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The knowledge of the global reservoir of submarine gas hydrates is of great relevance for understanding global climate dynamics, submarine geohazards, and unconventional hydrocarbon energy resources. Methane hydrate formation and preservation is favored by high pressure and low geothermal gradient and this leads the reservoir to be hosted mostly in cold passive continental margins. Several studies describe the Mediterranean basin's potential to host a Methane hydrate reservoir. However, in spite of the ample evidence of subsurface hydrocarbons, especially biogenic methane, widespread evidence of gas hydrate either from samples or seismic data is missing. We modeled the theoretical Mediterranean distribution of methane hydrate stability field below the seafloor and in the water column using available geological information provided by 44 Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) boreholes, measured geothermal gradients, and thermohaline characteristics of the water masses from CMEMS (Copernicus Marine services). We find that the pervasive presence of high-salinity waters in sediments, coupled with the uniquely warm and salty water column, limits the thickness of the theoretical methane hydrate stability zone in the subsurface and deepens its top surface. Because of the homogeneous characteristics of water masses, the top surface in the Mediterranean sea lays uniformly from 1163 to 1391 mbsl, much deeper than the oceanic basins where it lays around 300 - 500 mbsl. The theoretical distribution of methane hydrates coincides well with the distribution of shallow, low-permeability Messinian salt deposits, further limiting the formation of pervasive gas hydrate fronts and controlling their distribution due to the prevention of upward hydrocarbon gas migration. We conclude that the Mediterranean Basin, hosting the youngest salt giant on Earth, is not prone to the widespread formation and preservation of gas hydrates in the subsurface and that the gas hydrate potential of salt-bearing rifted continental margins may be considerably decreased by the presence of subsurface brines. This study was entirely conducted using data (stratigraphy, pore water salinity, and where available downhole temperature measurements) obtained with scientific ocean drilling, thus demonstrating the importance of the legacy data as a source of quality information even decades after their acquisition.

Mass-transport deposits often show a low-amplitude, “acoustically transparent” seismic response compared to unfailed sediments. This amplitude signature is often interpreted as a lack of coherent internal reflectivity caused by a loss of internal structure during transport and emplacement, and is widely used to delineate mass-transport deposits in sub-bottom profiler data. An apparent contradiction is that cores penetrating such “acoustically transparent” deposits can sometimes retrieve well-stratified sediments that show little evidence of deformation.In this study we examine the variation in the single-channel seismic amplitude response with changing heterogeneity using synthetic seismic modelling. We model the internal structure of mass-transport deposits as a two-component binarised random medium, where the lateral correlation length is used to artificially control the degree of internal deformation/scale of internal structure, while maintaining the magnitude of the internal reflectivity constant. We construct two synthetic models: i) a simplified single-source marine example and ii) a multi-source example based on a real world “acoustically transparent” mass-transport deposit imaged by a dense network of AUV sub-bottom profiles in the Black Sea. We use 2-D elastic finite-difference modelling to model the seismic response (at sub-bottom profiler bandwidths) of an ensemble of both synthetic models with varying geostatistical parameters and random seeds for the mass-transport deposit zones. For the single-source synthetic model a reduction in observed amplitude with reduced lateral scale length is consistently observed across a range of vertical correlation lengths. For the real world Black Sea example, with realistic elastic and geostatistical parameters based on cone-penetration tests and physical property measurements from sediment cores, we find that when the lateral scale length of the random medium is around 1 m, recorded seismic amplitudes are, on average, reduced by ∼15% relative to unfailed sediments.We conclude that relatively small amounts of deformation at scales larger than the dominant seismic wavelength are, in general, able to a generate significant decrease in seismic amplitude, without requiring a reduction in the average reflectivity. Our synthetic modelling results should discourage interpretation of the internal structure of mass-transport deposits based on seismic amplitudes alone as “acoustically transparent” mass-transport deposits may still preserve coherent, metre-scale internal structure. In addition, the minimum scale of heterogeneity required to produce a reduction in seismic amplitudes is likely much larger than the diameter of sediment cores, meaning that such mass-transport deposits may still appear well-stratified and undeformed when cored.

Physical connectivity between marine basins facilitates population exchange and hence controls biodiversity. The Mediterranean Sea is a semi-restricted basin with only a small two-way connection to the global ocean, and it is a region heavily impacted by climate change and biological invasions today. The massive migration of non-indigenous species into the basin through the Suez Canal, driven and enabled by climate warming, is drastically changing Mediterranean biodiversity. Understanding therefore the origin and cause(s) of pre-existing biodiversity patterns is crucial for predicting future impacts of climate change. Mediterranean biodiversity exhibits a west-to-east decreasing gradient in terms of species richness, but the processes that resulted in this gradient have only been hypothesized. By examining the fossil record, we provide evidence that this gradient developed 5.33 million years ago at the end of the Messinian Salinity Crisis, and it was therefore caused by the re-population of the basin by marine species with a dominating western source at the Mediterranean–Atlantic gateway.

The eastern Mediterranean has been the locus of catastrophic earthquakes and related tsunamis (e.g., the 365 Crete and 1222 Cyprus earthquakes). The primary sources of these seismic events are structures related to the subduction of the Nubian Plate along the Hellenic and Cyprus arcs. A detailed identification and description of the potential tsunamigenic sources are required as part of an assessment of earthquake and tsunami hazards. Here we focus on the Cyprus Arc region, in which the oceanic crust is still subducting beneath the Anatolian Plate in the west, whereas in the eastern sector, the oceanic crust has been completely subducted, and the lower plate consists of thinned continental crust. The rates of shortening are higher in the western sector than in the east. During recent decades, new data from extensive hydrocarbon exploration have allowed us to image structures that deform the seafloor and influence the shape of the recent basins in the eastern sector. The Latakia Ridge is the most prominent tectonic structure in the area. The present-day architecture of this ridge is the result of Meso-Cenozoic convergence followed by a transpressive phase related to the northward migration of the Arabian Plate. Therefore, the present geometry of the tectonic structure results from a complex interplay between reverse and strike-slip faults. Our reinterpretation of previously published seismic reflection profiles crossing the Latakia Ridge allows us to reconstruct the geometry of the main active faults and suggests their recent kinematics. Our findings could be crucial for the reassessment of seismic and tsunami hazards in the eastern sector of the Cyprus Arc.

Hydrological restriction from the Atlantic Ocean and a negative freshwater balance transformed the Mediterranean Sea into a giant saline basin during the Messinian Salinity Crisis (MSC) (5.97 – 5.33 million years ago). After more than 50 years of research, it is still unclear if the deposition of nearly one million km3 of evaporite salts during this event was accompanied by a major (≥ 1.5 km) drawdown of Mediterranean sea level; and if halite deposition occurred only during this drawdown event, or also in a filled Mediterranean connected to the Atlantic.We present evidence based on the chlorine stable isotope composition of halite for a sea level drawdown of 2 km in the eastern Mediterranean during the final stages of deposition of the Mediterranean halite layer. This is the largest sea level drop ever reported from the geological record and implies a short (~20 kyr), but nearly complete hydrological disconnection of the Mediterranean from the Atlantic. About half of the halite volume in the eastern Mediterranean was deposited during this drawdown event. Scant chlorine isotope data from the western Mediterranean, together with new estimates of western basin halite volume, suggest that the complete western halite deposit accumulated during the drawdown event. This mode of halite deposition - termed “evaporative drawdown” - had been already proposed as an evolution of the “deep-basin, shallow-water” scenario for the MSC (Hsü et al., 1973).Chlorine isotopes indicate that the remaining half of the eastern Mediterranean halite volume accumulated prior to the drawdown, in a filled Mediterranean that received a continuous input of Atlantic waters. This halite accumulation phase lasted about 70 kyr and was driven by a restricted - but not fully blocked - outflow of deep western Mediterranean waters to the Atlantic. This model of halite deposition corresponds to the “deep-basin, deep-water” scenario for the MSC (Schmaltz, 1969). In summary, our results show that both the “deep-basin, deep-water” and the “deep-basin, shallow-water” modes of halite accumulation took place during the MSC, and that the complete deep-basin MSC halite deposit accumulated in less than 100 kyr. Hsu, K., Ryan, W. & Cita, M. Late Miocene Desiccation of Mediterranean. Nature 242, 240–244 (1973).Schmalz, R. F. Deep-water evaporite deposition, a genetic model. American Association of Petroleum Geologists Bulletin53, 798–823 (1969).

