Oscar Fernández

3D structure and evolution of an oblique system of relaying folds: the Ainsa basin (Spanish Pyrenees)

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.

Extension and inversion structures in the Tethys–Atlantic linkage zone, Algarve Basin, Portugal

Abstract The Algarve Basin is a Meso-Cenozoic sedimentary basin overlying Carboniferous basement, located in the southwestern margin of the Iberian Peninsula. Its structure reveals a protracted tectonic history comprising various pulses of Mesozoic extension followed by Cenozoic compression. This work deals with the structure along the northern margin, where the Mesozoic extensional structures and Cenozoic inversion structures crop out. The strike of the extensional structures ranges from E–W to N–S, as controlled by a shift from Tethyan-dominated extension in the east to Atlantic-dominated extension in the west. Contractional structures are inverted extensional structures, following their same trends. It is argued that the thickness of the Hettangian evaporite layer exerts a strong control on the structural style throughout the basin during the extensional and inversion episodes. The basin is affected by thick-skinned deformation along the northern margin, where salt is thin or absent, basement involved fault systems and short-cut structures. Basinward, as the Hettangian salt thickens, the margin is affected by thin-skinned deformation, with listric and down-to-the-basin growth faults, diapirism and salt-cored detachment folds. The aim was to discuss the key tectonic features, the relevance of salt, and understand the nature, timing, and significance of all these structures in the regional tectonic evolution.

Neogene to recent contraction and basin inversion along the Nubia‐Iberia boundary in SW Iberia

The SW of Iberia is currently undergoing compression related to the convergence between Nubia and Iberia. Multiple compressive structures, and their related seismic activity, have been documented along the diffuse Nubia-Iberia plate boundary, including the Gorringe bank west of the Gulf of Cadiz, and the Betic-Rif orogen to the east. Despite seismic activity indicating a dominant compressive stress along the Algarve margin in the Gulf of Cadiz, the structures at the origin of this seismicity remain elusive. This paper documents the contractional structures that provide linkage across the Gulf of Cadiz and play a major role in defining the present-day seismicity and bathymetry of this area. The structures described in this paper caused the Neogene inversion of the Jurassic oblique passive margin that formed between the Central Atlantic and the Ligurian Tethys. This example of a partially inverted margin provides insights into the factors that condition the inversion of passive margins.

Crustal Structure of the Southern Portuguese Margin - Constraints from Potential Field Methods

The southern Portuguese margin recorded significant extension and subsidence during the Jurassic, resulting in the formation of the Algarve basin. Recent studies have revealed the existence of oceanic crust, of potentially Jurassic age, underlying significant portions of the Gulf of Cadiz to the south and west of the Algarve basin, but the exact relationship between this basin and the oceanic crust is still ambiguous. In this study we integrate data derived from field outcrop studies, interpretation of commercial seismic, and gravity and magnetic modelling to better understand the transition from the rifted continental crust underlying the Algarve basin to the oceanic crust of the Gulf of Cadiz. This integrated approach reveals that the Gulf of Cadiz oceanic crust is related to the WSW-ENE trending Jurassic passive margin of southern Portugal, and is separated from the Algarve Basin by a domain of highly thinned continental crust.