Research papers

The current filters are: Starting year = 2020, Ending year = 2021
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Lee S.-H., Jou H.-T., Bahk J.-J., Jun H., Moon S.-H., Kim H.-J., Horozal S., Cukur D., Um I.-K., Yoo D.-G., Urgeles R. (2021)
Geosciences Journal, 25, 93–105. DOI: 10.1007/s12303-020-0008-9. (BibTeX: lee.etal.2021a)
Abstract: See
In the western margin of the Ulleung Basin, a detailed analysis of cores with geophysical data from a fan-shaped body, just downslope of a submarine gully associated upslope with failure scars, reveals various modes of mass-transport processes. The arcuate failure scars occurs in water depths exceeding 600 m. The fan-shaped body, less than ca. 10 km long in radius, displays strong backscatter intensity in sonar images, and corresponds to the uppermost transparent mass in Chirp sub-bottom profiles. Sediment cores penetrating to the uppermost transparent mass consist mostly of various facies of mass-transport deposits (MTDs), causing the strong back-intensity in the sonar images. The interval of MTD facies comprises the upper and lower units without hemi-pelagic muds between them, implying that the fan-shaped body was probably deposited during a single event separated in at least two stages without a significant time break. The lower unit shows brittle to plastic deformation of soft muds (slides/slumps), whereas the upper units exhibits fully fragmented soft mud clasts (low viscous debris flows). Both the upper and lower units involve same original lithology (i.e., soft hemi-pelagic mud) prior to failures, suggesting that the lithology could not significantly affect depositional processes. The fully fragmented soft mud clasts of the upper unit are probably indicative of more shearing than the brittle to plastic deformation of soft muds in the lower unit. Considering the small dimension of the failure scars/gully and the same original lithology, the more shearing of the upper unit was most likely caused by longer transport distance than that of the lower unit. The rare turbidites with absence of channellevee systems in the fan-shaped body and the failure scars confined in the upper to middle slopes suggest that the submarine gully probably formed by slope failures, not by erosion of turbidity currents.
Keywords: Mass-transport processes; Mass-transport deposits; Slope failures; Late Quaternary; Ulleung Basin (East Sea)
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Tendero-Salmerón V., Lafosse M., d’Acremont E., Rabaute A., Azzouz O., Ercilla G., Makkaoui M., Galindo-Zaldivar J. (2021)
Frontiers in Earth Science, 9, 645942. DOI: 10.3389/feart.2021.645942. (BibTeX: tenderosalmeron.etal.2021a)
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Automation of the throw backstripping method has proven to be an effective tool for the determination of the evolution of tectonic activity in wide fault zones. This method has been applied to the Al Hoceima Bay (southwesternmost Mediterranean, Alboran Sea) for a time period covering the last 280 kyr on 672 faults imaged on 265 high-resolution seismic reflection profiles. This area was affected by major earthquakes and corresponds to a transtensional basin deformed by growth faults. The automated application of throw backstripping allowed for a faster deciphering of the migration of tectonic activity. Results show a westward migration of the deformation with quickly increasing deformation rates in the most recent time frames near Al Hoceima, one of the most populated cities. This migration is in agreement with the current seismicity, the GPS data, and recent brittle deformation data. Vertical throw rates of up to 0.47 mm/year have been calculated, for the most recent time periods, in segments of the Bokkoya fault zone. The westward migration of the deformation fits with the reconstruction suggested by the westernmost Mediterranean geodynamic models during the Pleistocene epoch, and it might be the consequence of the interaction between the northwest (NW) movement of the South Alboran indenter and the back Rif south-westward displacement. The highly accurate constraints of the evolution of the tectonic activity offered by this automation will substantially improve the seismic hazard assessment.