In an ever more challenging context for the acquisition of seismic data in the Mediterranean Sea, reprocessing to improve the quality of legacy data has become increasingly important. This work presents the newly reprocessed, open access dataset SALTFLU acquired in the Algerian basin by the National Institute of Oceanography and Applied Geophysics (OGS) in 2012. We apply a ‘broadband’ reprocessing strategy adapted for offset-limited (3km streamer for a target 4 km below the sea level) airgun reflection seismic data acquired in deep water settings. We then assess if the reprocessed images provide new geological insights on the Mediterranean sub-surface. The workflow relies on an integrated approach combining geophysics and geological interpretation to iteratively build the velocity model. In this way we aim to tackle some of the challenges linked to imaging deep complex geological structures containing high velocity contrasts with 2-D, offset-limited seismic data. We first broaden the bandwidth of the data through multi-domain de-noising, deghosting and a source designature using an operator derived from the seabed reflection. We then perform iterative migration velocity analysis, pre-stack time migration and multiple attenuation in the Radon domain to obtain time-migrated images. The initial velocity model is derived from the resulting time migration velocities, and geologically driven model updates are generated using a combination of travel-time tomography, seismic interpretation of the major salt horizons and velocity gradient flooding. The gradient flooding aims to reproduce the large scale first-order velocity variations, while the travel-time tomography aims to resolve the smaller second-order velocity variations. The results improve our deep geological knowledge of the under-explored Algerian basin down to the base salt and the pre-salt. Fluid indicators are imaged within the Plio-Quaternary of the Algerian basin, which we interpret as thermogenic or biogenic gas sourced from either the Messinian Upper Unit or from the pre-salt, migrating through a hydro-fractured salt. The reprocessed data image lateral and vertical seismic facies variation within the Messinian units that could shed new light on the tectono-stratigraphic processes acting during the Messinian Salinity Crisis. It also reveals numerous previously unresolved volcanic structures within the Formentera basin.

Data and methods, Figure S1, Tables S1 and S2, and Plates S1 and S2 (the graphical results of modeling of DSDP and ODP boreholes, displayed with lithostratigraphy).

In an ever more challenging context for the acquisition of seismic data in the Mediterranean Sea, reprocessing to improve the quality of legacy data has become increasingly important. This work presents the newly reprocessed, open access dataset SALTFLU acquired in the Algerian basin by the National Institute of Oceanography and Applied Geophysics (OGS) in 2012. We apply a ‘broadband’ reprocessing strategy adapted for short-offset, deep water airgun reflection seismic data and assess if the reprocessed images provide new geological insights on the Mediterranean sub-surface. The workflow relies on an integrated approach combining geophysics and geological interpretation to iteratively build the velocity model. In this way we aim to tackle some of the challenges linked to imaging complex geological structures containing high velocity contrasts with 2-D, short-offset seismic data. We first broaden the bandwidth of the data through multi-domain de-noising, deghosting and a source designature using an operator derived from the seabed reflection. We then perform iterative migration velocity analysis, pre-stack time migration and multiple attenuation in the Radon domain to obtain time-migrated images. The initial velocity model is derived from the resulting time migration velocities, and geologically driven model updates are generated using a combination of travel-time tomography, seismic interpretation of the major salt horizons and velocity gradient flooding. The gradient flooding aims to reproduce the large scale first-order velocity variations, while the travel-time tomography aims to resolve the smaller second-order velocity variations. The results improve our deep geological knowledge of the under-explored Algerian basin down to the base salt and the pre-salt. Fluid indicators are imaged within the Plio-Quaternary of the Algerian basin, which we interpret as thermogenic or biogenic gas sourced from either the Messinian Upper Unit or from the pre-salt, migrating through a hydro-fractured salt. The reprocessed data image lateral and vertical seismic facies variation within the Messinian units that could shed new light on the tectono-stratigraphic processes acting during the Messinian Salinity Crisis. It also reveals numerous previously unresolved volcanic structures within the Formentera basin.

The eastern Mediterranean is shaped by the interaction between the African, Arabian, and Eurasian plates resulting in a complex tectonic framework. The Hellenic subduction is well documented and studied but, the northeast corner of the eastern Mediterranean Sea remains enigmatic. It is a tectonically active region where different plate boundary conditions coexist (i.e., oceanic subduction, continental collision, extension, and strike-slip movements). An active and tsunamigenic system has been interpreted west and east of Cyprus by using deep seismic reflection lines. Vintage deep-penetrating seismic reflection profiles of the Mediterranean Sea project (MS project) - acquired during the ’70 - were re-analyzed and merged with a synthesis of available subsurface data from the scientific literature. This study focuses on two transects (MS53 and MS56) that cross the major offshore structures (i.e., Florence Rise, Latakia Ridge, and Kyrenia Ridge) from north to south. The western transect (MS53) shows the Herodotus oceanic crust subducting northward beneath the Eurasian plate. The Florence Rise is the leading edge of the system, and the Antalya Basin is its forearc basin. Close to the Turkish coast, a buried block seems to act as a backstop for the offshore system, and north of it, some out-of-sequence thrusts have been interpreted. The strain is partitioned between the Florence Rise and the Taurides front. The eastern transect (MS56) crosses the Latakia Ridge, i.e., the northern boundary of the Levant Basin, where shortening is greater than in the western area. The seismic line continues northward into the Cyprus – Latakia Basin, crossing the Kyrenia Ridge, and reaching the Turkish coast. On the seismic section, we interpreted the Mesozoic subduction front now hindered by strike-slip movements on the Latakia Ridge. Another prominent transpressive structure is the Kyrenia Ridge, which is interpreted as an active structure with a well-imaged thrust system in front of it. The seismic sections were depth converted to provide a regional geologic model for the northeastern Mediterranean Sea. Active subduction fronts, which are only partially imaged, were structurally modeled and then crosschecked with previous studies to better constrain their geometry. In the northeastern Mediterranean Sea, a plate boundary is buried offshore with active subduction west of Cyprus and mainly transpressional tectonics to the east. A better understanding of its nature and kinematics would be useful to assess the tsunami hazard in this area.

The Late Miocene deposits in the Sorbas Basin (Spain) have been of an extreme importance in the understanding of the Messinian Salinity Crisis (MSC) events (5.97-5.33 Ma). They consist of four formations. The pre-crisis Abad marls topped by the evaporitic Yesares gypsum member, followed by two non-evaporitic units known as the Sorbas and Zorreras members. Those deposits have been widely explored and studied thanks to the numerous outcropping sections in the basin.The ‘SaltGiant’ European Training Network held a training school in October 2021 in the Sorbas Basin, where four boreholes (named SG0, 1, 2 and 3) covering most of the Messinian Salinity Crisis sequence, were drilled, cored and logged in this context along an overall thickness of about 175 m. The drillings took place inside and in the vicinity of the Torralba gypsum mine. It allowed for the first time in the scientific non-industrial domain, access to a continuous and non-outcropping succession of the Messinian deposits in the Sorbas basin. In addition to the recovered cores, borehole geophysical data were obtained from the four holes and digital images of the area were collected with a drone. Prior to the drilling, an OBO (Outcrop / Behind Outcrop) workflow was followed, which will allow integrating the outcrop and subsurface data by combining the 3D geometry of geobodies with geophysical information.Optical borehole wall images provide mm-scale images of the borehole walls, highlighting the sedimentological and structural characteristics of the deposits. Downhole geophysical measurements included acoustic velocity, electrical resistivity and natural spectral gamma ray, which allowed determining the petrophysical characteristics of the penetrated lithologies. In addition to the petrophysical logs, a Vertical Seismic Profiling was performed in holes SG2 and SG3, including a multi-offset VSP survey in hole SG3.The petrophysical characterization of the Messinian deposits will provide a reference case study for the lithologic characterization of MSC deposits in the subsurface elsewhere. VSP analysis provided an in-field preliminary seismic velocity evaluation in the encountered formations. Preliminary results confirm the astronomical precession-driven cyclicity observed elsewhere in the Messinian gypsum. Further processing and analyses of the large amount of acquired data will lead to identifying the astronomical and possibly higher-frequency cyclicity in the post-evaporitic deposits in the Sorbas member.

The global reservoir of submarine gas hydrates is favored by the cold temperature of oceanic bottom water and the generally low geothermal gradients along passive continental margins. The continental margins of the land-locked Mediterranean basin are a remarkable exception for the lack of evidence of extensive presence of gas hydrates. Using public data of the physics and chemistry of the subsurface available from 44 Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) wells as lithologic logs, downhole temperature measurements, and pore water salinity values, and observed physical characteristics of bottom waters, we model the theoretical methane hydrate stability zone (MHSZ) below the seafloor and in the water column.We find important positive pore water salinity anomalies in the subsurface indicating the pervasive presence of concentrated brines up to saturation concentration of halite and gypsum (> 300 ‰). The resulting sub-bottom MHSZ is thinner by up to 90-95% with respect to its thickness calculated assuming constant salinity with depth equal to bottom waters salinity. In the Eastern Mediterranean deep basins the thickness of the subsurface MHSZ is largest (up to ~ 350 m) and the anomaly induced by subsurface brines is highest (~ -300 m), while in the Alboran, Western Mediterranean, Tyrrhenian, Sicily Channel, Adriatic and Aegean basins the MHSZ, where present, thins to less than 100 m with mostly negligible anomaly induced by the presence of subsurface brines.Modelling results suggest that subsurface brines can produce dramatic reductions of the thickness of the MHSZ only where the geothermal gradient is low (Eastern Mediterranean). We have modelled the same brine-induced limiting effect on the thickness of the MHSZ in synthetic cases of high and low heat flow to simulate Western and Eastern Mediterranean subsurface thermo-haline conditions. The salinity effect is attenuated by the thermal effect in the Western Mediterranean that produces the most relevant thinning of the MHSZ.The distribution of the MHSZ resulting from the modelling coincides well with the distribution of the Late Miocene salt deposits which limit further the possibility of formation of gas hydrates acting as low permeability seal to the up-ward migration of hydrocarbon gases.This modelling exercise provides a robust explanation for the lack of evidence of widespread gas hydrates on Mediterranean continental margins, with the exception of areas of local methane upward advection such as mud volcanoes, and it outlines a number of local hydrate-limiting factors that make this basin unfavorable to gas hydrate occurrence.

