ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Implications for focused fluid transport at the northern Cascadia accretionary prism from a correlation between BSR occurrence a d near-sea-floor reflectivity anomalies imaged in a multi-frequency seismic data set (2000)
    Springer
    International journal of earth sciences 88 (2000), S. 655-667 
    Details
    ISSN: 1437-3262
    Keywords: Key words Cascadia accretionary prism ; Very high-resolution seismics ; Fluid migration ; Bottom simulating reflector ; Near-surface reflectivity anomalies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  A high-resolution seismic survey was carried out at the accretionary prism on the continental slope off Vancouver Island, Canada. Two GI-Gun data sets with different source frequency ranges of 50–150 and 100–500 Hz were combined with 4 kHz narrow-beam echosounding data (Parasound). The data allow spatial correlation between a gas hydrate bottom simulating reflector (BSR) and distinct areas of high near-sea-floor reflectivity. An integrated interpretation of the multi-frequency data set provides insight into the regional distribution of tectonically induced fluid migration and gas hydrate formation in the vicinity of ODP Leg 146 Sites 889 and 890. The BSR at the base of the gas hydrate stability field is observed within accreted and deformed sediments, but appears to be absent within bedded slope basin deposits. It is suggested that these basin deposits inhibit vertical fluid flow and prevent the formation of a BSR, whereas the hydraulic conductivity of the accreted sediments is sufficiently high to allow for pervasive gas migration. An elevation of the BSR beneath the flanks of a topographic high is interpreted as an indicator for local upflow of warm fluids along permeable pathways within outcropping accreted sediments. Parasound data reveal discontinuous zones of high reflectivity at or directly beneath the sea floor, which may indicate local cementation of surface sediments. In combination with GI-Gun data, the occurrence of these reflective areas can be related to the location of slope sedimentary basins acting as hydraulic seals. It is proposed that the seals sometimes fail along faults extending beneath the BSR, leading to focused upflow of methane-bearing fluid and the formation of carbonate pavements at the sea floor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005310050295
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    facet.materialart.
    Unknown
    Implications for focused fluid transport at the northern Cascadia accretionary prism from a correlation between BSR occurrence a d near-sea-floor reflectivity anomalies imaged in a multi-frequency seismic data set (2000)
    Springer
    Details
    Publication Date: 2000-03-22
    Print ISSN: 1437-3254
    Electronic ISSN: 1437-3262
    Topics: Geosciences
    Published by Springer
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 3
    facet.materialart.
    Unknown
    Investigating the structural evolution of the western Baltic (2004)
    American Geophysical Union
    Details
    Publication Date: 2004-01-01
    Print ISSN: 0096-3941
    Electronic ISSN: 2324-9250
    Topics: Geosciences
    Published by American Geophysical Union
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 4
    facet.materialart.
    Unknown
    Crustal structure of the Peruvian continental margin from wide-angle seismic studies (2004)
    Oxford University Press
    Details
    Publication Date: 2004-11-01
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 5
    facet.materialart.
    Unknown
    The link between bottom simulating reflections and methane flux into the gas hydrate stability zone – New evidence from Lima Basin, Peru Margin (2001)
    Elsevier
    In:  Earth and Planetary Science Letters, 185 . pp. 343-354.
    Details
    Publication Date: 2016-11-15
    Description: Bottom-simulating reflections (BSRs) are probably the most commonly used indicators for gas hydrates in marine sediments. It is now widely accepted that BSRs are primarily caused by free gas beneath gas-hydrate-bearing sediments. However, our insight into BSR formation to date is mostly limited to theoretical studies. Two endmember processes have been suggested to supply free gas for BSR formation: (i) dissociation of gas hydrates and (ii) migration of methane from below. During a recent campaign of the German Research Vessel Sonne off the shore of Peru, we detected BSRs at locations undergoing both tectonic subsidence and non-sedimentation or seafloor erosion. Tectonic subsidence (and additionally perhaps seafloor erosion) causes the base of gas hydrate stability to migrate downward with respect to gas-hydrate-bearing sediments. This process rules out dissociation of gas hydrates as a source of free gas for BSRs at these locations. Instead, free gas at BSRs is predicted to be absorbed into the gas hydrate stability zone. BSRs appear to be confined to locations where the subsurface structure suggests focusing of fluid flow. We investigated the seafloor at one of these locations with a TV sled and observed fields of rounded boulders and slab-like rocks, which we interpreted as authigenic carbonates. Authigenic carbonates are precipitations typically found at cold vents with methane expulsion. We retrieved a small carbonate-cemented sediment sample from the seafloor above a BSR about 20 km away. This supported our interpretation that the observed slabs and boulders were carbonates. All these observations suggest that BSRs in Lima Basin are maintained predominantly by gas that is supplied from below, demonstrating that this endmember process for BSR formation exists in nature. Results from Ocean Drilling Program Leg 112 showed that methane for gas hydrate formation on the Peru lower slope and the methane in hydrocarbon gases on the upper slope is mostly of biogenic origin. The δ13C composition of the recovered carbonate cement was consistent with biologic methane production below the seafloor (although possibly above the BSR). We speculate that the gas for BSR formation in Lima Basin also is mainly biogenic methane. This would suggest the biologic productivity beneath the gas hydrate zone in Lima Basin to be relatively high in order to supply enough methane to maintain BSRs.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER (OCEANREP)
  • 6
    facet.materialart.
