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The AAPG/Datapages Combined Publications Database

CSPG Special Publications

Abstract


Shelf Sands and Sandstones — Memoir 11, 1986
Pages 335-335
Symposium Abstracts: Sediment Source, Supply and Dispersal

Sedimentary Setting and Character of Sand and Gravel Bed Forms on the Open Continental Shelf Off Western Canada — Status of Knowledge: Abstract

John L. Luternauer1

Abstract

Sand and gravel were deposited on the shelf primarily during the Pleistocene glaciations of the mainland and outer islands. Relatively little sediment has been introduced to the shelf since, and most of this has consisted of silt and clay. The proportion of sand and gravel can be highly variable, even on comparably deep parts of the shelf. This is in part a reflection of original differences in the character of sediment supplied to the shelf. It may also reflect non-uniform isostatic depression of the shelf by Pleistocene ice. Variable depression could have exposed what are now comparably deep parts of the shelf to different Previous HitwaveNext Hit and current intensities at the time of the last sea level minimum. The present Previous HitwaveNext Hit regime of the shelf is characterized by peak storm Previous HitwaveNext Hit periods as high as 17 to 20 s and maximum probable Previous HitwaveNext Hit heights, which can exceed 17 m, but are ≤ m 90% of the time. Surface tidal currents generally do not exceed 50 cm/s.

The major sand and/or gravel bed forms that have been recognized to date are ripples, waves and patches. Most, if not all, of these features are generated by prevailing oceanographic processes. Combined flow (Previous HitwaveNext Hit- and current-generated) ripples have been observed in medium- to fine-grained foraminifer-rich sands as deep as 130 m. Linguoid current ripples and asymmetric waves (∼40 m Previous HitwaveNext Hit length; 2 to 3 m Previous HitwaveNext Hit height) are evident in shelly sand at 40 and 90 m respectively, where surface current velocities can exceed 150 cm/s in the vicinity of passages between small islands on a shelf bank. Symmetric waves up to 50 cm high with Previous HitwaveNext Hit lengths of up to 1.5 m in coarse shelly sand at a depth of 80 to 105 m, and gravel waves 1.5 m high with Previous HitwaveTop lengths of 4 to 5 m at a depth of 40 to 60 m are being generated by storm swells originating from the southwest. Sand patches with a thickness of 2 m or less and variable width extend for > 1 km at a depth of 60 to 70 m. They are nestled in gravel and are oriented transversely or longitudinally to the present long axis of the local tidal current ellipse.


 

Acknowledgments and Associated Footnotes

1 Geological Survey of Canada, Pacific Geoscience Centre, Box 6000, Sidney, British Columbia, Canada V8L 4B2

Copyright © 2008 by the Canadian Society of Petroleum Geologists