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TitleShelfbreak gullies; products of sea-level lowstand and sediment failure: examples from Bowser Basin, northern British Columbia
AuthorRicketts, B D; Evenchick, C A
SourceJournal of Sedimentary Research vol. 69, no. 6, 1999 p. 1232-1240,
Alt SeriesGeological Survey of Canada, Contribution Series 1998188
PublisherSociety for Sedimentary Geology
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia
NTS104A; 104B/01; 104B/02; 104B/07; 104B/08; 104B/09; 104B/10; 104B/15; 104B/16; 104G/01; 104G/02; 104G/07; 104G/08; 104G/09; 104G/10; 104G/15; 104G/16; 104H
AreaTsatia Mountain
Lat/Long WENS-131.0000 -128.0000 58.0000 56.0000
Subjectssedimentology; marine geology; slope deposits; shales; plate margins; continental shelf; debris flow deposits; debris flows; sedimentary basins; sea level changes; sea level fluctuations; slope failures
Illustrationslocation maps; geological sketch maps; stratigraphic columns; photographs; cross-sections, stratigraphic
AbstractThe transition from cyclothemic shelf to shale-dominated slope deposits (Callovian to Oxfordian) that accumulated along the northern convergent margin of Bowser Basin is delineated by spectacular, conglomerate-filled channels, or gullies. The gullies, representing the shelf-slope break, formed in two stages: (1) Slumping of upper slope-outer shelf sediment created topography, which determined (2) the course of fluvial, distributary-type channels and focused gravel-dominated sediment transport during relative sea-level lowstands. Gully fill consists predominantly of debris-flow deposits, locally incorporated into small (lowstand) fan deltas that prograded from gully margins. Lowstand fluvial channels overlie shelf cycles, incise the underlying highstand deposits, and are overlain by fossiliferous, transgressive sandstone. However, the shelfbreak gullies deposits are up to 10 times thicker than those of the associated lowstand fluvial channels.
Although the lowstand fluvial channels likely acted as bypass conduits for gravel and sand during times of low sea level, the initiation and "overdeepening" of the shelfbreak gullies by slumping probably took place during both high and low relative sea levels. Deposition within gullies may also have continued during relative highstands, from sediment in storage on the outer shelf.
The implications for sequence stratigraphic models are: shelf-break gullies can form at any stage of sea level fluctuation; gully thickness may not be related to the magnitude of lowstand incision on the adjacent shelf; and gullies formed by sediment gravity failure do not provide quantitative information about the magnitude of sea-level fall.

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