Distribution of linear mesostructures in oblique folded surfaces: Unravelling superposed Ordovician and Variscan folds in the Pyrenees

Detailed mapping and structural analysis yielded new data on the geometry of Ordovician folds in the Pyrenees. These folds caused the Variscan mainphase folds to develop over non-horizontal bedding surfaces in the pre-Upper Ordovician rocks. As a result, the Variscan mainphase fold axes and intersection lineations in these rocks present a wide range of orientations. Bedding surfaces exhibit a complex pattern in map view making it necessary to reconstruct the structure in 3D. Computer aided reconstruction tools such as FoldPlot proved useful for visualizing and reconstructing the geometry of such refolded structures in 3D. In the absence of map-scale key horizons, evidence of superposed folds is provided by detailed mapping of mesostructures. This requires a good and continuous outcrop over an extended area since one single fold system can account for a complex distribution of the subsequent intersection lineation. As a result, a cartographic study and a structural analysis are warranted because the direction of the Ordovician folds cannot be established only by the orientation of the L2 mesostructures.