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1
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High-resolution, deep tow, multichannel seismic and sidescan sonar survey of the submarine mounds and associated BSR off Nicaragua pacific margin (2007)
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In: Marine geology, Amsterdam [u.a.] : Elsevier Science, 1964, 241(2007), 1/4, Seite 33-43, 1872-6151
In: volume:241
In: year:2007
In: number:1/4
In: pages:33-43
Description / Table of Contents: Bathymetric and conventional multichannel seismic surveys offshore Nicaragua and Costa Rica have revealed numerous mud mounds beneath which the generally widespread BSR is not well imaged. However, many of the mounds are partially capped by patches of authigenic carbonate crusts, so it was not clear if the semitransparent seismic facies and the apparent gaps in the BSR beneath the mounds are real or due to poor normal-incidence seismic penetration through the cap rocks. To address these problems, a high-resolution seismic survey was carried out over the continental slope of the Nicaraguan Pacific margin using a deep towed multichannel seismic streamer (DTMCS) along with a sidescan sonar system (DTS) to image submarine mud mounds and the associated BSR. The proximity of the very short (39 m active length) but high-resolution 17 channel streamer to the seafloor of the deep towed system allows greatly improved lateral resolution whereas the relatively large sourcereceiver offset allows the undershooting of the cap rocks. For the first time our data show that the BSR in many cases continues but rises beneath the mounds. This is consistent with the advection of deep warm fluids and thus increased heat flow through the mounds. The occurrence of mud mounds seems to be controlled by the locations of faults.
Type of Medium: Online Resource
Pages: graph. Darst., Kt
ISSN: 1872-6151
DOI: 10.1016/j.margeo.2007.03.002
Language: English
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  • 2
    Online Resource
    Online Resource
    Pockmarks in the Northern Congo Fan area, SW Africa: Complex seafloor features shaped by fluid flow (2008)
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    In: Marine geology, Amsterdam [u.a.] : Elsevier Science, 1964, 249(2008), 3/4, Seite 206-225, 1872-6151
    In: volume:249
    In: year:2008
    In: number:3/4
    In: pages:206-225
    Description / Table of Contents: Three pockmarks named "Hydrate Hole", "Black Hole", and"Worm Hole" were studied in the northern Congo Fan area at water depths around 3100 m. The cross-disciplinary investigations include seafloor observations by TV-sled, sampling by TV-guided grab and multicorer as well as gravity coring, in addition to hydroacoustic mapping by a swath system, a parametric sediment echosounder and a deep-towed sidescan sonar. The pockmarks are morphologically complex features consisting of one or more up to 1000 m wide and 10-15 m deep depressions revealed by swath-mapping. High reflection amplitudes in the sediment echosounder records indicate the presence of a 2530 m thick shallow sediment section with gas hydrates, which have been recovered by gravity corer. Hydrates, chemosynthetic communities, and authigenic carbonates clearly indicate fluid flow from depths, which we propose to be mainly in the form of ascending gas bubbles rather than advection of methane-rich porewater. Evidence for seepage at the seafloor is confined to small areas within the seafloor depressions and was revealed by characteristic backscatter facies. Small meter-scale sized depressions signified as pitsʺ exist in or close to the pockmarks but seafloor observations did not reveal evidence for the presence of typical seep organisms or authigenic carbonates. Areas of intermediate backscatter were inhabited by vesicomyid clams in soft sediments. High backscatter was associated with vestimentiferan tubeworms (Siboglinidae) and authigenic carbonates. We discuss the three different environments "pits","vesicomyid clams", "vestimentifera/carbonate" in the light of differences in the geochemical setting. Pits are probably formed by escaping gas bubbles but seepage is too transient to sustain chemosynthetic life. Vesicomyid clams are present in sediments with gas hydrate deposits. However, the hydrates occur several meters below the surface indicating a lower flux compared to the vestimentifera/carbonate environment. In the latter environment, accumulated carbonates and clam shells indicate that fine grained particles have been eroded away. Gas hydrates were found in this environment at depths below about 50 cm suggesting the highest supply with methane compared to the other environments.
