Offshore fault system in the Al Hoceima region from new high-resolution bathymetric and seismic reflection data

Lafosse, Manfred ... et. al.-- European Geosciences Union General Assembly 2014 (EGU2014), 27 april - 2 may 2014, Vienna, Austria.-- 1 pageThe Al-Hoceima Region (Morocco) is the one of the most active seismic area of the western Mediterranean Sea. Detailed surveys in a shallow water environment are required to identify the connecting onshore-offshore active structures and to propose a tectonic framework. We use combined high-resolution seismic reflection and swath-bathymetry data from the Marlboro-2 cruise, which took place in 2012 off the coast of Al Hoceima, to detail the fault system through the Nekor basin, between the Trougout Fault and the Boussekour Agdal fault. The Boussekour-Agdal fault is a N026 oriented fault, dipping east and affecting the plio-quaternary sequence offshore and the internal units of the oriental Rif onshore. The fault trace shows a vertical offset of 6.5 m on the high-resolution swath bathymetry close to the shoreline, while the northern prolongation of the fault is buried. The Bokkoya fault (Calvert et al. 1997) is a N029 oriented fault dipping east. The vertical offset at the seafloor is 13m. This fault affects sedimentary structures above a paleo-terrace at -105mbsl, probably related to the last sea-level fall. The onshore-offshore N-S oriented Trougout fault corresponds to the eastern boundary between the plio-quaternary Nekor basin and the volcano-clastic deposits of Ras Tarf. This fault produces a vertical offset of 2.3m at the sea-floor. These three major fault zones limit two basins: the Nekor basin between the Bokkoya and the Trougout faults, and a depression between the Boussekour-Agdal and the Bokkoya Faults. The quaternary deposits are syn-tectonic. In the Nekor basin secondary normal faults are oriented N150, shift the sea-floor and affect the Messinian unconformity. Successive positions of a paleo-canyon (seen in the seismic lines) show a migration of the subsidence from east to west inside the Nekor basin. Faults affecting the Messinian unconformity control this subsidence. Between the Boussekour-Agdal and the Bokkoya faults, the thickness and the geometry of the plioquaternary deposits over the Messinian unconformity may indicate a more recent subsidence. We interpret these structures as a sinistral transtensional tectonic system. The migration of the subsidence from east to west during the Plio-Quaternary and the geometry of the tectonic structures indicate the progressive abandoning of eastern structures in the Nekor basinPeer Reviewe

The El Masnou Infralittoral sedimentary environment (Barcelona province, NW Mediterranean Sea): morphology and Holocene seismic stratigraphy

A detailed analysis of the morphology and the Holocene seismic and sequence stratigraphy and architecture of the infralittoral sedimentary environment of the El Masnou coast (Catalonia, NW Mediterranean Sea) was carried out using multibeam bathymetry and GeoPulse seismic data. This environment extends down to 26-30 m water depth, and is defined morphologically by two depositional wedges whose seafloor is affected by erosive furrows, slides, fields of large- and small-scale wavy bedforms, and dredging trenches and pits. Erosive terraces are also identified in the transition domain toward the inner continental shelf. The Holocene stratigraphy of the infralittoral environment is defined by two major seismic sequences (lower and upper), each one formed by internal seismic units. The sequences and units are characterised by downlapping surfaces made up of deposits formed by progradation of coastal lithosomes. The stratigraphy and stratal architecture, displaying a retrogradational arrangement with progradational patterns of minor order, were controlled by different sea-level positions. The stratigraphic division represents the coastal response to the last fourth-order transgressive and highstand conditions, modulated by small-scale sea-level oscillations (≈1-2 m) of fith to sixth order. This study also highlights the advantage of an integrated analysis using acoustic/seismic methods for practical assessment of the anthropogenic effects on infralittoral domains based on the association of marine geological observations

Sedimentary evolution of the Le Danois contourite drift systems (southern Bay of Biscay, NE Atlantic):A reconstruction of the Atlantic Mediterranean Water circulation since the Pliocene

