Search

New bathymetric and subsurface data from the Santos Basin, offshore southeast Brazil, reveal sharp lateral morphological variations facing the margin-parallel (along-margin) flow of the Antarctic Intermediate Water. The data, derived from 3D Pre-Stack Depth Migrated (PSDM) seismic reflection volumes, show on a ∼100 km long Southern segment slope gullies, mass transport deposits, and scars. These morphologies sharply shift laterally to a ∼50 km long Northern segment, typified by a smooth relief built of plastered contourite drifts with occasional elongated depressions. We examine this sharp lateral shift in the morphology of bottom current indicators in view of the hydrodynamical regime, sediment sources, and their distribution pattern. Results indicate that the sharp lateral morphological shift is attributed to (1) a 30° change in slope orientation, and (2) a northward increase in the across-margin velocity component of the Intermediate Water Boundary Current (IWBC). Subsurface data suggest this flow pattern has persisted since the mid-Miocene. In this case study, the lateral morphological shifts under contemporary hydrodynamic conditions emphasize the importance of understanding the coupling between ocean bottom currents and the seafloor in any marine environment.

This research aims to distinguish genetic sedimentary processes building canyon geomorphological patterns and the factors driving different sedimentary activities in two nearby Mediterranean shelf-incised submarine canyons (Carchuna and Motril) that exhibit different degrees of incision on the narrow margin of the northern Alboran Sea. The straight Carchuna Canyon incises the shelf up to 200 m off the coastline and exhibit steep canyon walls featuring narrow terraces, muddy sands with high contents of organic matter along the thalweg, and transported shelf benthic foraminifera in distal settings. The Motril Canyon head is wider and incises the shelf edge, ca. 2 km off the coastline. It exhibits a sinuous morphology and less steep walls, wider terraces, and higher sedimentation rates with muddy sediments along the thalweg. In both canyons, cross-section relief, width, incision, and area decrease downslope, although these parameters increase locally. The downslope variations of geomorphological parameters are attributed to enhanced erosional/depositional processes promoted by tectonically controlled abrupt changes of the axial channel orientation. The degree of shelf incision, the location of the canyon heads in relation with the local sediment sources, and the seasonally variable hydrodynamic regimes determine the different degrees of recent canyon activity. The Motril Canyon is interpreted as a mature system that reflects episodic activity, collecting fine-grained sediments from the nearby Guadalfeo River. The Carchuna Canyon exhibits a youthful developmental stage whose activity is more continuous and involves sediment trapping of littoral cells and continuous downslope sand transport

[EN] The formation and development of a small Mediterranean deltaic system are investigated through a primary seismic stratigraphic interpretation of a high-resolution seismic profile network, combined with multiple bathymetric data (including multibeam bathymetric imagery) and collated with shallow sediment cores collected with a vibro-corer device. The submarine delta of the Adra River is divided into a basal patchy seismic unit and five wedge-shaped younger seismic units that are related to the Holocene highstand stabilization. Limited age control indicates that the two uppermost seismic units are very recent, most likely related to a dearth of fluvial fluxes led by channel deviations and by sediment retention. The formation of the three older seismic units is correlated to three humid periods during the middle Holocene, late Holocene and Little Ice Age, under a general context of progressive aridification of southeastern Iberia. The stacking patterns and spatial distribution of individual seismic units document a history of episodic progradation of successive prodeltaic lobes, with a long-term evolution mediated by climatically-induced changes in the river basin and more recent anthropogenic interventions. Overall, the prodeltaic system registers the complete modification of a deltaic system that evolves from a fluvial-dominated delta to recent wave-dominated wedges. In between, the deltaic system exhibits a progressive asymmetric character, due to the instauration of Atlantic waters on the shelf and their subsequent eastward redistribution. The Adra deltaic system is proposed as an outstanding example of a small deltaic system that reacts almost immediately to the complex interaction between natural changes in the system and anthropogenic interventions in the drainage basin., [ES] La formación y la evolución de un pequeño sistema deltaico mediterráneo se ha estudiado mediante la interpretación estratigráfica de una red de perfiles sísmicos de alta resolución, combinada con múltiples datos batimétricos (incluidas datos de batimetria multihaz) y cotejada con testigos de sedimentos someros recogidos con vibro-corer. En el delta submarino del río Adra se diferencia una unidad sísmica basal y cinco unidades sísmicas más jóvenes en forma de cuña que están relacionadas con la estabilización del alto nivel del Holoceno. A partir de las dataciones realizadas se observa que las dos unidades sísmicas superiores son muy recientes, muy probablemente relacionadas con una disminución en los aportes fluviales provocada por las desviaciones del cauce y por la retención de sedimentos. La formación de las tres unidades sísmicas más antiguas se correlaciona con tres periodos húmedos durante el Holoceno medio, el Holoceno tardío y la Pequeña Edad de Hielo, en un contexto general de progresiva aridificación del sureste de Iberia. Los patrones de sedimentación y la distribución espacial de las unidades sísmicas indican una progradación episódica de sucesivos lóbulos prodeltaicos , con una evolución a largo plazo en la cuenca fluvial mediada por cambios climáticos y más recientemente por intervenciones antropogénicass. En conjunto, el sistema prodeltaico registra la modificación de un sistema deltaico que evoluciona en principio como un delta dominado por flujos fluviales hasta cuñas recientes dominadas por el oleaje. Entre medias, el sistema deltaico muestra un carácter asimétrico progresivo, debido a la influencia de las aguas atlánticas en la plataforma y su posterior redistribución hacia el este. El sistema deltaico del río Adra se propone como ejemplo de un pequeño sistema deltaico que reacciona de forma casi inmediata a la compleja interacción entre los cambios naturales del sistema y las intervenciones antropogénicas en la cuenca de drenaje.

