Depositional and erosional bedforms that shape prodelta deposits in the Gulf of Patti (southern Tyrrhenian Sea) and in the Al-Hoceima Bay (northern Morocco) were investigated using multibeam bathymetry as a basis for morphometric analysis. The two study areas have comparable structural settings and oceanographic regimes and share the occurrence of sediment undulations and closely spaced gullies. The resulting bedform fields are confined on prodelta deposits, from the inner to the outer shelf. The infrequent coexistence of these two types of bedforms on other Mediterranean margins makes our case study an ideal opportunity to investigate the processes that may control the combined or independent genesis of each type of bedform. Whereas gullies are more confidently interpreted as the result of erosion of the seafloor by hyperpycnal flows generated at river mouths and/or triggered by settling plumes and small-scale instabilities on delta front, unveiling the genetic mechanism behind sediment undulations is more difficult, and makes identifying the underlying processes, ranging from bottom currents to gravity flows or even internal waves, more ambiguous. Quantitative measurements of the main morphometric parameters of sediment undulations and gullies were computed to resolve relationships between their variability and their distribution over the prodelta area. Particular attention was paid to statistical analysis of sediment undulations using multivariate analysis based on principal component analysis (PCA) and k-mean fuzzy clustering. The individual and comparative analyses suggest that shelf gradients, location and distance from the river mouth, and sediment supply are keys in controlling the growth and scale of sediment undulations with respect to their distribution downslope. Although from our analysis, sediment gravity flows stand out as the most likely mechanism triggering the generation of sediment undulations, alternative causes (i.e., soft-sediment deformation or sediment remobilization by oceanographic processes) cannot be ruled out. Our results provide new insights into the possible origin of sediment undulations under the control of river-driven sediment gravity flows in prodelta settings, indicating that their concomitant occurrence with gullies is not accidental.

In the South Alboran Sea, the moderate seismicity (Mw=6.4) of the strike-slip Al Idrissi Fault Zone does not appear to control directly the landslides distribution. To provide a preliminary geohazard assessment, we characterized the spatial distribution, the volume and the ages of the submarine landslides from multibeam and seismic reflection data in the southern part of the Alboran Sea. Since the Quaternary numerous submarine landslide processes affect the marine sedimentary cover with volumes of the mass transport deposits (MTD) estimated between 0.01 to 15 km3. West of the Al Idrissi Fault Zone, along the South Alboran Ridge’s northern flank, the distribution of the MTD follows the SW-NE bank and ridge trend that correlates with blind thrusts and folds covered by a plastered contourite drift. A pockmark field, related to fluid escape, is visible near landslide scars where the contourite drift is relatively thicker. In this area, landslide scars occur on variable slopes (2-24°) and their associated MTD have variable decompacted volumes (0.01-10km3). East of the Al Idrissi Fault Zone, between the Alboran Ridge and the Pytheas Bank, the mapped MTDs have uneven volumes. The smaller ones (<1 km3) have their slide scars on steep slopes (>10°), whereas those of the largest ones (3-15 km3) occur on gentler slopes (<5°). These observations and a slope stability analysis suggest that the combination of seismic shaking, blind thrusts activity, relatively high sedimentation of contourite deposits, and fluid escape dynamics are likely the main controlling mechanisms rather than seismic shaking only. These causal factors would explain the concentration of landslide head scarps at the edge of the thickest parts of the contourite drifts (i.e. crests) may have been controlled locally by fluid overpressures in line with blind thrusts. Additionally, low to moderate seismicity potentially triggered by nearby faults might regionally have played a role in destabilising the seafloor sediments since 1.12 Ma, which coincides with the propagation of the Al Idrissi Fault Zone in the southern Alboran Sea.

