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  • 1
    Electronic Resource
    Electronic Resource
    Constraints on the state of in situ effective stress and the mechanical behavior of ODP Leg 186 claystones in the Japan Trench forearc (2004)
    Melbourne, Australia : Blackwell Science Pty
    The @island arc 13 (2004), S. 0 
    Details
    ISSN: 1440-1738
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract   The Japan Trench forearc offshore Honshu Island in northeast Japan, where the 130-m.y.-old Pacific oceanic plate is presently subducted, was drilled during the Ocean Drilling Program Leg 186. Results from mechanical and sedimentological studies of claystones recovered from Sites 1150 and 1151 in the overlying erosional forearc wedge are reported in the present study. Although many physical properties are similar in the seismic (Site 1150) and aseismic portion (Site 1151) of the shallow forearc, Site 1150 displayed a higher abundance of open fractures, two prominent fault zones and enigmatic pore fluid signatures in the claystones. The abundance of weak mineral phases, together with high smectite contents (from X-ray diffraction), control the low friction coefficients of 0.33–0.39 of the claystones in ring-shear experiments. Results from triaxial testing proposed overall low magnitudes of in situ effective vertical stress, with somewhat lower values at Site 1150 than at Site 1151. Similarly, samples from Site 1150 displayed slightly higher pore fluid pressures than those at Site 1151. The high sediment porosities, which are in part also a result of intact diatom tests (from scanning electron microscope), together with the anomalous fluid signatures and elevated pore fluid pressures, could very likely result from upward migration and influx of deep-seated waters. Dewatering reactions at depth result in enhanced pore fluid pressure transients along out-of-sequence thrusts and consequently lower effective stress. At depths greater than that of Leg 186 drilling, elevated pressure–temperature conditions trigger mineral transformation and cementation, which result in increasing friction, unstable sliding and seismic rupture. Such earthquakes could have repeatedly disaggregated the consolidated claystone fabrics at the seismic site, and could be responsible for differences in yield strength and cementation when compared to the aseismic Site 1151.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1440-1738.2003.00423.x
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  • 2
    Electronic Resource
    Electronic Resource
    Evidence for fluid flow in the Japan Trench forearc using isotope geochemistry (Cl, Sr, B): Results from ODP Site 1150 (2004)
    Melbourne, Australia : Blackwell Science Pty
    The @island arc 13 (2004), S. 0 
    Details
    ISSN: 1440-1738
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract  Interstitial pore waters from Ocean Drilling Program Site 1150, where ∼1200 m of sub-sea-floor sediment from the upper Japan Trench forearc were recovered, were analyzed for element concentrations and Cl, Sr and B isotopes. Although chlorinity showed profound down-hole freshening to values as low as ∼310 mm (0.55 × seawater) in the deeper part of the claystone-dominated succession, both Sr and B concentrations showed an overall increase. Sr reached concentrations of up to 〉250 µm (∼3.00 × seawater), whereas B-enrichment was even stronger (3920 µm; i.e. 9.30 × seawater). The strong variations in concentration correspond to fractionation reactions in the deep, tectonically deformed part of the forearc. The heavily fractured portion of Site 1150 (from ∼700 m to the total depth of the hole) has two shear zones that very likely act as conduits that expel deep-seated fluids to the sea floor. These fluids not only showed the strongest freshening of Cl, but were also characterized by low δ37Cl measurements (down to −1.1‰), the heaviest δ11B measurements (∼40–46‰) and the least radiogenic 87Sr/ 86Sr measurements. The profound isotope anomalies together with the excursions in element concentrations suggest that diagenetic processes operate at that depth. These include clay mineral diagenesis, alteration of tephra from the Japan and Izu Arcs, and possibly transformation of biogenic silica from abundant diatoms. Given the strong enrichment of some mobile elements (e.g. Sr, B, Li), enhanced fluid flow through permeable penetrative faults through the forearc (like the shear zones at Site 1150) could be an efficient mechanism for back-flux of those elements from the deep forearc into the hydrosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1440-1738.2003.00424.x
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  • 3
    Electronic Resource
    Electronic Resource
