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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 9. (September)

First Page: 1672

Last Page: 1672

Title: Sediment Transport on Georges Bank and Southern New England Shelf: ABSTRACT

Author(s): David C. Twichell

Article Type: Meeting abstract


Four bed-form provinces have been identified on Georges Bank by means of sidescan-sonar and echo-sounding techniques: large sand waves, small sand waves, megaripples, and featureless sea floor. The large sand waves are on the bank crest where tidal currents exceed 70 to 80 cm/sec; they are bordered, north and south, by areas of small sand waves and/or megaripples where tidal currents are 40 to 80 cm/sec. Featureless sea floor is present farthest from the bank crest where tidal currents are less than 40 cm/sec.

Directions of sediment transport can be inferred from bed-form asymmetry and from surface-sediment texture. On the crest of the bank large sand waves are on northwest-striking ridges. The asymmetry of these sand waves indicates southward transport on one side of the ridges and northward transport on the other, implying erosion from the troughs separating the ridges, and growth of the ridges. The asymmetry of the small sand waves along the south side of the bank indicates that sand is also transported southward away from the bank. Though the asymmetry of megaripples could not be determined in the study, the presence of megaripples between the sand-wave provinces and areas of featureless sea floor suggests decreasing effectiveness of sand transport away from the bank crest. This pattern of sand transport is supported by surface-sediment texture, which becomes progressively finer both north and southwest away from the crest of Georges Bank. One end of the sediment-transport path is the southern New England shelf where silt and clay are deposited. Here tidal currents drop from 30 to 6 cm/sec, permitting the fine suspended sediments to accumulate.

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