Keywords: Active tectonics; Throw backstripping; Faulting migration; Marine faulting; Alboran Sea
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Yenes M., Casas D., Nespereira J., López-González N., Casalbore D., Monterrubio S., Alonso B., Ercilla G., Juan C., Bárcenas P., Palomino D., Mata P., Martínez-Díaz P., Pérez N., Vázquez J.T., Estrada F., Azpiroz-Zabala M., Teixeira M. (2021)
Marine Geology DOI: 10.1016/j.margeo.2021.106505. (BibTeX: yenes.etal.2021b)
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Two Quaternary plastered contourite drifts, with terraced and low-mounded morphologies, make up the continental slope and base-of-slope in the northwestern Alboran Sea, respectively, between the Guadiaro and Baños turbidite systems, close to the Strait of Gibraltar. Considering their significant lateral extent, the link between the contourite drift deposits and landslides may be particularly important for hazard assessment. The physical properties, composition and geometry of contourite drifts have been proposed as key factors in slope stability, although this relationship still needs to be better constrained. In this work, new in-situ geotechnical data (cone penetration tests; CPTu) has been combined with morphostratigraphic, sedimentological, and (laboratory) geotechnical properties to determine the stability of the Guadiaro-Baños drifts. For the depositional domains of both drifts, the resulting sedimentary and geotechnical model describes low-plasticity granular and silty sands on the erosive terraced domain that evolve seawards to silty and silty-clay deposits with a higher plasticity and uniform geomechanical properties. For the shallower coarse-grained contourite sediments, the cohesion (c') and internal friction angle (ϕ') values are 0–9 kPa and 46–30°, respectively, whereas for the distal fine contourites the undrained shear strength gradient (∇Su) is 2 kPa/m. These properties allow us to establish high factors of safety for all the scenarios considered, including seismic loading. Slope failure may be triggered in the unlikely event that there is seismic acceleration of PGA > 0.19, although no potential glide planes have been observed within the first 20 m below the seafloor. This suggests that the contourite drifts studied tend to resist failure better than others with similar sedimentary characteristics. The interplay of several processes is proposed to explain the enhanced undrained shear strength: 1) the geometry of the drifts, defined by an upper contouritic terrace and lower low-mounded shapes; 2) recurrent low-intensity earthquakes with insufficient energy to trigger landslides, favouring increased strength due to dynamic compaction; and 3) cyclic loading induced by solitons/internal waves acting on the sediment.
Keywords: Contourite drift; Submarine landslide; Alboran Sea; Sedimentology; In-situ geotechnical tests (CPTu); Factor of Safety (FoS)
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, López L., Guillén J., Puig P. (2020)
Science of The Total Environment, 735, 139482. DOI: 10.1016/j.scitotenv.2020.139482. (BibTeX: .etal.2020b)
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Trace metal pollution of coastal sediment is monitored in many countries to control its evolution and the effectiveness of preventive and corrective measures. However, temporal variability of trace metal pollution is not always due to changes in pollution management, as natural processes can induce a significant variability in the trace metal content of sediment and particulate matter, especially in strongly polluted coastal areas. To study this variability, time series of trace metals in particulate matter and bottom sediments were recorded along with hydrographic and hydrodynamic parameters in the most highly polluted zone of the Besòs River prodelta. Two benthic tripods equipped with current meters, turbidimeters and sediment traps were deployed at 20 and 30 m water depth from late-September to mid-June and sediment cores were taken four times at each site during the deployment period. Trace metal content in the trapped particulate matter and the surface sediment increased during storm events, which can resuspend and erode several cm of subsurface sediments with higher pollution levels from earlier industrial times. After the storms, significant accumulation of less polluted sediment began, and near-bottom currents redistributed it, decreasing trace metal contents in surface sediments and trapped particulate matter. Therefore, energy conditions previous to monitoring sampling must be considered in order to evaluate the evolution of trace metals in inner shelf polluted sediments.
