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  • 1
    Online Resource
    Online Resource
    Fine-grained sediments : deep-water processes and facies. (Proceedings and discussion) (1984)
    Details Availability
    Keywords: Sediments (Geology) Congresses ; Facies (Geology) Congresses ; Sedimentation and deposition Congresses ; Turbidites Congresses ; Fine-grained sediments. Transport & deposition by water ; Feinkörniges Sediment++Kongress++Halifax 〈Nova Scotia, 1982〉
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (VI, 659 Seiten)
    ISBN: 0632010754
    Series Statement: Geological Society special publication 15
    URL: http://sp.lyellcollection.org/content/15/1
    DDC: 551.36
    Language: English
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  • 2
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    Chronology of the Fram Slide Complex offshore NW Svalbard and its implications for local and regional slope stability (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Geology, ELSEVIER SCIENCE BV, 393, pp. 141-155, ISSN: 0025-3227
    Details
    Publication Date: 2017-11-19
    Description: The best known submarine landslides on the glaciated NW European continental margins are those at the front of cross-shelf troughs, where the alternation of rapidly deposited glycogenic and hemi pelagic material generates sedimentary overpressure. Here, we investigate landslides in two areas built of contourite drifts bounded seaward by a ridge-transform junction. Seismic and bathymetric data from the Fram Slide Complex are compared with the tectonically similar Vastness area ~120km to the south, to analyze the influence of local and regional processes on slope stability. These processes include tectonic activity, changes of climate and oceanography, gas hydrates and fluid migration systems, slope gradient, toe erosion and style of contourite deposition. Two areas within the Fram Slide Complex underwent different phases of slope failures, whereas there is no evidence at all for major slope failures in the Vastness area. The comparison cannot reveal the distinct reason for slope failure but demonstrates the strong impact of variation in the local controls on slope stability. The different failure chronologies suggest that toe erosion, which is dependent on the throw of normal faults, and the different thickness and geometry of contourite deposits can result in a critical slope morphology and exert pronounced effects on slope stability. These results highlight the limitations of regional hazard assessments and the need for multi-disciplinary investigations, as small differences in local controlling factors led to substantially different slope failure histories.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
    Electronic Resource
    Electronic Resource
    Modelling of turbidity currents on Navy Submarine Fan, California Continental Borderland (1984)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 31 (1984), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Several Holocene turbidites can be correlated across much of Navy Fan through more than 100 sediment core localities. The uppermost muddy turbidite unit is mapped throughout the northern half of the fan; its volume, grain-size distribution and the maximum height of deposition on the basin slopes are known. These parameters can be related to the precise channel morphology and mesotopography revealed by deep-tow surveys. Thus there is sufficient information to estimate detailed flow characteristics for this turbidity current as it moved from fan valley to distal basin plain.On the upper fan, the gradient and the increasing downstream width of the channel and only limited flow overspill suggest that the flow had a Froude number close to 1.0. The sediment associated with the channel indicates friction velocities of about 0.06 m s−1 and flow velocities of about 0.75 m s−1. Using this flow velocity and channel dimensions, sediment concentration (∼2×10−3) and discharge are estimated, and from a knowledge of the total volume of sediment deposited, the flow duration is estimated to be from 2 to 9 days. It is shown that the estimates of Froude number, drag coefficient, and sediment concentration are not likely to vary by more than a factor of 2.On the mid-fan, the flow was much thicker than the height of the surface relief of the fan and it spread rapidly. The cross-flow slope, determined from the horizontal extent of turbidite sediment, is used to estimate flow velocity, which is confirmed by consideration of both sediment grain size and rate of deposition. This again allows sediment concentration and discharge to be estimated. The requirements of flow continuity, entrainment of water during flow expansion, and observed sediment deposition provide checks on all these estimates, and provide an integrated picture of the evolution of the flow. The flow characteristics of this muddy turbidity current are well constrained compared to those for more sand-rich late Pleistocene and early Holocene turbidity currents on the fan.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1984.tb01957.x
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  • 4
    Electronic Resource
    Electronic Resource
