A chronology of post-glacial mass-transport deposits on the Canadian Beaufort Slope

Abstract

Extent and chronology of 24 buried and seabed-exposed mass transport deposits (MTDs) on the continental slope of the Canadian Beaufort Sea were compiled towards a regional geo-hazard assessment of the Beaufort region. A total of 2220 lines of 3.5 kHz sub-bottom profiler (SBP) data (~40,000-line kilometres) covering an area of 9740 km2 were analyzed to allow a new understanding of slope instability in the region. Several sediment cores acquired across the region allow dating of the sediment cover. A regionally representative seismic-stratigraphy (type section, ca. 60 m thick) of the stratified sediments mantling the slope was defined. The MTDs all occur above a marked change in sedimentation style from a deeper-situated slope fan that varies substantially laterally to the above-lying stratified layers that host the MTDs. The type section comprises three sedimentary units bound by two prominent markers. Relative ages for the MTDs were defined by measuring the thickness of sediments overlying each MTD and linking that sediment package to the type section. Two 3-D seismic data volumes across the study region verified interpretations from 2D data by imaging internal deposit character and down-slope continuity of the MTDs. Seismic amplitude and similarity attributes enabled identification of further MTD events, incompletely imaged by the SBP data. A composite chronostratigraphy based on 14C dating of foraminifera and shells was assembled despite the fact that the type section is far thicker than sediment coring limits. Sub-unit thickness varies up- and down-slope such that a selection of cores across the study region enabled its compilation. The marked change in sedimentation style at the base of the type section required substantial extrapolation to date. Simple (quadratic function) age models project that the base of the type section signals the end of the last glacial maximum (Wisconsinan, or marine isotope stage 2 glaciation) and initiation of pro-glacial plume sedimentation (the deglacial), and finally post-glacial (marine) ultimately from the Mackenzie River. The MTD abundance above this contact defines an average theoretical recurrence rate of one MTD per ~1000 yrs.; however, MTDs are clustered temporally with the highest number of events occurring just prior to the onset of the Younger Dryas at around 13 ka BP (cal.).