    Type of Medium: Online Resource
    ISSN: 1872-6151
    DOI: 10.1016/j.margeo.2007.11.010
    Language: English
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  • 3
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    Mineralogical and chemical mass changes in mafic and ultramafic rocks from the Logatchev hydrothermal field (MAR 15°N) (2008)
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    In: Marine geology, Amsterdam [u.a.] : Elsevier Science, 1964, 256(2008), 1/4, Seite 18-29, 1872-6151
    In: volume:256
    In: year:2008
    In: number:1/4
    In: pages:18-29
    Type of Medium: Online Resource
    Pages: Ill., graph. Darst
    ISSN: 1872-6151
    DOI: 10.1016/j.margeo.2008.09.004
    Language: English
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  • 4
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    A new s̕chlieren ̕technique application for fluid flow visualization at cold seep sites (2004)
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    In: Marine geology, Amsterdam [u.a.] : Elsevier Science, 1964, 204(2004), 1/2, Seite 145-159, 1872-6151
    In: volume:204
    In: year:2004
    In: number:1/2
    In: pages:145-159
    Type of Medium: Online Resource
    Pages: Ill., graph. Darst
    ISSN: 1872-6151
    DOI: 10.1016/S0025-3227(03)00370-0
    Language: English
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  • 5
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    New evidence for massive gravitational mass-transport deposits in the southern Cretan Sea, eastern Mediterranean (2009)
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    In: Marine geology, Amsterdam [u.a.] : Elsevier Science, 1964, 263(2009), 1/4, Seite 97-107, 1872-6151
    In: volume:263
    In: year:2009
    In: number:1/4
    In: pages:97-107
    Description / Table of Contents: 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 km3 covering an area of about 135 km2. 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 slopebasin-transition in 450 m water depth. Numerous faults with an orientation almost parallel to the southwestnortheast-trending basin axis occur along the northern and southern boundaries of the Malia Basin and have caused a partial steepening of the slopebasin-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.
    Type of Medium: Online Resource
    Pages: graph. Darst
    ISSN: 1872-6151
    DOI: 10.1016/j.margeo.2009.04.002
    Language: English
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  • 6
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    A late Miocene-early Pliocene Antarctic deepwater record of repeated iron reduction events (2009)
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    In: Marine geology, Amsterdam [u.a.] : Elsevier Science, 1964, 266(2009), 1/4, Seite 198-211, 1872-6151
    In: volume:266
    In: year:2009
    In: number:1/4
    In: pages:198-211
    Description / Table of Contents: In this study we present a late Miocene-early Pliocene record of sixty-four zones with prominent losses in the magnetic susceptibility signal, taken on a sediment drift (ODP Site 1095) on the Pacific continental rise of the West Antarctic Peninsula. The zones are comparable in shape and magnitude and occur commonly at glacial-to-interglacial transitions. High resolution records of organic matter, magnetic susceptibility and clay mineral composition from early Pliocene intervals demonstrate that neither dilution effects nor provenance changes of the sediments have caused the magnetic susceptibility losses. Instead, reductive dissolution of magnetite under suboxic conditions seems to be the most likely explanation. We propose that during the deglaciation exceptionally high organic fluxes in combination with weak bottom water currents and prominent sediment draping diatom ooze layers produced temporary suboxic conditions in the uppermost sediments. It is remarkable that synsedimentary suboxic conditions can be observed in one of the best ventilated open ocean regions of the World.