The numerous processes (superficial and deep) occurring on margins, their origins, consequences, interactions and quantifications are only very partially described and understood. The identification of the relative role of factors is sometimes completely contradictory between authors. Here, we showed the results of a long-term multidecadal and multidisciplinary study (using geophysical, geological, stratigraphic, paleontological, geomorphologic, geochemical, microbiological and numerical models) in the Western Mediterranean Sea that acts as a natural laboratory at many different scales. We showed how sediments efficiently recorded at the same time: variations of glacio-eustatic sea-level changes, variations of sediments yield and sources, and also enabled quantifying vertical movements and geodynamic worldwide events but also detailed regional mass transport, turbidites and contourites deposits. They are also an archive of paleoclimatic, palaeoceanographic and diagenetic processes.

Automation of the throw backstripping method has proven to be an effective tool for the determination of the evolution of tectonic activity in wide fault zones. This method has been applied to the Al Hoceima Bay (southwesternmost Mediterranean, Alboran Sea) for a time period covering the last 280 kyr on 672 faults imaged on 265 high-resolution seismic reflection profiles. This area was affected by major earthquakes and corresponds to a transtensional basin deformed by growth faults. The automated application of throw backstripping allowed for a faster deciphering of the migration of tectonic activity. Results show a westward migration of the deformation with quickly increasing deformation rates in the most recent time frames near Al Hoceima, one of the most populated cities. This migration is in agreement with the current seismicity, the GPS data, and recent brittle deformation data. Vertical throw rates of up to 0.47 mm/year have been calculated, for the most recent time periods, in segments of the Bokkoya fault zone. The westward migration of the deformation fits with the reconstruction suggested by the westernmost Mediterranean geodynamic models during the Pleistocene epoch, and it might be the consequence of the interaction between the northwest (NW) movement of the South Alboran indenter and the back Rif south-westward displacement. The highly accurate constraints of the evolution of the tectonic activity offered by this automation will substantially improve the seismic hazard assessment.

The tectonics of the Alboran Sea control the distribution of topographic highs and depressions, influencing the water masses' paths controlling the deep basins sedimentation rates. Altogether tectonics and deep currents shaped the seafloor on which we map active faults, contourites, pockmarks, and submarine landslides. Recent numerical models highlight that some of those landslides can generate tsunamis waves on nearby coastal areas, creating the need to describe better and understand those seabed features. Consequently, we put together bathymetric and seismic data to measure Pleistocene slides affecting the deep Alboran basin in an unprecedented collective effort. We mapped and relatively dated 66 mass transport deposits (MTDs) in the West Alboran and Pytheas fields on the north and south flank of the Alboran Ridge. We measured their surfaces, decompacted volumes, slopes, run out, scars heights, scars elevations, and described their type (debris flow or slide) qualitatively from their echo facies. When possible, we also measured the run-off from the scar. We investigated the factor of safety (FOS) and computed based seismic moments based on empirical relationship and faults geometry to characterize the preconditioning factors and triggering mechanisms. The first important result is that post-1.12 Ma MTDs mobilized the most important volumes, in line with the Alboran Sea's topographic highs. Second, seismic lines and the bathymetric images evidence blind reverse faults related to fluid escapes that could contribute to local overpressures in shallow contouritic sediments. Third, we show that local slopes are too flat to allow slopes to destabilize under gravity force only, suggesting that other causal factors need to be considered. Fourth, known seismicity on strike-slip faults in the Alboran Sea is unlikely to trigger MTDs in most investigated areas, suggesting that a combination of preconditioning factors, such as local overpressures and/or reduced strength properties with reverse faults activity, seems the most plausible explanation to trigger the observed MTDs. The overall results highlight that the Alboran tectonics explain the slope destabilization, with varying local sediment properties. However, those properties and past overpressures, deformations, and fluid flows remain to be locally detailed. Future works involving sediments characterizations and dating will follow after the ALBACORE survey scheduled in 2021.

