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The extensional period in the Bay of Biscay-Pyrenean domain during the Early Cretaceous influenced subsequent Upper Cretaceous contractional Alpine structures of the Pyrenean orogen. In the Pyrenees, the Lower Cretaceous rift system shows en echelon geometries for different basins, with the Organyà Basin being one of the most important. This basin is located in the southern central Pyrenees, and the inversion of its W-E southern margin has been related to the development of the Bóixols thrust sheet, the northernmost of the south Pyrenean thrust sheets. Detailed interpretation of outcrop and seismic reflection data has revealed the presence of a NNW-SSE trending relay area, which corresponds to the western boundary of the Organyà Basin. The postrift facies belts parallel this boundary. The geometry of the contractional structures shows related variations such as changes in the structural relief and the plunge and the wavelength across this relay area. The synorogenic sediments also show characteristic thickness variations and onlap geometries perpendicular to thrust-transport direction. These evidences highlight the presence of this extensional margin and corroborate its influence in the subsequent stages of the evolution of the area. Seismic, well, and field data have been incorporated into a 3-D structural model in order to better understand the 3-D geometry of the study area.

The study area is located within the Central Andes, a complex region composed of different structural styles. The region is characterized by highly elevated basement cored ranges, which abruptly break the foreland plain. These ranges were uplifted mainly by deep detached high-angle faults or by the inversion of former extensional faults of the Cretaceous rift. Palaeozoic orogenies generated crustal scale discontinuities in the basement, some of them reactivated during the Andean orogeny. Sedimentary sequences and layers architecture in the basins bordering ranges recorded the tectonic evolution of the region. Basement, syn–rift, post-rift and three foreland stages were interpreted in the seismic sections according to the arrangement of the horizons and the main outcropping geological units in bordering ranges. Based on seismic data sets and field data, here we document a particular style of activation of basement faults. Thick-skinned structures that are not always related to the tectonic inversion but to the reactivation of older basement anisotropies represent a paradox since they were not active during the rifting stage. A flat slab subduction and a subsequent angle recovery conditioned the structural evolution of the area.

Structures mapped in the southern Cordillera Oriental of the Andes show an unexpected geometry in an east-west cross-sectional view, with a remarkable predominance of west-directed thrusts. Although some of the Andean structures trend north-south perpendicular to the main eastwest direction of Andean shortening, many of them clearly differ from this expected orientation. This peculiar structural style has been largely related to the inversion of the Cretaceous Salta Rift Basin; however, some of these anomalously trending Andean folds and faults do not result from the inversion of Cretaceous faults. This lack of inversion of some Cretaceous structures becomes evident where west-dipping extensional faults rest in the footwall of west-directed thrusts instead of developing east-directed thrusts, as would be expected. Detailed study of several structures and examination of the geometry and facies distribution of several basins highlight not only the role played by the inversion of Cretaceous extensional faults on the geometry of the Andean structures, but also that played by basement anisotropies on the development of both the Cretaceous extensional faults and the Andean contractional structures.

Detailed geological mapping of the La Cerdanya area (Canigó unit, Eastern Pyrenees) provides new data characterizing the different structural styles exhibited by Cambrian-Lower Ordovician (Jujols Group) and Upper Ordovician successions. Their unconformable contact, related to the Sardic Phase, ranges from 0° (paraconformity) to 90° (angular discordance). The Jujols Group rocks topped by the unconformity are affected by Sardic foliation-free open folds. The pre-Sardic succession, the Sardic Unconformity and the lower part of the post-Sardic succession (Rabassa Conglomerate and Cava formations) are cut and offset by several Late Ordovician NNE-SSW-trending synsedimentary extensional faults associated with hydrothermal activity, which dramatically affected the thickness of the lower part of the Upper Ordovician succession. We relate (i) the Mid-Ordovician Sardic uplift and erosion, and (ii) a Mid-Late Ordovician upward propagating extensional fault system bounding the outline of half-grabens, subsequently infilled by alluvial deposits, to a thermal doming event (about 475-450 Ma) that led to the uplift and stretching of the Ordovician lithosphere. Thermal doming may be caused by mafic magma underplating and responsible for the coeval calcalkaline magmatic activity broadly developed in the Eastern Pyrenees. We discuss the similarities between the Mid-Ordovician Sardic Unconformity and other Early Palaeozoic unconformities described in neighbouring areas. Finally, we suggest a geodynamic scenario in which a regional-scale thermal event was related to the opening of the Rheic Ocean that led to the drift of Avalonia from the SW-European margin of Gondwana. Introduction text file Click here to access/download;text file;Puddu et al rev.docx Lines 525-530: Cite references. Revision: Done Lines 539-541: Same, cites would help. Revision: Done Lines 547: Do not recommend start a paragraph by "As a result". It should be continuation of the previous because continues talking about the same.

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