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8 - Sedimentary Processes in a Tectonically Active Region: Puerto Rico North Insular Slope
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- By Kathryn M. Scanlon, U.S. Geological Survey, Woods Hole, Massachusetts, Douglas G. Masson, Institute of Oceanographic Sciences, Southampton, United Kingdom
- Edited by James V. Gardner, United States Geological Survey, California, Michael E. Field, United States Geological Survey, California, David C. Twichell
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- Book:
- Geology of the United States' Seafloor
- Published online:
- 25 January 2010
- Print publication:
- 13 August 1996, pp 123-134
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Summary
Abstract
GLORIA long-range sidescan sonar data extending from the shelf edge north of Puerto Rico across the insular slope to the floor of the Puerto Rico Trench reveal numerous canyons, amphitheater-shaped scarps, and sediment ponds. Interpretation of these data, in light of previously collected geophysical and sample data, indicates that tectonic forces have played a major role in the depositional and erosional history of the study area. Regional northward tilting of the flat, shallowwater Tertiary carbonate bank north of Puerto Rico created the insular slope and set the stage for the development of submarine canyons. The distinctive morphology of these canyons can be attributed to the character of the strata into which they have been cut. The front of the former carbonate bank has been eroded by large-scale mass wasting, which has left large amphitheater-shaped scarps on the lower slope. Shelf-derived sediment, along with material eroded from the canyon walls, is transported through the canyons to the basin and ridge province at the base of the slope where most sediment is trapped in basins south of the trench floor. The discovery of a depositional lobe on the trench floor confirms the presence of a turbidite entry point and suggests that some sediment reaches the trench floor as well.
Introduction
The deepest part of the Puerto Rico Trench, which has depths in excess of 8,000 meters (m), lies 150 km north of the island of Puerto Rico (Figure 8–1).
Introduction
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- By David C. Twichell, U.S. Geological Survey, Woods Hole, Massachusetts, Kathryn M. Scanlon, U.S. Geological Survey, Woods Hole, Massachusetts, William P. Dillon, U.S. Geological Survey, Woods Hole, Massachusetts
- Edited by James V. Gardner, United States Geological Survey, California, Michael E. Field, United States Geological Survey, California, David C. Twichell
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- Book:
- Geology of the United States' Seafloor
- Published online:
- 25 January 2010
- Print publication:
- 13 August 1996, pp 81-84
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Summary
The Gulf of Mexico Exclusive Economic Zone (EEZ) and parts of the northern Caribbean plate margin were surveyed using GLORIA (Geologic LOng-Range Inclined Asdic) during the U.S. Geological Survey EEZ-SCAN program. In the Gulf of Mexico, the first cruise was conducted in 1982 and three more were completed in the summer and fall of 1985. The survey of U.S. waters around Puerto Rico and the U.S. Virgin Islands was completed during a twenty-five-day cruise in the fall of 1985 as well. In addition, surveys were conducted in the Cayman Trough and north of Hispaniola during a transit in 1985 from the Gulf of Mexico to the Caribbean. In total, these surveys mapped approximately 600,000 km2 of the U.S. Gulf of Mexico and Caribbean EEZ along survey tracklines that were spaced 10 to 30 km apart. The data collected included digital GLORIA sidescan sonar images, 40- to 160-in3 airgun and 3.5-kHz seismic-reflection profiles, 10-kHz bathymetry profiles, and total magnetic field measurements.
The Gulf of Mexico is a small, geologically diverse ocean basin that can be divided into three distinct geologic provinces: a salt deformation province underlying the continental slope of the northern and western Gulf of Mexico, the Mississippi Canyon and Fan system in the central Gulf, and a carbonate province along its eastern and southern boundaries.
9 - A Review of the Tectonic Problems of the Strike-Slip Northern Boundary of the Caribbean Plate and Examination by GLORIA
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- By William P. Dillon, U.S. Geological Survey, Woods Hole, Massachusetts, N. Terence Edgar, U.S. Geological Survey, Reston, Virginia, Kathryn M. Scanlon, U.S. Geological Survey, Woods Hole, Massachusetts, Dwight F. Coleman, U.S. Geological Survey, Woods Hole, Massachusetts
- Edited by James V. Gardner, United States Geological Survey, California, Michael E. Field, United States Geological Survey, California, David C. Twichell
-
- Book:
- Geology of the United States' Seafloor
- Published online:
- 25 January 2010
- Print publication:
- 13 August 1996, pp 135-164
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- Chapter
- Export citation
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Summary
Introduction
The Caribbean region, south of Cuba (Figure 9–1A), forms one of the distinct lithospheric plates of the Earth's surface (Case and Holcombe 1980). Targets of a scale appropriate for GLORIA imaging are provided by tectonic disruptions of the seafloor along the plate's northern edge. We selected three areas to survey using GLORIA, which allows us to examine the variety of structures produced along this active plate boundary (Figure 9–1B). In the central Cayman Trough, plate motion and geometry cause extension, which creates a short spreading axis that is not connected to the world rift system; GLORIA is used to analyze the crustal structures that are created. Off northwestern Hispaniola, an irregularity in the plate boundary results in compressional motion, and GLORIA is used to analyze the accretionary wedge that is formed by sediments that are scraped off the North American Plate as it is forced against the Caribbean Plate. North of Puerto Rico, the plates appear to slide past each other with neither compression nor extension, yet, surprisingly, a major oceanic trench exists, which exhibits the world's greatest negative free-air gravity anomaly. Structural trends displayed by GLORIA and earthquake distribution are used to hypothesize the plate interactions that form the trench and analyze the response at a corner of a plate (the North American Plate) that is being overrun by another plate (the Caribbean Plate).
Tectonic setting of the Caribbean Plate
The Caribbean Plate is marked by clearly defined subduction zones to its east and west (Figure 9–1B).