Layer parallel shortening in salt-detached folds: Constraint on cross-section restoration

Cleavage-fissility perpendicular to bedding is a common feature in the external part of fold-and-thrust belts. Three techniques were used to determine the internal distortion in the frontal Southern Pyrenees: the analysis of strain markers such as burrows and rain drops, the measurement of fissility, and the measurement of anisotropy of magnetic susceptibility (AMS). The comparison of the three techniques showed a good fit although they differ in sensitivity to penetrative strain variations in the range of deformation values explored in the study case. On the regional scale, the values of layer parallel shortening (LPS) derived from the markers analysis are very constant and account for 16-23% of shortening. These values are two to three times larger than the shortening values calculated from the restoration of the macroscopic scale structures and indicate a good decoupling above the Cardona salt Formation. This study permitted an accurate restoration of the low-amplitude el Guix detached anticline. © 2003 Elsevier B.V. All rights reserved.This work has been partially financed by ElfAquitaine Production and Grups de Recerca Consol-idats (II Pla de Recerca de Catalunya) Project 2001SGR 00339. We would like to thank Iberpotash forgiving permission to access the railway outcrop andJordi Bayona and Ester Sans for their technicalsupport in the field scaling of the detailed outcrop.Jordi Corbera processed the outcrop image. TheServeis Cientificote`cnics de la Universitat de Barce-lona developed the IMAT program. We are alsograteful to David Durney who developed the fissilityprograms and with whom we have had constructivediscussions in the field. J.M. Casas and J.A. Mun ̃ozhelped us in the data processing and in improving themanuscript. We also want to thank R. Groshong, M.Rowan and K. McClay for their fruitful comments onthe paper as well as to G. Mitra and an anonymousreviewer for the helpful comments on the final versionof the manuscript