Keywords: Trace metals; Pollutants resuspension; Seasonal pollution variability; Polluted sediment dynamics; Inner continental shelf; Mediterranean Sea
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Bo M., , Al Mabruk S.A.A., Balistreri P., Bariche M., , , Betti F., Bilan M., Canese S., Cattaneo-Vietti R., Corsini-Foka M., Crocetta F., Deidun A., Dulćić J., Grinyó J., Kampouris T.E., Ketsilis-Rinis V., Kousteni V., Koutsidi M., Lubinevsky H., Mavruk S., Mytilineou Ch., Petani A., Puig P., Salomidi M., Sbragaglia V., Smith C.J., Stern N., Toma M., Tsiamis K., Zava B., Gerovasileiou V. (2020)
Mediterranean Marine Science, 21, 3, 608-630. DOI: 10.12681/mms.23674. (BibTeX: bo.etal.2020a)
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This Collective Article presents information about 21 taxa belonging to seven Phyla (one Ochrophyta, one Porifera, three Cnidaria, two Arthropoda, three Mollusca, one Echinodermata, and ten Chordata) and extending from the western Mediterranean Sea to the Levantine Sea. The new records were reported from nine countries as follows: Spain: first records of three deep-sea species from the Blanes Canyon along the Catalan margin, namely the gorgonian Placogorgia coronata, the bivalve Acesta excavata, and the Azores rockling Gaidropsarus granti; Italy: first record of the mesopsammic nudibranch Embletonia pulchra from Ligurian shallow-waters; first record of the deep-sea carnivorous sponge Lycopodina hypogea from the north-central Tyrrhenian Sea, living in dense clusters over dead black corals; new records of the Portuguese man o’ war Physalia physalis from Sardinian and Sicilian waters; first Italian record of the large asteroid Coronaster briareus from the Ionian Sea; first record of the white grouper Epinephelus aeneus in the northernmost point of the Adriatic Sea; Croatia: first record of the gastropod Haliotis mykonosensis for the Adriatic Sea; Malta: new sightings of Physalia physalis from Maltese waters; Libya: first record of the sand crab Albunea carabus from two localities along the Libyan coast; Greece: first records of the deep-sea black coral Parantipathes larix from the eastern Mediterranean Sea; first verified record of the agujon needlefish Tylosurus imperialis in the Hellenic Ionian Sea; first confirmed record of the brown algae Treptacantha squarrosa in the eastern Mediterranean Sea; new records of three deep-sea fish species from the Aegean Sea, namely the bluntnose sixgill shark Hexanchus griseus, the Atlantic pomfret Brama brama, and the rudderfish Centrolophus niger; new record of the tripletail Lobotes surinamensis from Lesvos Island; new record of the shrimp Brachycarpus biunguiculatus from the gut content of the non-indigenous lionfish Pterois miles; Turkey: new record of the imperial blackfish Schedophilus ovalis from Turkish waters; Lebanon: first record of the slender sunfish Ranzania laevis, stranded along the Lebanese coast; Israel: new record, after about 60 years from the last catch, of the spotted dragonet Callionymus maculatus.
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Collico S., Arroyo M., Urgeles R., Gràcia E., Devincenzi M., Peréz N. (2020)
Marine Geology, 429, 106296 DOI: 10.1016/j.margeo.2020.106296. (BibTeX: collico.etal.2020a)
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The SW Iberian continental margin is well recognized as a tectonically active area, where major canyons and mass wasting events are both present. Earthquake triggered submarine landslides may cause tsunami and result in catastrophic damage to bordering coastal areas. In this setting, submarine landslide susceptibility mapping represents a major step towards a regional risk mitigation strategy. Landslide susceptibility mapping in large offshore areas presents significant challenges as a result of the limited information on controlling variables, large uncertainties in triggering mechanisms and limited geotechnical data. In this study, a geotechnical model-based approach has been followed that narrows the range of controlling factors and, within a probabilistic framework, allows a systematic treatment of parameter uncertainties. This model-based analysis covers the whole SW Iberian margin increasing by three orders of magnitude the areal extent of precedent offshore slope stability susceptibility studies. This jump in spatial scale is facilitated by application of a systematic Bayesian updating procedure, to combine geotechnical information from global databases and that available from regional sites. Seismic shaking is estimated using an available regional database of seismogenic faults. These tools are implemented within a GIS to generate, via Montecarlo simulations, probabilistic landslide susceptibility maps based on two different analytical seismic infinite slope stability models. These models differ mainly in the form of their final results, either as distributions of slope stability safety factors or as distributions of seismic-triggered slope displacements. Receiving Operator Curves are used to assess the different landslide susceptibility predictions obtained against a comprehensive regional database of submarine landslides. It turns out that the models analyzed correctly predict 92% and 82% of the mapped landslide subset chosen for validation for pseudo-static and displacement-based method respectively. This suggests that, within the limits of the currently available databases, seismic events are the dominant factor at the origin of the submarine landslides mapped in the study area. An advantage of the framework presented is that it can quickly incorporate new regional geotechnical information or better regional landslide databases, as they become available.