    Unknown
    Ridge subduction at an erosive margin - the collision zone of the Nazca Ridge in southern Peru (2004)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 109 . B02101.
    Details
    Publication Date: 2018-04-25
    Description: The 1.5-km-high, obliquely subducting Nazca Ridge and its collision zone with the Peruvian margin have been imaged by wide-angle and reflection seismic profiles, swath bathymetry, and gravity surveying. These data reveal that the crust of the ridge at its northeastern tip is 17 km thick and exhibits seismic velocities and densities similar to layers 2 and 3 of typical oceanic crust. The lowermost layer contributes 10–12 km to the total crustal thickness of the ridge. The sedimentary cover is 300–400 m thick on most parts of the ridge but less than 100 m thick on seamounts and small volcanic ridges. At the collision zone of ridge and margin, the following observations indicate intense tectonic erosion related to the passage of the ridge. The thin sediment layer on the ridge is completely subducted. The lower continental slope is steep, dipping at ∼9°, and the continental wedge has a high taper of 18°. Tentative correlation of model layers with stratigraphy derived from Ocean Drilling Program Leg 112 cores suggests the presence of Eocene shelf deposits near the trench. Continental basement is located 〈15 km landward of the trench. Normal faults on the upper slope and shelf indicate extension. A comparison with the Peruvian and northern Chilean forearc systems, currently not affected by ridge subduction, suggests that the passage of the Nazca Ridge along the continental margin induces a temporarily limited phase of enhanced tectonic erosion superposed on a long-term erosive regime.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER (OCEANREP)
  • 7
    facet.materialart.
    Unknown
    Crustal structure of the Peruvian continental margin from wide-angle seismic studies (2004)
    Wiley
    In:  Geophysical Journal International, 158 (2). pp. 749-764.
    Details
    Publication Date: 2018-07-17
    Description: Active seismic investigations along the Pacific margin off Peru were carried out using ocean bottom hydrophones and seismometers. The structure and the P-wave velocities of the obliquely subducting oceanic Nazca Plate and overriding South American Plate from 8°S to 15°S were determined by modelling the wide-angle seismic data combined with the analysis of reflection seismic data. Three detailed cross-sections of the subduction zone of the Peruvian margin and one strike-line across the Lima Basin are presented here. The oceanic crust of the Nazca Plate, with a thin pelagic sediment cover, ranging from 0–200 m, has an average thickness of 6.4 km. At 8°S it thins to 4 km in the area of Trujillo Trough, a graben-like structure. Across the margin, the plate boundary can be traced to 25 km depth. As inferred from the velocity models, a frontal prism exists adjacent to the trench axis and is associated with the steep lower slope. Terrigeneous sediments are proposed to be transported downslope due to gravitational forces and comprise the frontal prism, characterized by low seismic P-wave velocities. The lower slope material accretes against a backstop structure, which is defined by higher seismic P-wave velocities, 3.5–6.0 km s−1. The large variations in surface slope along one transect may reflect basal removal of upper plate material, thus steepening the slope surface. Subduction processes along the Peruvian margin are dominated by tectonic erosion indicated by the large margin taper, the shape and bending of the subducting slab, laterally varying slope angles and the material properties of the overriding continental plate. The erosional mechanisms, frontal and basal erosion, result in the steepening of the slope and consequent slope failure.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER (OCEANREP)
  • 8
    facet.materialart.
