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TitleHow turbidity current frequency and character varies down a fjord-delta system: Combining direct monitoring, deposits and seismic data
AuthorStacey, C DORCID logo; Hill, P RORCID logo; Talling, P J; Enkin, R JORCID logo; Hughes Clarke, J; Lintern, D GORCID logo
SourceSedimentology vol. 66, issue 1, 2018 p. 1-31, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20170026
Mediapaper; on-line; digital
File formatpdf; html
ProvinceBritish Columbia
AreaHowe Sound; Squamish River; Squamish Delta; Britannia Creek
Lat/Long WENS-123.2333 -123.1333 49.7167 49.5500
Subjectssedimentology; surficial geology/geomorphology; marine geology; geophysics; geochemistry; geochronology; stratigraphy; sedimentary environment; marine environments; depositional environment; submarine features; fiords; deltas; turbidity currents; landslides; tsunami; earthquakes; channels; geophysical interpretations; seismic interpretations; seismic data; seismic surveys, marine; seismic reflection surveys; marine sediment cores; marine sediments; deltaic sediments; sands; landslide deposits; sediment distribution; sediment dispersal; sediment transport; bedforms; flow regimes; bathymetry; mining; mine waste products; tailings disposal; seafloor topography; slope development; radiometric dating; radiocarbon dating; isotopic studies; radioisotopes; lead; lithofacies; stratigraphic analyses; stratigraphic correlations; x-ray fluorescence analyses; sedimentation rates; Britannia Fan; monitoring; alluvial sediments
Illustrationstables; location maps; geoscientific sketch maps; bathymetric profiles; photographs; lithologic logs; correlation sections; seismic profiles; profiles; schematic representations; charts; graphs
ProgramMarine Geohazards Mapping & Monitoring (MGMM)
Released2018 05 07
AbstractSubmarine turbidity currents are one of the most important processes for moving sediment across our planet; they are hazardous to offshore infrastructure, deposit petroleum reservoirs worldwide, and may record tsunamigenic landslides. However, there are few studies that have monitored these submarine flows in action, and even fewer studies that have combined direct monitoring with longer-term records from core and seismic data of deposits. This article provides one of the most complete studies yet of a turbidity current system. The aim here is to understand what controls changes in flow frequency and character along the turbidite system. The study area is a 12 km long delta-fed fjord (Howe Sound) in British Columbia, Canada. Over 100 often powerful (up to 2 to 3 m/sec) events occur each year in the highly-active proximal channels, which extend for 1 to 2 km from the delta lip. About half of these events reach the lobes at the channel mouths. However, flow frequency decreases rapidly once these initially sand-rich flows become unconfined, and only one to five flows run out across the mid-slope each year. Many of these sand-rich, channelized, delta-sourced flows therefore dissipated over a few hundred metres, once unconfined, rather than eroding and igniting. Upflow migrating bedforms indicate that supercritical flow dominated in the proximal channels and lobes, and also across the unconfined mid-slope. These supercritical flows deposited thick sand beds in proximal channels and lobes, but thinner and finer beds on the unconfined mid-slope. The distal flat basin records far larger volume and more hazardous events that have a recurrence interval of ca 100 years. This study shows how sand-rich delta-fed flows dissipate rapidly once they become unconfined, that supercritical flows dominate in both confined and unconfined settings, and how a second type of more hazardous, and much less frequent event is linked to a different scale of margin failure.
Summary(Plain Language Summary, not published)
Turbidity currents are dense underwater flows consisting of suspended sediment that travel down slope for great distances and can be very powerful and destructive. They occur at deltas of large rivers where high sedimentation rates occur and are often associated with large landslides. Because large earthquakes may trigger landslides, deposits from these flows are sometimes used to infer a history of seismic activity. Thick sand deposits from these flows have produced important oil and gas reservoir rock globally. Turbidity currents are very difficult to monitor as they are not always predictable and they tend to damage the monitoring instruments. Most of what is known about these events comes from ancient deposits but most records are incomplete. The Squamish Delta is a rare example where daily turbidity currents occur and were instrumented and monitored over a summer melt period. These live observations are linked to recent deposits in the basin and a longer term history was revealed.

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