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Conventional reflection profiling reveals a deep-ocean sedimentary column up to 3,500 m. thick. Sedimentary layers are grouped into an upper acoustically transparent zone, 20-510 m. thick, and a lower acoustically responsive zone up to 3,000 m. thick. The former, exhibiting a minimum of internal structure, has an average Vi = 1.70 km./sec. determined from X2, T2 analyses, an average thickness of 200-250 m., and is interpreted as unconsolidated, water-saturated red clay or pelagic ooze. The responsive zone is strongly layered, has an average Vi = 3.0 km./sec., and is interpreted to be semi-consolidated to consolidated mixed red clay and ooze, turbidites, or volcanic products. Low-velocity sediments blanket ocean-bottom topography and exhibit relief (up to 100 m.) largely at the water-sediment interface suggesting bottom scour and transport. Higher-velocity, stratified sediments lie on an irregular basement with pronounced discordance; thickness is dependent on basement topography and suggests differing depositional processes and rates of diagenesis. The uniform, plane surface interface between the two sedimentary units and extraordinary smoothness of layers within the stratified zone may be explained by the leveling effect of turbidity currents in rapidly filling sediment basins.
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