    Unknown
    Frequent channel avulsions within the active channel-levee system of the middle Bengal Fan - an exceptional channel-levee development derived from Parasound and Hydrosweep data (2003)
    Pergamon Press
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 50 (5). pp. 1023-1045.
    Details
    Publication Date: 2020-08-05
    Description: The active channel–levee system of the middle Bengal Fan was studied by a combined analysis of Parasound echosounder and Hydrosweep swathsounder data. The channel is characterized by highly variable sinuosities. Compared to other mud-rich submarine fans, an exceptionally low channel slope is found. The system can be subdivided into inner and outer zones of significantly different depositional architecture. The inner zone consists of the active channel and sharply separated vertical blocks, which are characterized by parallel, distinct reflectors and planforms of bends. These blocks are interpreted as abandoned channel segments (cut-off loops). The outer zones represent undisturbed levees, which are constructed of parallel and wedge-shaped sedimentary units. The wedge-shaped units, varying significantly in thickness and lateral extent, are found at the outer convex arcs of active and abandoned channel loops caused by overspilling of channelized turbidity currents at sharp bends. The parallel units are the deposits of turbidity currents, which spread their sediments over wide areas as their size significantly exceeds the cross-section of the channel. The complex vertical and horizontal distribution of partially small sedimentary units suggests a more complicated deposition in time and space as hitherto reported from other submarine fans. Within the inner zone, more than 20 cut-off loops were identified over a channel length of 90 km. In contrast to most other large mud-rich submarine fans, channel avulsion within the active channel–levee system is a frequent process. In particular, a temporal succession of at least 4 cut-off loops was reconstructed in the southern study area, indicating channel avulsion on average every 750 years. Channel avulsion seems to be a repetitious process caused by erosion through turbidite currents in a highly sinuous channel. Compared to other submarine fans, no morphological parameter shows a remarkable difference except the channel slope, which is significantly smaller than, for example, on Amazon, Congo and Mississippi fans. The interaction between this low channel slope and the flow parameter of the turbidity currents is most likely the reason for the instability of the active channel planform, leading to an exceptionally large number of meander loop breaches and cut-off loops.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER (OCEANREP)
  • 9
    facet.materialart.
    Unknown
    Struktur des jüngsten Channel levee Systems im mittleren Bengalfächer (2000)
    In:  EPIC360. Jahrestagung der Deutschen Geophysikalischen Gesellschaft, 28 Feb - 3 März, München.
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER (OA)
  • 10
    facet.materialart.
    Unknown
    Seismic indications for free gas within the gas hydrate stability zone in the Yaquina Basin off Peru (2004)
    In:  EPIC3European Geosciences Union, 1st General Assembly, 25 - 30 April, Nice, France.
    Details
    Publication Date: 2019-07-17
    Description: MCS data from the Yaquina forearc basin off Peru reveal a complex distribution of gas and gas hydrate related reflections. Intricate lateral variations of the reflection pattern at the assumed base of the GHSZ in terms of continuity, reflection amplitude, and signal attenuation underneath are observed, as well as the occurrence of paleo-BSR. Phase reversed reflections at an erosional unconformity above the BSR indicate free gas within the GHSZ. In order to further constrain the interpretation of the observed reflection pattern we calculated the velocity distribution along the MCS line from high-resolution ocean bottom hydrophone recordings with two independent methods. The results from 2D-forward modelling and interactive velocity analysis show consistentresults. They exhibit a low velocity layer almost directly beneath the seafloor. Another low velocity layer with less than 1.5 km/s is present between the unconformity and the BSR.. In the vicinity and beneath prominent chemoherms, high velocities have been observed between the BSR and seafloor. Heat flux values calculated on the basis of the velocity-depth functions increase with decreasing amplitude of the bottom simulating reflector and peak near chemoherms. These results suggest a model of the Yaquina Basin where free gas is present under parts of the BSR, and within the hydrate stability zone, particularly under the sea floor and under the erosional unconformity. The higher interval velocities near and beneath the chemoherms are suspected to be caused either by thick gas hydrate lenses or a significant amount of precipitated carbonate within the sediment or a combination of both. The hypothesis of a paleo-BSR that reflects the uplift of the base of the GHSZ caused by the deposition of a particular sediment sequence is supported by the estimated heat flux values.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER (OA)
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...