in pre-existing folds. Finally, we evaluate the impact of this body of work, its limitations, and future prospects for extending the research, particularly by using the results obtained as a foundation for dynamic modelling.