Storm-generated currents and offshore sediment transport on a sandy shoreface, Tibjak Beach, Canadian Beaufort Sea

Héquette, Arnaud; Hill, Philip R.

doi:10.1016/0025-3227(93)90023-o

Cited by 67 publications

(32 citation statements)

References 24 publications

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“…During the open water season, mean nearbottom currents and oscillatory flows associated with surface gravity waves represent significant sources of bottom sediment remobilization in water depths of less than 10 m (Hodgins et al, 1986;Hequette and Hill, 1993). According to a wave hindcast model and calculations of orbital threshold velocity, Harper and Penland (1982) concluded that, even between 10 and 20 m water depths, the seabed is disturbed by wave orbital currents up to 10% of the time.…”

Section: Discussionmentioning

confidence: 99%

Sea ice scouring on the inner shelf of the southeastern Canadian Beaufort Sea

1995

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About 2200 ice scours were observed and analyzed over a distance of approximately 500 km on the inner shelf of the southeastern Canadian Beaufort Sea. Ice scours were divided into two types based on their morphology: multiple scours consisting of a series of parallel scours and ridges, and single scours. Single scours are the dominant type representing more than 85% of the total observations. The mean scour depth and width are 0.3 m and 11 m respectively, but scour depths of more than 2 m and a scour width up to 345 m were documented.The magnitude of ice scouring processes increases with water depth. In water depths less than 10 m, less than 25% of the seafloor surface is reworked by ice scours. This percentage increases significantly seaward of the 10 m isobath, being more than 75% in water depths in excess of 12 m. A break in the seabed slope at about 10 to 12 m water depth marks a boundary between a nearshore zone moderately influenced by ice processes and an outer zone affected by intense ice scouring. This morphological boundary could be due to intense erosion by the keels of pressure ice ridges at the inner edge of a zone of grounded ice ridges. Most of the observed ice scours appear to be reworked, especially in water depths of less than 10 m, and represent small-scale sediment sinks. Inshore of the 10 m isobath, scour reworking is believed to be mainly due to frequent bottom disturbance by wave orbital currents and mean near-bottom flows during the open water season. Scour orientations show that the dominant motion of ice during scouring events is east or west, which is subparallel to the bathymetric contours and coastline. Scour terminal push mounds, however, suggest a dominant east to southeast movement that may contribute to onshore sediment transport during ice push events.

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Section: Discussionmentioning

confidence: 99%

Sea ice scouring on the inner shelf of the southeastern Canadian Beaufort Sea

1995

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“…In addition, oceanographic observations of storms indicated that they formed geostrophic flows and that these flows had far too low suspended sediment concentrations (SSCs;50-150 mg/l;Swift 1985, table 3). However, threshold sediment concentration for autosuspension is about 1 g/l (Middleton 1966;Lowe 1982), and a number of studies of modern shorelines indicate that very high SSCs (up to 4 g/l) are produced on shorefaces and inner shelves and lead to powerful seaward-directed sediment-laden flows (Lavelle et al 1978;Wright et al 1986;Madsen et al 1993;Héquette and Hill 1993;Wright et al 1994). Such high concentrations can extend far above the bed; Wright et al (1994) documented a SSC of ϳ 1.4 g/l at 120 cm above the bed at 13 m water depth.…”

Section: Excess-weight Forces and Storm Depositional Modelsmentioning

confidence: 99%

Wave-Modified Turbidites: Combined-Flow Shoreline and Shelf Deposits, Cambrian, Antarctica

Myrow¹,

Fischer²,

Goodge³

2002

Journal of Sedimentary Research

174

118

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Sandstone tempestite beds in the Starshot Formation, central Transantarctic Mountains, were deposited in a range of shoreline to shelf environments. Detailed sedimentological analysis indicates that these beds were largely deposited by wave-modified turbidity currents. These currents are types of combined flows in which storm-generated waves overprint flows driven by excess-weight forces. The interpretation of the tempestites of the Starshot Formation as wave-dominated turbidites rests on multiple criteria. First, the beds are generally well graded and contain Bouma-like sequences. Like many turbidites, the soles display abundant well-developed flutes. They also contain thick divisions of climbing-ripple lamination. The lamination, however, is dominated by convex-up and sigmoidal foresets, which are geometries identical to those produced experimentally in current-dominated combined flows in clear water. Finally, paleocurrent data support a turbidity-current component of flow. Asymmetric folds in abundant convolute bedding reflect liquefaction and gravity-driven movement and hence their orientations indicate the downslope direction at the time of deposition. The vergence direction of these folds parallels paleocurrent readings of flute marks, combined-flow ripples, and a number of other current-generated features in the Starshot event beds, indicating that the flows were driven down slope by gravity. The wave component of flow in these beds is indicated by the presence of small-to largescale hummocky cross-stratification and rare small two-dimensional ripples.Wave-modified turbidity currents differ from deep-sea turbidity currents in that they may not be autosuspending and some proportion of the turbulence that maintains these flows comes from storm waves. Such currents are formed in modern shoreline environments by a combination of storm waves and downwelling sediment-laden currents. They may also be formed as a result of oceanic floods, events in which intense sediment-laden fluvial discharge creates a hyperpycnal flow. Event beds in the Starshot Formation may have formed from such a mechanism. Oceanic floods are formed in rivers of small to medium size in areas of high relief, commonly on active margins. The Starshot Formation and the coeval Douglas Conglomerate are clastic units that formed in response to uplift associated with active tectonism. Sedimentological and stratigraphic data suggest that coarse alluvial fans formed directly adjacent to a marine basin. The geomorphic conditions were therefore likely conducive to rapid fluvial discharge events associated with storms. The abundance of current-dominated combinedflow ripples at the tops of many Starshot beds indicates that excessweight forces were dominant throughout deposition of many of these beds.

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“…During the past decades, several studies have focused on sediment dynamics on arctic shelves (e.g., Harper and Penland, 1982;Hill and Nadeau, 1989;Hill et al, 1991;Hequette and Hill, 1993;Macdonald et al, 1998;Johnson et al, 2000;McClimans et al, 2000;Sternberg et al, 2001) and on the variability of suspended particulate matter (SPM) flux under permanent ice cover (e.g., Hargrave et al, 1994). However, direct current and SPM measurements throughout one seasonal cycle are still rare and insights into the sediment dynamics on arctic shelves are limited, especially for periods of ice coverage (e.g., Macdonald et al, 1998).…”

Section: Introductionmentioning

confidence: 99%