    Cross-section through the frontal Japan Trench subduction zone: Geochemical evidence for fluid flow and fluid–rock interaction from DSDP and ODP pore waters and sediments (2004)
    Melbourne, Australia : Blackwell Science Pty
    The @island arc 13 (2004), S. 0 
    Details
    ISSN: 1440-1738
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract  Fluids and sediments from Deep Sea Drilling Project/Ocean Drilling Program Legs (56, 57, 87 and 186) along a transect extending from the subducting plate, across the midslope and upper slope of the Japan Trench forearc were analyzed for B and B isotopes in order to assess their composition and fluid–sediment interaction. At the reference Site 436 on the subducting plate, changes in B contents and B isotopes are controlled by the lithology and diagenesis only. The midslope Sites 440 and 584 showed stronger variations in the B geochemistry, which can be related to diagenesis and tectonic dewatering along faults. The strongest changes in the B geochemistry were observed on the upper slope Sites 1150 and 1151, where profound down-hole freshening (chlorinities as low as ∼310 mmol) coincides with a B enrichment (up to 9.3 × seawater concentration). The B isotope pore fluid profile of Site 1150 displayed a bimodal variation with depth, first increasing to values more positive than seawater, then shifting to lower signatures typical for deep-seated fluids, whereas Site 1151 showed a constant B decrease with depth. Sites 1150 and 1151 sediments showed B increases with depth to values as high as ∼164 p.p.m. and isotopic compositions ranging from ∼+4 to −9‰. A linear decrease in Bsolid/Bfluid ratio, suggests that B geochemistry of the upper slope sites is controlled by fluid–rock interaction and deep-seated fluid flow, whereas constant Bsolid/Bfluid ratios were observed at the reference site on the incoming plate. This fluid overprint is probably caused by normal faults in the sediment cover which might be interconnected to deep thrusts in the underlying Cretaceous accreted wedge. This suggests that the erosive Japan Trench margin is characterized by back-flux of deep-seated, B-enriched fluids into the ocean, which is facilitated by extensional normal faulting as a result of tectonic erosion and subsidence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1440-1738.2003.00425.x
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  • 4
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    Heat flow anomalies in the Gulf of Cadiz and off Cape San Vincente, Portugal (2009)
    Elsevier
    In:  Marine and Petroleum Geology, 26 . pp. 795-804.
    Details
    Publication Date: 2017-09-13
    Description: Heat flow anomalies provide critical information in active tectonic environments. The Gulf of Cadiz and adjacent areas are affected by the plate convergence between Africa and Europe, causing widespread deformation and faulting. Active thrust faults cause lateral movement and advection of heat that produces systematic variations in surface heat flow. In December 2003 new heat flow data were collected during the research vessel Sonne cruise SO175 in the Gulf of Cadiz over two sites of recent focused research activity: (i) the Gulf of Cadiz sedimentary prism and (ii) the Marques de Pombal escarpment. Both features have also been discussed as potential source areas of the Great Lisbon earthquake and tsunami of 1755. Background heat flow at the eastern terminus of the Horseshoe abyssal plain is about 52–59 mW/m2. Over the Gulf of Cadiz prism, heat flow decreases from ∼57 mW/m2 to unusually low values of 45 mW/m2 roughly 120 km eastward. Such low values and the heat flow trend are typical for active thrusting, supporting the idea of an east-dipping thrust fault. Slip rates are 10 ± 5 mm per year, assuming that the fault dips at 2°. A fault dipping at 5°, however, would result into slip rates of 1.5–5 mm per year, suggesting that subduction has largely ceased. Based on seismic data, the Marques de Pombal fault is interpreted as part of an active fault system located ∼100 km westward of Cape San Vincente. Heat flow over the fault is affected by refraction of heat caused by the 1 km high escarpment. Thermal models suggest that the slip rate along the fault must either be small or shear stresses acting on the fault are rather high. With respect to other fault zones, however, it is reasonable to assume that the fault's slip rate is small.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.marpetgeo.2008.08.006
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    A new evidence for mass wasting at the NE Cretan slope: a multi-stage slide complex from the eastern Mediterranean (2009)
    Elsevier
    In:  Marine Geology, 263 . pp. 97-107.