Introduction and methods: Marine litter density, distribution and potential sources, and the impact on canyon seafloor habitats were investigated in the Motril, Carchuna and Calahonda canyons, located along the northern margin of the Alboran Sea. During the ALSSOMAR-S2S oceanographic survey carried out in 2019, canyon floor imagery was collected by a Remotely Operated Vehicle along 5 km in the Motril Canyon, 10 km in the Carchuna Canyon, and 3 km in Calahonda Canyon, together with 41 surficial sediment samples. Additionally, coastal uses, maritime traffic and fishing activity data were analyzed. A 50 m resolution multibeam bathymetry served as base map. Results: In the Motril and Calahonda canyons, the density of marine litter was low and the material was dispersed, very degraded and partially buried. In contrast, the Carchuna Canyon contained a greater amount and variety of litter. The Carchuna Canyon thalweg exhibited a density of marine litter up to 8.66 items·100 m-1, and litter hotspots with a density of up to 42 items·m2 are found along the upper reaches of the canyon thalweg. Discussion: Low litter abundances found in the studied canyons most likely reflect low population densities and the absence of direct connections with streams in the nearby coasts. The high shelf incision of the Carchuna Canyon and its proximity to the coastline favor littoral sediment remobilization and capture as well as the formation of gravity flows that transport the marine litter along the thalweg toward the distal termination of the channel. Litter hotspots are favored by the canyon morphology and the occurrence of rocky outcrops. Most debris is of coastal origin and related to beach occupation and agricultural practices in the adjacent coastal plain. A third origin was represented by fishing gear in the study area. Fishing activity may be producing an impact through physical damage to the skeletons of the colonial scleractinians located in the walls of the Carchuna Canyon. In con

The Southern Atlantic Spanish continental margin extending from Tarifa to the Gracia Point is characterized by a narrow, sediment-starved continental shelf exposed to an intense hydrodynamic regime resulting from the combination of tidal currents, wind-driven storms and oceanic currents near the Strait of Gibraltar. This area is a good example to study sediment routing across a dispersive margin. Its coastal domain is characterized by highly mobile subaerial dunes (Navarro et al., 2011). However, the adjacent continental shelf remains poorly studied. In this sense, recent surveys led by the University of Cadiz allowed to characterize the major morpho-stratigraphic features of the shelf and to provide a first assessment of prevailing sedimentary processes (Lujan et al., 2011). Deformed basement rocks mainly formed by Flysch Complex units outcrop at the seabed over extensive shelf areas. These rocks are part of the Betic-Rif thrust wedge and are locally covered by Pliocene to Quaternary deposits. The sedimentary cover is molded by different fields of bedforms such as submarine dunes and comets marks that indicate the influence of hydrodynamics processes. Shelf sediment transport patterns seem to be eventually captured by a submarine channel that provides an efficient mechanism for sediment export toward deep-water settings. Nevertheless, major sediment transport pathways are still to be characterized across the continental shelf. A new data set allowed to further investigate sediment bedform distributionoff Gracia Point . Results obtained so far have revealed the occurrence of a sandy banner bank located offshore Gracia Point. The bank extends over an area of 20 km² from -10 to -90 m water depths. The banner bank is covered by a field of very large dunes, where individual dunes exhibit significative short-term (i.e., annual) displacements ranging from 0 to 10 m with an apparent westward migration trend parallel to the coastline influenced by a continental margin-scale

