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TitleThe influence of turbidity currents and contour currents on the distribution of deep-water sediment waves offshore eastern Canada
AuthorNormandeau, AORCID logo; Campbell, D CORCID logo; Cartigny, M J B
SourceSedimentology 2018 p. 1-22,
Alt SeriesNatural Resources Canada, Contribution Series 20170327
Mediapaper; on-line; digital
File formatpdf; html
ProvinceEastern offshore region; Nova Scotia
Lat/Long WENS -58.7500 -56.2500 43.2500 41.5000
Subjectsmarine geology; surficial geology/geomorphology; sedimentology; geophysics; stratigraphy; geochronology; continental margins; continental slope; marine sediments; landslide deposits; slumps; turbidity currents; currents; contourites; offshore areas; bedforms; antidunes; depositional environment; depositional cycles; depositional models; bathymetry; geophysical interpretations; acoustic surveys, marine; side-scan sonar; seismic interpretations; morphology; sediment distribution; flow regimes; flow velocities; erosion; deposition; submarine features; submarine canyons; channels; marine sediment cores; piston cores; radiometric dating; radiocarbon dating; Scotian Margin; Scotian Slope; Laurentian Fan; The Gully; Shortland-Haldimand Channel; Classic Labrador Sea Water; Denmark Strait Overflow Water; Iceland-Scotland Overflow Water; Upper Labrador Sea Water; Western Levée of Western Valley; Phanerozoic; Cenozoic; Quaternary
Illustrationslocation maps; geoscientific sketch maps; tables; seismic profiles; bathymetric profiles; geophysical images; lithologic sections; plots; geophysical profiles; schematic models; schematic representations
ProgramDelineating Canada's Continental Shelf Under UNCLOS
Released2018 11 01
AbstractSediment waves are commonly observed on the sea floor and often vary in morphology and geometry according to factors such as seabed slope, density and discharge of turbidity currents, and the presence of persistent contour currents. This paper documents the morphology, internal geometry and distribution of deep-water (4000 to 5000 m) bedforms observed on the sea floor offshore eastern Canada using high-resolution multibeam bathymetry data and seismic stratigraphy. The bedforms have wavelengths of >1 km but fundamentally vary in terms of morphology and internal stratigraphy, and are distinguished into three main types. The first type, characterized by their long-wavelength crescentic shape, is interpreted as net-erosional cyclic steps. These cyclic steps were formed by turbidity currents flowing through canyons and overtopping and breaching levées. The second type, characterized by their linear shape and presence on levées, is interpreted as net-depositional cyclic steps. These upslope migrating bedforms are strongly aggradational, indicating high sediment deposition from turbidity currents. The third type, characterized by their obliqueness to canyons, is observed on an open slope and is interpreted as antidunes. These antidunes were formed by the deflection of the upper dilute, low-density parts of turbidity currents by contour currents. The modelling of the behaviour of these different types of turbidity currents reveals that fast-flowing flows form cyclic steps while their upper parts overspill and are entrained westward by contour currents. The interaction between turbidity currents and contour currents results in flow thickening and reduced sediment concentration, which leads to lower flow velocities. Lower velocities, in turn, allow the formation of antidunes instead of cyclic steps because the densiometric Froude number (Fr') decreases. Therefore, this study shows that both net-erosional and net-depositional cyclic steps are distributed along channels where turbidity currents prevail whereas antidunes form on open slopes, in a mixed turbidite/contourite system. This study provides insights into the influence of turbidity currents versus contour currents on the morphology, geometry and distribution of bedforms in a mixed turbidite-contourite system.
Summary(Plain Language Summary, not published)
Deep-water sediment waves observed offshore Nova Scotia allow us to model the behaviour of past turbidity currents coming down the continental slope.

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