    Type of Medium: Online Resource
    Pages: Ill., graph. Darst
    ISSN: 1872-6151
    DOI: 10.1016/j.margeo.2009.08.006
    Language: English
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  • 7
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    Evaluation of gas hydrate deposits in an active seep area using marine controlled source electromagnetics : results from Opouawe Bank, Hikurangi Margin, New Zealand (2009)
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    In: Marine geology, Amsterdam [u.a.] : Elsevier Science, 1964, (2009), 1872-6151
    In: year:2009
    In: extent:10
    Description / Table of Contents: Several known gas seep sites along the Hikurangi Margin off the east coast of New Zealand were surveyed by marine controlled source electromagnetic (CSEM) experiments. A bottom-towed electric dipole-dipole system was used to reveal the occurrence of gas hydrate and methane related to the seeps. The experiments were part of the international multidisciplinary research program "New Vents" carried out on German R/V Sonne in 2007 (cruise SO191) to study key parameters controlling the release and transformation of methane from marine cold vents and shallow gas hydrate deposits. Two CSEM lines have been surveyed over known seep sites on Opouawe Bank in the Wairarapa region off the SE corner of the North Island. The data have been inverted to sub-seafloor apparent resistivity profiles and one-dimensional layered models. Clearly anomalous resistivities are coincident with the location of two gas seep sites, North Tower and South Tower on Opouawe Bank. A layer of concentrated gas hydrate within the uppermost 100 m below the seafloor is likely to cause the anomalous resistivities, but free gas and thick carbonate crusts may also play a role. Seismic data show evidence of fault related venting which may also indicate the distribution of gas hydrates and/or authigenic carbonate. Geochemical profiles indicate an increase of methane flux and the formation of gas hydrate in the shallow sediment section around the seep sites. Takahe is another seep site in the area where active venting, higher heat flow, shallow gas hydrate recovered from cores, and seismic fault planes, but only moderately elevated resistivities have been observed. The reasons could be a) the gas hydrate concentration is too low, even though methane venting is evident, b) strong temporal or spatial variation of the seep activity, and c) the thermal anomaly indicates rather temperature driven fluid expulsion that hampers the formation of gas hydrate beneath the vent.
    Type of Medium: Online Resource
    Pages: 10 , Ill., graph. Darst
    ISSN: 1872-6151
    DOI: 10.1016/j.margeo.2009.07.006
    Language: English
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  • 8
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    Episodic methane concentrations at seep sites on the upper slope Opouawe Bank, southern Hikurangi Margin, New Zealand (2009)
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    In: Marine geology, Amsterdam [u.a.] : Elsevier Science, 1964, (2009), 1872-6151
    In: year:2009
    In: extent:8
    Description / Table of Contents: Along many active and some passive margins cold seeps are abundant and play an important role in the mechanisms of methane supply from the subsurface into seawater and atmosphere. With numerous cold seeps already known, the convergent Hikurangi Margin east of North Island, New Zealand, was selected as a target area for further detailed, multidisciplinary investigation of cold seeps within the New Vents and associated projects. Methane and temperature sensors (METS) were deployed at selected seep sites on the Opouawe Bank off the southeastern tip of North Island and near the southern end of the imbricate-thrust Hikurangi Margin, together with seismic ocean bottom stations. They remained in place for about 48 h while seismic data were collected. The seeps were associated with seep-related seismic structures. Methane concentrations were differing by an order of magnitude between neighbouring stations. The large differences at sites only 300 m apart, demonstrate that the seeps were small scale structures, and that plumes of discharged methane were very localised within the bottom water. High methane concentrations recorded at active seep sites at anticlinal structures indicate focused fluid flow. Methane discharge from the seafloor was episodic, which may result from enhanced fluid flow facilitated by reduced hydrostatic load at low tides. The strong semi-diurnal tidal currents also contribute to the fast dilution and mixing of the discharged methane in the seawater. Despite dispersal by currents, fluid flow through fissures, fractures, and faults close to the METS positions and tidal fluctuations are believed to explain most of the elevated methane concentrations registered by the METS. Small earthquakes do not appear to be correlated with seawater methane anomalies.
