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The structure of the Eocene Ainsa basin is dominated by kilometre-scale thrusts and folds that have trends at c. 70° to that of the main Pyrenean structures. Late uplift and erosion provide excellent exposure of this fold-and-thrust system and its growth strata. Field observations integrated with 2D seismic and well data support the 3D reconstructions presented in this paper. Structural reconstructions of pre-and syn-growth geometries contribute substantial improvements to the understanding of the structure of the area and provide a unique insight into the timing of Pyrenean structures. This study demonstrates that oblique features in the Ainsa basin can be grouped into two main systems: the La Fueba thrust system, an oblique-lateral ramp to one of the main Pyrenean thrusts, and the kilometre-scale folds of the Sobrabe system, a set of anticlines that grew as part of a relaying system of folds. In this study we propose a chronology of deformation based on the geometry of the basin fill, which has been used to frame the general tectonosedimentary evolution of the Ainsa basin. The relative timing of structures indicates that the La Fueba structures predate the Sobrarbe structures, which originated as orogen-parallel structures, and obliquity developed during the growth of these structures through clockwise vertical-axis rotation.

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