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  • 1
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    Controls on the tectono-magmatic evolution of a volcanic transform margin: the Vøring Transform Margin, NE-Atlantic (2001)
    Springer
    In:  Marine Geophysical Research, 22 (3). pp. 133-152.
    Details
    Publication Date: 2017-06-22
    Description: Ocean bottom seismograph (OBS), multichannel seismic and potential field data reveal the structure of the Vøring Transform Margin (VTM). This transform margin is located at the landward extension of the Jan Mayen Fracture Zone along the southern edge of the Vøring Plateau. The margin consists of two distinctive segments. The northwestern segment is characterized by large amounts of volcanic material. The new OBS data reveal a 30–40 km wide and 17 km thick high-velocity body between underplated continental crust to the northeast and normal oceanic crust in the southwest. The southeastern segment of the mar is similar to transform margins elsewhere. It is characterized by a 20–30 km wide transform margin high and a narrow continent-ocean transition. The volcanic sequences along this margin segment are less than 1 km thick. We conclude from the spatial correspondence of decreased volcanism and the location of the fracture zone, that the amount of volcanism was influenced by the tectonic setting. We propose that (1) lateral heat transport from the oceanic lithosphere to the adjacent continental lithosphere decreased the ambient mantle temperature and melt production along the entire transform margin and (2) that right-stepping of the left-lateral shear zone at the northwestern margin segment caused lithospheric thinning and increased volcanism. The investigated data show no evidence that the breakup volcanism influenced the tectonic development of the southeastern VTM.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1023/A:1012089532282
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    The Fugløy Reef at 70°N; acoustic signature, geologic, geomorphologic and oceanographic setting (2007)
    Springer
    In:  International Journal of Earth Sciences, 96 (1). pp. 201-213.
    Details
    Publication Date: 2017-05-18
    Description: This is the first in-depth study of a cluster of cold-water coral reefs, the Fugløy Reefs, found at 70°N on the Norwegian margin. Combining high resolution seismic reflection data, side-scan sonar, video-images, and oceanographic measurements reveals the geologic, geomorphologic and oceanographic setting in which the reefs occur. The reefs consist mainly of the scleractinian ahermatypic Lophelia pertusa, and exist below the thermocline at water depths between 140 m and 190 m. The reefs appear as cone-shaped, acoustically transparent features on seismic reflection data, consistently located in places characterized by the availability of hard substrate, high relief, and periodical exposure to high tidal cur-rents (〉30 cm/s). These currents transport water of the Norwegian Atlantic Current to the reefs from an area with fluid expulsion-related pockmarks. The spatial relationship between reef and pockmark locations and current directions suggests that seepage of biogenic gas might be a catalyst to reef growth. With a height of more than 40 m some of the Fugløy reefs are among the highest reported from the Norwegian Margin. This indicates highly fa-vourable growth conditions, and conservative estimates indicate a net growth rate for the reefs of ~5 mm/yr. We expect that cold-water reefs will be found further north along the Barents Sea margin as general awareness on the geophysical signature and appearance of the reefs increases, because all known factors involved in reef establishment and growth are within the required intervals also further north. Introduction
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00531-005-0495-y
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Seabed characterization through a range of high-resolution acoustic systems - a case study offshore Oman (2006)
    Springer
    In:  Marine Geophysical Research, 27 (3). pp. 167-180.
    Details
    Publication Date: 2017-06-22
    Description: This study uses three acoustic instruments (different in their operating frequencies, 13, 3.5, and 6–10 kHz, and deployment type, hull-mounted, surface-towed and deep-towed) to investigate and characterize the acoustic response of seafloor NE of Oman in a frequency-independent manner. High-resolution control was achieved by having selected areas of our acoustic transects ground-truthed by sampling and/or sea-floor photography. On the regional scale, the greatest degree of change in backscatter amplitude was correlated with major changes of seabed morphology and lithology. However, small-scale roughness had the biggest effect on amplitude on the local scale, i.e. within each area of specific seafloor type. The study also shows that seafloor reflection amplitude changes are far more easily detected by deep-towed instrument than by surface-towed or hull-mounted systems. Whilst there are significant changes in bioturbation types and density along the transects, the suite of instruments deployed was not able to pick up the effect of the bioturbation on acoustic signals.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s11001-005-5999-0
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Sidescan backscatter variations of cold seeps on the Hikurangi Margin (New Zealand): indications for different stages in seep development (2014)
    Springer
    In:  Geo-Marine Letters, 34 (2/3). pp. 169-184.
