Instability: processes and products
Published:January 01, 2005
Subduction of seamounts at destructive sedimented plate margins results in spectacular deformation of the overriding plate. High-resolution sidescan sonar imagery from the Costa Rica margin show the tracks of five individual seamounts, of which four are described in this paper. These were subducted at various times during the last 690 ka and each represents a different stage in the subduction process. Each subducted seamount leaves a parallel-sided depression in its wake, that can be traced for up to 55 km landward of the deformation front. This wake is created by deformation and uplift of the continental slope as the seamount passes beneath it, followed by collapse due to landsliding as support for the uplifted area is withdrawn. Areas of uplift above seamounts are characterized by complex normal and strike-slip fault patterns. Collapse of the uplift along the trailing edge of the seamount creates a zone of slope failure (landsliding) that migrates upslope (or landward) with the seamount. Landslide processes are dominated by debris flow, but also include sliding of coherent blocks and debris avalanche. Erosion occurs by repeated landslides, which produce a series of overlapping debris flows. Downslope sediment transport typically extends over limited distances, resulting in partial ‘backfilling’ of the scar as its headwall moves up slope. The amount of margin material disrupted by seamount subduction is four to five times the volume of the subducting seamount, of which about three quarters seems to be recycled downslope, backfilling the scar, and nearly one quarter is subducted with the seamount.
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Submarine Slope Systems: Processes and Products
Submarine slopes provide the critical link between shallow-water and deep-water sedimentary environments. They accumulate a sensitive record of sediment supply, accommodation creation/destruction, and tectonic processes during basin filling. There is a complex stratigraphic response to the interplay between parameters that control the evolution of submarine slope systems, e.g. slope gradient, topographic complexity, sediment flux and calibre, base-level change,tectonic setting, and post-depositional sediment remobilization processes. The increased understanding of submarine slope system has been driven partly by the discovery of large hydrocarbon fields in morphologically complex slope settings, such as the Gulf of Mexico and offshore West Africa, and has led to detailed case studies and improved generic models for their evolution. This volume brings together research papers from modern, outcrop and subsurface settings to highlight these recent advances in understanding of the stratigraphic evolution of submarine slope systems.