Since the Miocene, the thinned continental crust below the Alboran Sea and its overlying sedimentary cover have been undergoing deformation caused by both convergence of Eurasia and Africa and by deep processes related to the Tethyan slab retreat. Part of this deformation is recorded at the Xauen and Tofino banks in the southern Alboran Sea. Using swath bathymetry and multichannel seismic reflection data, we identified different stages and styles of deformation. The South Alboran Basin is made up of Early Miocene to Pliocene sedimentary layers that correlate with the West Alboran Basin depocenter and are dominated by E-Wtrending folds and thrusts. The Xauen and Tofino Banks first recorded the phase of extension and strike-slip movement during the slab retreat, followed by the phase of compressional inversion since the Tortonian and are now structured by tight folds, thrusts, and mud bodies. This study proposes that the Banks were located on the southern-inherited Subduction Tear Edge Propagator (STEP) fault related to the westward migration of the Alboran domain during the Miocene. The STEP fault zone, acting as a boundary between the African block and the Alboran block, was located along the onshore Jebha-Nekor fault and the offshore Alboran Ridge and the Yusuf fault zone. Thick-skinned and thin-skinned shortening occurred when slab retreat stopped, and inversion began. The present-day style of the deformation seems to be linked to a decollement level made of undercompacted shale on top of the Ghomaride complex.

Progress in the understanding and dating of the sedimentary record of the Alboran Basin allows us to propose a model of its tectonic evolution since the Pliocene. After a period of extension, the Alboran Basin underwent a progressive tectonic inversion starting around 9–7.5 Ma. The Alboran Ridge is a NE–SW transpressive structure accommodating the shortening in the basin. We mapped its southwestern termination, a Pliocene rhombic structure exhibiting series of folds and thrusts. The active Al-Idrissi Fault zone (AIF) is a Pleistocene strike-slip structure trending NNE–SSW. The AIF crosses the Alboran Ridge and connects to the transtensive Nekor Basin and the Nekor Fault to the south. In the Moroccan shelf and at the edge of a submerged volcano we dated the inception of the local subsidence at 1.81–1.12 Ma. The subsidence marks the propagation of the AIF toward the Nekor Basin. Pliocene thrusts and folds and Quaternary transtension appear at first sight to act at different tectonic periods but reflect the long-term evolution of a transpressive system. Despite the constant direction of Africa–Eurasia convergence since 6 Ma, along the southern margin of the Alboran Basin, the Pliocene–Quaternary compression evolves from transpressive to transtensive along the AIF and the Nekor Basin. This system reflects the logical evolution of the deformation of the Alboran Basin under the indentation of the African lithosphere.

This study provides a first characterization of the geomorphic features and relative habitats of the Francesc Pages Bank, located on the upper slope of the Moroccan continental margin in the southern Alboran Sea, western Mediterranean. The Francesc Pages Bank is an ellipsoidal structural high covering 80 km(2) within a depth range of 76-580 m. High-resolution swath mapping allowed to recognize different geomorphic features on the top of the Bank, including crests, banks and ridges. An automatic classification of multibeam sonar data has been performed to identify and map the different physical habitats using terrain parameters derived from the bathymetry as surrogate descriptors. A remotely operated vehicle (ROV) video track acquired in the area showed the occurrence of several dense and uncommonly well-preserved megabenthic assemblages composed of gorgonians, soft corals, and several demosponge species. Multivariate statistical analyses performed on species abundance and terrain parameters derived from ROV observations allowed to define the main substrates governing the distribution of the observed benthic species, which coincide with some of the physical habitats detected by the multibeam automated classification.

