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GLORIA Side-Scan Sonar Surveys in Caribbean: Puerto Rico and U.S. Virgin Islands Exclusive Economic Zone and Cayman Trough

K. M. Scanlon, D. G. Masson, N. T. Edgar, L. M. Parson, R. W. Rodriguez, W. P. Dillon, G. W. Hill, R. B. Halley

During October and November 1985, the U.S. Geological Survey and the United Kingdom Institute of Oceanographic Sciences undertook a GLORIA long-range side-scan sonar survey of the Puerto Rico and U.S. Virgin Islands Exclusive Economic Zone and part of the Cayman Trough. More than 65,000 mi2 were imaged by the GLORIA system, and 6,500 line-mi of single-channel seismic data were collected.

North of Puerto Rico, GLORIA data show that the upper part of the continental slope is cut by several dozen straight, parallel-sided channels that trend directly downslope and terminate or become less distinct at a series of escarpments between 3,000 and 5,000 m water depth. Between the base of the slope and the axis of the Puerto Rico Trench lies a series of sediment-filled basins and basement ridges that are slightly oblique to the trench axis. Sonographs show the trench floor to be featureless and flat. The outer wall of the trench consists of a series of steps where the oceanic basement has down-faulted into the trench. North of the outer wall, north-south-trending ridges parallel the oceanic magnetic anomaly pattern.

South of Puerto Rico, the upper slope is cut by channels that are less regular than those north of the island. At the base of the landward wall of the Muertos Trough, a lobate deformation front is particularly well defined. The GLORIA data suggest that the island of St. Croix is being thrust northward over the Virgin Islands Trough in a direction opposite to thrusting at the Muertos Trough.

The central part of the Cayman Trough was also included in this GLORIA survey. North-south-trending ridges resulting from spreading predominate in the center of the trough, whereas near the north and south walls east-west-trending ridges are well developed. Only a few volcanoes were found, and one field of small volcanic structures lies near the central rift.

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