    Details
    Publication Date: 2017-05-19
    Description: Cold seeps on the Hikurangi Margin off New Zealand exhibit various seabed morphologies producing different intensity patterns in backscatter images. Acoustic backscatter characteristics of 25 investigated seep sites do not show a continuous range of patterns between two end members, but fall into four distinct types characterised by variations in backscatter intensity, distribution and inferred structural heights. The types reflect different carbonate morphologies including up to 20 m high structures (type 1), low-relief crusts (type 2), scattered blocks (type 3) and carbonate free sites (type 4). Each seep corresponds to a single type; ntermediates were not observed. Although the observed morphologies and backscatter patterns may have been caused by variations in sediment burial of seep carbonates or differential exhumation by erosion, they probably epresent varying onsets of authigenic carbonate precipitation. Precipitation of carbonate is episodic, which is likely the result of internal forcing. Blocking and subsequent reorganisation of the seep plumbing system lead to abandonment of old seeps and formation of new sites.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00367-014-0361-7
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Fluid venting and seepage at accretionary ridges: the Four Way Closure Ridge offshore SW Taiwan (2016)
    Springer
    In:  Geo-Marine Letters, 36 (3). pp. 165-174.
    Details
    Publication Date: 2019-02-01
    Description: Within the accretionary prism offshore SW Taiwan, widespread gas hydrate accumulations are postulated to occur based on the presence of a bottom simulating reflection. Methane seepage, however, is also widespread at accretionary ridges offshore SW Taiwan and may indicate a significant loss of methane bypassing the gas hydrate system. Four Way Closure Ridge, located in 1,500 m water depth, is an anticlinal ridge that would constitute an ideal trap for methane and consequently represents a site with good potential for gas hydrate accumulations. The analysis of high-resolution bathymetry, deep-towed sidescan sonar imagery, high-resolution seismic profiling and towed video observations of the seafloor shows that Four Way Closure Ridge is and has been a site of intensive methane seepage. Continuous seepage is mainly evidenced by large accumulations of authigenic carbonate precipitates, which appear to be controlled by the creation of fluid pathways through faulting. Consequently, Four Way Closure Ridge is not a closed system in terms of fluid migration and seepage. A conceptual model of the evolution of gas hydrates and seepage at accretionary ridges suggests that seepage is common and may be a standard feature during the geological development of ridges in accretionary prisms. The observation of seafloor seepage alone is therefore not a reliable indicator of exploitable gas hydrate accumulations at depth.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00367-015-0431-5
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Gas migration through Opouawe Bank at the Hikurangi margin offshore New Zealand (2016)
    Springer
    In:  Geo-Marine Letters, 36 (3). pp. 187-196.
    Details
    Publication Date: 2019-09-23
    Description: This study presents 2D seismic reflection data, seismic velocity analysis, as well as geochemical and isotopic porewater compositions from Opouawe Bank on New Zealand’s Hikurangi subduction margin, providing evidence for essentially pure methane gas seepage. The combination of geochemical information and seismic reflection images is an effective way to investigate the nature of gas migration beneath the seafloor, and to distinguish between water advection and gas ascent. The maximum source depth of the methane that migrates to the seep sites on Opouawe Bank is 1,500–2,100 m below seafloor, generated by low-temperature degradation of organic matter via microbial CO2 reduction. Seismic velocity analysis enabled identifying a zone of gas accumulation underneath the base of gas hydrate stability (BGHS) below the bank. Besides structurally controlled gas migration along conduits, gas migration also takes place along dipping strata across the BGHS. Gas migration on Opouawe Bank is influenced by anticlinal focusing and by several focusing levels within the gas hydrate stability zone.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.1007/s00367-016-0441-y
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    The SW African volcanic rifted margin and the initiation of the Walvis Ridge, South Atlantic (2009)
    Springer
    In:  Marine Geophysical Research, 30 (3). pp. 207-214.