In active basins, tectonics can segment the continental shelf and control its stratigraphic architecture and physiography. Segmentation can explain the local evolution and morphology of the continental shelf because of sea-level variations, local tectonic segmentation and hydrodynamic processes. Here we investigate the tectonically active Morocco continental margin (southern Alboran Sea) using high-resolution seismic profiles and multibeam bathymetric data. The active faults bounding the transtensive Nekor basin triggered the segmentation of the shelf into three sectors showing different subsidence rates: a western sector corresponding to an extensive fault relay, a central sector corresponding to the subsiding Al-Hoceima Bay and an eastern sector corresponding to the footwall of the Trougout senestral normal fault. Results show that the staircase morphology of the shelf corresponds to successive submarine terraces at the shelf edge (ST1), mid-shelf (ST2) and inner-shelf (ST3) around -110 m,-80 m, and -40 to -20 m deep, respectively. The terraces correspond to the top of prograding wedges seaward and are erosive landward. They are correlated with stillstand from the Last Glacial Maximum to the Holocene highstand. Above the terraces, sub-aqueous dune fields are interpreted as degraded and deposited during the post-glacial transgression. In the central sector, typical delta front seafloor undulations on the shelf and crescent shaped bedforms at the head of marine incisions on the upper slope denote a fluvial influence during the Holocene. Seismic stratigraphy analysis revealed the preservation of six seismic units bounded by polygenic regional unconformities (S1, S2, S3, S4 and S5). Based on comparison with other Mediterranean margins, S1 to S5 are attributed to 4th order maximum regressive surface. We discuss the local preservation of the system tracts as a function of the vertical motion and the physiography of this tectonically active domain. This study provides useful clues for future local paleo-seismic analysis and to advance our understanding of sedimentary processes in active areas.

The active Eurasia-Nubia plate boundary runs across the Alboran Sea in theWestern Mediterranean Sea, where the connection between the Atlantic and Mediterranean water masses occurs. Earthquakes above magnitude M-w > 6 may favour the occurrence of landslides within contouritic drifts in the Alboran Sea. A compilation of recent multibeam data reveals for the first time the distribution of slope failures along the Xauen-Tofino banks, in the southern Alboran Sea. Here, we provide a detailed mapping and description of the morphology of eight Holocene landslides, including volume estimations of the failed mass and the related mass transport deposits (MTDs). The most voluminous landslide mobilized similar to 0.5 km(3) of sediment at the initial stage of slope failure, and formed a similar to 2.2-5.6 km(3) MTD. A finite-difference numerical model, assimilating the landslide to a granular flow, simulates tsunami generation and propagation for a slide similar to the most voluminous one. Simulations show that the coastline of Al Hoceima may be impacted by a similar to 0.5-m-high tsunami wave, whereas the coastline of Al Jebha may be impacted by a similar to 1-m-high tsunami wave, only similar to 13 min after sediment failure. The 0.2-m-high tsunami waves may impact the southern Spanish coast of the Iberian Peninsula similar to 20 min after slide initiation. Although the elevations of the modeled tsunami waves are modest, landslides from the Xauen-Tofino banks may represent a more dangerous source of tsunami in some parts of the Moroccan coast than earthquakes.

La convergence oblique des plaques tectoniques par rapports aux marges continentales conduit à la distribution de la déformation entre zones soulevées et zones en subsidence. Dans ce contexte, les mouvements verticaux peuvent être contrôlés par l’héritage structural et peuvent influencer l’architecture des dépôts sédimentaires de la plateforme continentale et du bassin profond. La sismique réflexion et la bathymétrie permettent d’imager les architectures des plateformes et du bassin profond. En Méditerranée Occidentale, la convergence Afrique-Eurasie et le contexte d’arrière-arc contrôle depuis le Miocène la déformation du domaine d’Alboran. La convergence oblique a conduit à la formation de grandes structures transpressives traversant le bassin et de couloirs décrochants Miocène réutilisant localement les limites des nappes chevauchantes mises en place lors de la collision Oligo-Miocène. Trois aspects sont développés dans cette thèse: 1) la caractérisation des structures tectoniques actives et Pléistocène associées au bassin de Nekor, un bassin périphérique du domaine d’Alboran situé sur sa marge sud, et la démonstration de l’importance de l’héritage Oligo-Miocène dans l’évolution de ce bassin, 2) le décryptage de l’architecture de la plateforme sédimentaire du bassin de Nekor, pour proposer un modèle d’âge des séquences de dépôts pour les derniers 500 000 ans, et enfin 3) la démonstration de l’influence de la segmentation de la marge par la tectonique sur la géométrie de la plateforme sédimentaire, l’histoire de l’évolution des plis et des failles décrochantes affectant le bassin profond depuis le Pliocène et la chronologie des structures décrochantes.