School of Rock is a summer school for science teachers during which they become familiar with the International Ocean Discovery Program (IODP) and Earth Sciences through the interactions with IODP scientists and Education/Outreach Officers. The European School of Rock 2018 was held in Italy at the University of Pavia and was focused on “Understanding the Climate System through ocean sediments”. The summer school included scientific lectures, practical hands-on activities on IODP cores and databases and was based on the immersion in the process of doing science alongside researchers. Sixteen Science teachers from Italian junior high schools (students 11-13 year old) and high schools (14-18 year old) attended the School of Rock.Our research aimed to understand if School of Rock could improve the confidence of teachers in Earth Sciences and in the use of an inquiry based science education approach in their classes. We collected information from the participants through ex-ante and ex- post surveys. The participants outlined the acquisition of several benefits such as a general improvement of the content knowledge and new ideas for their teaching practice highlighting that School of Rock represented in the teachers’ perception an effective professional development.

About 6 million years ago, the Mediterranean basin was the location of one of the most extraordinary events in the recent geological history of the Earth: the Messinian Salinity Crisis. Restriction of the seawater exchange between the Atlantic and the Mediterranean led to excess evaporation and deposition on the bottom of the deep Mediterranean basins of a 1.5 km-thick salt layer. Research on this event initiated a long-term scientific controversy. COST (European Cooperation in Science and Technology) and Marie Skłodowska-Curie European Training Networks were identified as the most appropriate tools to address and solve the controversy using a highly cross-disciplinary approach.

This study presents the interpretation of reprocessed seismic data covering the southwestern Balearic promontory and the central Algerian basin. The new depth processing of 2D seismic lines dataset allows for the first time a good resolution on salt structures in the deep basin. Most of the salt structures result from active diapirism. In the deep basin, sedimentary loads and regional shortening are proposed to be the dominant driving forces, showing an overall contractional salt system. The north Algerian margin tectonic reactivation could have provoked a regional shortening of the salt structures and overburden. Identified unconformities suggest that this process probably started shortly after salt deposition and is still active nowadays. It is expressed by salt sheets, pinched diapirs and a décollement level. The African convergence and the narrowness of the western Algerian basin could be the explanation of an overall greater salt deformation intensity compared to the eastern Algerian basin. This demonstrates how in tectonic and sedimentary components appear to be dominant in salt deformation in the central Algerian basin compared to gravitational gliding, only localized in the proximal parts of the margin.

In the Mediterranean Basin, gas hydrate bottom simulating reflectors (BSR) are absent, with very few and spatially limited exceptions occurring in Eastern Mediterranean mud volcanoes and in the Nile deep sea fan. This is in spite of widespread occurrence of hydrocarbon gases in the subsurface, mainly biogenic methane, from a wide range of stratigraphic intervals.In this study we model the methane hydrate stability field using all available information on DSDP and ODP boreholes in the Western Mediterranean and in the Levant Basin, including the downhole changes of pore water salinity. The models take into account the consequent pore water density changes and use known estimates of geothermal gradient. None of the drilled sites were located on seismic profiles in which a BSR is present.The modelled base of the stability field of methane hydrates is located variably within, below, or even above the drilled sedimentary section (the latter case implies that it is located in the water column). We discuss the results in terms of geodynamic environments, areal distribution of Messinian evaporites, upward ion diffusion from Messinian evaporites, organic carbon content, and the peculiar thermal structure of the Mediterranean water column. We conclude that the cumulative effects of geological and geochemical environments make the Mediterranean Basin a region that is unfavorable to the existence of BSRs in the seismic record, and most likely to the existence of natural gas hydrates below the seabed.

The present‐day tectonic setting of the Eastern Mediterranean Sea results from a long deformation history, characterized by an alternation of extensional and contractional phases: from Mesozoic rifting to Late Cretaceous-present-day compression. This study focused on the tectonic reconstruction of the north-eastern side of the Mediterranean Sea, on a sector located between the Turkish coast and the northern Levantine Basin, using seismic reflection profiles. Previous studies dealt with the recent (Neogene) evolution because they did not have enough depth of investigation to recognize deeper reflections. We used vintage data such as MS and Strakhov surveys to analyze the deeper part of the area. We interpreted and depth-converted these seismic data, and we developed a sequential restoration to reconstruct the stratigraphic and structural evolution of the study area. In general, from north to south, we recognize the Cilicia Basin: a piggy-back basin bordered to the south by the offshore continuation of the Kyrenia Range. The Kyrenia Range is a positive flower structure generated during a transpressional phase because of the rotation of the Arabic plate. Southward, a secondary contractional system with an onlapping wedge is present in the area between the Kyrenia Range and another prominent ridge, i.e. the Larnaca Ridge. In the southern part, the same transpressional phase that generated the Kyrenia Range led to a positive inversion of an ancient extensional system, i.e. the Latakia Ridge. Beyond these positive flowers, the Levantine Basin is affected by extensional structures showing weak positive reactivation, including halokinetic features.In summary, we found that the inherited extensional structures strongly impacted the following contractional ones affecting both their geometry and their kinematics.

Salt tectonics at salt-bearing margins is often interpreted as the combination of gravity spreading and gravity gliding, mainly driven by differential sedimentary loading and margin tilting, respectively. Nevertheless, in the Western Mediterranean Sea, the classical salt tectonics models are incoherent with its morpho-structural setting: the Messinian salt was deposited in a closed system, formed several Ma before the deposition, horizontally in the entire deep basins, above a homogenous multi-kilometre pre-Messinian thickness. The subsidence is purely vertical in the deep basin, implying a regional constant initial salt thickness, the post-salt overburden is homogenous and the distal salt deformation occurred before the mid-lower slope normal faults activation. Instead, the compilation of MCS and wide-angle seismic data highlighted a clear coincidence between crustal segmentation and salt morphology domains. The geometrical variation of salt structures seems to be related to the underlying crustal nature segmentation. Regional thermal anomalies and/or fluid escapes, associated with the exhumation phase, or the mantle heat segmentation, could therefore play a role in adding a further component on the already known salt tectonics mechanisms. The compilation of crustal segmentation and salt morphologies in different salt-bearing margins, such as the Santos, Angolan, Gulf of Mexico and Morocco-Nova Scotia margins, seems to depict the same coincidence. In view of what is observed in Western Mediterranean Sea, the heat segmentation influence in the passive margins should not be overlooked and deserves further investigation.

25 pages, 10 figures, 1 appendix, supporting information, https://doi.org/10.1029/2020JB021474.-- Data Availability Statement: Preprocessed prestack seismic data, processing horizons, migration velocities, and code to reproduce the results using Madagascar (Fomel et al., 2013) are archived in Ford (2020), Mass‐transport complexes (MTCs) are often characterized by small‐scale discontinuous internal structure, such as slide blocks, rough interfaces, faults, and truncated strata. Seismic images may not properly resolve such structure because seismic reflections are fundamentally limited in lateral resolution by the source bandwidth. The relatively weak seismic diffractions, instead, encode information on subwavelength‐scale structure, with superior illumination. In this paper, we compare diffraction imaging to conventional, full‐wavefield seismic imaging to characterize MTCs. We apply a seismic diffraction imaging workflow based on plane‐wave destruction filters to two 2D marine multichannel seismic profiles from the Gulf of Cadiz. We observe that MTCs generate a large amount of diffracted energy relative to the unfailed confining sediments. The diffraction images show that some of this energy is localized along existing discontinuities imaged by the full‐wavefield images. We demonstrate that, in combination with full‐wavefield images, diffraction images can be utilized to better discriminate the lateral extent of MTCs, particularly for thin bodies. We suggest that diffraction images may be a more physically correct alternative to commonly used seismic discontinuity attributes derived from full‐wavefield images. Finally, we outline an approach to utilize the out‐of‐plane diffractions generated by the 3D structure of MTCs, normally considered a nuisance in 2D seismic processing. We use a controlled synthetic test and a real‐data example to show that under certain conditions these out‐of‐plane diffractions might be used to constrain the minimum width of MTCs from single 2D seismic profiles, Data for this study were collected in the framework of the project INSIGHT (CTM2015‐70155‐R) funded by the Spanish “Ministerio de Ciencia e Innovación” and the European Regional Development Fund. J. Ford was supported by a Marie Curie Doctoral Fellowship through the SLATE Innovative Training Network within the European Union Framework Program for Research and Innovation Horizon 2020 under grant agreement no. 721403. With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

