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  • 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
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  • 2
    Electronic Resource
    Electronic Resource
    Late Quaternary Seismic Stratigraphy of the Eastern Bengal Shelf (1998)
    Springer
    Marine geophysical researches 20 (1998), S. 57-71 
    Details
    ISSN: 1573-0581
    Keywords: Bengal Shelf ; seismic stratigraphy ; Parasound ; Late Quaternary ; subaqueous delta ; lowstand delta
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract An ultra-high-resolution seismic study of the eastern Bengal Shelf with the parametric narrow-beam echosounder Parasound allows the interpretation of late Quaternary depositional patterns in terms of seismic stratigraphy. Accommodation space was still present on the outer shelf during the last lowstand, where a prograding delta developed in the western survey area. Oolitic beach ridges were later formed on top of this lowstand delta. Farther east, large parts of the shelf were exposed to subaerial erosion and a river system extended seaward across the area. A subaqueous highstand delta prograded southwards following the maximum transgression about 7,000 years ago. Its foreset beds exhibit acoustic voids very likely generated by sediment liquefaction, possibly caused by episodic energetic events such as major cyclones and/or earthquakes. Bottomset sediments extend seaward close to the shelf break in the west, whereas no Holocene sediments cover the outer shelf in the east.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004375908399
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