The geodynamic processes in the western Mediterranean are driven by both deep (mantle) processes such as slab-rollback or delamination, oblique plate convergence and inherited structures. The present-day deformation of the Alboran Sea and in particular the Nekor basin area is linked to these coeval effects. The seismically active Nekor basin is an extensional basin formed in a convergent setting at the eastern part of the Rif Chain whose boundaries extend both onshore and offshore Morocco. We propose a new structural model of the Nekor basin based on high-resolution offshore data compiled from recent seismic reflection profiles, swath bathymetry acquisitions and industrial seismic reflection profiles. The new data set shows that the northern limit of the basin is oriented N49 degrees with right-stepping faults from the Bousekkour-Aghbal fault to the sinistral Bokkoya fault zone. This pattern indicates the presence of an inherited left-lateral basement fault parallel to the major inherited Nekor fault. This fault has been interpreted as a Quaternary active left-lateral transfer fault localized on weak structural discontinuities inherited from the orogenic period. Onshore and offshore active faults enclose a rhombohedral tectonic Nekor Basin. Normal faults oriented N155 degrees offset the most recent Quaternary deposits in the Nekor basin, and indicate the transtensional behaviour of this basin. The geometry of these faults suggests a likely rollover structure and the presence at depth of a crustal detachment. Inactive Plio-Quaternary normal faults to the east of the Ras Tarf promontory and geometries of depocentres seem to indicate the migration of deformation from east to west. The local orientations of horizontal stress directions deduced from normal fault orientations are compatible with the extrusion of the Rifian units and coherent with the westward rollback of the Tethyan slab and the localization of the present-day slab detachment or delamination.

Abstract The style of inversion of inherited extensional basins in the Western Alps is investigated through thermo-mechanical modelling. Two-dimensional models consist of a half-graben embedded in a relatively strong crust (basement) and filled with weak syn-rift sediments (cover). We investigate the relative influence of the internal friction (µ) of the basin-bounding normal fault, tectonic burial (h) under an overlying nappe and the geothermal gradient. We use a viscoplastic model with symmetrical shortening. The inherited normal fault is implemented as a curved thin body with a variable friction coefficient (µ) ranging from 0.1 to 0.6. The style of basin inversion is controlled at shallow depth by the internal friction coefficient, whose influence decreases with the increase of both burial depth and geothermal gradient. With increasing burial and/or geothermal gradient, fault reactivation is inhibited and distributed deformation in the basement induces the vertical extrusion of the cover. The basin inversion is accompanied by distributed deformation in the cover and by the shearing of the basin and basement interface. The results are consistent with the style of inversion of inherited half-grabens in the external Western Alps, where no significant fault reactivation occurred owing to tectonic burial underneath the Alpine internal units during the early Alpine collision.

We explored the submarine portions of the Enriquillo-Plantain Garden Fault zone (EPGFZ) and the Septentrional-Oriente Fault zone (SOFZ) along the Northern Caribbean plate boundary using high-resolution multibeam echo-sounding and shallow seismic reflection. The bathymetric data shed light on poorly documented or previously unknown submarine fault zones running over 200 km between Haiti and Jamaica (EPGFZ) and 300 km between the Dominican Republic and Cuba (SOFZ). The primary plate-boundary structures are a series of strike-slip fault segments associated with pressure ridges, restraining bends, step overs and dogleg offsets indicating very active tectonics. Several distinct segments 50-100 km long cut across pre-existing structures inherited from former tectonic regimes or bypass recent morphologies formed under the current strike-slip regime. Along the most recent trace of the SOFZ, we measured a strike-slip offset of 16.5 km, which indicates steady activity for the past similar to 1.8 Ma if its current GPS-derived motion of 9.8 +/- 2 mm a(-1) has remained stable during the entire Quaternary.