Narrow continental shelves such as those surrounding the Mediterranean basin are usually dominated by active depositional features such as major prodeltaic wedges located off major rivers (e.g. the Gulf of Lions, the northern Adriatic Sea), or by infralittoral wedges in settings where fluvial supply is more limited and hydrodynamic regimes are more energetic. However, the knowledge of the geomorphological patterns of undernourished shelves remains much less documented. In this contribution, we aim to characterize the submarine geomorphology and the sub-surface sedimentary bodies of a shelf sector located west of the Guadalfeo River, a major regional source in the northern margin of the Alboran Sea, where fluvial supply is provided by small seasonal rivers. To reach those goals, we analysed a data base comprising multibeam bathymetric and backscatter data, seafloor video images and Parasound acoustic sections. The studied shelf exhibits a distinctive zonation, where three major domains could be characterised. In the inner shelf, the most significant depositional bodies are composed by wedge-shaped deposits with limited lateral extent. Over the surface, several geomorphic indicators reveal the occurrence of high-energy processes in relation to the seasonal inputs of the Verde and Seco rivers. Recent to modern sedimentation seems to be much reduced distally. The middle shelf is marked by two main breaks of slopes, the surficial expression of highly reflective depositional bodies, likely marking the location of ancient paleo-shorelines and extensive development of paleo-coastal plains. The outer shelf is a flat domain covered by several elongated sedimentary bodies, which are disposed oblique to the middle shelf paleo-shorelines. Below those bodies, sub-surface architectures exhibit several unconformity-bounded regressive wedges. We discuss the shelf zonation observed in the study area considering the confinement of recent infralittoral and prodeltaic wedges to the inne

This work aims to understand the link between the seafloor morphology and sub-seafloor stratigraphy of the Eastern Bransfield Basin (EBB; Antarctic Peninsula) with the water masses circulation established since the opening of the basin at around 3.3 Ma. Bottom currents (contourite) features identified from swath bathymetry data and parametric echo-sounder profiles acquired in the DRAKE2018 and POWELL2020 cruises are correlated with published information about water masses circulation and hydrological data. The EBB is the easternmost sector of the Bransfield Strait, oriented SW-NE and bounded by the Antarctic Peninsula to the southeast and the South Shetland and Elephant islands to the north and northwest. Contourite features are identified based on their sedimentary stacking pattern and morphological characteristics. They locate at distinctive depth levels in the EBB. A large mounded drift has been identified in an intra-slope platform in the SE margin, at water depths of 1000-1500 m. It is 35 km long and 20 km wide and is bounded by erosional contourite moats. These features are interpreted to result from the southwestward flow of the East Basin Deep Water (EBDW) at intermediate depths, formed by a mix of water masses from the Weddell Sea. Plastered drifts topped by contourite terraces occupy depths of 1100-1200 m along the SE margin of the basin, and are related to the high-energy oceanographic regime formed at the transitional boundary between the EBDW and the East Bransfield Bottom Water (EBBW). Contourite features on the deep, flat seafloor of the EBB at 2000-2300 m water depth are also formed by the EBBW. Mounded contourite drifts prograde and thin towards the outer limits of the basin, where contourite moats are interbedded with mass transport deposits. These contourite features have been generated by the episodic entrance of bottom water masses from the Central Basin and their mix with deep water masses flowing from the NE. This work reveals the highly dynam

