ALBERT

Description: The northwest Mediterranean Basin includes a thick Messinian salt sequence composed of three evaporitic units. From these, the intermediate unit, which is dominantly composed of halite, acted as a gravitational detachment favoring the downslope failure of the overlying sediments in a thin-skinned deformation regime. As a result, the structure of the margin is characterized by an upper extensional domain with basinward-dipping listric normal faults and a lower contractional domain that accommodates upslope extension by folding, salt inflation, or diapir squeezing. Lower to middle Miocene volcanic seamounts (presalt reliefs) located at the upper extensional domain locally disrupted the evaporitic units and produced salt flow perturbations. They acted as passive buttresses during the gravitational failure modifying the structural zonation of the margin. Using an experimental approach (sandbox models), we analyze the role played by seamounts during the kinematic evolution of passive margins and how they alter salt flow and suprasalt deformation during gravitational gliding. The experiments found that the seamounts locally interrupt the structural zonation of the margin because they hindered downdip salt flow during early deformation. Seamounts initially compartmentalize the margin architecture, resulting in the development of two gravitational subsystems with two extensional/contractional pairs that are subsequently reconnected when the accumulation of salt analog upslope of the relief is enough to overthrust it. From this point onward, the cover is passively translated downslope as a regional system. The changes in the viscous layer flow velocity related to the dip differences between the flanks and edges of the seamount determine the kinematic evolution of this system. Our experiments also provide geometric constraints to consider during interpretation of these structures, which are commonly poorly imaged in seismic data.

Description: Salt-detached ramp-syncline basins are developed in extensional settings and are characterized by wide synclinal sedimentary basins detached on salt and formed above the hanging wall of active ramp-flat-ramp extensional faults. They are rarely fault bounded; instead, they are bounded by salt structures that are in general parallel to the major subsalt structures. As such, the formation of these extensional systems requires the presence of (1) a subsalt extensional fault with significant dip changes and (2) an evaporitic unit above the extensional fault, which partially or completely decouples the basin from a subsalt extensional fault. Salt-detached ramp-syncline basins have a significant exploration potential when their extensional geometry is preserved and when they have undergone positive tectonic inversion and consequent uplift and fold amplification. However, in some cases, their subsalt geometry may not be fully recognizable, especially when subsalt seismic imaging is poor. To obtain a deeper understanding of the geometry and kinematic evolution of these salt-detached ramp-syncline basins, we performed a series of analog modeling experiments, in which the models’ cross sections had been sequentially restored. Analog models and restoration results reveal that the kinematic evolution of the salt-detached ramp-syncline basins during extension and inversion depends on the interaction of different factors that may function simultaneously. Our results are used to improve the interpretation of seismic sections in inverted Mesozoic salt-detached ramp-syncline basins on the Atlantic margins, where subsalt faults are not well-imaged, and thus the suprasalt geometries must be used to infer the subsalt structure.

Description: Southern Pyrenean frontal thrusts are usually blind or partially covered by syn- and post-tectonic sediments of the Ebro Foreland hampering their interpretation. We have investigated the geometry and evolution of the Súria Anticline, a frontal structure of the Southern Pyrenees, which is characterized by the presence of multiple buried and blind thrusts displaying a complex triangle zone and several fishtail structures at depth. To characterize the geometry and structural evolution, a combination of surface geology, subsurface data interpretation, and analog modeling have been integrated into a unique 3D geologic model. The surface geology of this area depicts a rather simple structure, characterized by a north-directed backthrust and a gentle anticline, both striking west–southwest/east–northeast. In contrast, geophysical data indicate that the subsurface structure is more complex, exhibiting several northward- and southward-directed thrusts and folds detaching on the Pyrenean foreland Eocene evaporites. Integration of surface (geologic maps and dip measurements) and subsurface data (seismic and wells) allowed us to reconstruct the 3D structure of this area. To produce a more robust kinematic model, we used an experimental approach to investigate the evolution of frontal structures in folds and thrust belts on evaporitic detachments. Different viscous layer configurations were tested in a series of sandbox models comparing them with the evolution of the Súria Anticline. Taking into account the deformation and that seismic quality is in general poor, the experimental results allow us to better characterize the structures developed in this area. Our structural evolution is characterized by an early stage of salt inflation and fold nucleation. With increasing shortening, the structure evolved to a detachment anticline eventually developing a northward-directed thrust that broke through the northern anticline limb. The present-day geometry developed in a later stage of fold reactivation, when a new regional fold formed, and tightened the preexisting structure.