28 pages, 10 figures, 1 table, supporting information https://doi.org/10.1111/sed.12844.-- Data availability The data that support the findings of this study are available from the corresponding author upon reasonable request., Synchronous interaction between bottom currents and turbidity currents has been reported often in channel–levée systems where the thickness of the turbidity currents exceeds that of the levées. Such interplay between along-slope and down-slope sedimentary processes is one of the mechanisms by which ‘mixed turbidite–contourite systems’ can originate. However, bottom currents flow over large areas of the seafloor, including continental slopes characterized by deeply incised submarine canyons rather than channel levées. In these cases, a direct interaction between along-slope and down-slope currents is, theoretically, unlikely to take place. In this study, oceanographic, swath bathymetry, multichannel seismic data and sediment cores are used to investigate a 25 km long, 10 km wide and up to 0.5 km thick deep-sea late Quaternary deposit that sits adjacent to the north-west flank of one of the major canyons in the North Atlantic, the São Vicente Canyon, in the Alentejo Basin (south-west Iberian margin). The area receives the influence of a strong bottom current, the Mediterranean Outflow Water, which has swept the continental slope at different water depth ranges during glacial and interglacial periods. Architectural patterns and sediment characteristics suggest that this sedimentary body, named Marquês de Pombal Drift, is the result of the interaction between the Mediterranean Outflow Water (particularly during cold periods) and turbidity currents flowing along the São Vicente Canyon. Because the canyon is incised significantly deeper (ca 1.5 km) than the thickness of turbidity currents, an additional process, in comparison to earlier models, is needed to allow the interaction with the Mediterranean Outflow Water and transport sediment out of the canyon. In the São Vicente Canyon, and likely in other canyons worldwide, interaction of turbidity currents with contour currents requires intermediate nepheloid layers that export the finer-grained fraction of turbidity currents out of the canyon at the boundary between major water masses, This research received funding by the European Union’s Horizon 2020 research and innovating programme under the Marie Sklodowska-Curie grant via project ITN-SLATE (grant agreement No 721403). The Spanish “Ministerio de Ciencia e Innovación” and the European Regional Development Fund are also acknowledged for funding through grant CTM2015-70155-R (project INSIGHT), With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)

In this study, we present a comparative analysis between two types of gravity data used in geophysical applications: satellite altimeter-derived gravity and sea-bottom gravity.It is largely known that the marine gravity field derived from satellite altimetry in coastal areas is generally biased by signals back-scattered from the nearby land. As a result, the derived gravity anomalies are mostly unreliable for geophysical and geological interpretations of near-shore environments.To quantify the errors generated by the land-reflected signals and to verify the goodness of the geologic models inferred from gravity, we compared two different altimetry models with sea-bottom gravity measurements acquired along the Italian coasts from the early 50s to the late 80s.We focused on the Gulf of Manfredonia, located in the SE sector of the Adriatic Sea, where: (i) two different sea-bottom gravity surveys have been conducted over the years, (ii) the bathymetry is particularly flat, and (iii) seismic data revealed a prominent carbonate ridge covered by hundreds of meters of Oligocene-Quaternary sediments.Gravity field derivatives have been used to enhance both: (i) deep geological contacts, and (ii) coastal noise. The analyses outlined a “ringing-noise effect” which causes the altimeter signal degradation up to 17 km from the coast.Differences between the observed gravity and the gravity calculated from a geological model constrained by seismic, showed that all datasets register approximately the same patterns, associated with the Gondola Fault Zone, a major structural discontinuity traversing roughly E-W the investigated area.This study highlights the importance of implementing gravity anomalies derived from satellite-altimetry with high-resolution near-shore data, such as the sea-bottom gravity measurements available around the Italian coasts. Such analysis may have significant applications in studying the link between onshore and offshore geological structures in transitional areas.

Mass-transport complexes are characterised by complex, laterally discontinuous internal structure, such as pressure ridges, local shear zones and intact translated blocks. Their internal structure is often poorly imaged by seismic reflection techniques, which are fundamentally limited in lateral resolution by the bandwidth of the seismic source. Diffraction imaging, instead, directly images subsurface heterogeneity by primarily imaging the diffracted part of the seismic wavefield. We apply seismic diffraction imaging to two marine multi-channel seismic profiles containing mass-transport complexes from the Gulf of Cadiz (south west Iberian Margin). We observe that mass-transport complexes generate a large amount of diffracted energy relative to the un-failed sediments. We demonstrate that, in combination with conventional seismic reflection images, diffraction images can be used to better discriminate the lateral extent (runout) of mass-transport complexes, particularly for thin bodies that are not well-resolved using conventional imaging. We suggest that diffraction imaging may have similar applications for marine geohazard assessment to seismic discontinuity attributes, such as the similarity attribute, with the advantage of being closer to a true image of the heterogeneous subsurface. Applying diffraction imaging to image mass-transport complexes from 2-D seismic data is challenging, but may provide some unique insights that are not available from conventional reflection images.

About 6 million years ago, the Mediterranean basin was the focus of one of the most extraordinary events in the recent geological history of the Earth: the so-called Messinian Salinity Crisis (MSC). MEDSALT aims to create a new flexible scientific network addressing the causes, timing, emplacement mechanisms, and consequences – at local and planetary scale – of the largest and most recent ‘salt giant’ on Earth: the Mediterranean Salt Giant (MSG). The MSG is a 1.5 km thick salt layer that was deposited on the bottom of deep Mediterranean basins about 5.5 million years ago, in late Miocene (Messinian), and is preserved beneath the deep ocean floor today. The origin of the Mediterranean salt giant is linked the Messinian Salinity Crisis. Research on the MSC has initiated one of the longest-living scientific controversies in Earth Science. Pioneering scientific drilling in 1970 induced some researchers to publish the theory of the ‘desiccation’ of the Mediterranean during the Messinian. In their view the Mediterranean Sea level dropped by 1–2 km and the basin was transformed into a huge hot, dry salt lake as a consequence of the tectonically-driven closure of the Atlantic gateway at the present-day Gibraltar strait.This interpretation was successful not only among the scientific community, but also in public opinion. On one hand, the progress of scientific research provided additional evidence for the desiccation theory. On the other hand, researchers questioned the theory, providing alternative interpretations of the geological data, and theoretical arguments supporting a model of salt deposition from a deep brine, assuming a very limited sea level change. Controversial views also exist on the mechanisms that ended the MSC: was it a catastrophic flood of Atlantic waters from the re-opening of the Atlantic gateway, or a slow mixing with brackish water from the Black Sea area first before the re-establishment of the normal marine connection with the Atlantic Ocean? In order to trigger progress on the understanding of the MSC, a widespread international scientific community has promoted the largest coordinated research on the MSC since its discovery, clustered around scientific drilling. COST (European Cooperation in Science and Technology) was identified as the most appropriate tool, as COST Actions provide tools for networking, training, mobility and dissemination. The network has further promoted one Marie Skłodowska-Curie European Training Network (SALTGIANT) offering 15 PhD fellowships across Europe. New contacts have been activated with a variety of stakeholders, including governmental administrations, non-governmental organizations, the industry and, indirectly, society at large, demonstrating the importance that science and society renew a relationship of trust and confidence. In all, 200 scientists are working together – across disciplines such as geophysics, geology, biology, microbiology, and also social sciences – towards a common scientific goal: uncovering the Mediterranean salt giant.

