Relationships Between Sediment Mass-Failure Modes And Magnitudes In The Evolution Of The Scotian Slope, Offshore Nova Scotia

Abstract

Abstract The role of seabed failure in the regional development of continental margins is not well reported in the literature. Recently, large amounts of scientific and industry seismic reflection data have been collected along the Scotian margin, offshore Nova Scotia. The new datasets allow for the regional assessment of the complete range of magnitude and recurrence of seabed failure for this area, from a time dominated by prodeltaic sedimentation to a time dominated by proglacial sedimentation. The results show that large scale seabed failure was uncommon during the early Tertiary, but became widespread after ? 40 Ma. Failure deposits are more abundant on the eastern and western portions of the margin compared tothe central portion. The largest failure deposits observed on the margin occurred during non-glacial periods, whereas the highest recurrence of failure occurred during periods of deglaciation. The modern slope of the seabed, from shelf break to continental rise, appears to be related to seabed failure history, with exponential slope curvature in areas of large-scale or abundant failure and linear slope curvature in areas of small-scale failure. Several glacial and non-glacial related trigger mechanisms are possible, but more research and improved age control is required to identify which were active. Introduction Sediment mass failure processes play a significant role in the construction and destruction of continental slopes, including those along passive margins. However the complete range of spatial and temporal scales associated with various styles of mass-failure within mass transport complexes (MTCs) is poorly documented for even the best studied margins. Extensive modern datasets allow, for the first time, comprehensive regional assessment of the full range of failure events preserved beneath the Scotian Slope. In this paper, we provide a synopsis of the distribution and magnitude of Cenozoic failure and estimate the impact on margin development. The goal is to assess the recurrence intervals of different modes and magnitudes of failure, and contrast the relative significance of sediment mass failure in the evolution of the Scotian Margin from a time when sedimentation was dominated by small deltas and sea level change to a time when sedimentation was dominated by glaciation. Geological Setting The Scotian Slope trends northeast/southwest, parallel to the modern coastline of Nova Scotia, Canada (Figure 1). During the Mesozoic and Cenozoic, it formed the landward margin of the Scotian Basin. The Scotian Basin is part of the Mesozoic rifted margin of the central North Atlantic Ocean. The basin is bound to the southwest by the Yarmouth Arch and to the northeast by the Avalon Uplift and is floored by Triassic salt and redbeds1. Throughout the Jurassic and Cretaceous, thick deposits of clastic, evaporitic and carbonate sediments accumulated on the margin. Through the Tertiary, the Scotian margin accumulated prodeltaic shales and was deeply incised by canyons during sealevel lowstands. Prodeltaic sedimentation continued into the Pliocene, with the onset of terrestrial glaciation resulting in rapid sedimentation seaward of major shelf outlets. The first shelf-crossing glaciation occurred about 0.5 Ma2 and since that time, the continental slope has been dominated by proglacial sediment deposition, with little sediment accumulation at highstands.