Abstract:One thousand two hundred twenty kilometres of multichannel seismic data were acquired in the Beaufort Sea in 2013 and 2014 to interpret shallow sedimentary structures associated with the upper Cenozoic Iperk and Shallow Bay depositional sequences. Seismic velocity analyses suggest a remarkably consistent regional velocity-depth trend on the slope within the upper 4 s two-way traveltime. A separate velocity trend was not defined beneath the shelf in this region, where data are influenced by the occurrence of permafrost. Deviations from this trend were noted at unconformities including an upper erosional unconformity.The seismic data in the Mackenzie Trough region suggest a different velocity-depth trend within the upper section and the region is marked by a large erosional unconformity, likely the base of the Shallow Bay sequence. Velocity analyses suggest the removal of up to 425 m of overburden; however, this is an overestimate of erosion as differential compaction from the glacial history has not yet been taken into account. In deeper water (>750 m) a bottom-simulating reflector is present, characterized by the occurrence of free gas and a low-velocity zone.Analyses of three fluid-expulsion features on the slope indicate that the Pokak fluid-expulsion feature and the Triple-Mound fluid-expulsion feature are linked to underlying anticline structures. A flat-topped fluidexpulsion feature at the flank of an equivalent anticline was also examined, but the occurrence of shallow gas creates a blank zone beneath this structure. Pronounced changes in the velocity-depth function at these fluid-expulsion features are linked to occurrence of free gas, and/or fluidized mud extrusions. Résumé :En 2013 et 2014, des données sismiques multicanal ont été acquises sur 1220 km dans la mer de Beaufort afin d'interpréter les structures sédimentaires à faible profondeur associées aux séquences sédimentaires d'Iperk et de Shallow Bay du Cénozoïque supérieur. Des analyses de la vitesse sismique indiquent une tendance vitesse-profondeur remarquablement constante à l'échelle régionale sous le talus pour les quatre premières secondes de temps de trajet double. Dans cette région, nous n'avons pas défini une tendance vitesse-profondeur distincte pour le secteur sous-jacent à la plate-forme continentale, un endroit où les données sont influencées par la présence de pergélisol. Des écarts par rapport à la tendance ont été relevés au niveau de discordances, notamment d'une discordance d'érosion supérieure.Dans la région de la cuvette de Mackenzie, les données sismiques révèlent une tendance vitesseprofondeur différente dans la partie supérieure de la coupe et la région est marquée par la présence d'une importante discordance d'érosion, qui correspond vraisemblablement à la base de la séquence de Shallow Bay. Les analyses de la vitesse laissent croire à la suppression de terrains de couverture sur une épaisseur pouvant atteindre 425 m. Cependant, il s'agit là d'une surestimation de l'importance de l'érosion, étant donné que la compac...
Expedition ARA04C (conducted from September 10 -September 26, 2013 in Canadian waters) on the Korean icebreaker IBRV Araon was laid out to investigate the Beaufort Sea shelf and slope region and collect geo-scientific data for various aspects relevant to the GSC's mandated regional geo-hazard assessment of the offshore Beaufort region. A critical element of the geohazards is the distribution of permafrost across the submerged shelf. To address this question and to verify data from earlier attempts made by the GSC in the mid 1980ies, a set of multichannel seismic (MCS) lines were collected across and along the shelf edge. Refracted arrivals were picked on all MCS lines acquired and velocities for the first and where occurring, second and even third refractions were determined. The depth to the first refractor was determined using simple ray-path geometry for a refracted, planar 2 layer case, with a fixed velocity of the upper layer (ocean water) of 1450 m/s determined from measurements of physical properties in the water column using a standard Conductivity-Temperature-Depth (CTD) tool. Using this velocity value creates a fully flat direct arrival when the shot-gather is reduced by this velocity value, confirming that this value is appropriate. Depths to 2 nd or 3 rd refractor where not determined in this study. Arrivals from deeper refractions are often masked by the occurrence of refractions generated by multiples and from strong linear noise occurring along the streamer. The results from the refraction velocity analysis allow verification of major boundaries of permafrost or icebearing sediment occurrences from previous work, but also define several critical corrections, especially near the shelf edge zone. Correlation of the MCS refraction data and the coincident 3.5 kHz sub-bottom profiler data reveal that a regional unconformity (~5 to ~15 meter below seafloor) often is the source of the first detectable refraction instead of the seafloor.2 IntroductionA two-ship scientific research expedition in the southern Beaufort Sea was carried out between September 10 to October 10, 2013, using the research icebreaker Araon operated by the Korea Polar Research Institute (KOPRI) and the Canadian Coast Guard Ship (CCGS) Sir WilfridLaurier. The multidisciplinary science program included geological, geophysical, and oceanographic investigations of the continental shelf and slope. The research conducted will help improve the understanding of geohazards in this setting by assessing the regional geology, the stability of decomposing offshore permafrost and gas hydrates, mechanisms for surficial gas/fluid migration, and active geologic processes. Priorities for the Araon Expedition ARA04C (see Figure 1 for a complete ship track) included a multi-channel seismic (MCS) survey and detailed bathymetric mapping with high-resolution sub-bottom profiling with the goal to collect site-survey data supporting the Integrated Ocean Drilling Program (IODP) pre-proposals 806 (Dallimore et al., 2012) and 753 (O'Regan, et al. 2010)....
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