European Geosciences Union (EGU) General Assembly 2020, 4-8 May 2020, Using a combination of geophysical and geotechnical data from the Storfjorden Trough Mouth Fan, off southern Svalbard, we investigate the role of glacial advances and retreats over the continental shelf on the hydrogeology of the continental margin. The results of compressibility and permeability tests are used together with margin stratigraphic models from seismic data, as input for numerical finite element models to understand focusing of interstitial fluids in glaciated continental margins. The modeled evolution of the Storfjorden TMF from 2.7 to 0.2 Ma shows that onset of glacial sedimentation (~1.5 Ma) had a significant role in developing aquicludes (tills) on the shelf that decreased the vertical fluid flow towards the sea floor and diverted it towards the slope. This model shows that prior to 220 ka, high overpressure ratio (λ~0.6) develops below the shelf edge and in the middle slope. A more detailed, high resolution model for the last 220 kyrs accounting for ice loading during Glacial Maxima shows that the less permeable glacigenic debris flows deposited during glacial maxima on the slope hinder fluid evacuation from the plumites. This effect in combination with the fluid flow focusing from the shelf allows high overpressure ratio (λ~0.7) to develop in the shallower-most plumite layers. These high overpressures likely persist to the Present and are critical in determining the onset of submarine slope failure. The safety factor of the upper continental slope is reduced by 60% due to the combination of high sedimentation rates, ice loading and focusing of fluids during Glacial Maxima with values of the factor of safety reaching 1.2 during the LGM and beginning of the last deglaciation

This study intends to contribute to the understanding of the Mediterranean Salt Giant in the Western Mediterranean, formed about 6 Ma ago during the Messinian Salinity Crisis. It provides reprocessed multichannel seismic reflection data that aim at improving our knowledge of the stratigraphy in the Algero-Balearic deepwater basin and its continental margins, in the absence of lithological information from wells.We investigate the seismic expression of the Messinian salinity crisis from the south-east of the Balearic promontory to the central Algero-Balearic abyssal basin and the salt tectonic processes associated to these facies. Here the segmentation of salt structures has been previously described using shallow chirp sonar data, low-resolution vintage multichannel seismic data and high-resolution multi-channel seismic data post-stack migrated with a constant velocity field. The structure of the northern Algero-Balearic basin is controlled by two abrupt fault scarps oriented SW–NE (mainly the Emile Baudot Escarpment transform fault) and WSW-ENE (mainly the Mazarron Escarpment transform fault) emplaced during the basin extension, and later intruded by steep and narrow volcanic ridges of Pleistocene age. It is a good analogue to early stage salt tectonic for older and more complex salt giants in the North Sea or the Gulf of Mexico.We reprocessed 2D Kirchhoff PSTM multichannel seismic data acquired by the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale – OGS (SBALDEEP Cruise of 2005 and SALTFLU cruise of 2012; the latter within a Eurofleet cruise) spanning the South-East continental margin of the Balearic islands and the Algero-Balearic basin. The reprocessing was designed for improving the continuity of the reflectors by applying Kirchhoff PSTM using a detailed velocity model, while preserving amplitude information. The objectives are to better apprehend the structural complexity of the area and to retrieve the amplitude variation within the Messinian units, in an attempt to derive the composition of the salt and the pressure regime.We present preliminary results where we delineate four different domains based on i) the seismic facies, ii) the amount of salt deformation, iii) the thickness of the overburden and iv) the pre-salt configuration. We try to assess the presence of the Messinian trilogy in the south-eastern continental slope. We attempt to reconstitute the paleo-depositionnal environment of the various depositional units, and the effect of crustal structures and salt tectonic gravity spreading and gliding on their syn to post-depositional evolution. Finally, we search for evidence of fluid circulation within the Messinian and the Plio-Quaternary deposits over the study area.

The origin of massive dolomite deposits has been an enduring and challenging problem for carbonate sedimentologists since the initial recognition of dolomite as a discrete carbonate mineral [CaMg(CO3)2]. The dolomite problem or enigma involves the fact that the mineral is very abundant in the geologic record, but it is rarely found forming in modern environments. However, when modern dolomite is observed, it is generally, but not exclusively, found forming in hypersaline environments and in minor amounts. Although the geologic record indicates that many ancient massive dolomite deposits formed in association with evaporites, modern examples of extensive amounts of dolomite being deposited under hypersaline conditions have not, or only rarely, been reported. One example of a massive hypersaline dolomite deposit of relatively recent origin may be the dolomite units associated with the end phase, at approximately 5.33 Ma, of the Messinian Salinity Crisis (MSC) in the Ionian Basin, Central Mediterranean (Hsü, Montadert, et al., 1978, Initial Reports of DSDP, Vol. 42, Part 1). Drill core and interstitial waters obtained at DSDP Leg 42A, Site 374 in the Ionian abyssal plain revealed the presence of approximately 25 m of latest Miocene dolomitic mudstone (Lithologic Unit IIIa) capped by 8.5 m of earliest Pliocene dolomite (Lithologic Unit II). Significantly, the pore-water geochemical data indicate that the dolomitization of the overlying earliest Pliocene nannofossil ooze may be an ongoing process. Deeper drilling below the two dolomite units (Lithologic Unit II and IIIa) to the bottom of Site 374 recovered a further 29.5 m of gypsum/dolomitic mudstone cycles (Lithologic Unit IIIb) followed by 21 m of anhydrite and salts (Lithologic Unit IIIc). Hence, the latest Miocene/earliest Pliocene dolomite sequence recovered at DSDP Site 374 is directly associated with the Messinian Salt Giant and potentially represents a massive dolomite deposit of an undetermined horizontal extent.In order to measure the lateral dimensions of the combined dolomite/evaporite lithologic units in the central Ionian Sea, the University of Hamburg, using the facilities of the RV Meteor, conducted a multi-channel reflection seismic survey centered at DSDP Leg 42A, Site 374. A powerful 6 kJoule sparker created the seismic signals, while a digital 144-channel streamer with an active length of 600 m recorded the data. The lowermost Pliocene reveals high lateral continuity and low reflection amplitudes, which is typical for the entire Pan-Mediterranean realm. The uppermost Messinian unit is characterized by a package of strong and positive reflection amplitudes (High Amplitude Reflection Package, HARP). The lateral continuity of the corresponding reflections is very low and the upper boundary is quite irregular. It is unlikely that the reflection configuration results from depositional processes, but it rather suggests diagenetic processes. We correlate the HARP with the dolomite- and gypsum-bearing sediments cored at DSDP Site 374 (Lithologic Unit IIIa, IIIb, IIIc), which is also consistent with the calculated depth. Based on preliminary estimates derived from the seismic survey, the areal extent of the dolomite deposit beneath the Ionian abyssal plain corresponds to a few 10’000 Km2, potentially representing a massive hypersaline dolomite deposit.

About six million years ago, the Mediterranean Sea underwent a period of isolation from the ocean and widespread salt deposition known as the Messinian Salinity Crisis (MSC), allegedly leading to a kilometer-scale level drawdown by evaporation. One of the competing scenarios proposed for the termination of this environmental crisis 5.3 million years ago consists of a megaflooding event refilling the Mediterranean Sea through the Strait of Gibraltar: the Zanclean flood. The main evidence supporting this hypothesis is a nearly 390 km long and several hundred meters deep erosion channel extending from the Gulf of Cádiz (Atlantic Ocean) to the Algerian Basin (Western Mediterranean), implying the excavation of ca. 1000 km3 of Miocene sediment and bedrock. Based on the understanding obtained from Pleistocene onshore megaflooding events and using ad-hoc hydrodynamic modeling, here we explore two predictions of the Zanclean outburst flood hypothesis: 1) The formation of similar erosion features at sills communicating sub-basins within the Mediterranean Sea, specifically at the Sicily Sill; and 2) the accumulation of the eroded materials as megaflood deposits in areas of low flow energy. Recent data show a 6-km-wide amphitheater-shaped canyon preserved at the Malta Escarpment that may represent the erosional expression of the Zanclean flood after filling the western Mediterranean and spilling into the Eastern Basin. Next to that canyon, a ~1600 km3 accumulation of chaotic, seismically transparent sediment has been found in the Ionian Sea, compatible in age and facies with megaflood deposits. Another candidate megaflood deposit has been identified in the Alborán Sea in the form of elongated sedimentary bodies that parallel the flooding channel and are seismically characterized by chaotic and discontinuous stratified reflections, that we interpret as equivalent to gravel and boulder megabars described in terrestrial megaflood settings. Numerical model predictions show that sand deposits found at the Miocene/Pliocene (M/P) boundary in ODP sites 974 and 975 (South Balearic and Tyrrhenian seas) are consistent with suspension transport from the Strait of Gibraltar during a flooding event at a peak water discharge of ~108 m3 s−1. © 2019 The Authors, Funding has been provided by the COST Action Medsalt CA15103 , by the ETN SaltGiant ( European Union funded , Horizon2020 , Marie Skłodowska-Curie grant agreement No 765256 and 674899 ) and by the Spanish public projects MITE ( CGL2014-59516 ) FAUCES ( CMT2015-65461-C2-R , MINECO / FEDER ) and DAMAGE (AEI/FEDER CGL2016-80687-R )., With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

