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B.A. McGregor

Publications and source records attributed to B.A. McGregor.

10 recordsLinked to original sources
USGS1989

Seismic-reflection data from R/V FARNELLA cruises FRNL82-7, FRNL85-1, FRNL85-2, and FRNL85-3A in the U.S. Gulf of Mexico EEZ

During the winter of 1982 and the summer and early fall of 1985, the U.S. Geological Survey (USGS) in cooperation with the Institute of Oceanographic Sciences of the United Kingdom collected approximately 30,508 line kilometers of seismic-reflection data in the U.S. Gulf of Mexico Exclusive Economic Zone (EEZ) as part of a USGS program to map the EEZ. In water depths exceeding 3,000 m, survey line spacing was about 25 km and gradually decreased to about 5 km in 250 m water depths. No areas were surveyed with depths shallower than 250 m. Orientation of the tracklines was in general parallel to the trend of the bathymetric contours (Figs. 1, 2, 3, and 4).

Open-File Report↗
USGS1983

Submarine canyon and slope processes of the U.S. Atlantic continental margin

Two regions on the U.S. Atlantic continental margin were surveyed using single-channel, seismic-reflection profiling techniques: the Mid-Atlantic Continental Slope and Rise seaward of New Jersey in the vicinity of Baltimore Canyon and the Continental Slope and upper Rise just north of Cape Hatteras. Submarine canyons are the dominant morphologic feature in both areas. The Continental Slope in the Baltimore Canyon area has a general sea-floor gradient of 3?-4? and a width of approximately 40 km, whereas the study area north of Cape Hatteras has a general sea-floor gradient of approximately 9? and a width of 20 km. The dominant slope process differs in each area. In the Baltimore Canyon area, subbottom reflectors suggest that sediment deposition with progradation of the slope is related to canyon processes. In the study area north of Cape Hatteras, the canyons appear erosional and mass wasting is the dominant erosional process. Dominant slope processes appear to be correlated with the width and sea-floor gradient of the Continental Slope. Although the absolute age of the canyons is difficult to determine without rotary-drill cores for stratigraphic control, Baltimore Canyon is suggested to be older than the shelf-indenting canyon just north of Cape Hatteras. An anomalously large ridge flanking Baltimore Canyon on the upper rise appears to be related to canyon depositional and erosional processes.

Open-File Report↗
USGS1982

3.5-kHz Data Collected in the Wilmington Canyon Area During 1980, Endeavor Cruise 80-EN-056

During 1980, geophysical data were collected seaward of New Jersey in the vicinity of Wilmington Canyon on three cruises, GYRE 80-G-7B, GYRE 80-G-BB, and ENDEAVOR 80-EN-056 (discussed here). The objectives of these surveys of the Continental Slope and upper Rise, including Wilmington Canyon and the adjacent margin, were to extend existing geophysical coverage to the south of Wilmington Canyon and to provide detailed geologic and geophysical data on the poss.ible origin and evolution of submarine canyons and on sediment transport and other processes within the canyon domain. The geology of this area near Wilmington Canyon was discussed by McGregor, Stubblefield, and others and Stubblefield and others. On ENDEAVOR Cruise 80-EN-056, during October 9-10, 1980, a series of 3.5-kHz profiles was collected. The objective of acquiring these data was to supplement data from GYRE 80-G-7B so that a bathymetric map based on 1-km-spaced grid of data could be constructed. The 3.5-k.Hz system consisted of a hull-mounted transducer and a signal correlator. Ship's speed during the survey was 10 knots (18 km/hr). Data were recorded on a strip chart at a 1-second sweep rate. Navigational control for the cruise was based on Loran C. All times given on the data and navigation plots are in Greenwich mean time (GMT or Z). The quality of the records is very good, although time marks had to be added manually. Maximum subbottom penetration was approximately 100 m. Original records may be viewed at the u.s. Geological Survey, Woods Hole, MA 02543. Microfilms of the data and 1:40,000 scale trackcharts can be purchased only from the National Geophysical and Solar-Terrestr.ial Data Center, NOAA/EDIS/NGSDC, Code D621, 325 Broadway, Boulder, Colorado, 80303 (303-497-6338).

Open-File Report↗
USGS1981

Smooth seaward-dipping horizons — An important factor in sea-floor stability?

Mass movement has influenced in varying degrees the morphology of the United States east coast continental margin seaward of the Baltimore Canyon trough as revealed by detailed geophysical studies using high-resolution 3.5-kHz, and seismic reflection data. Each of three areas studied is along the slope within a distance of 225 km, and is seaward of a nonglaciated shelf but near major land drainage systems. Thick sequences of material believed to be Pleistocene were deposited on the slope in all three areas. Sediment failure in the form of large block movement involving block thicknesses of more than 100 m, however, has taken place in only two of the areas. A factor common to the two areas where failure took place, but absent in the area where no failure took place, is smooth seaward-dipping sub-bottom horizons. Whatever the triggering mechanism, a smooth slip surface that has a seward slope may contribute to mass movement by reducing the internal friction. This may be one of several factors that should be considered in assessing slope stability.

Marine Geology↗