Cover-basement relationships in a fold-and-thrust belt with inherited uneven weak horizons distribution: example from the southern Pyrenees across the Jaca basin

We present a new cross-section across the Jaca basin in the southern Pyrenees, aiming to analyze the temporal and spatial distribution of deformation in a fold-and-thrust belt. In this study, we have integrated all available subsurface data, including seismic sections and well data, with surface data to construct a balanced cross-section and partial restored cross-sections that illustrate the evolution of the south-Pyrenean fold-and-thrust belt.

Contractional deformation, initiating the development of the Pyrenean Mountain belt, started during Late Cretaceous times due to the reactivation of the Early Cretaceous hyperextended margin. Subsequently, deformation progressed during the Paleogene within the unstretched Iberian plate. In this region, the kinematics of the thrust wedge was controlled by inherited extensional faults and the unevenly distribution of Triassic evaporites above the basement.

Although deformation progressed toward the foreland, synchronous thrusting characterized the internal deformation of the thrust wedge. The localization and switching of deformation along the fold-and-thrust belt resulted from the interaction of unevenly distributed weak layers, including salt, and syntectonic sedimentation.

This work illustrates how detailed fieldwork, when combined with subsurface data and news concepts and methodologies (such as the use of drone imagery and analogue and numerical modelling), can significantly improve the understanding of the structure and evolution of fold-and-thrust belts.