European Geosciences Union (EGU) General Assembly 2020, 4-8 May 2020, Outcrop examples of mass-transport complexes (MTCs) often show a complex internal fabric which reflects disaggregation, deformation and entrainment that occurred during transport and emplacement. This can include intense folding, included blocks of substratum and internal shear zones. Seismic reflection images often cannot properly image this internal fabric as the scale of such structure is usually below the effective resolution. This can limit seismic interpretation to characterising only the overall morphology of the deposits (the top and basal reflectors). Seismic reflections are primarily generated by smooth, laterally continuous interfaces. Discontinuities at or below the scale of the seismic wavelength instead generate seismic diffractions (“diffraction hyperbolae” in unmigrated images). Diffractions are often ignored during seismic processing as they are generally lower in amplitude than reflections, though they do not suffer from the same lateral resolution limit as reflections so are potentially sensitive to smaller scale structure. We suggest that the discontinuous internal fabric of MTCs will generate a significant amount of diffraction energy relative to unfailed sediments. The main goal of this study is to use diffraction imaging to image the small-scale, heterogeneous internal fabric of MTCs. We demonstrate this using two high-resolution, multi-channel 2-D marine seismic profiles (3.125 m CMP spacing, 500 m maximum offset) acquired in 2018 and 2019 as part of the INSIGHT project to investigate submarine geohazards in the Gulf of Cadiz. Profile 1 intersects the Marques de Pombal reverse fault and shows a series of stacked MTCs (~1 s TWTT from top to bottom) in the footwall, thought to be related to episodic fault activity. Profile 2 is located in the Portimão Bank area and contains two large MTCs thought to be related to the mobilisation of a salt diapir. The diffraction imaging method proceeds as i) dip-guided plane-wave destruction to separate reflected and diffracted wavefields; ii) velocity analysis by cascaded constant velocity migrations of the diffraction wavefield; iii) post-stack Kirchhoff time migration of the diffraction wavefield. The unmigrated profiles show that the MTC bodies do generate more internal diffractions than the surrounding unfailed sediments. We also observe large contributions of diffraction energy from the rugose top and base of the MTCs, the rugose top salt interface and from faults within the unfailed sediments. The migrated diffraction images reveal distinct internal structure, thought to represent rafted blocks, ramps and both extensional and compressional faulting. The envelope of the diffraction image is used as an overlay on the conventional reflection image to guide interpretation and highlight potential diffractors. This allows interpretation of thin MTCs and improved delineation of their lateral extent (runout) above conventional reflection images. Diffraction imaging has previously been used to image heterogeneous geology such as fracture networks, channel systems and karst topography. Here we apply the technique to study the internal fabric of MTCs. The resulting images resolve small-scale internal structure that is not well resolved by conventional reflection images. Such structures can be used as kinematic indicators to constrain flow direction and emplacement dynamics, which inform the geohazard potential of future subaqueous mass-movements, This project has received funding from the European Union’sHorizon 2020 research and innovation programme under grantagreement No 721403

European Geosciences Union (EGU) General Assembly, 4-8 May 2020., The Mediterranean Sea underwent restriction from the ocean and widespread salt deposition during the Messinian Salinity Crisis (MSC), allegedly leading to a kilometer-scale level drawdown by evaporation. One of the competing scenarios proposed for the termination of this environmental crisis 5.3 million years ago consists of a megaflooding event refilling the Mediterranean Sea through the Strait of Gibraltar: the Zanclean flood. The main evidence supporting this hypothesis is a nearly 390 km long and several hundred meters deep erosion channel extending from the Gulf of Cádiz (Atlantic Ocean) to the Algerian Basin (Western Mediterranean), implying the excavation of ca. 1000 km3 of Miocene sediment and bedrock.

13 pages, 12 figures, 5 tables, Sample disturbance is still a key issue in offshore investigations, especially when logistic and financial limitations do not allow the use of drilling equipment. This paper focuses on the comparison between the disturbance induced by a conventional free-fall piston corer (FF) and a modified piston corer (AD) equipped with a velocity control (Angel Descent method). Twin core samples were retrieved in two successions of pelitic sediments with a prevailing non-clayey fraction and a non-negligible sandy fraction. Comparison was based on different acquisition, physical and mechanical parameters ranging from accelerometer data to magnetic susceptibility logs and geotechnical parameters from laboratory investigations, including oedometer compression tests and cyclic simple shear tests. Accelerometer data highlighted the sharp reduction in velocity obtained for AD samples. Magnetic susceptibility logs, characterized by a pattern of peaks induced by several volcaniclastic levels present in the succession, indicated that the AD method significantly reduces core shortening. Among geotechnical investigations, cyclic shear tests provided small-strain shear moduli always higher in AD samples, whilst the response of oedometer compression tests was equivocal. In fact, methods for assessing sample disturbance have demonstrated to bear limited effectiveness when applied to soils with relatively low clay content and significant overconsolidation as it is the case of the studied sediments, R. Urgeles and J. Llopart acknowledge funding from project INSIGHT (CTM2015-70155-R) jointly funded by the Spanish Ministerio de Economía y Competitividad and the European Regional Development Fund. The research was funded by grants awarded to FB, AC and PT from the National Research Program Flagship Projects RITMARE – The Italian Research for the Sea - coordinated by the Italian National Research Council

The southern Tyrrhenian continental margin is the product of Pliocene-Recent back-arc extension. An area of approximately 30 km of gentle (about 1.5°) lower slope of the last glacial outer shelf sedimentary wedge in water depths of between 200 and 300 m failed between 14 and 11 ka BP. We approached the landslide by multibeam and sub-bottom profiler surveying, high-resolution multichannel seismics, and coring for stratigraphic and geotechnical purposes. With regard to a slope-stability analysis, we carried out an assessment of the stratigraphic and structural setting of the area of the Licosa landslide. This analysis revealed that the landslide detached along a marker bed that was composed of the tephra layer Y-5 (c. 39 ka). Several previously unknown geological characteristics of the area are likely to have affected the slope stability. These are the basal erosion of the slope in the Licosa Channel, a high sedimentation rate in the sedimentary wedge, earthquake shaking, the volcanic ash nature of the detachment surface, subsurface gas/fluid migration, and lateral porewater flow from the depocentre of wedge to the base of the slope along the high-permeability ash layers. A newly discovered prominent structural discontinuity is identified as the fault whose activity may have triggered the landslide.

SUMMARY Seismic reflection images of mass-transport deposits often show apparently chaotic, disorded or low-reflectivity internal seismic facies. The lack of laterally coherent reflections can prevent horizon-based interpretation of internal structure. This study instead inverts for geostatistical parameters which characterize the internal heterogeneity of mass-transport deposits from depth-domain seismic reflection images. A Bayesian Markov Chain Monte Carlo inversion is performed to estimate posterior probability distributions for each geostatistical parameter. If the internal heterogeneity approximates an anisotropic von Kármán random medium these parameters can describe the structural fabric of the imaged mass-transport deposit in terms of lateral and vertical dominant scale lengths and the Hurst number (roughness). To improve the discrimination between vertical and lateral dominant scale lengths an estimate of the vertical dominant scale length from a borehole is used as a prior in the inversion. The method is first demonstrated on a synthetic multichannel seismic reflection image. The vertical and lateral dominant scale lengths are estimated with lower uncertainty when data from a synthetic borehole data are included. We then apply the method to a real data example from Nankai Trough, offshore Japan, where a large mass-transport deposit is imaged in a seismic profile and penetrated by a borehole. The results of the inversion show a downslope shortening in lateral scale length, consistent with progressive down-slope disaggregation of the mass-flow during transport. The dominant scale lengths can be used as a proxy for strain history, which can improve understanding of post-failure dynamics and emplacement of subacqueous mass-movements, important for constraining the geohazard potential from future slope failure.

27 pages, 14 figures, 4 tables, supporting information https://doi.org/10.1111/bre.12331, Using a combination of geophysical and geotechnical data from Storfjorden Trough Mouth Fan off southern Svalbard, we investigate the hydrogeology of the continental margin and how this is affected by Quaternary glacial advances and retreats over the continental shelf. The geotechnical results show that plumites, deposited during the deglaciation, have high porosities, permeabilities and compressibilities with respect to glacigenic debris flows and tills. These results together with margin stratigraphic models obtained from seismic reflection data were used as input for numerical finite element models to understand focusing of interstitial fluids on glaciated continental margins. The modelled evolution of the Storfjorden TMF shows that tills formed on the shelf following the onset of glacial sedimentation (ca. 1.5 Ma) acted as aquitards and therefore played a significant role in decreasing the vertical fluid flow towards the sea floor and diverting it towards the slope. The model shows that high overpressure ratios (up to λ ca. 0.6) developed below the shelf edge and on the middle slope. A more detailed model for the last 220 kyrs accounting for ice loading during glacial maxima shows that the formation of these aquitards on the shelf focused fluid flow towards the most permeable plumite sediments on the slope. The less permeable glacigenic debris flows that were deposited during glacial maxima on the slope hinder fluid evacuation from plumites allowing high overpressure ratios (up to λ ca. 0.7) to develop in the shallowest plumite layers. These high overpressures likely persist to the Present and are a critical precondition for submarine slope failure, This study is funded by the ‘Ministerio Economia y Competitividad’ through grants DEGLABAR, (CTM2010‐17386), CORIBAR‐ES (CTM2011‐14807‐E) and SVAIS (POL2006‐07390). UNESCO and IUGS are also acknowledged for funding through projects IGCP‐585 and IGCP‐640. The Italian contribution was supported by PNRA project 2013/B2.08 VALFLU

Reconstruction of Paleomagnetic Secular Variation (PSV) of the geomagnetic field is fundamental both to assess geodynamo models and to obtain age constraints for rocks, sediments and archaeological material. We present refined age-calibrated Holocene PSV and relative paleointensity (RPI) stack curves derived from Arctic marine sediments (Northwestern Barents Sea). The Holocene sections of four sedimentary cores were correlated on the basis of paleomagnetic trends and age models, and stacked. The resultant composite PSV and RPI Holocene records (NBS stack) and the reconstructed Holocene Virtual Geomagnetic Pole (VGP) path were evaluated in comparison with the most recent paleomagnetic stack curves and geomagnetic field models. The data indicate that during the Holocene time, the VGPs moved within the superficial projection of the inner core tangent cylinder, with the exception of short time intervals around 5600 and 3200 cal yr BP when VGPs extended to lower latitudes. These deviations might reflect regional geomagnetic features, such as persistent geomagnetic flux lobes at core-mantle boundary. Our data confirm that the large VGP shift observed around 5600 cal yr BP is the result of an increased radial magnetic field at the core-mantle boundary over North America, whilst the VGP shift around 3200 cal yr BP represents a major swing to middle latitudes toward the Middle East and might be associated to a regional high paleointensity peak, known as Levantine Iron Age Anomaly (LIAA).

