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  • 11
    Electronic Resource
    Electronic Resource
    Chemical and isotopic evidence for the nature of the fluid in CH4-containing sediments of the Håkon Mosby Mud Volcano (1999)
    Springer
    Geo-marine letters 19 (1999), S. 76-83 
    Details
    ISSN: 1432-1157
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The pore waters of CH4-containing sediments of the Håkon Mosby Mud Volcano were rich in NH+ 4, Br-, and I-; exhibited a high total alkalinity; but were poor in Cl-and SO2- 4. The geological evidence and our data suggest that organic matter decomposition in preglacial or early interglacial sediments took place during early diagenesis (bacterial processes) and during metamorphism (thermogenic processes under the 3100-m-thick layer of glacial sediments), accompanied by mud volcano fluid generation. It is argued that the CH4of the mud volcano sediments has a mixed, biogenic and thermogenic, origin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003670050095
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  • 12
    Electronic Resource
    Electronic Resource
    Gas hydrates that outcrop on the sea floor: stability models (1999)
    Springer
    Geo-marine letters 19 (1999), S. 68-75 
    Details
    ISSN: 1432-1157
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The detection of sea-floor gas hydrates (GHs) proves that they can coexist in contact with seawater. We calculate that sea-floor hydrates undergo rapid dissolution, yet they are maintained by the constant high rate of upward migration of gas-saturated waters. If upward migration originates from a point source, then the thickness of sea-floor hydrates varies with distance from the center of the upwelling (depending on heat flow). However, near-surface fracturing may control the actual points of exit onto the sea floor above. If gas migration rates decrease from the center of the mud volcano to its periphery, a concentric pattern in distribution of temperature, methane concentration, and GH contents can be described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003670050094
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  • 13
    Electronic Resource
    Electronic Resource
    The Norwegian–Barents–Svalbard (NBS) continental margin: Introducing a natural laboratory of mass wasting, hydrates, and ascent of sediment, pore water, and methane (1999)
    Springer
    Geo-marine letters 19 (1999), S. 2-21 
    Details
    ISSN: 1432-1157
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Side-scan sonar mapping and ground-truthing of the Norwegian–Barents–Svalbard continental margin shed new light on shelf glaciation, mass wasting, hydrates, and features like the Håkon Mosby mud volcano (HMMV), reflecting upward mobility of gas, pore fluids, and sediments. Detailed HMMV examination revealed thermal gradients to 10°/m, bottom-water CH4 and temperature anomalies, H2S- and CH4-based chemosynthetic ecosystems, and subbottom methane hydrate (to 25%). Seismic and chemical data suggest HMMV origins at 2–3 km depth within the 6-km-thick depocenter. The HMMV and mound fields bordering the Bjørnøyrenna slide valley and pockmarks bordering the Storegga slide may all have formed in response to sediment failure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003670050088
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  • 14
    Electronic Resource
    Electronic Resource
    Gas hydrate accumulation at the Håkon Mosby Mud Volcano (1999)
    Springer
    Geo-marine letters 19 (1999), S. 57-67 
    Details
    ISSN: 1432-1157
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Gas hydrate (GH) accumulation is characterized and modeled for the Håkon Mosby mud volcano, ca. 1.5 km across, located on the Norway–Barents–Svalbard margin. Pore water chemical and isotopic results based on shallow sediment cores as well as geothermal and geomorphological data suggest that the GH accumulation is of a concentric pattern controlled by and formed essentially from the ascending mud volcano fluid. The gas hydrate content of sediment peaks at 25% by volume, averaging about 1.2% throughout the accumulation. The amount of hydrate methane is estimated at ca. 108 m3 STP, which could account for about 1–10% of the gas that has escaped from the volcano since its origin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003670050093
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  • 15
    Electronic Resource
    Electronic Resource
    Large-scale mass wasting on the north Spitsbergen continental margin, Arctic Ocean (1999)
    Springer
    Geo-marine letters 19 (1999), S. 131-142 
    Details
    ISSN: 1432-1157
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Closely spaced, single-beam bathymetric and side-scan sonar investigations on the northern slope of the western Svalbard insular platform have revealed the presence of a Late Quaternary slump complex forming a hanging-wall slump canyon near the head of the Malene Bukta (Malene Bay) bathymetric embayment in the northern continental margin. Repeated slump erosion may be responsible for development of this young feature and the Malene Bukta Embayment. Focusing of the slumping may be due to the trapping of gas at shallow sea-floor depths by gas hydrate, with the consequent formation of subjacent gas-rich, low shear-strength decollement zones. Faults have likely controlled the upward migration of gas into the younger sedimentary prism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003670050100