Keywords: Landslide susceptibility; Earthquake triggering; SW Iberian margin; Regional-scale; Probabilistic modelling; Bayesian updating
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Cukur D., Um I.-K., Chun J.-H., Lee G.-S., Kim S.-R., Bahk J.-J., Urgeles R., Horoza S. (2020)
Marine Geology, 428, 106282 DOI: 10.1016/j.margeo.2020.106282. (BibTeX: cukur.etal.2020a)
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Submarine landslides are common geomorphological features of continental margins. Some of the largest submarine landslides occurred on low-angle (< 4°), sediment-starved margins, yet their preconditioning and trigger mechanisms are still largely unconstrained. The southwestern continental margin of the East Sea (between 37.5°N and 38.0°N), Korea, occupies a narrow shelf (< 10 km), is characterized by low sedimentation rates (~3–7 cm /ka) with an average gradient of less than 2°. Here, we investigate submarine landslides using newly collected datasets including multibeam echosounder (MBES), chirp sub-bottom profiler, multichannel seismic (MCS) data and ten piston cores. MBES data from the margin reveal at least four major submarine landslides initiated at depths of 400 m to over 600 m. These landslides left clear headwall scarps on the seafloor with reliefs reaching over ~130 m and extend for over 40 km. MCS data show that some of the failures have resulted in the complete disintegration of the failed mass, while others have resulted in the deposition of well-defined hummocky debris flows. Sediments recovered downslope of the headwall scarps contain slides and debris flow deposits and turbidites that are overlain by bioturbated hemipelagic layers. Radiocarbon dating from hemipelagic units overlying MTDs within the headwall scarps reveal that major failures occurred at ca. 11 to 19 ka, coinciding with the time of the Last Glacial Maximum (LGM) to early deglaciation. Since then, hemipelagic sedimentation has prevailed throughout the sediment starved slope. Slope stability analyses based on geotechnical properties of sediments indicate that all areas are stable under static, and even stable under loads derived from earthquakes in instrumental records, but there were probably earthquakes in pre-historical records (i.e., with a longer recurrence interval) of potentially significant larger magnitude. We suggest that the preferential occurrence of major failures adjacent to the major faults on the lower slope may ultimately be tectonic-controlled although other factors may have contributed as well. Our work shows that coarse-grained clastic sediments are abundant in the shallow subsurface and that these higher-permeability units, often identified as weak layers, would focus fluid flow and could act as slip planes for slope failure. Our data also indicate that tectonic steepening and gas charging are other key parameters for controlling instability in sediment-starved margins.
Keywords: Submarine landslides; East Sea of Korea; Sediment-starved margins; Slope stability; Headwall scarps; Earthquakes
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d\'Acremont E., Lafosse M., Rabaute A., Teurquety G., Do Couto D., Ercilla G., Juan C., Mercier de Lépinay B., Lafuerza S., Galindo‐Zaldivar J., Estrada F., T. Vazquez J., Leroy S., Poort J., Ammar A., Gorini C. (2020)
Tectonics, 39, 3, e2019TC005885. DOI: 10.1029/2019TC005885. (BibTeX: d\acremont.etal.2020)
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Since the Miocene, the thinned continental crust below the Alboran Sea and its overlying sedimentary cover have been undergoing deformation caused by both convergence of Eurasia and Africa and by deep processes related to the Tethyan slab retreat. Part of this deformation is recorded at the Xauen and Tofiño banks in the southern Alboran Sea. Using swath bathymetry and multichannel seismic reflection data, we identified different stages and styles of deformation. The South Alboran Basin is made up of Early Miocene to Pliocene sedimentary layers that correlate with the West Alboran Basin depocenter and are dominated by E‐W trending folds and thrusts. The Xauen and Tofiño Banks first recorded the phase of extension and strike‐slip movement during the slab retreat, followed by the phase of compressional inversion since the Tortonian and are now structured by tight folds, thrusts, and mud bodies. This study proposes that the Banks were located on the southern‐inherited Subduction Tear Edge Propagator (STEP) fault related to the westward migration of the Alboran domain during the Miocene. The STEP fault zone, acting as a boundary between the African block and the Alboran block, was located along the onshore Jebha‐Nekor fault and the offshore Alboran Ridge and the Yusuf fault zone. Thick‐skinned and thin‐skinned shortening occurred when slab retreat stopped, and inversion began. The present‐day style of the deformation seems to be linked to a decollement level made of undercompacted shale on top of the Ghomaride complex.
