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Recently obtained high-energy multichannel seismic reflection profiles across the Blake Escarpment show that the oceanic basement, identified as a hyperbolic reflector, forms a deep sediment-filled trough at the base of the escarpment. The western boundary of the trough is formed by a steep rise (45°-60°) of acoustic basement producing an apparent structural relief of more than 2.5 sec for the trough. Seismic velocities were determined as 3.23 to 3.95 km/sec and indicate 4.03 to 4.94 km of sediments in the trough, which deepens to approximately 11 to 12 km. The steep west side suggests fault control and deposition in a fault-bounded half-graben trough. Undisturbed sediments lie over Horizon ß which passes across the trough without deflection on one profile, nd which is the shallowest disturbed and upturned reflector on another profile.
Correlation of reflectors involved in the structure of the trough with the nearby DSDP Site 391 indicates that the deeper seismic layers include sediments older than Late Jurassic. These old sediments filling the fault-bounded trough at the base of the Blake Escarpment should include facies deposited during the earliest opening of the Atlantic, perhaps in the Early Jurassic.
The seismic reflection profiles also show reflectors at the edge of the Blake Plateau which can be correlated with DSDP Drill Site 390. Important reflectors of earliest Eocene, Campanian/Albian and Barremian age can be traced westward to depths of 3.4 km (2.8 sec) under the Blake Plateau. Hyperbolic reflectors, not associated with igneous basement, occurring over acoustically opaque zones are interpreted to be well-cemented, high-velocity carbonate bank-margin complexes as drilled at DSDP Site 392.
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