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  • 1
    Electronic Resource
    Electronic Resource
    Geo-marine letters 7 (1987), S. 91-101 
    ISSN: 1432-1157
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Nine carbonate megaturbidites occur within the succession of siliciclastic turbidite systems of the Eocene Hecho Group. The megaturbidites form exceptionally thick units of virtually basin-wide extent, thus forming excellent marker beds. Each megaturbidite consists of a graded bed which displays a basal megabreccia containing huge slabs of shallow-marine limestones and out-size slope marlstone rip-up clasts. The megaturbidite flows were derived from adjacent carbonate shelves and were probably triggered by major earthquakes associated with thrust propagation. The term of megaturbidite, as descriptively used in this paper. denotes the deposit of an exceptionally large-volume sediment gravity flow.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2017-04-10
    Description: The interrelation between deformation styles and behavior of fluids in accretionary prisms is under debate, particularly the possibility that overpressuring within the basal decollement may enable mechanical decoupling of the prism from the subducting material. Anisotropy of magnetic susceptibility (AMS) data from sediments spanning the basal decollement of the Barbados accretionary prism show a striking progression across this structure that strongly supports the hypothesis that it is markedly overpressured. In the accretionary prism, above the decollement, the minimum AMS axes are subhorizontal and oriented nearly east-west, whereas the maximum AMS axes are oriented nearly north-south and shallowly inclined. At the top of the decollement, the minimum AMS axes orientations abruptly change to nearly vertical; this orientation is maintained throughout the decollement and in the underthrust sediments below. The AMS orientations in the prism sediments above the decollement are consistent with lateral shortening due to regional tectonic stress, as the minimum axes generally parallel the convergence vector of the subducting South American plate and the maximum axes are trench-parallel. Because the orientations of the AMS axes in deformed sediments usually parallel the orientations of the principal strains, the AMS results indicate that the incremental strain state in the Barbados prism is one dominated by subhorizontal shortening. In contrast, the AMS axes within and below the decollement are consistent with a strain state dominated by vertical shortening (compaction). This abrupt change in AMS orientations at the top of the decollement at Site 948 is a direct manifestation of mechanical decoupling of the off-scraped prism sediments from the underthrust sediments. The decoupling horizon occurs at the top of the decollement zone, coinciding with the location of flowing, high-pressure fluids.
    Type: Article , PeerReviewed
    Format: text
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