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Garcia-Castellanos D., Micallef A., Estrada F., Camerlenghi A., Ercilla G., Periáñez R., Abril J.M. (2020)
Earth-science reviews, 201, 103061. DOI: 10.1016/j.earscirev.2019.103061. (BibTeX: garciacastellanos.etal.2020a)
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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.
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Isla E., Ribó M., Puig P. (2020)
Marine Geology, 430, 106377. DOI: 10.1016/j.margeo.2020.106377. (BibTeX: isla.etal.2020a)
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Three instrumented lines were installed on the continental slope and the basin of the Gulf of Valencia for thirteen months (May 2010 to June 2011) aiming to study particle fluxes and their relationship with environmental parameters. Total mass flux varied between 52 mg m−2 d−1 in the central part of the basin and 7199 mg m−2 d−1 in the northern slope sector. The main biogenic constituent was calcium carbonate (estimated fraction) representing more than 26% of the total flux, whereas organic matter and biogenic silica add together <10%. These percentages were similar to the proportional contents in the sea floor sediment and were mainly attributed to advection of particles from the Ebro shelf during wave resuspension events. The coincidence in the temporal variation of the Ebro River discharges with the total mass flux observed in the Gulf of Valencia suggests that the effect of river discharges >400 m−3 s−1 can be detected at least 155 km to the southwest. The temporal variation of satellite-derived chlorophyll-a abundance and organic matter flux indicated that biogenic material collected in the Gulf of Valencia is related to sea surface spring phytoplankton blooms developing in the northwestern Mediterranean. However, the temporal variation of biogenic silica corresponded better with the usual pattern of deep chlorophyll-a maxima reached during the fall season, suggesting that diatoms are a main component in subsurface phytoplankton blooms.
Keywords: Shelf and slope processes; Pelagic sediments; Particle fluxes; NW Mediterranean; Biogenic fluxes
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Juan C., Ercilla G., Estrada F., Alonso B., Casas D., Vázquez J.T., d'Acremont E., Medialdea T., Hernández-Molina F.J., Gorini C., El Moumni B., Valencia J. (2020)
Marine Geology, 423, 106138. DOI: 10.1016/j.margeo.2020.106138. (BibTeX: juan.etal.2020b)
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A new basin-scale comprehensive view of contourite features, turbidite systems, and mass-wasting deposits comprising the Spanish and Moroccan margins and basins of the Alboran Sea has been achieved after a new detailed seismic stratigraphic analysis and the construction of sedimentary maps for the Pliocene and Quaternary sedimentary units. Multiple contourite systems were defined in this sea: i) the Intermediate Mediterranean contourite system (IMCS), formed under the action of the LMW on the Spanish continental margin; ii) the Deep Mediterranean contourite system (DMCS), formed under the action of the DMW and made up of contourites mostly found on the Moroccan margin and annex sub-basins; and iii) the Atlantic contourite system (ACS), shaped by the AW and its interfaces with the LMW and DMW on the uppermost continental slopes of both margins. The contourite features (drifts, moats, channels and terraces) coexist during the various stages of the Plio-Quaternary with turbidite systems showing different onsets and cessations in activity, and with mass-wasting deposits. In this work, the temporal and spatial distributions of contourite and turbidite systems can be considered as proxies to deduct the long-term impacts of bottom-current circulations and related processes, and ultimately allowed to decipher past bottom-current dynamics and the multiple factors controlling Plio-Quaternary sedimentation in the Alboran Sea.