The Barents Sea Ice Sheet was a marine-based ice sheet, i.e., it rested on the Barents Sea floor during the Last Glacial Maximum (21 ky BP). The Bjørnøyrenna Ice Stream was the largest ice stream draining the Barents Sea Ice Sheet and is regarded as an analogue for contemporary ice streams in West Antarctica. Here, the retreat of the Bjørnøyrenna Ice Stream is simulated by means of two numerical ice sheet models and results assessed against geological data. We investigate the sensitivity of the ice stream to changes in ocean temperature and the impact of grounding-line physics on ice stream retreat. Our results suggest that the role played by sub-shelf melting depends on how the grounding-line physics is represented in the models. When an analytic constraint on the ice flux across the grounding line is applied, the retreat of Bjørnøyrenna Ice Stream is primarily driven by internal ice dynamics rather than by oceanic forcing. This suggests that implementations of grounding-line physics need to be carefully assessed when evaluating and predicting the response of contemporary marine-based ice sheets and individual ice streams to ongoing and future ocean warming.

Carbonate escarpments are submarine limestone and dolomite cliffs that have been documented in numerous sites around the world. Their geomorphic evolution is poorly understood due to difficulties in assessing escarpment outcrops and the limited resolution achieved by geophysical techniques across their steep topographies. The geomorphic evolution of carbonate escarpments in the Mediterranean Sea has been influenced by the Messinian salinity crisis (MSC). During the MSC (5.97–5.33 Ma), the Mediterranean Sea became a saline basin due to a temporary restriction of the Atlantic-Mediterranean seaway, resulting in the deposition of more than one million cubic kilometres of salt. The extent and relative chronology of the evaporative drawdown phases associated to the MSC remain poorly constrained. In this paper we combine geophysical and sedimentological data from the central Mediterranean Sea to reconstruct the geomorphic evolution of the Malta Escarpment and infer the extent and timing of evaporative drawdown in the eastern Mediterranean Sea during the MSC. We propose that, during a MSC base-level fall, fluvial erosion formed a dense network of canyons across the Malta Escarpment whilst coastal erosion developed extensive palaeoshorelines and shore platforms. The drivers of geomorphic evolution of the Malta Escarpment after the MSC include: (i) canyon erosion by submarine gravity flows, with the most recent activity taking place, This research was undertaken with funding from Marie Curie Career Integration Grant PCIG13-GA-2013-618149 (SCARP), ERC Starting Grants n°258482 (CODEMAP) and n°677898 (MARCAN), and collaborative project n°228344 (EUROFLEETS), all within the 7th European Community Framework Programme and the Horizon 2020 Programme. Financial support was also provided by the Fulbright Visiting Scholar Program, Royal Society of New Zealand (through the International Mobility Fund), New Zealand Crown Research Institute SSIF funding to NIWA, the Griffith Geoscience Awards (Department of Communications, Energy and Natural Resources under the National Geoscience Programme 2007–2013 of Ireland), and the David and Lucile Packard Foundation. MAG acknowledges INSU for cruise-related funding and the European Union FP7 project ASTARTE for post-cruise financial support. The article is based upon work from COST Action CA15103 “Uncovering the Mediterranean salt giant” (MEDSALT) supported by COST (European Cooperation in Science and Technology).

The values of delta C-13 in benthic foraminifera have been measured in a gas-hydrate-bearing sediment core collected from an area of active methane venting on the Vestnesa Ridge (West Svalbard continental margin) to reconstruct the local history of methane emissions over the past 23.500 yrs BP. The chronostratigraphic framework of the core has been derived from AMS C-14 dates and biostratigraphic analysis. While foraminifera from some intervals have delta C-13 within the normal marine range (0 to-1%.), five intervals are characterized by a much lower delta C-13, as low as -17.4%.. These intervals are interpreted to record the incorporation of C-13-depleted carbon in the presence of methane emissions at the seafloor during biomineralization of the carbonate foraminiferal tests and subsequent secondary mineralization. Methane emission events (MEE) occur from the Last Glacial Maximum (LGM) to the Holocene, with the most prominent one, in terms of delta C-13 depletion, predating the Bolling-Allerod Interstadial (GI-1 in the Greenland ice core record). The lack of correlation between the values of delta C-13 and delta O-18, however, appears to preclude warming of bottom waters as the principal control on methane release. Rather, it seems likely that methane release is a consequence of episodicity in the supply of gas to the hydrate system and in the processes that enable methane gas to migrate through the hydrate stability field to the seabed, or of other geological processes still under debate. (C) 2014 Elsevier B.V. All rights reserved.

Oceanic basins are shaped by a variety of natural drivers that impact the seafloor morphology at different scales, spanning from hundreds of kilometres for plate motions to decimetres for bio-constructions by benthic organisms. In the post-industrial period of the oceanic basin history, anthropic activity on the seabed has started to provide an additional morphologic imprint. Because oceanic basins are sinks for sediments produced on land, the majority of the seafloor morphology is produced by forces acting on sediments, resulting in sediment accumulation, transport, erosion and deformation. Plate tectonics forces are reflected dramatically in the morphology of areas of the oceans where the sedimentary cover is thin, or even absent, along the mid ocean ridges, and fracture zones. Chemical reactions in the oceanic subsurface induce mineral precipitation, dissolution or transformation that may also indirectly impact the seafloor.

The presence of gas hydrates on the Blake Ridge diapir, northeastern Atlantic Ocean, offers an opportunity to study the impact of methane seepage on the ecology and geochemistry of benthic foraminifera in the late Holocene. Three push cores, covering a time span of ~ 1000 yrs, were retrieved from three distinct microhabitats at the top of the diapir at a water depth of ~ 2150 m: (i) sediments away from seepage (control core), (ii) sediments overlain by clusters of methanotrophic and thiotrophic bivalves, and (iii) chemoautotrophic microbial mats. The foraminiferal assemblages at the two seep sites are marked by a reduction in benthic foraminiferal species diversity, coupled with a near-absence of agglutinated species. However, an opportunistic population rise in CH4- or H2S-tolerant calcareous species (e.g., Globocassidulina subglobosa and Cassidulina laevigata) that utilize the abundant trophic resources at the seeps has led to an increase in the overall assemblage density there. The δ18O and δ13C values of three species of benthic foraminifera – Gyroidinoides laevigatus, Globocassidulina subglobosa, and Uvigerina peregrina – and the planktonic species Globorotalia menardii were acquired from all three cores. The benthic species from methane seeps yield δ13C values of 0.1 to − 4.2 (‰VPDB), that are distinctly more 13C-depleted relative to the δ13C of 0.4 to − 1.0 (‰VPDB) at the control (off seep) site. The species from a mussel-bed site exhibit more negative δ13C values than those from microbial mats, possibly reflecting different food sources and higher rate of anaerobic oxidation of methane. The positive δ13C values in the paired planktonic species suggest that authigenic carbonate precipitation did not overprint the observed 13C depletions. Hence the probable cause of negative δ13C of benthic foraminifera is primary calcification from Dissolved Inorganic Carbon (DIC) containing mixed carbon fractions from (a) highly 13C-depleted, microbially-oxidized methane and (b) a seawater source.

The aim of this study is to discuss the onset and growth of the Bellsund, Hornsund and Storfjorden Trough-Mouth Fans (TMFs) on the North-Western Barents Sea margin. This is done on the basis of a seismo-stratigraphic analysis of new 2D seismic reflection profiles, and a new correlation between ODP Site 986 west of Spitsbergen and the seismo-stratigraphic network in the central part of the Western Barents Sea margin. We infer that reflector R4A marks the onset of both the development of the TMFs and the contourite deposition which dominate this part of the margin from this time onward. We conclude that these deposits were frequently affected by episodes of small-scale mass-wasting, focused at the mouth of the glacially eroded cross-shelf troughs. With a new interpolation between the few available constraints, we propose an age of about 1.3 Ma for the onset of both the development of the TMFs and the contourite deposition. Thus, we hypothesize, from our results and from previous studies, that the Barents Sea/Svalbard Ice Sheet expanded first beyond the coast north of Svalbard, later reaching the shelf edge at the mouth of Bjornoyrenna and then to Storfjorden/southern Spitsbergen.