The southern Scotia Sea hosts several small oceanic basins developed through continental break-up and oceanic spreading during the Cenozoic. Ona Basin is the southwestern most basin of the Scotia Sea. It is bounded by several structural highs: the Shackleton Fracture Zone to the west, Terror Bank to the east, and the South Scotia Ridge to the south. The southern part of the basin is further divided in two sub-basins (the western and eastern Ona basins) separated by the submarine relief called Ona High. The Ona Basin is mainly affected by two major water masses, the deeper branch of the Antarctic Circumpolar Current flowing eastwards and a westward flowing branch of the Weddell Sea Deep Water (WSDW). Interaction between mass movements and contouritic processes are likely to occur as a consequence of the complex geologic, physiographic and oceanographic setting. A combined approach including geomorphological, stratigraphic and seismic analyses allows us to document, for the first time, the record of repeated large-scale submarine landslides in the western Ona Basin. A major morphological feature named as 'Ona Paleovalley' is genetically related to large-scale Middle Pleistocene to recent mass movements. Deposition of large-scale mass transport deposits (MTDs) formed a template which guided and fostered major valley incision during the Middle Pleistocene. The valley infill records channelized depositional periods with possible development of turbidites alternating with erosive events when sediments were evacuated basinwards. This morpho-sedimentary pattern is attributed to the interplay between tectonic events leading to gravitational processes and the channelized flow of the WSDW.

The Santos Basin slope is a physiographic feature whose seafloor morphology is influenced by both geological and oceanographic processes. Regarding geological processes, halokinesis has been one of the main forces driving the geological evolution of this margin and influencing the present-day seafloor morphology. Salt dynamics is considered to be responsible for the development of faults and fractures, which behave as fluid conduits toward the seafloor surface. The supply of fluids added to the nature of the sediments provide favourable conditions for the formation of gas-escape seafloor morphologies, such as pockmarks, carbonate mounds and ridges. Additionally, the observation of exhumed salt diapirs in the south-western part of the Santos Basin seafloor is suggestive of active halokinesis. Besides, oceanographic processes leave a conspicuous fingerprint in the formation of an extensive array of morphological and sedimentary seafloor features. The interaction of bottom currents with pockmarks, carbonate structures and exhumed salt diapirs erodes the seafloor relief and contributes to the formation of moats, comet marks and scours. Associated with the prevailing erosive features, bottom currents-related deposits are formed along the slope structures constituting contourite systems.

The Southeastern Brazilian Continental Shelf (SBCS) is characterized by its great width (120 km), with the shelf break situated around 140 meters. The inner continental shelf, located between São Sebastião Island and Ubatuba, has a width of 50 km, and its outer limit is located at depths around 50 meters, exhibiting a gradient of 1:550. Thus, during most of the late Quaternary, the inner continental shelf was exposed to subaerial conditions favoring the formation of incised valleys, even though the sea level never fell below the shelf break. The inner shelf of the study area is inserted in the Neogene graben of Ubatuba, which is part of a Coastal Rif t System, whose limiting faults present preferential ENE orientation. Such faults seem to give origin to knickpoints, separating the inner from the outer shelf. This tectonostratigraphic architecture favored the creation of additional accommodation space, about which, during episodes of lowstand, a paleodrainage system has developed, in which sedimentary deposits were preserved in a complex of small incised valleys carved into the coastal prism developed in the highstand of 120 ka AP. The present work is ba sed on the analysis of 1200 km of CHIRP and sparker seismic records and aims to investigate how the geometric arrangement associated with this antecedent topography favored the development, during the last glacial period, of a complex of incised valleys c arved into the 120 ka BP coastal prism.

Clay minerals are major constituents of materials deposited in marine environments. Green-clay (glaucony) authigenesis, particularly in the marine and diagenetic realms, has played an important role in the understanding of Cenozoic climates. However, the genesis, depositional setting and paleoenvironmental implications of glaucony occurrences in the continental shelves/margin off southern Iberian Peninsula are loosely constrained. In this study, Holocene glaucony grains extracted from a sediment core retrieved from a highstand muddy depocenter off the Guadiana River, northern Gulf of Cadiz, were investigated by digital microscopy, X-ray diffraction (XRD) and electron microscopic methods (SEM-EDX and TEM-HRTEM). This multi-proxy approach allows to assess the physico-chemical conditions that prevailed during the glaucony-forming process in the northern Gulf of Cadiz, and to establish paleoenvironmental conditions that favoured glaucony formation during the recent Holocene highstand. In the studied sediment core, glauconitization occurred mostly by the replacement of faecal pellets during ~4.2-1.0 cal. ka BP. XRD and TEM-HRTEM analyses indicate that glaucony consists mainly of R1, with minor presence of R0, smectite-rich (nontronite with minor berthierine layer) interstratified glauconite-smectite. It consists of 35-75% glauconitic layers and 65-25% of interstratified smectite layers. The occurrence of shallow radial cracks in the pellet surface along with globular and caterpillar-like biomorphic to low packing density lamellar-flaky nanostructures, mineralogical properties, and K-poor content (~0.4 atoms p.f.u.), indicate a low mature glauconitization process. The mineralogy, chemistry and detailed morpho-textural properties demonstrate that glaucony has formed in situ (autochthonous). Conditions for the Holocene glaucony authigenesis occurred in an open-shelf environment at water depths of ~70 m, under suboxic, partially reducing conditions near the sediment-water in