The evolution of the Le Danois contourite depositional systems (CDS) during the Pliocene and Quaternary was investigated based on high-resolution seismic reflection data. From old to young, six seismic units (U1-U6) bounded by major discontinuities (H1-H6) were identified. Regarding variations of the bottom-current circulation, four evolution stages of the Le Danois CDS were identified, including onset (similar to 5.3 to 3.5-3.0 Ma), initial (3.5-3.0 to 2.5-2.1 Ma), intermediate (2.5-2.1 to 0.9-0.7 Ma) and drift-growth (0.9-0.7 Ma to present day) stages. The CDS associated with the Atlantic Mediterranean Water (AMW) along the middle continental slope initiated at similar to 3.5-3 Ma and was widely built after the Mid-Pleistocene Transition (MPT; 0.9-07 Ma). At a shallower water depth, a second CDS associated with the Eastern North Atlantic Central Water (ENACW) started to develop from the late Quaternary (similar to 0.47 Ma) onwards. In the AMW-related drift system, the Le Danois Drift was generated both under glacial and interglacial climatic oscilations. Repeated internal structures in unit 5 that consist of acoustically transparent lower parts, moderate amplitude upper parts and high amplitude erosional surfaces at the top, are compared with interglacial/glacial cycles since the middle Pleistocene to the present day. These cyclic features suggest coarsening-upward sequences of the Le Danois Drift and processes related to enhanced AMW during glacial stages. The estimated sedimentation rate of the Le Danois CDS reached a maximum during the MPT (at least similar to 27 cm/ky) and then decreased until present-day (similar to 5 cm/ky). Variations of sedimentary stacking patterns and processes of the Le Danois CDS imply full domination of the intermediate water mass along the central Atlantic and southwest European continental slopes from the late Pliocene (similar to 3.5-3.0 Ma) onwards

An exploratory modelling study on sediment transport during the Zanclean flood of the Mediterranean

A nearly 400-km-long erosion channel through the Strait of Gibraltar has been interpreted as evidence for a catastrophic refll of the Mediterranean at the end of the Messinian salinity crisis, 5.33 million years ago. This channel extends from the Gulf of Cadiz to the Algerian Basin and implies the excavation of ca. 1000 km3 of Miocene sediment from the Alboran Basin and bedrock from the Strait of Gibraltar. The fate of these eroded materials remains unknown. In a frst attempt to predict the distribution of those food deposits, we develop a numerical model to simulate the transport of material eroded from the Strait of Gibraltar. It is a Lagrangian model based upon standard sediment transport equations which is able to simulate suspended and bed load sediment transport. Water circulation during the food was obtained from a hydrodynamic model of the whole Mediterranean Sea previously developed by the authors and applied to the Zan clean food. Five particle sizes were considered for suspended load and three for bed load transport. Areas of sediment deposition in the Mediterranean Sea were determined. In the case of suspended load, these are related to hydrodynamic conditions: areas sheltered from the jet of incoming water by local topography and areas where water currents abruptly decrease due to a sudden increase in water depth. In the case of bed load transport, sediments follow water streamlines and deposits are much more localized than in the case of suspended load. Single channel seismic records were also analysed to identify and characterize food-related deposits in the eastern Alboran Sea.Ministerio de Economía y Competitividad FAUCES CMT2015-65461-C2-

The Mediterranean and Atlantic connection: Seismic Clues from the Alboran Sea

Ercilla, Gemma ... et. al.-- Regional Committee on Mediterranean Neogene Stratigraphy (RCMNS) Interim Colloquium 2015 - Mediterranean-Atlantic Gateways (Neogene to present), 5-8 May 2015, Rabat, Marocco.-- 1 pageThe spatial and temporal evolution of contouritic features as well as changes in their morphology and type suggest: i) their formation roughly agrees with the present-day Mediterranean water masses distribution, i.e., the Low Dense Mediterranean Water-LMW (Winter Intermediate Water + Levantine Intermediate Water) in the Spanish margin, and the High Dense Mediterranean Water ¿DMW( Deep Mediterranean Water) in the subbsains and Moroccan margin; ii) the important role played by the changing landscape during the Pliocene and Quaternary, with important consequences for the water masses circulation, especially for the DMW. Point and linear barriers, and troughs and elongated subbasins, condition a complex current distribution, especially for the Quaternary; iii) a higher energetic recirculation of the DMW in the Western Alboran Basin; iv) a more an enhanced density contrast between the LMW and DMW during the Quaternary; and v) larger vertical and horizontal displacements of the water mass interfaces during the Quaternary related to 4th-order glacioeustatic change. These frist paleoceanographic reconstructions have implication for the ventilation of Mediterranean waters trough the Strait of Gibraltar, Mediterranean Outflow Water formation, Altantic-Mediterranean interchange and then for the AMOC and climatic changes in the past.Peer Reviewe