[1] Submarine landslides are ubiquitous along Mediterranean continental margins. With the aim of understanding mass-wasting processes and related hazard at the scale of a large marine basin encompassing multiple geological settings, we have compiled data on their geometry, age, and trigger mechanism with a geographic information system. The distribution of submarine landslides in the Mediterranean reveals that major deltaic wedges have a higher density of large submarine landslides, while tectonically active margins are characterized by relatively small failures. In all areas, landslide size distributions display power law scaling for landslides > 1 km3. We find consistent differences on the exponent of the power law (θ) depending on the tectonic setting. Available age information suggests that failures exceeding 1000 km3 are infrequent and may recur every ~40 kyr. Smaller failures that can still cause significant damage might be relatively frequent (failures > 1 km3 may recur every 40 years). The database highlights that our knowledge of submarine landslide activity with time is limited to a few tens of thousands of years. Available data suggest that submarine landslides may preferentially occur during lowstand periods, but no firm conclusion can be made on this respect, as only 70 landslides (out of 696 in the database) have relatively accurate age determinations. The temporal pattern and changes in frequency-magnitude distribution suggest that sedimentation patterns and pore pressure development have had a major role in triggering slope failures and control the sediment flux from mass wasting to the deep basin.

Atlas of Submarine Glacial Landforms: Modern, Quaternary and Ancient.-- 2 pages, 1 figures, Glacigenic debris-flow deposits (Laberg & Vorren 1995; Laberg et al. 2012) are the most prominent component of high-latitude trough-mouth fans (TMFs), which develop off fast-flowing ice streams which occupy cross-shelf troughs during full-glacial periods. Glacial erosion and sediment transport to the shelf edge are most effective during glacial maxima; debris-flow deposits therefore represent short periods of a very high input of glacigenic sediments to the continental slope when the ice front reaches the shelf break. Conversely, relatively limited amounts of mostly hemipelagic sediments accumulate on the continental slope during interglacial periods (Dowdeswell et al. 2002)

Submarine slope failures are a well-known geohazard. They are able to destroy seafloor installations along their path and by generating tsunamis they may threaten coastal infrastructures. While the mechanisms involved in submarine landslide generation remain poorly known, there are observations that slope stability can be reduced in the presence of free gas. Here, we present new high-resolution 3D seismic data from the Eivissa Channel between the Iberian Penninsula and the Balearic Promontory in the Western Mediterranean Sea. The data reveal slope stability reduction in this area at least since mid-Quaternary times, and an intimate relationship between fluid migration and slope stability. We show that two landslides, i.e. pre-Ana Slide and Ana Slide, occurred at almost the same location above an erosional channel in the Messinian unconformity. There is seismic evidence that fluids including gas are migrating upwards through this erosional surface and that they charge sedimentary layers at the base of the Ana Slide possibly reducing its strength and predisposing it to failure. Our data show in unprecedented detail the ways in which the presence of gas influences slope stability. The findings illustrate the importance of including high-resolution 3D seismic data in slope stability and tsunami risk assessments to identify shallow gas distribution as one of the main controls on slope stability in gas prone areas.

17 pages, 12 figures, 3 tables, supplementary material http://dx.doi.org/10.1016/j.quascirev.2015.10.002, The development of two Arctic Trough Mouth Fans (TMFs), the Storfjorden and Kveithola TMFs, is investigated by means of sub-bottom and seismic reflection profiles, multibeam bathymetry and sediment samples allowing their detailed stratigraphic architecture to be defined. We find that the TMFs mainly consist of an alternation of rapidly deposited glacigenic debris flows during glacial maxima and a sequence of well-layered plumites and hemipelagic sediments, which were mainly deposited during the deglaciation phase of the adjacent glacial trough. We have identified eight units above regional reflector R1, which indicate that the ice sheet reached the shelf edge within the Storfjorden Trough on at least three occasions during the last ∼200 ka. A shallow subsurface unit of glacigenic debris flows suggests that the ice sheet had a short re-advance over the northern and central part of Storfjorden after the Last Glacial Maximum. From stratigraphy, core and literature data, we estimate that ice sheets reached the shelf edge between 19.5 to 22.5 ka, 61 to 65 ka and 135 to 167 ka. Detailed seismic imaging allows us to refine the sedimentary model of Arctic TMFs. The main differences to previous models involve gully formation during not only the deglaciation phase, but also during interglacials by dense shelf water cascading, and a specific timing for the occurrence of slope failures (i.e., shortly after the deglaciation phase). High mean sedimentation rates during glacial maxima of up to 18 kg m−2 yr−1 likely allow excess pore pressure to develop in the water rich plumites and hemipelagic sediments deposited in the previous deglacial period, particularly where such plumites attain a significant thickness. The position of the submarine landslides in the stratigraphic record suggest that such excess pore pressure is not enough to trigger the slope failures and suggests that earthquakes related to isostatic rebound are likely involved in the final activation, This study was funded by the “Ministerio de Economia y Competitividad” through the IPY projects SVAIS (POL2006-07390/CGL) and IPY-NICE STREAMS (CTM2009-06370-E/ANT), as well as projects DEGLABAR (CTM2010-17386) and CORIBAR-ES (CTM2011-14807-E). The “Generalitat de Catalunya” is acknowledged for support through an excellence research group grant (2014SGR940). The Italian projects EGLACOM, CORIBAR-IT and VALFLU are also acknowledged. The first author was funded by an FPI grant BES-2011-043614

The upper continental slope of the Storfjorden-Kveithola Trough Mouth Fans (NW Barents Sea) contains a several m-thick late Pleistocene sequence of plumites composed of laminated mud interbedded with sand/silt layers. Radiocarbon ages revealed that deposition occurred during about 130 years at a very high sedimentation rate of 3.4 cm a−1, at about 7 km from the present shelf break. Palaeomagnetic and rock magnetic analyses confirm the existence of a prominent, short-living sedimentary event. The plumites appear laterally continuous and were correlated with the sedimentary sequences described west of Svalbard and neighboring glacial depositional systems representing a major event at regional scale appointed to correspond to the deep-sea sedimentary record of Meltwater Pulse-1a. We also present new sedimentological and geochemical insights, and multi-beam data adding information on the palaeoenvironmental characteristics during MWP-1a and ice sheet decay in the NW Barents Sea.

article Kveithola Trough, an E-W trending glacial trough in the NW Barents Sea, was surveyed for the first time during the EGLACOM cruise of R/V OGS-Explora in summer 2008. Swath bathymetry shows that the seafloor is characterized by E-W trending mega-scale glacial lineations (MSGL) that record a fast flowing ice stream draining the Svalbard/Barents Sea Ice Sheet (SBIS) during the Last Glacial Maximum (LGM). MSGL are overprinted by transverse sediment ridges about 15 km apart which give rise to a staircase axial profile of the trough. Such transverse ridges are interpreted to be grounding-zone wedges (GZWs) formed by deposition of subglacial till during episodic ice stream retreat. Sub-bottom (CHIRP) and multi-channel reflection seismic data show that the present-day morphology is largely inherited from the palaeo-seafloor topography at the time of deposition of the transverse ridges, overlain by a draping glaciomarine unit which in places is over 15 m thick. Our data allow the reconstruction of depositional processes which accompanied deglaciation of the Spitsbergen Bank area. The sedimentary drape deposited on top of the GZWs is suggested to have accumulated at a very high rate, (on average in the order of 1-1.5 m ka �1

We present new 3D seismic and well data from the Ebro Margin, NW Mediterranean Sea, to shed new light on the processes that formed the Messinian Erosion Surfaces (MES) of the Valencia Trough (Mediterranean Sea). We combine these data with backstripping techniques to provide a minimum estimate of the Messinian sea level fall in the EBRO Margin, as well as coupled isostasy and river incision and transport modeling to offer new constraints on the evolution of the adjacent subaerial Ebro Basin. Four major seismic units are identified on the Cenozoic Ebro Margin, based on the seismic data, including two major prograding megasequences that are separated by a major unconfirmity: the MES. The 3Dseismic data provide an unprecedented view of the MES and display characteristic features of subaerial incision, including a drainage network with tributaries of at least five different orders, terraces and meandering rivers. The Messinian landscape presents a characteristic stepped-like profile that allows the margin to be subdivided in three different regions roughly parallel to the coastline. No major tectonic control exists on the boundaries between these regions. The boundary between the two most distal regions marks the location of a relatively stable base level, and this is used in backstripping analysis to estimate the magnitude of sea level drop associated with the Messinian Salinity Crisis on the Ebro Margin. The MES on the Ebro Margin is dominated by a major fluvial system, that we identify here as the Messinian Ebro River. The 3Dseismic data, onshore geology and modeling results indicate that the Ebro River drained the Ebro Basin well in advance of the Messinian.