The postglacial sea-level rise after the Last Glacial Maximum provided ideal conditions to study the transgressive sedimentary response to sudden shelf flooding driven by different rates of sea-level rise. In this study, a high-resolution seismic stratigraphic interpretation and sedimentological analysis were conducted on data from the northern Gulf of Cadiz continental shelf (SW Iberian Peninsula), in order to: 1) understand the succession of sedimentary processes during each shelf flooding episode and 2) explore the significance of variable rates of sea-level rise, sediment fluxes, and climatic conditions on the development of postglacial deposits. Four backstepping seismic postglacial transgressive units (PTUs; 4 to 1 from oldest to youngest) that are linked to the retreating mouth of the Guadiana River were interpreted. Together, these seismic units display a wedge-shape geometry, are located over the inner to middle shelf, and overlie a regional unconformity formed during the Last Glacial Maximum. Each PTU can be divided into several sub-units with distinctive seismic facies that have a similar stratigraphic organization. Each PTU contains lower sub-units that are composed of low-angle tangential-oblique clinoforms. The clinoforms are locally topped by a channelized sub-unit. The distal and/or lateral parts of the clinoforms are occasionally buried by sheet-like semitransparent subunits. The uppermost sub-units are present over the proximal and central parts of each seismic unit and are also sheet-like. PTUs can also be subdivided and described sedimentologically. Fine-grained sands with intercalated silty layers dominate the lower part of each PTU (lower clinoform sub-units). The upper part of each PTU (upper sheet-like sub-units) is characterized by reworked facies, composed of highly fragmented bioclasts within a mixture of silt and coarse to medium sand. Finally, mud deposits occur as a sediment drape over the PTUs. The internal structure of each PTU reveal

[EN] The Gulf of Cadiz upper slope in the area close to the Strait of Gibraltar is covered by a plastered drift deposited by the activity of the Mediterranean Outflow Water (MOW) and the North Atlantic Central Water (NACW). A number of small gullies are incised across the plastered drift, due to the interaction between gravitational and contouritic processes. The study of parametric sounder profiles and sedimentological analyses of nine sediment cores obtained from the axes of two gullies and from the undisturbed upper slope, giving a Holocene age frame, has allowed analyzing the recent sedimentary processes and their spatial and temporal variability. The upper slope shows a general increase in grain size towards the NW, suggesting bottom current intensification and/or the occurrence of gravity flows from the continental shelf and shelf-edge. The two studied upper slope gullies display significant differences in their recent activity and dominant processes. The one located to the SE seems to have been inactive since about 5.9 ka, and it has been draped by contouritic deposits. In contrast, the gully located to the NW has been a sediment transport conduit for the entire time span recorded in the sediment cores, [ES] El talud superior del margen Ibérico del Golfo de Cádiz en las proximidades del Estrecho de Gibraltar está ocupado por un depósito contornítico adosado resultado de la circulación del Agua Mediterránea de Salida (Mediterranean Outflow Water, MOW) y de la Masa de Agua Central Noratlántica (North Atlantic Central Water, NACW). En él se encajan pequeños valles submarinos (gullies) debido a la interacción entre los procesos gravitacionales y contorníticos. Mediante el estudio de perfiles de sonda paramétrica y el análisis sedimentológico de nueve testigos obtenidos en el área del talud superior no afectada por gullies y en los ejes de dos gullies, cuya datación corresponde al Holoceno, este estudio analiza los procesos sedimentarios recientes y su variabilidad espacial y temporal. El talud superior muestra un incremento general del tamaño de grano hacia el NO, indicativo de intensificación de las corrientes y/o el aporte sedimentario de origen gravitacional desde la plataforma continental y borde de plataforma. Los dos gullies estudiados muestran una gran variabilidad en los procesos predominantes. El gully más meridional, dominado actualmente por la sedimentación contornítica, parece haber sido inactivo desde unos 5.9 ka. En cambio, el gully localizado más al NW ha canalizado flujos gravitacionales durante todo el intervalo registrado por los testigos

