|Titre||Shelfbreak gullies; products of sea-level lowstand and sediment failure: examples from Bowser Basin, northern British Columbia|
|Auteur||Ricketts, B D; Evenchick, C A|
|Source||Journal of Sedimentary Research vol. 69, no. 6, 1999 p. 1232-1240, https://doi.org/10.2110/jsr.69.1232|
|Séries alt.||Commission géologique du Canada, Contributions aux publications extérieures 1998188|
|Éditeur||Society for Sedimentary Geology|
|Document||publication en série|
|Media||papier; en ligne; numérique|
|SNRC||104A; 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|
|Lat/Long OENS||-131.0000 -128.0000 58.0000 56.0000|
|Sujets||dépôts de pentes; schistes; marges plaques; plate-forme continentale; dépôts de coulée de débris; coulées de débris; bassins sédimentaires; changements du niveau de la mer; variations du niveau de la mer;
glissements de pentes; sédimentologie; géologie marine|
|Illustrations||location maps; geological sketch maps; stratigraphic columns; photographs; cross-sections, stratigraphic|
|Résumé||(disponible en anglais seulement)|
The 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.