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TitleSlope instability on a shallow contourite-dominated continental margin, southeastern Grand Banks, eastern Canada
AuthorRashid, H; MacKillop, K; Sherwin, J; Piper, D J W; Marche, B; Vermooten, M; Oxford, B
SourceMarine Geology .,
Alt SeriesEarth Sciences Sector, Contribution Series 20160106
ProvinceNewfoundland and Labrador
NTS1; 2; 10N; 10O; 11B; 11G; 11I; 11J; 11O; 11P; 12A; 12B; 12G; 12H
AreaGrand Banks
Lat/Long WENS -60.0000 -45.0000 50.0000 40.0000
Subjectssedimentology; marine geology; glacial deposits; glacial features; debris flow deposits; debris flows; slope stability; slope failures; submarine transport; continental slope; seismic profiles; piston cores
Illustrationslocation maps; bathymetric profiles; seismic profiles; tables; formulae; drillhole logs; graphs; core logs
ProgramMarine Geohazards, Public Safety Geoscience
AbstractSubmarine sediment failures and related mass-transport deposits (MTDs) are widespread on the eastern Canadian continental slope settings and in general, have been related to ice sheets crossing the outer shelf and upper slope. The southeastern Grand Banks margin was not glaciated in the last 105 years and has a deep shelf break. As a result, the upper continental slope consists principally of sediment transported from the north by the Labrador Current. High-resolution seismic profiles and 10-m long piston cores show widespread sediment failure and mass-transport deposits in a plastered contourite drift from 500¿1,000 m water depth. This study documents the stratigraphy of the past 48,000 years and the record of sediment failure events. Heinrich layers H1 to H5 have been recognized from distinctive petrology, physical properties, and bulk geochemistry and are constrained by numerous 14C-AMS dates. The geotechnical analysis shows that the latest Quaternary sediment section is mildly underconsolidated, perhaps related to high sedimentation rates (up to 0.5 m/ka) enhanced by some leakage of deep fluids. Nevertheless, factor of safety calculations using Su/P0 and friction angles from triaxial testing suggest the slope is statically stable up to gradients of 9°. Atterberg limit measurements of silty contourite sediments indicate susceptibility to liquefaction under cyclic loading. Regionally, there is evidence that synchronous failure occurs over many tens of kilometres of the slope, probably as a result of rare passive margin earthquakes. These shallow water contourite deposits have a higher sand and coarse silt content, much less biogenic material, and more rapid variations in sediment and geotechnical properties than those of the deep-water equivalents, all of which make them more susceptible to sediment failure.
Summary(Plain Language Summary, not published)
Describes submarine landslides that occurred around 20 000 and 40 000 years ago on the SE Grand Banks slope, an area of active petroleum exploration.