First results on velocity analyses of multichannel seismic data acquired with the icebreaker Araon across the southern Beaufort Sea

• Main Authors: Riedel, Michael, Hong, J. K., Jin, Y. K., Rohr, K. M. M., Cote, M. M.
• Format: Report
• Language: English
• Published: Natural Resources Canada 2016
• Subjects: MacKenzie Trough; Shallow Bay; Beaufort Sea; permafrost
• Online Access: https://oceanrep.geomar.de/id/eprint/34022/; https://oceanrep.geomar.de/id/eprint/34022/1/cr_2016_03_GSC.pdf; https://doi.org/10.4095/298840

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 fluid-expulsion 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.