The seafloor of the Alboran Sea reflects its complex tectonic, sedimentary, and oceanography dynamics as a consequence of the geological context, involving interaction between the Eurasian and African plates, and oceanographic context, as it is where the Atlantic and Mediterranean waters meet. Their physiography has a semi-enclosed configuration characterized by two margins (the Spanish Iberian and North Africa—mostly Moroccan margins) enclosing deep basins. Tectonic activity is mainly attested by folds and faults that predominantly affect the central and eastern seafloor sectors, as well as numerous seamounts and fluid-flow features (pockmarks, mud volcanoes, and diapirs) that dot the seafloor. The sedimentary and oceanographic processes allow us to distinctly define two principal environments in the Alboran Sea: the shallow proximal margin (continental shelf); and the deep distal margin (continental slope and base of the slope) with the adjacent sub-basins. The shelf mostly comprises prodeltaic and infralittoral prograding wedges, with local bedform fields, submarine valleys, and wave-cut terraces. Coastal and fluvio-marine sedimentary processes, acting since the last glacial period, are responsible for these features. The deep marine environment is characterised by the ubiquity of contourites, whose continuity is interrupted by turbidite systems, canyons, and landslides. The alongslope action of the Mediterranean waters and their interfaces with the Atlantic water has been the main process governing transport, seafloor reworking, and sedimentation of contourites. Mass-movement processes are responsible for the formation of: (1) turbidite systems—turbidity flows and mass flows were dominant during the last glacial sea-level lowstand, evolving to dilute gravity flows during present interglacial high stand; and (2) landslides—the main triggering factors comprising over-steepening, seismicity, under consolidation due to overpressure by interstitial fluids, stratigrap

A morphological and seismic-stratigraphic analysis of the Gulf of Cadiz area near the Strait of Gibraltar is presented in this work, focused on the sedimentary evolution of the upper and proximal middle-continental slope since the Mid-Pleistocene. Based on the analysis of seismic reflection profiles and swath bathymetry data, this work analyses the close influence of the activity of buried and outcropping diapiric ridges and late Quaternary sea-level changes on the evolution of contouritic features related to the Mediterranean Outflow Water (MOW) and Eastern North Atlantic Central Water (ENACW), gravitational features and fluid-escape structures. The stratigraphic architecture reveals that, under active diapiric deformation, the upper slope plastered drift grew during low sea-level stages, when sediment supply was high and the ENACW swept the upper slope, contrasting with the present-day highstand situation dominated by northwest-trending MOW flow. The south-estward ENACW flow forced asymmetry and lateral migration of gullies incised in the plastered drift. Two evolutionary stages have been established: 1) After the Mid Pleistocene, activity of diapirs with a NE trend determined the location of the deepest depressions which were infilled by plastered contouritic drifts; 2) Between Late Quaternary and present, a drastic change of buried diapirs growth pattern and orientation to a NW trend enhanced slope-derived gravitational processes affecting the bottom current dynamics. Adjustments to tectonic changes led to a phase of plastered drift growth on the upper slope during which depocenters varied their distribution and orientation. In a long-term the structural control on sedimentation shows a northwestward displacement of deformation, resulting in an overall extension of the contourite depositional system to the NW. In a short-term, sea-level changes favored drift deposition, gullies incision and the strengthening of water masses. This work evidences the importance of

The MOW exits the Mediterranean Sea through the Strait of Gibraltar as a highly energetic overflow into the Gulf of Cadiz (Figs. 1 and 2). It splits into an Upper Core (MU) and a Lower Core (ML), that is further sub-divided into smaller branches by the interaction with diapiric ridges and morphological highs on the middle slope. The Intermediate Branch flows through the Diego Cao Channel. The present-day oceanographic regime was established in the early Pliocene, after the opening of the oceanic gate in the Strait of Gibraltar. The MOW has been affected by climatic changes during the Plio-Quaternary, undergoing successive periods of intensification