    Type of Medium: Online Resource
    Pages: 8 , graph. Darst
    ISSN: 1872-6151
    DOI: 10.1016/j.margeo.2009.08.001
    Language: English
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  • 9
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    The structures beneath submarine methane seeps : seismic evidence from Opouawe Bank, Hikurangi Margin, New Zealand (2009)
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    In: Marine geology, Amsterdam [u.a.] : Elsevier Science, 1964, (2009), 1872-6151
    In: year:2009
    In: extent:12
    Description / Table of Contents: The role of methane in the global bio-geo-system is one of the most important issues of present-day research. Cold seeps, where methane leaves the seafloor and enters the water column, provide valuable evidence of subsurface methane paths. Within the New Vents project we investigate cold seeps and seep structures at the Hikurangi Margin, east of New Zealand. In the area of Opouawe Bank, offshore the southern tip of the North Island, numerous extremely active seeps have been discovered. High-resolution seismic sections show a variety of seep structures. We see seismic chimneys either characterised by high-amplitude reflections or by acoustic turbidity and faults presumably acting as fluid pathways. The bathymetric expression of the seeps also varies: There are seeps exhibiting a flat seafloor as well as a seep located in a depression and small mounds. The images of the 3.5 kHz Parasound system reveal the near-surface structure of the vent sites. While high-amplitude spots within the uppermost 50 m below the seafloor (bsf) are observed at the majority of the seep structures, indicating gas hydrate and/or authigenic carbonate formations with an accumulation of free gas underneath, a few seep structures are characterised by the complete absence of reflections, indicating a high gas content without the formation of a gas trap by hydrates or carbonates. The factors controlling seep formation have been analysed with respect to seep location, seep structure, water depth, seafloor morphology, faults and gas hydrate distribution. The results indicate that the prevailing structural control for seep formation at Opouawe Bank is the presence of numerous minor faults piercing the base of the gas hydrate stability zone.
    Type of Medium: Online Resource
    Pages: 12 , graph. Darst
    ISSN: 1872-6151
    DOI: 10.1016/j.margeo.2009.07.005
    Language: English
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  • 10
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    The Håkon Mosby mud volcano : 330 000 years of focused fluid flow activity at the SW Barents Sea slope (2009)
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    In: Marine geology, Amsterdam [u.a.] : Elsevier Science, 1964, 262(2009), Seite 105-115, 1872-6151
    In: volume:262
    In: year:2009
    In: pages:105-115
    Description / Table of Contents: Studying the morphology and subsurface geometry of mud volcanoes provides insights into their activity. This paper describes the internal structure of the Håkon Mosby mud volcano (HMMV) in the southwestern Barents Sea and presents a conceptual model of its evolution. The lack of a mud edifice and the profuse gas flares suggest that in the recent past the mud volcano evolution was predominantly controlled by venting of gas-rich fluids and free gas. However, the analysis of high-resolution single-channel seismic (SCS) data reveals for the first time the existence of a pseudo-mud chamber at the top of the 3 km deep central conduit. It was once created at the seabed and is now a buried expression that acts as mud chamber. The pseudo-mud chamber is situated approximately 300 m below the seafloor, directly above the 330 ka Bear Island Slide (BIS) scar reflection and below glacigenic debris flow deposits that constitute the sediment on top. The sediment profiler data indicates a younger mud deposit above the debris flows, which points to a reactivation of the mud volcano. The reactivation was most likely triggered by the contrast in density between the gas-rich mud chamber and the high-density debris flow deposits. Three stages, i.e. initiation, sealing and reactivation, and a second active period define the evolution of this young mud volcano. Both, the morphology and size of the conduit as well as in-situ temperature gradients point towards a focused and rapid fluid flow.
    Type of Medium: Online Resource
    Pages: graph. Darst
    ISSN: 1872-6151
    DOI: 10.1016/j.margeo.2009.03.022
    Language: English
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