    Details
    Publication Date: 2017-08-04
    Description: Newly acquired bathymetric and seismic reflection data have revealed mass-transport deposits (MTDs) on the northeastern Cretan margin in the active Hellenic subduction zone. These include a stack of two submarine landslides within the Malia Basin with a total volume of approximately 4.6 km(3) covering an area of about 135 km(2). These two MTDs have different geometry, internal deformations and transport structures. The older and stratigraphic lower MTD is interpreted as a debrite that fills a large part of the Malia Basin, while the second, younger MTD, with an age of at least 12.6 cal. ka B.P., indicate a thick, lens-shaped, partially translational landslide. This MTD comprises multiple slide masses with internal structure varying from highly deformed to nearly undeformed. The reconstructed source area of the older MTD is located in the westernmost Malia Basin. The source area of the younger MTD is identified in multiple headwalls at the slope-basin-transition in 450 m water depth. Numerous faults with an orientation almost parallel to the southwest-northeast-trending basin axis occur along the northern and southern boundaries of the Malia Basin and have caused a partial steepening of the slope-basin-transition. The possible triggers for slope failure and mass-wasting include (i) seismicity and (ii) movement of the uplifting island of Crete from neotectonics of the Hellenic subduction zone, and (iii) slip of clay-mineral-rich or ash-bearing layers during fluid involvement. (c) 2009 Elsevier B.V. All rights reserved.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.margeo.2009.04.002
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Cone penetration testing to assess slope stability in the 1979 Nice landslide area (Ligurian Margin, SE France) (2015)
    Elsevier
    In:  Marine Geology, 369 . pp. 162-181.
    Details
    Publication Date: 2015-09-24
    Description: Highlights: • Comprehensive morphological, seismic, sedimentological, and geotechnical data sets. • Dynamic CPTU provides a powerful, time- and cost-efficient in situ technique. • Development of a regional sub-seafloor strength model offshore Nice airport. • 2D finite element slope stability assessment gives slope failure depth of 〉 50 m. Abstract: In the landslide-prone area near the Nice international airport, southeastern France, an interdisciplinary approach is applied to develop realistic lithological/geometrical profiles and geotechnical/strength sub-seafloor models. Such models are indispensable for slope stability assessments using limit equilibrium or finite element methods. Regression analyses, based on the undrained shear strength (su) of intact gassy sediments are used to generate a sub-seafloor strength model based on 37 short dynamic and eight long static piezocone penetration tests, and laboratory experiments on one Calypso piston and 10 gravity cores. Significant strength variations were detected when comparing measurements from the shelf and the shelf break, with a significant drop in su to 5.5 kPa being interpreted as a weak zone at a depth between 6.5 and 8.5 m below seafloor (mbsf). Here, a 10% reduction of the in situ total unit weight compared to the surrounding sediments is found to coincide with coarse-grained layers that turn into a weak zone and detachment plane for former and present-day gravitational, retrogressive slide events, as seen in 2D chirp profiles. The combination of high-resolution chirp profiles and comprehensive geotechnical information allows us to compute enhanced 2D finite element slope stability analysis with undrained sediment response compared to previous 2D numerical and 3D limit equilibrium assessments. Those models suggest that significant portions (detachment planes at 20 m or even 55 mbsf) of the Quaternary delta and slope apron deposits may be mobilized. Given that factors of safety are equal or less than 1 when further considering the effect of free gas, a high risk for a landslide event of considerable size off Nice international airport is identified.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.margeo.2015.08.008
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    World Ocean Review: The Ocean – A Climate Champion? How to Boost Marine Carbon Dioxide Uptake (2024)
    Maribus
    Details
    Publication Date: 2024-03-19
    Description: What action should we take for the effective mitigation of climate change? Measures to avoid greenhouse gas emissions are surely the main priority – but the truth is that in the coming decades, we will also have to remove large quantities of carbon dioxide from the atmosphere and store it securely. Can – indeed, should – the ocean aid us in this task? The new World Ocean Review (WOR 8) explores this issue with reference to the oceans' role in the Earth's carbon cycle and looks at the benefits, risks and knowledge gaps around the main marine carbon dioxide removal techniques.
    Type: Book , NonPeerReviewed
    Format: text
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    OceanRep: Book
  • 8
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    World Ocean Review: Klimaretter Ozean? Wie das Meer (noch) mehr Kohlendioxid aufnehmen soll (2023)
    Maribus
    Details
    Publication Date: 2024-03-14
    Description: Wie soll der Mensch den Klimawandel wirkungsvoll begrenzen? Oberste Priorität haben sicherlich Maßnahmen zur Vermeidung von Treibhausgas-Emissionen. Fakt ist mittlerweile aber auch, dass wir der Atmosphäre in den kommenden Jahrzehnten viel Kohlendioxid entnehmen und sicher einlagern müssen. Kann oder sogar muss uns der Ozean bei dieser Aufgabe helfen? Der neue „World Ocean Review“ (WOR Nr. 8) erläutert diese Frage anhand der Rolle des Ozeans im Kohlenstoffkreislauf der Erde und stellt Vorteile, Risiken und Wissenslücken zu den wichtigsten meeresbasierten Verfahren zur Kohlendioxid-Entnahme vor.
    Type: Book , NonPeerReviewed
    Format: text
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    OceanRep: Book
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