Research papers

The current filters are: Starting year = 2021, Ending year = 2022
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Alonso B., Juan C., Ercilla G., Cacho I., López-González N., Rodríquez-Tovar F.J., Dorador J., Francés G., Casas D., Vandorpe T., Vázquez J.T. (2021)
Marine Geology, 437, 106488. DOI: 10.1016/j.margeo.2021.106488. (BibTeX: alonso.etal.2021a)
Abstract: See
The Western Mediterranean Deep Water (WMDW), on its way out toward the Atlantic Ocean, has favored the formation of contourite drifts in the Alboran Sea (SW Mediterranean) since the opening of the Strait of Gibraltar. Resolving the nature of these deposits is crucial for reconstructing the WMDW variability at a millennial scale, deciphering its bottom current paleo-velocity, and establishing paleoclimatic implications over the last 25 cal. kyr BP. Two sediment cores retrieved from elongated separated and plastered contourite drifts formed along its path are investigated by means of multi-sedimentological data (terrigenous grain-size, sortable silt, terrigenous and carbonate sediment fluxes, bioturbation and ichnofabric changes), geochemical data (Zr/Al and Si/(Si + Al) ratios), chronostratigraphic data (δ18O, and 14C data) as well as statistical analyses (grain-size end-member modelling and spectral analysis). Integration of these data confirms the contouritic nature of Alboran drift deposits. The high-resolution paleocurrent records of the WMDW inferred from the sortable silt of contourite sequences led us to define two regimes in terms of WMDW flow energy. Regime 1 (weak to moderate velocity) defined by paleo-velocities of ⁓4 to 23 cm s−1 is dominant during the last 24 cal kyr BP. Regime 2 (strong velocity) is characterized by estimated paleo-velocities of about ⁓36 cm s−1 during Heinrich Stadial 2. The spectral analysis of bottom current proxies (sortable silt and Zr/Al ratio) matches four cyclic climatic signals (1900 yr, 2300 yr, 4000 ye and 6100 yr), corroborating the occurrence of millennial-scale cyclicity. These cycles are related to atmospheric climate variability, in turn linked to variations in solar activity. Our results, when combined with published data from a neighboring NW Mediterranean contourite drift, provide for a better regional understanding of the WMDW millennial-scale dynamics.
Keywords: Contourites; Sortable silt; Western Mediterranean Deep Water; Paleoceanography; Alboran Sea
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Arjona-Camas M., Puig P., Palanques A., Durán R., White M., Paradis S., Emelianov M. (2021)
Marine Geophysical Researches, 42, 38 DOI: 10.1007/s11001-021-09457-7. (BibTeX: arjonacamas.etal.2021)
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Increases of water turbidity and suspended sediment transport in submarine canyons have been associated with high-energy events such as storms, river foods and dense shelf water cascading (DSWC), and occasionally with bottom trawling along canyon fanks and rims. To assess the variations on the water column turbidity and sediment transport in the Palamós Canyon linked to both natural and trawling-induced processes, an autonomous hydrographic profler, as well as a near-bottom current meter and a turbidimeter were deployed in the canyon axis (929 m depth) from February to June 2017, covering a trawling turbidity during the trawling closure were mostly associated with storms and DSWC events, transporting turbid dense waters into the canyon. In absence of such events, the water column displayed low suspended sediment concentrations (~ 0.3 mg L−1 ) until the trawling season began, when particulate matter detachments, ranging between > 1 mg L−1 and 3.8 mg L−1 , were observed at the water depths where the trawling grounds are found. During the trawling closure, high near-bottom suspended sediment fuxes (35–44 g m−2 s −1 ) were sporadically registered at ~ 920 m depth associated with a major storm and DSWC event. Smaller but more frequent increases of near-bottom suspended sediment fuxes (0.1–1.4 g m−2 s −1 ) were recorded during trawling activities. Despite these smaller trawling-induced suspended sediment fuxes, 30 days of continuous bottom trawling activity transported a total amount of 40 kg m−2 , of similar magnitude to that generated by a major DSWC event (50 kg m−2 ). Since bottom trawling in Palamós Canyon is practiced on a daily basis throughout the year, a much larger contribution of anthropogenically derived water turbidity and suspended sediment transport can be expected.
Keywords: Palamós Canyon · Dense shelf water cascading (DSWC) · Bottom trawling · Sediment transport · Nepheloid structure · NW Mediterranean
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Estrada F., González-Vida J.M., Peláez J.A., Galindo-Zaldívar J., Ortega S., Macías J., Vázquez J.T., Ercilla G. (2021)
Scientific Reports, 11, 16253. DOI: 10.1038/s41598-021-95729-6. (BibTeX: estrada.etal.2021a)
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Tsunamis are triggered by sudden seafloor displacements, and usually originate from seismic activity at faults. Nevertheless, strike-slip faults are usually disregarded as major triggers, as they are thought to be capable of generating only moderate seafloor deformation; accordingly, the tsunamigenic potential of the vertical throw at the tips of strike-slip faults is not thought to be significant. We found the active dextral NW–SE Averroes Fault in the central Alboran Sea (westernmost Mediterranean) has a historical vertical throw of up to 5.4 m at its northwestern tip corresponding to an earthquake of Mw 7.0. We modelled the tsunamigenic potential of this seafloor deformation by Tsunami-HySEA software using the Coulomb 3.3 code. Waves propagating on two main branches reach highly populated sectors of the Iberian coast with maximum arrival heights of 6 m within 21 and 35 min, which is too quick for current early-warning systems to operate successfully. These findings suggest that the tsunamigenic potential of strike-slip faults is more important than previously thought, and should be taken into account for the re-evaluation of tsunami early-warning systems.
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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)
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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, 437, 106505. DOI: 10.1016/j.margeo.2021.106505. (BibTeX: yenes.etal.2021c)
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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)