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TitreMorphology and sedimentary processes of large bedforms near Cape Split, upper Bay of Fundy, Canada
AuteurLi, M Z; Shaw, J; Todd, B J; Kostylev, V E
Source29th IAS Meeting of Sedimentology, third circular, programme; 2012 p. 250
LiensAbstract - Résumé
Séries alt.Secteur des sciences de la Terre, Contribution externe 20120138
Réunion29th IAS Meeting of Sedimentology; Schladming; AT; Septembre 10-13, 2012
ProvinceRégion extracotière de l'est
Sujetscaractéristiques sous-marines; sedimentation; dynamique sédimentaire; marées; milieux de marée; géologie marine; sédimentologie
Résumé(disponible en anglais seulement)
Various types of large bedforms develop under the influence of strong Bay of Fundy tides. Geomorphological characterization and mobility assessment of these bedforms are required for the design and siting of tidal power seabed installations. Multibeam bathymetry data are combined with geophysical surveys, seabed sampling, and tidal model predictions to investigate the geomorphology, mobility, and formation processes of the large bedforms near Cape Split in the upper Bay of Fundy.
The main seabed features in the study area include the Cape Split banner bank, the Scots Bay barchan dune field, and a megarippled gravel bank trapped in the Minas Passage. The banner bank, oriented southwest to northeast, is about 5.5 km long, 2.2 km wide and stands about 23 m above the surrounding seafloor. Sand waves with various sizes are superimposed on the banner bank. The height of these sand waves ranges from 0.4 to 18.6 m. The mean wavelength reaches 116 m near the top of the banner bank and become bifurcated and smaller (mean wavelength 56 m) towards the edges of the banner bank. Megaripples are superimposed on the flanks of sand saves. The sand waves are asymmetric to the southwest on the northern flank of the bank, and to the northeast on the southern flank. This asymmetry is indicative of the direction of sand wave migration and hence net sediment transport pattern on the banner bank. The sand body of the banner bank is composed of coarse to very coarse sand (mean grain size 0.75-1.02 mm), while the surrounding seafloor is covered by a lag surface of bouldery gravel with discontinuous veneers of sand. The barchan dune field lies south of the banner bank in outer Scots Bay. These dunes are generally oriented northwest to southeast with their horns pointing to the northeast. The barchan dunes are spaced from 20 m up to 250 m, 1 to 4 m high and generally asymmetric to northeast. The geometry of these bedforms indicates net sediment transport to the northeast. The sediment of the barchan dunes is medium sand with a mean grain size of 0.49 mm. The gravel bank is located in Minas Passage in depths of 85-120 m. The bank, oriented roughly east-west, is ~20 m thick, 850 m across and 3.5 km long. While the southern half of the gravel bank is featureless, the north face is covered by gravel megaripples with wavelengths of 10-108 m and heights of 0.15-5.2 m. The mean diameter of gravel is about 4 cm over the megaripples and increases to 7.9 cm, with significantly higher content of cobbles and boulders, on the smooth southern face of the gravel bank. The well-roundedness of the pebbles and cobbles with no biologic attachments indicates that they are mobile under the strong tidal current in the scour trough. Predictions of tidal and sediment transport models show that the Cape Split banner bank and associated barchan dunes are frequently mobilized by the strong tidal current. The formation of the banner bank was controlled by the development of an anti-clockwise tidal gyre west of the headland. The barchan dunes form in an area of strong flood-oriented asymmetry in both the tidal current and bottom shear stress.