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GLORIA Mosaic of West Coast U.S. Exclusive Economic Zone, Northern Sector

Monty A. Hampton, David A. Cacchione, David E. Drake, Neil H. Karl, Neil H. Kenyon, Douglas G. Masson

The GLORIA (Geological Long-Range Inclined Asdic) side-scanning sonar system was used to compile an image-enhanced acoustic mosaic, similar to an aerial photograph, of the sea floor of the West Coast U.S. Exclusive Economic Zone. The mosaic clearly shows the spreading centers, fracture zones, submarine fans and channels, and transform to convergent continental margins north of latitude 39°N. The linear basement ridges originally generated at the Gorda and Juan de Fuca spreading centers are abruptly truncated by the Mendocino and Blanco fracture zones, and their subtle to distinct divergence, bending, and offset attests to past changes in spreading rate and propagation of spreading centers. The major Delgada, Astoria, and Nitinat fans are traversed by lengthy channel- evee complexes extending from major canyons on the adjacent continental slope; areally extensive sediment-wave fields occur adjacent to the right side (facing down-channel) of these complexes. Other drainage features appear on the mosaic, and the range of channel sinuousity and continuity indicates fluviallike processes at work on the sea floor. Submarine canyons on the continental slope are irregularly distributed; their range of maturity and relation to substrate type and geologic structure are manifest as variations in length, width, and relief, by changes in trend, and by the degree of sidewall gullying. Compressional and diapiric ridges characterize the continental slope in areas of plate convergence, whereas along the transform margin south of the Mendocino fracture zone, the slope is relatively smooth and featureless, except where incised by large canyon systems.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.