Alboran Shelf-Slope cOupling processes and deep sediMent trAnsfeR: Source to sink approaches and implications for biodiversity (ALSSOMAR S2S) This research project intends to conduct a study of the continental margin and the adjacent slope, paying special attention to the storage capacity of sediments and their movement from the platform to the slope

The Cadiz upper slope is located at the Atlantic exit of the Strait of Gibraltar (latitude 36º10’-36º40’N). It runs from the continental shelf-edge at ~120 mwd to the connection with the middle slope at 400-500 mwd. It is covered by a plastered contouritic drift created by the Mediterranean Outflow Water (MOW) and incised by upper slope gullies. This work investigates the interaction between gravitational and contouritic processes under the influence of a highly dynamic tectonic regime controlled by diapiric activity rooted in the Gulf of Cadiz Allochtonous Unit. Tectonic activity and sedimentary processes are inferred from the stratigraphic analysis of airgun seismic profiles that cover the sedimentary record from the Mid Pleistocene. Two seismic units have been identified and placed in a regional chronostratigraphic framework. The lower unit SU-II (Mid Pleistocene to Late Quaternary) is deformed by the activity of NE-SW-oriented outcropping and buried diapirs. It shows layered and wavy reflections in the southern upper slope, where some gullies occur related to diapir-rooted faults; parallel layered reflections prevail in the northern upper slope where only a few gullies occur in inter-diapir basins. This unit is interpreted as patchy plastered drifts that infilled the space created by the diapiric uplift as the main Mediterranean Outflow Water (MOW) flowed through a channel located about 5 km to the east of a major present-day contourite channel (i.e., the Cadiz contourite channel). The upper seismic unit SU-I (Late Quaternary-Present) records the inactivation of most of the NE-SW-oriented buried diapirs, and the activity of the outcropping diapiric ridges and buried NW-SE-oriented diapirs. This unit is composed of four sub-units (SU-ID to SU-IA). The lower two sub-units led to the progradation of the southern upper slope and the migration of the main channel to its present-day position. Along-slope sedimentation took over as the main morpho-sedimentary process d

El talud superior de Cádiz se sitúa en las cercanías del Estrecho de Gibraltar (latitud 36º10’N-36º40’N), desde el borde de la plataforma, en torno a 120 m de profundidad, hasta la conexión con el talud medio a 400-500 m. Mediante el análisis de perfiles de sísmica de reflexión de diferentes resoluciones y de mapas batimétricos del talud, este trabajo explora la relación entre procesos estructurales profundos, principalmente diapiros y altos estructurales relacionados con la actividad de la Unidad Alóctona del Golfo de Cádiz, con los procesos sedimentarios deposicionales y erosivos derivados del flujo de las masas de agua y los procesos gravitacionales en el talud superior. El registro sedimentario reciente desde el Pleistoceno medio hasta la actualidad en el talud de Cádiz se divide en dos unidades sísmicas, correlacionadas con el marco estratigráfico regional (Hernández-Molina et al., 2016). Ambas unidades definen la construcción de un depósito contornítico adosado al talud superior (Hernández-Molina et al., 2013) y su continuación como depósito laminar en el talud medio. Sin embargo, muestran diferencias significativas en cuanto a su distribución y sus características sísmicas. También se identifican variaciones importantes en su configuración interna, entre la parte SE de la zona de estudio, donde el talud superior conecta con el canal contornítico de Cádiz, y la parte NW donde conecta con depósitos laminares del talud medio. La unidad inferior (Pleistoceno medio-Cuaternario inferior) está deformada por la actividad de numerosos diapiros, en particular en la zona SE, según revela la inclinación y acuñamiento de los reflectores hacia los edificios diapíricos. Sus principales depocentros se distribuyen en las zonas deprimidas entre altos diapíricos, y su configuración interna incluye reflectores estratificados paralelos en la zona NW y ondulados en la zona SE. Por el contrario, la unidad superior (Cuaternario inferior- presente) se distribuye de forma más homogéne