Keywords: Alboran Sea; Pliocene; Quaternary; Sedimentary systems; Palaeoceanography
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Michaud F., Dañobeitia J., Bartolomé R., Carbonell R., Delgado Argote L., Cordoba D., Monfret T. (2020)
Geo-Marine Letters, 20, 3, 168-173. DOI: 10.1007/s003670000050. (BibTeX: michaud.etal.2020a)
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New data collected between the northernmost tip of the East Pacific rise (18°05′N, 105°35′W) and the Middle America trench provide evidence that the seafloor, which lacks significant sedimentary cover, has a typical spreading-derived abyssal hill topography. The tectonic fabric of this seafloor is concave to the west, as it is today at the tip of the East Pacific rise. Farther to the east, at the outer wall of the trench, the seafloor topography exhibits a north-south trending fabric. We suggest that this fabric originated along the East Pacific rise, as it reached the trench and possibly subducted beneath the North America plate prior to the development of the complex connection of the East Pacific rise with the Rivera transform.
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Palanques A., Guillén J., Puiga P., (2020)
Journal of Environmental Management, 260, 110028. DOI: 10.1016/j.jenvman.2019.110028. (BibTeX: palanques.etal.2020a)
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Polluted sediments retained in water reservoirs are potential sources of deleterious materials downstream, especially during floods or flushing flows (FFs). Their interaction with these events is important for determining potential risks and evaluating management actions. In the Ebro River, the Flix Reservoir accumulated a deposit of more than 3 × 105 t of industrial waste with high Hg concentrations. Because suspended particulate matter (SPM) is the main driver of Hg pollution downriver, this study analyses the transport of particulate matter and Hg pollution from the Flix Reservoir to the Ebro Estuary during FFs. Time series of currents, turbidity and downward particulate matter fluxes were obtained by current meters, turbidimeters and sediment traps assembled in benthic tripods. They were deployed in the reservoir and at two locations in the estuary during two recording periods that each captured a flushing flow (FF) event. In addition, SPM samples were collected during the study period at several locations along the river course, from upstream of the Flix Reservoir down to the river mouth, to measure the suspended particulate matter and associated Hg mobilized downstream. A continuous background level of Hg pollution was observed during the deployment periods, but the Hg and particulate matter fluxes increased by between one and two orders of magnitude during FFs. Though the two events reached similar water discharges, the first FF was after the wet season and generated lower particulate matter concentrations and fluxes, but higher Hg contents than the second, which occurred after the dry season. The higher available particulate matter in the second event diluted the polluted Hg particle load more than the first event. Thus, similar FFs may result in different Hg concentration and sediment transport episodes, largely depending on the previous hydrological regime and the river sediment availability. These findings should be considered for FF management.
Keywords: Flushing flow; Mercury transport; Particulate matter; Polluted reservoir; Salt wedge estuary; Ebro river
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Piñeiro S., González-Pola C., Fernández-Díaz J.M., Naveira-Garabato A.C., Sánchez-Leal R., Puig P., Salat J., Balbin R. (2020)
Journal of Geophysical Research: Oceans, 126, 2 DOI: 10.1029/2020JC016535. (BibTeX: pineiro.etal.2020)
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Major deep-convection activity in the northwestern Mediterranean during winter 2005 triggered the formation of a complex anomalous deep-water structure that substantially modified the properties of the Western Mediterranean deep layers. Since then, evolution of this thermohaline structure, the so-called Western Mediterranean Transition (WMT), has been traced through a regularly sampled hydrographic deep station located on the outer continental slope of Minorca Island. A rapid erosion of the WMT\'s near-bottom thermohaline signal was observed during 2005–2007. The plausible interpretation of this as local bottom-intensified mixing motivates this study. Here, the evolution of the WMT structure through 2005–2007 is reproduced by means of a one-dimensional diffusion model including doublediffusive mixing that allows vertical variation of the background mixing coefficient and includes a source term to represent the lateral advection of deep-water injections from the convection area. Using an optimization algorithm, a best guess for the depth-dependent background mixing coefficient is obtained for the study period. WMT evolution during its initial stages is satisfactorily reproduced using this simple conceptual model, indicating that strong depth-intensified mixing (K∞(z) ≈ 22 × 10−4 m2 s−1; z ⪆ 1,400 dbar) is a valid explanation for the observations. Extensive hydrographic and current observations gathered over the continental slope of Minorca during winter 2018, the first deep-convective winter intensively sampled in the region, provide evidence of topographically localized enhanced mixing concurrent with newly formed dense waters flowing along-slope toward the Algerian sub-basin. This transport-related boundary mixing mechanism is suggested to be a plausible source of the water-mass transformations observed during the initial stages of the WMT off Minorca.