    Turbidite depositional patterns and flow characteristics, Navy Submarine Fan, California Borderland (1983)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 30 (1983), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The late Pleistocene and Holocene stratigraphy of Navy Fan is mapped in detail from more than 100 cores. Thirteen 14C dates of plant detritus and of organic-rich mud beds show that a marked change in sediment supply from sandy to muddy turbidites occurred between 9000 and 12,000 years ago. They also confirm the correlation of several individual depositional units. The sediment dispersal pattern is primarily controlled by basin configuration and fan morphology, particularly the geometry of distributary channels, which show abrupt 60° bends related to the Pleistocene history of lobe progradation. The Holocene turbidity currents are depositing on, and modifying only slightly, a relict Pleistocene morphology.The uppermost turbidite is a thin sand to mud bed on the upper-fan valley levées and on parts of the mid-fan. Most of its sediment volume is in a mud bed on the lower fan and basin plain downslope from a sharp bend in the mid-fan distributary system. Little sediment occurs farther downstream within this distributary system. It appears that most of the turbidity current overtopped the levée at the channel bend, a process referred to as flow stripping. The muddy upper part of the flow continued straight down to the basin plain. The residual more sandy base of the flow in the distributary channel was not thick enough to maintain itself as gradient decreased and the channel opened out on to the mid-fan lobe.Flow stripping may occur in any turbidity current that is thick relative to channel depth and that flows in a channel with sharp bends. Where thick sandy currents are stripped, levée and mid-fan erosion may occur, but the residual current in the channel will lose much of its power and deposit rapidly. In thick muddy currents, progressive overflow of mud will cause less declaration of the residual channelised current. Thus both size and sand-to-mud ratio of turbidity currents feeding a fan are important factors controlling morphologic features and depositional areas on fans. The size-frequency variation for different types of turbidity currents is estimated from the literature and related to the evolution of fan morphology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1983.tb00702.x
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  • 5
    Electronic Resource
    Electronic Resource
    Surface textures of turbidite sand grains, Laurentian Fan and Sohm Abyssal Plain (1982)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 29 (1982), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Surface textures of quartz grains have been examined from five samples from the Laurentian Fan and Sohm Abyssal Plain, representing varied transport distances and power of the depositing turbidity current. The grains retain their primary irregular shape derived from glacial erosion, and glacial surface textures are preserved in dish-shaped depressions. These features have been superimposed by a slight rounding of edges and an abundance of collision-induced markings, particularly mechanical V-forms. The most intense current modification of this sort occurs in mid-Wisconsinan or earlier sands that have been transported over 1000 km to the distal Sohm Abyssal Plain by turbidity currents. Collision textures probably develop during grain flow on the steep continental slope: delicate resedimented shelf foraminifera are preserved in the same turbidites and most have been transported exclusively in suspension.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1982.tb00077.x
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  • 6
    Electronic Resource
    Electronic Resource
    A reconnaissance of the sedimentology of lower Silurian mudstones, English Lake District (1975)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 22 (1975), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Polished slabs and thin sections of lower Silurian graptolitic mudstones and interbedded barren mudstones show three main lithologies are present (a) unfossili-ferous green mudstones, sometimes with indistinct silt laminae, (b) a similar black pyritic lithology, with rare graptolites, (c) striped mudstones, with prominent carbonaceous and silt laminae, and common graptolites. The abundance of silt laminae suggests that the striped mudstone facies represents the highest energy depositional conditions. Comparison of sedimentary structures with modern deep sea muds suggests this facies is distal turbidite. Graptolite preservation was favoured by rapid burial.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1975.tb00250.x
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  • 7
    Electronic Resource
    Electronic Resource
    The character of seismo-turbidites in the S-1 sapropel, Zakinthos and Strofadhes basins, Greece (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 38 (1991), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The early Holocene S-1 sapropelic sequence in the northwest Hellenic Trench has been studied in six piston cores from the Zakinthos and Strofadhes basins. The S-1 sequence, 0.7-3.5 m thick, consists principally of silt to mud turbidites, with rare, thick, disorganized, sandy turbidites. These lithofacies are described and compared with fine-grained turbidites from the literature. Petrographical data, including the abundance of organic carbon and planktonic microfossils, indicate that the principal source of sediment to the turbidites was from the continental slope. On the basis of composition and texture, five turbidite units can be correlated between the two basins. These basins are fed by separate but adjacent drainage systems. The apparently synchronous occurrence of turbidites in the two drainage systems suggests that the turbidity currents were seismically triggered. Some of the turbidites show poorly organized beds which may reflect the slump origin and the short (30 km) distances of travel. Turbidites were deposited more frequently in the S-1 sapropelic interval than in the over- and underlying sediments. Application of slope stability analysis shows that on the 8° slopes above the basins, a 10-cm-thick sapropel would have a factor of safety of about 2, and would fail with earthquake accelerations in excess of 0.08 g. The frequency of earthquakes likely to produce such accelerations is similar to the observed frequency of turbidites. The low strength of the sapropelic sediment makes it particularly susceptible to such failure. Similar thin-skinned slumping may be an important process for the initiation of turbidity currents in other environments where there are steep slopes or high sedimentation rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1991.tb01016.x
