NJG85-4-05
2005
Late Cenozoic evolution of the continental margin of eastern Canada
85
4
pp. 305-318
82-92394-23-0

Almost the entire continental shelf off eastern Canada has been glaciated and its morphology consists of transverse troughs, which are deeper in the north, and intervening banks. Following Miocene prodeltaic muddy sedimentation, with deep bottom current reworking on the continental rise, in many areas submarine canyons, leveed channels and turbidite deposition became prominent in the Early to mid Pliocene. An abrupt change in sedimentation style is marked by the diachronous onset of shelf-crossing glaciation, ranging from Late Pliocene age at Hudson Strait to mid Pleistocene on the Scotian margin.

Pliocene and Early Quaternary progradation was marked by prodeltaic or shelf-edge clinoforms; later Quaternary progradation by stacked till tongues. In the Late Quaternary, plume fallout sediments dominate on the middle and lower continental slope, with mud turbidites on the rise. Major deep-water constructional features include submarine fans, notably off Hudson Strait and the Laurentian Fan, modified by episodic catastrophic release of meltwater that cut submarine valleys. Sediment drifts formed along the Labrador and Grand Banks margins, notably in the Late Miocene and Pliocene. On southern margins, shelf-indenting canyons remained active through interglacials. Turbidites are most common around glacial maxima: some result from direct hyperpycnal flow of meltwater and others from fallout of plume sediments. Sediment failures, such as the 1929 "Grand Banks" failure, also result in turbidity currents. Storm waves can trigger sandy flows in shelf-indenting canyons.

Modern iceberg draft at the Grand Banks is ca. 200 m but was nearly 500 m at times in the Late Pleistocene and as much as 650 m during major icerafting (Heinrich) events. Iceberg scour, together with storm-driven currents, strongly influenc the geology of the upper continental slope. Multiple input points of ice-rafted detritus (IRD) are distinguished at the Last Glacial Maximum. Both IRD and plume sediments of carbonate-dominated rock flour were deposited along the entire eastern Canadian margin from Hudson Strait to off Georges Bank during Heinrich events.

Styles of sediment failure include: simple slump failures; shallow retrogressive slump failures that evolve into debris flows; "stripped off" bedding planes that might result from glides but more likely from evacuation of retrogressive failures; slides with toe compression; and creep deformation that may lead to major valley wall collapses creating enormous debris avalanche deposits on the continental rise. Magnitude-frequency relationships and correlative failures in multiple valley systems suggest that most failures are earthquake triggered, with some seismicity induced by glacio-isostasy.

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