Gullies are ubiquitous erosive features in continental margins that are mainly related to downslope, low-density gravitational flows (turbidites), although mass transport and fluids migration may be involved in their genesis and evolution. A series of downslope-trending gullies have been identified on the relatively smooth, slightly concave-upward upper slope of the Gulf of Cadiz, close to the Strait of Gibraltar. They extend from 205-250 m (beyond the continental shelf) to 510-580 m water depth, at the Cadiz Channel northern flank along the middle slope. The occurrence of gullies in this region, characterized by active contouritic processes affected by diapiric ridges, suggests an interaction between bottom current processes and the downslope-trending gullies. This interaction is investigated in this work, based on the analysis of very high-resolution data including swath bathymetry, echo-sounder parametric profiles and sediment cores up to 310 cm long. The gullies are generally asymmetric, with steeper and higher NE walls. Overall, they are arranged in a dendritic, convergent pattern laterally spaced 0.4-2 km. Parametric profiles show that both the gullies and inter-gully areas are covered by a thin, low reflectivity sheet-like layer, up to 10 milliseconds (two-way travel time) thick, that become thicker in the gullies SE flank. Three sediment cores collected along the axis of one single gully exhibit vertically homogeneous muddy sand and sandy mud, but with clear occasional smaller coarsening-upward sequences. In contrast, two sediment cores collected in the adjacent undisturbed upper slope contain finer sediment (mud to sandy mud) that exhibit general and smaller-scale coarsening-upward trends. These results suggest that the upper slope is affected by an increasing effect of the Mediterranean flow and the gullies are inactive features at present. This may imply that the upper slope of the Gulf of Cadiz records changes in the oceanographic control and turbiditic

Clinoform depositional features along the Iberian Mediterranean margin are investigated in this study, with the aim of establishing the causes of their varied shapes and other characteristics. We have analyzed the broad-scale margin physiography and seismic stratigraphic patterns based on high-resolution bathymetric data and previously interpreted seismic data. In addition, we have evaluated regional supply conditions and the uplift-subsidence regime of the different shelf sectors. The upper Quaternary record is strongly dominated by shelf-margin regressive wedges affected by the prevailing 100 ka cyclicity. However, the margins exhibit considerable lateral variability, as the result of the balance between the amount of sediment supply and the uplift-subsidence relationship. Three major shelf sectors with distinct morpho-sedimentary features have been defined. The relatively narrow northern shelves (Roses, La Planassa and Barcelona) are supplied by discrete river outlets that collectively constitute a linear source and are mainly affected by tectonic tilting. The wide middle shelves (Ebro Shelf, the Gulf of Valencia, and the Northern Arc) receive the sediment supply from the large Ebro River and other medium rivers. Although the tectonic regime changes laterally (strong subsidence in the north and uplift in the south), shelf growth is maintained by lateral advection of sediments. The southern shelves (the Southern Arc and the northern Alboran Shelf) are very abrupt and narrow because of the uplifting Betic Cordillera, and the torrential fluvial regimes that determine a very efficient sediment by-pass toward the deep basin. Submarine canyons deeply incised in the continental margin constitute a key physiographic feature that may enhance the transport of sediment to the deep sea or individualize shelf sectors with specific sedimentation patterns, as occurs in the Catalan margin

Multibeam swath bathymetry, high-resolution seismic data and sediment samples were used to characterize a field of sand ridges and subaqueous dunes on the outer Murcia continental shelf (western Mediterranean Sea). Sand ridges are 1.5–3 m high and show a predominant E-W orientation oblique to the present-day shoreline. High-resolution seismic data reveal a backstepping stacking pattern of high-angle clinoforms dipping towards the southwest, interpreted as buried sand bodies. Subaqueous dunes have a mean height of 0.3 m and appear superimposed on the sand ridges showing a NW-SE orientation oblique to the ridges. They are composed of sandy sediments and display asymmetric morphology, with the lee side towards the southwest. Ridge and dune asymmetry and internal structure are indicative of long-term sediment transport towards the southwest. At present, dune migration rates deduced from repeated bathymetric surveys indicate that the dunes remain stationary or migrate at very low rates on a decadal scale Dune migration rates were determined from the net displacement of the crests and troughs positions deduced from repeated multibeam surveys (2003 and 2013). Results indicate that the subaqueous dunes remain stationary or migrate at low rates towards the southwest (migration rates < 1 m yr-1). Bedform asymmetry and migration are consistent with the general circulation of the margin, characterized by a predominant geostrophic current flowing south-westward along the shelf break