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  • 8
    Electronic Resource
    Electronic Resource
    Quantitative analysis of variations in depositional sequence thickness from submarine channel levees (2002)
    Oxford, UK : Blackwell Science Ltd
    Sedimentology 49 (2002), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract Thickness variations across-levee and downchannel in acoustically defined depositional sequences from six submarine channel-levee systems show consistent and quantifiable patterns. The thickness of depositional sequences perpendicular to the channel trend, i.e. across the levee, decreases exponentially, as characterized by a spatial decay constant, k. Similarly, the thickness of sediment at the levee crest decreases exponentially down the upper reaches of submarine channels and can be characterized by a second spatial decay constant, λ. The inverse of these decay constants has units of length and defines depositional length scales such that k−1 is a measure of levee width and λ−1 is a measure of levee length. Quantification of levee architecture in this way allowed investigation of relationships between levee architecture and channel dimensions. It was found that these measures of levee e-folding width and levee e-folding length are directly related to channel width and relief. The dimensions of channels and levees are thus intimately related, thereby limiting the range of potential channel-levee morphologies, regardless of allocyclic forcing. A simple sediment budget model relates the product of the levee e-folding width and e-folding length to through-channel volume discharge. A classification system based on the quantitative downchannel behaviour of levee architecture allows identification of a ‘mid-channel’ reach, where sediment is passively transferred from the through-channel flow to the levees as an overspilling flow. Downstream from this reach, the channel gradually looses its control on guiding turbidity currents, and the resulting flow can be considered as an unconfined or spreading flow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3091.2002.00506.x
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  • 9
    Electronic Resource
    Electronic Resource
    Giant flute-like scour and other erosional features formed by the 1929 Grand Banks turbidity current (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 37 (1990), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Erosional features on the floor of Eastern Valley of the Laurentian Fan, in 2800 m water depth, have been mapped with SeaMARC I side-scan sonar images and Seabeam multi-beam echo-soundings, and were directly observed during a dive with the deep submersible Alvin. The most spectacular feature is a 100-m-deep flute-shaped scour, more than 1 km long. The surrounding valley is floored by an unconsolidated coarse conglomerate, which was moulded into transverse bedforms by the turbidity current that was triggered by the 1929 Grand Banks earthquake. Direct observations and seismic-reflection profiles show that the flute-shaped scour cuts through this conglomerate and into Plio-Pleistocene valley-floor sediments, thereby exposing a section through the 1929 deposit. Application of the Allen defect theory suggests that the flute is unusually deep because general channel-floor erosion was inhibited by the conglomerate veneer.Valley-floor channels typically 1 km wide and 10m deep contain series of closed depressions that occasionally deepen to 30 m. These are also interpreted as erosional scours, analogous to pools cut on the beds of bedrock rivers. The large flute was probably formed by detached flow enlarging an initial scour depression. Such scours probably play an important role in channel-floor erosion, increasing the volume of sediment transported by large turbidity currents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1990.tb00626.x
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  • 10
    Electronic Resource
    Electronic Resource
    The sequence of events around the epicentre of the 1929 Grand Banks earthquake: initiation of debris flows and turbidity current inferred from sidescan sonar (1999)
    Oxford UK : Blackwell Science Ltd
    Sedimentology 46 (1999), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Continental slope sediment failures around the epicentre of the 1929 ‘Grand Banks’ earthquake have been imaged with the SAR (Système Acoustique Remorqué) high-resolution, deep-towed sidescan sonar and sub-bottom profiler. The data are augmented by seismic reflection profiles, cores and observations from submersibles. Failure occurs only in water depths greater than about 650 m. Rotational, retrogressive slumps, on a variety of scales, appear to have been initiated on local steep areas of seabed above shallow (5–25 m) regional shear planes covering a large area of the failure zone. The slumps pass downslope into debris flows, which include blocky lemniscate bodies and intervening channels. Clear evidence of current erosion is found only in steep-sided valleys: we infer that debris flows passed through hydraulic jumps on these steep slopes and were transformed into turbidity currents which then evolved ignitively. Delayed retrogressive failure and transformation of debris flows into turbidity currents through hydraulic jumps provide a mechanism to produce a turbidity current with sustained flow over many hours.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3091.1999.00204.x
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