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  • 16
    Electronic Resource
    Electronic Resource
    The Tamayo transform fault in the mouth of the Gulf of California (1979)
    Springer
    Marine geophysical researches 4 (1979), S. 129-151 
    Details
    ISSN: 1573-0581
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The Tamayo transform fault is located at the north end of the East Pacific Rise where it enters the Gulf of California. This paper presents bathymetric, seismic reflection, magnetic, and gravity data from a detailed survey of the transform fault. The dominant feature of the offset region is a bathymetric ridge trending 120°, parallel to the predicted transform plate boundary. This transform ridge is associated with a large (600 γ) positive magnetic anomaly, and a very small positive free-air gravity anomaly. Magnetic and gravity models indicate either a basalt or serpentinite composition for the ridge, but cannot distinguish between these possibilities. At its eastern end, the modern zone of strike-slip motion is in a narrow valley south of the transform ridge. The transform plate margin appears to pass through a saddle in the transform ridge and meet the western spreading center segment in the trough north of the transform ridge. On the basis of this survey and previous work, the history of the Tamayo from continental breakup to the present has been reconstructed. Initial rifting occurred along a trend of 130° at approximately 3.5 m.y.b.p. Once the transform fault was free of the constraints imposed by continent-continent and continent-oceanic lithospheric interaction, the trend of the transform fault rotated counter-clockwise. This rotation resulted in a ‘leaky’ transform fault and intrusion of a large continuous transform ridge. Further adjustments in the spreading center/transform fault plate boundary configuration have given rise to an incipient zone of rifting cutting across the transform ridge and emplacement of diapiric structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00286401
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  • 17
    Electronic Resource
    Electronic Resource
    Tectonics at the intersection of the East Pacific Rise with Tamayo Transform fault (1984)
    Springer
    Marine geophysical researches 6 (1984), S. 159-185 
    Details
    ISSN: 1573-0581
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract During the Fall of 1979, a manned submersible program, utilizing DSRV ALVIN, was carried out at the intersection of the East Pacific Rise (EPR) with the Tamayo Transform boundary. A total of seven dives were completed in the vicinity of the EPR/Tamayo intersection depression and documented the geologic relationships that characterize the juxtaposition of these types of plate boundaries. The young volcanic terrain of the EPR axis can be traced into and across the Tamayo Transform valley but becomes buried by sedimentary talus that is being shed from sediment scarps along the unstable sediment slope that defines the north side of the intersection depression. Within 4 km of the transform boundary, the dominant trend (000°) of the fissures and faults that disrupt the rise-generated volcanics is markedly oblique to the regional direction of sea floor spreading (120°). Since no evidence was found to suggest that these structures accommodate significant amounts of strike-slip displacement, they are taken to reflect a distortion of the EPR extensional tectonic regime by a transform generated shear couple. The floor of the Tamayo Transform valley in this area is inundated by mass-wasted sediment, and the principal transform displacement zone is characterized at the surface by a narrow (〈1.5 km) interval of fault scarps in sediment that trends parallel with the transform valley. Extrapolated to the west, this zone links with zones of transform deformation investigated during earlier submersible studies (CYAMEX and Pastouret, 1981). Evidence of low-level hydrothermal discharge was seen at one locality on the EPR axis and at another 8 km west of the axis at the edge of the zone of transform deformation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00285958
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  • 18
    Electronic Resource
    Electronic Resource
    The geology of the Oceanographer Transform: The ridge-transform intersection (1984)
    Springer
    Marine geophysical researches 6 (1984), S. 109-141 
    Details
    ISSN: 1573-0581