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Poort J., Lucazeau F., Le Gala V., Dal Cin M., Leroux E., Bouzi A., Rabineau M., Palomino D., Battani A., Akhmanov G.G., Ferrante G.M., , Si Bachir R., Koptevr A., , Bellucci M., Pellen R., Camerlenghi A., Migeon S., Alonso B., Ercilla G., Yelles-Chaouche A.K., Khlystov O.M. (2020)
Marine Geology, 419, 106064. DOI: 10.1016/j.margeo.2019.106064. (BibTeX: poort.etal.2020b)
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The Western Mediterranean basin has been formed by Miocene back-arc extension and is underlain by a thin and young lithosphere. This young lithosphere is warm, as testified by an overall elevated offshore heat flow. Heat flow within the Western Mediterranean is, however, highly variable and existing data are unevenly distributed and poorly studied in the central part of the Liguro-Provençal and Algero-Balearic basins. This central part is floored by a young oceanic crust, bordered by different continental margins, cut by transform faults, and filled by up to 8 km of sediments. We present a total of 148 new heat flow data collected during the MedSalt and WestMedFlux cruises in 2015 and 2016 and aligned along seven regional profiles that show an important heat flow variability on the basin-scale, but also locally on the margins. A new heat flow map for the Western Mediterranean outlines the following regional features: (1) a higher average heat flow in the Algero-Balearic basin compared to the Liguro-Provençal basin (94 ± 13 mW/m2 and 78 ± 16 mW/m2, respectively), and (2) a regional thermal asymmetry in both basins, but with opposed heat flow trends. Up to 20% of this heat flow difference can be explained by sediment blanketing, but age and heterogeneity of ocean crust due to an asymmetric and polyphased opening of the basins are believed to have given the major thermal imprint. Estimates of the age of the oceanic crust based on the new heat flow suggest a considerably younger West Algerian basin (16–23 Ma) compared to the East Algerian basin and the West Sardinia oceanic floor (31–37 Ma). On the margins and ocean-continent transitions of the Western Mediterranean the new heat flow data point out the existence of two types of local anomalies (length scale 5–30 km): (1) locally increased heat flow up to 153 mW/m2 on the Gulf of Lion margin results from thermal refraction of large salt diapirs, and (2) the co-existing of both low (<50 mW/m2) and high (>110 mW/m2) heat flow areas on the South Balearic margin suggests a heat redistribution system. We suspect the lateral heat advection is resulting from a regional fluid circulation in the sediments associated to the widespread Plio-Pleistocene volcanism on the South Balearic margin.
Keywords: Heat flow; Western Mediterranean Sea; Liguro-Provençal basin; Algero-Balearic basin; Continental margins; Oceanic crust
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Silva P.F., Roque C., Drago T., Belén A., Henry B., Gemma E., .Lopes A, López-González N., Casas D., Naughtond F., Vázquez J.T. (2020)
Marine Geology, 420, 106086. DOI: 10.1016/j.margeo.2019.106086. (BibTeX: silva.etal.2020)
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We present a multidisciplinary study of the seismic stratigraphy, sedimentology, geochemistry and magnetism to characterize the Quaternary mass movement deposits (MMD) and the associated deformation in the Portimão Bank (Gulf of Cadiz, offshore SW Iberia). Two scales of approach have been applied. At large-scale (m to km) approach, were recognized and characterized a series of important and subsequent slide scars (tens of meters high) and MMD (the larger one with 10 km length) related to landslides, more prominent at Portimão Bank\'s southern flank. At small-scale (cm) approach, we point out on a piston core collected within a scar affected by MMD, a replication of the sedimentary column as evidenced by geochronological results and corroborated by sedimentology, geochemistry and magnetic data. Magnetic fabric data enabled the identification and characterization of the internal structure and deformation of MMD along the sedimentary column. For last, geochronology and the morphology of Portimão seamount are discussed in order to constraint the factors controlling MMD triggering. The multidisciplinary approach is useful in a better characterization of the MMD at different scales and improved the understanding of its dynamics.
