Acoustic facies interpretation, high-resolution velocity analysis and amplitude versus offset modelling have been performed on high resolution seismic data acquired on the West African margin offshore Angola, in water depths of about 2000 m. The area has a complex structural, thermal and fluid-flow setting, in which sediments are affected by salt diapirism and faulting associated with sediment compaction. A discontinuous bottom-simulating reflector (BSR) at a depth of about 200 m below sea floor could mark the base of the gas hydrate occurrence zone, which does not always coincide with the top of the free gas zone. Within the gas hydrate stability zone, a shallow bottom-simulating reflector is observed at a depth of about 75 m below seafloor. This shallow bottom simulating reflector, that is termed "sheep back reflector" (SR), correspond to a small amount of gas being trapped in the sediments. It could mark the top of the gas hydrate occurrence zone, where gas hydrate dissociation may occur. A reversed polarity reflector (R1) is also observed about 25 m below the sea floor. This reflector could correspond to a limit between normally compacted and underconsolidated sediments, possibly related to a permeability change in the sediments. Thus, the occurrence of excess pore pressure generated during gas hydrate dissociation could explain some subsurface sediment mobilization processes.

West: 9.3000 East: 12.0000 North: -4.3000 South: -6.0000

Expedition: 175

Site: 175-1076

Provider: SEDIS Publication Catalogue

Data set link: http://sedis.iodp.org/pub-catalogue/index.php?id=2004-078149 (c.f. for more detailed metadata)

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