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Seven dives in the submersible ALVIN and four deep-towed (ANGUS) camera lowerings have been made at the eastern ridge-transform intersection of the Oceanographer Transform with the axis of the Mid-Atlantic Ridge. These data constrain our understanding of the processes that create and shape the distinctive morphology that is characteristic of slowly-slipping ridge-transform-ridge plate boundaries. Although the geological relationships observed in the rift valley floor in the study area are similar to those reported for the FAMOUS area, we observe a distinct change in the character of the rift valley floor with increasing proximity to the transform. Over a distance of approximately ten kilometers the volcanic constructional terrain becomes increasingly more disrupted by faulting and degraded by mass wasting. Moreover, proximal to the transform boundary, faults with orientations oblique to the trend of the rift valley are recognized. The morphology of the eastern rift valley wall is characterized by inward-facing scarps that are ridge-axis parallel, but the western rift valley wall, adjacent to the active transform zone, is characterized by a complex fault pattern defined by faults exhibiting a wide range of orientations. However, even for transform parallel faults no evidence for strike-slip displacement is observed throughout the study area and evidence for normal (dip-slip) displacement is ubiquitous. Basalts, semi-consolidated sediments (chalks, debris slide deposits) and serpentinized ultramafic rocks are recovered from localities within or proximal to the rift valley. The axis of accretion-principal transform displacement zone intersection is not clearly established, but appears to be located along the E-W trending, southern flank of the deep nodal basin that defines the intersection of the transform valley with the rift floor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00285956
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  • 19
    Electronic Resource
    Electronic Resource
    Thermal evolution of the western Svalbard margin (1988)
    Springer
    Marine geophysical researches 9 (1988), S. 165-194 
    Details
    ISSN: 1573-0581
    Keywords: transform margins ; heat flow ; ridge propagation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The northern Norwegian-Greenland Sea opened up as the Knipovich Ridge propagated from the south into the ancient continental Spitsbergen Shear Zone. Heat flow data suggest that magma was first intruded at a latitude of ≈75° N around 60 m.y.b.p. By 40–50 m.y.b.p. oceanic crust was forming at a latitude of 78° N. At ≈12 m.y.b.p. the Hovgård Transform Fault was deactivated during a northwards propagation of the Knipovich Ridge. Spreading is now in its nascent stages along the Molloy Ridge within the trough of the Spitsbergen Fracture Zone. Spreading rates are slower in the north than the south. For the Knipovich Ridge at 78° N they range from 1.5–2.3 mm yr-1 on the eastern flank to 1.9–3.1 mm yr-1 on the western flank. At a latitude of 75° N spreading rates increase to 4.3–4.9 mm yr-1. Thermal profiles reveal regions of off-axial high heat flow. They are located at ages of 14 m.y. west and 13 m.y. east of the northern Knipovich Ridge, and at 36 m.y. on the eastern flank of the southern Knipovich Ridge. These may correspond to episodes of increased magmatic activity; which may be related to times of rapid north-wards rise axis propagation. The fact that the Norwegian-Greenland Sea is almost void of magnetic anomalies may be caused by the chaotic extrusion of basalts from a spreading center trapped within the confines of an ancient continental shear zone. The oblique impact of the propagating rift with the ancient shear zone may have created an unstable state of stress in the region. If so, extension took place preferentially to the northwest, while compression occurred to the southeast between the opening, leaking shear zone and the Svalbard margin. This caused faster spreading rates to the northwest than to the southeast.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00369247
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  • 20
    Electronic Resource
    Electronic Resource
    The geology of the Oceanographer Transform: The transform domain (1985)
    Springer
    Marine geophysical researches 7 (1985), S. 329-358 
    Details
    ISSN: 1573-0581
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Three dives in submersible ALVIN and four deep-towed camera lowerings have been made along the transform valley of the Oceanographer Transform. These data constrain our understanding of the processes that create and shape the distinctive morphology that is characteristic of slowly slipping ridge-transform-ridge (RTR) plate boundaries. Our data suggest that the locus of strike-slip tectonism, called the transform fault zone (TFZ), is confined to a narrow swath (〈4 km) that is centered along the axis of maximum depth. The TFZ is flanked by the inward facing slopes of the transform valley. The lower portions of the valley walls are characterized by broad sloping exposures of undisrupted sediment but at higher elevations the walls are made up of inward facing scarps and terraces of variable dimensions. Although the scarps have been badly degraded by mass wasting, there is no evidence to suggest that these scarps have accommodated significant amounts of strike-slip motion. Plutonic and ultramafic rocks are exposed on these scarps and the occurrence of this diverse assemblage on small-throw faults indicates that the crust is thin and/or discontinuous in this environment. We suggest that this complex igneous assemblage is the product of anomalous accretionary processes that are characteristic of slowly-slipping RTR plate boundaries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00316773
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