Keywords: Mass movement deposits; Bathymetric and seismic profiles; Piston core analyses; Magnetic fabric; Deformed sediments
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Villaseñor A., Herrmann R.B., Gaite B., Ugalde A. (2020)
Solid Earth, 11, 63-74. DOI: 10.5194/se-11-63-2020. (BibTeX: villasenor.etal.2020a)
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During September–October of 2013 an intense swarm of earthquakes occurred off the east coast of Spain associated with the injection of the base gas in an offshore underground gas storage. Two weeks after the end of the injection operations, three moderate-sized earthquakes (Mw 4.0–4.1) occurred near the storage. These events were widely felt by the nearby population, leading to the indefinite shut-down of the facility. Here we investigate the source parameters (focal depth and mechanism) of the largest earthquakes in the sequence in order to identify the faults reactivated by the gas injection and to help understand the processes that caused the earthquakes. Our waveform modeling results indicate that the largest earthquakes occurred at depths of 6–8 km beneath the sea floor, significantly deeper than the injection depth (∼1800 m). Although we cannot undoubtedly discriminate the fault plane from the two nodal planes of the mechanisms, most evidence seems to favor a NW–SE-striking fault plane. We propose that the gas injection reactivated faults in the Paleozoic basement, with regional orientation possibly inherited from the opening of the Valencia Trough
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Yenes M., Monterrubio S., Nespereira J., Casas D. (2020)
Engineering Geology, 264, 105375. DOI: 10.1016/j.enggeo.2019.105375. (BibTeX: yenes.etal.2020)
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In recent years, apparent overconsolidation (AOC) has been observed in the most superficial sections of the sedimentary column of the seabed. AOC has been detected in sediment samples taken from deep and shallow waters, independent of the source area. Although the origin of this phenomenon remains controversial, it seems to be linked principally to physical-chemical bonds and ionic changes that cause strong attractions between particles. This work uses an experimental approach based on standardized oedometer tests to study the presence of AOC in surface sediments and its disappearance at depth. The results obtained show that the existence of AOC is related to the formation of a structured sediment generated by both secondary consolidation and aging processes. In addition, the results obtained facilitate a discussion of how AOC influences the potential development of plane translational slides. The development of this type of instability in areas affected by AOC generates a subsequent stabilization of the ocean floor and, consequently, a lower recurrence of large landslides in these areas than would be expected from a sedimentary process with no AOC.
Keywords: Apparent overconsolidation; Submarine sediment; Sub-bottom; Submarine landslide
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Zitellini N., Ranero C.R., F. Loreto M., Ligi M., Pastore M., D’Oriano F., Sallares V., Grevemeyer I., Moeller S., Prada M. (2020)
Geology, 48, 2, 123-127. DOI: 10.1130/G46774.1. (BibTeX: zitellini.etal.2020a)
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The Tyrrhenian Basin is a region created by Neogene extensional tectonics related to slab rollback of the east-southeast–migrating Apennine subduction system, commonly believed to be actively underthrusting the Calabrian arc. A compilation of >12,000 km of multichannel seismic profiles, much of them recently collected or reprocessed, provided closer scrutiny and the mapping of previously undetected large compressive structures along the Tyrrhenian margin. This new finding suggests that Tyrrhenian Basin extension recently ceased. The ongoing compressional reorganization of the basin indicates a change of the regional stress field in the area, confirming that slab rollback is no longer a driving mechanism for regional kinematics, now dominated by the Africa-Eurasia lithospheric collision