Deep-water turbidite systems: a review of their elements, sedimentary processes and depositional models. Their characteristics on the Iberian margins - Sistemas turbidíticos de aguas profundas: revisión de sus elementos, procesos sedimentarios y modelos deposicionales. Sus características en los márgenes Ibéricos

Turbidite systems or submarine fans are considered the most important clastic accumulations in the deep sea and represent the sediment-transfer system between the hinterland source area and the deep-sea depositional sink. Their deposits contain information about global factors and local factors. Different scales and varying observational methods have contributed to the lack of a unifying terminology. In order to solve this problem several authors have proposed an “elemental approach”. The main architectural elements defining a turbidite system are: large-scale erosive features (mass-movements and canyons), channels and channel-fill deposits, overbank deposits and lobes. The sediment making up these elements is principally from gravity flow deposits, the most widely recognised being the turbidite, and other submarine mass movements. The genesis and character of these elements, as well as the overall geometry of the systems, indicate they are formed by a complex interaction between global and local factors. Various turbidite-system classifications are found in the literature, the most widely-used being based on grain size and feeder systems. Besides the scientific importance of turbiditic systems, they are predominantly studied because of the economic interest in them, as turbidite sandstones constitute important gas and oil reservoirs. Turbidite systems shape the seafloor of the Iberian continental margins and contribute in a large part to their outbuilding and basin infilling. They are hugely variable in size, location within the physiographic domains, style and overall geometry of the architectural elements, as well as sediment composition. The most studied Iberian turbidite fans are in the Mediterranean Sea whereas those of the Atlantic Ocean remain poorly known

New insights on the Alboran Sea basin extension and continental collision from magnetic anomalies related to magmatism (western Mediterranean)

The comments of two anonymous reviewers have improved the quality of this manuscript. This study was supported by projects CGL2016-80687-R AEI/FEDER , P18-RT-3275 , B-RNM-301-UGR18 and RNM148 ( Junta de Andalucía/FEDER ). Y.M.M was supported by NASA under award number 80GSFC17M0002 . V.T.S. was supported by the FPU PhD grant ( 16/04038 ). ICM-CSIC author acknowledges the Severo Ochoa funding from the Spanish government through the “ Severo Ochoa Centre of Excellence ” accreditation ( CEX2019-000928-S ). University of Granada supported this study by funding the APC for publishing as an Open Access articile through an agreement with Elsevier.In the Alboran Sea there are a few well exposed Neogene and Quaternary volcanic zones, often geographic highs, that are generally associated with magnetic anomalies. In this paper, we present a characterization of these magnetic anomalies based on a recent and accurate magnetic data compilation for the Abloran Sea area. The anomalies reveal the distribution of magmatism and shed light into the discussion about the origin and evolution of the westernmost Mediterranean. One of the most relevant magnetic anomalies is the Nador dipole, which extends from the Gourougou volcano to the Chafarinas Islands, and is related to an E-W crustal scale intrusion. However, the main NE-SW elongated continuous dipoles of the central Alboran Sea are not related to any surface structure, but they are parallel to the Alboran Ridge, which is the main volcanic high in the Alboran Sea, and are located to the north of it. These anomalies extend discontinuously eastward along the NW-SE dipoles located along the Yusuf fault zone. The results of our 2D magnetic forward modeling suggest that the causative bodies of these main magnetic dipoles are deep igneous bodies. According to the tectonic evolution of the region, and the high magnetic susceptibility values obtained, these igneous bodies probably are made of a basic igneous rocks. Their emplacement may represent the westward tip of the rift axis of the AlKaPeCa Domain, which is related to the Oligocene-Miocene NW-SE extension, and associated with the southern slab retreat stage and oceanic spreading of the Algerian basin. Afterwards, these bodies were displaced toward the west, together with the Alboran Domain, and affected by the STEP fault located at its southern limit. Since the Late Miocene, the north Alboran Ridge elongated intrusions acted as a backstop that conditioned the folding and uplift of the Alboran Ridge in a tectonic indentation setting. In this setting, the STEP fault is deformed and the eastern part of the bodies were segmented along the Yusuf transtensional fault system. Simultaneously, the E-W crustal body related to the Nador magnetic dipole was emplaced, possibly evidencing a slab tearing process. The deep seated basic igneous bodies constitute main crustal heterogeneities that reveal and drive the Alboran Sea tectonic inversion.FPU 16/04038Spanish government CEX2019-000928-SNational Aeronautics and Space Administration 80GSFC17M0002Universidad de GranadaJunta de Andalucí