    Details
    Publication Date: 2017-06-22
    Description: The continental margin of SW Africa is typical of a volcanic rifted margin associated with a hotspot trail characterized by a large volcanic ridge, the Walvis Ridge, defining the hotspot migration, and extensive extrusive volcanism that produced seaward-dipping reflectors (SDR). Previously unpublished seismic data show two significant anomalies of the SW African Margin when compared to other typical volcanic rifted margins: (1) Hyaloclastitic outer highs are rare, and (2) the SDR in the North dip towards the Walvis Ridge. We explain these anomalies by a major transform segment close to the centre of volcanism combined with pulsed volcanism. The Walvis Ridge represents an east-west striking extrusive centre which produced a SDR sequence. Following break-up the northern boundary of the Walvis Ridge became a left lateral transform fault. Our data support the idea that a transform fault system interacting with a ridge jump were responsible for the accretion of the São Paulo Plateau to the American plate.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s11001-009-9077-x
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Submarine Landslides on Continental Margins (2003)
    Springer
    In:  In: Ocean Margin Systems. , ed. by Wefer, G., Billet, D., Hebbeln, D., Jorgensen, B. B., Schlüter, M. and van Veering, T. Springer, Berlin, Germany, pp. 179-193. ISBN 3-540-43921-8
    Details
    Publication Date: 2018-01-19
    Type: Book chapter , NonPeerReviewed
    Format: text
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    OceanRep: Book chapter
  • 9
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    Volcanic-Island Lateral Collapses and Their Submarine Deposits (2021)
    Springer
    In:  In: Volcanic Debris Avalanches. , ed. by Roverato, M., Dufresne, A. and Procter, J. Springer, Cham, pp. 255-279, 25 pp. ISBN 978-3-030-57411-6
    Details
    Publication Date: 2021-01-19
    Description: Landslide deposits offshore many volcanic islands provide evidence of catastrophic lateral collapses. These deposits span a larger volume range than their continental equivalents, and can generate devastating tsunamis. All historical volcanic-island lateral collapses have occurred in arc settings, and have been characterised by rapid failure and efficient tsunami generation. The varied morphology of their deposits is influenced both by lithological properties and the nature of the substrate. Many deposits show evidence of extensive seafloor erosion and transformation into debris flows, and the propagation of frontally-confined sediment deformation beyond and beneath the primary deposit. Mobilised volumes can far exceed that of the initial failure, and accurate deposit interpretation requires internal geophysical imaging and sampling. Around intraplate ocean-island volcanoes, multi-unit turbidites suggest that lateral collapses may occur in discrete stages; although this would reduce their overall tsunamigenic potential, the volumes of individual stages of collapse remain very large. Numerical models of both landslide and tsunami processes in ocean-island settings are difficult to test, and the smaller collapses that typify island arcs are an important focus of research due to their higher global frequency, availability of direct failure and tsunami observations, and a need to better understand the signals of incipient collapse to develop approaches for tsunami hazard mitigation.
    Type: Book chapter , NonPeerReviewed
    Format: text
    DOI: 10.1007/978-3-030-57411-6_10
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    OceanRep: Book chapter
  • 10
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    Shallow 3D Reflection Seismics (2016)
    Springer
    In:  In: Encyclopedia of Earthquake Engineering. , ed. by Beer, M., Kougioumtzoglou, I. A., Patelli, E. and Au, S. K. Springer, Berlin, Heidelberg, pp. 1-9. ISBN 978-3-642-36197-5
    Details
    Publication Date: 2017-05-30
    Description: High-resolution 3D reflection seismology for near-surface applications is a noninvasive geophysical approach that uses sound wave reflected from subsurface discontinuities to infer and delineate the discontinuities. It results in high-resolution 3D structural images of the subsurface displaying mainly the interfaces between geological units and faults. The attributes “near surface” or “shallow” refer to sounding depths of typically some 10 m to 1 km. The 3D seismic method has been developed since the late 1960s. It is applied on- and offshore. This article gives an overview of the aims, principles, and realizations of shallow 3D reflection seismics. More details on field technique and data processing can be found, for example, in Meunier (2011) and Biondi (2006).
    Type: Book chapter , NonPeerReviewed
    Format: text
    DOI: 10.1007/978-3-642-36197-5_371-1
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    OceanRep: Book chapter
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