麻豆传媒

A detailed bathymetric, seismic and sidescan survey in a small intercanyon area of the Nova Scotian continental slope reveals a complex surficial morphology. On the upper slope, large scale slumping has left a steep 150 m escarpment, below which a chaotic mass of slumped debris has accumulated. Large coherent blocks of sediment up to 50m thick lie within the debris resulting in the characteristically irregular relief of the upper slope. In the mid-slope area, the relief is less; mass-movements on the scale of tens of metres control the morphology, resulting in a disjunct system of hummocks and depressions. An erosive channel some 50 m deep and 1 km wide traverses the upper and middle slopes, rapidly decreasing in depth and width below 800 m water depth, where it crosses a broad depositional lobe. The lobe is similar in profile and dimensions to the suprafan of a small submarine fan and is thought to have been deposited during an early stage in the channel development. A small part of the study area shows a very smooth morphology and has been largely unaffected by destructional processes.

Detailed textural analysis indicates that surficial sand at the shelfbreak and on the upper slope is in equilibrium with the modern current regime. Active sediment transport of sand in suspension is dominantly alongslope with a small, but important downslope component. Finer sediment remains in suspension for longer periods and is finally deposited in quieter downslope environments.

Gravity and piston cores indicate that this sedimentation pattern has remained essentially similar during the last 18,000 years. As a result, the post-glacial stratigraphic sequence is very uniform over much of the Nova Scotian slope. Sedimentation patterns in the late Wisconsinan were, in contrast, very complex and were largely related to the meso-scale morphology of the area. Gravity-driven processes of slumping, debris flow and turbidity flow were important and resulted in a greater variety of sediment facies.

Distinct facies associations are defined for the upper slope, middle slope and channel margin / depositional lobe environments. Mid-slope hummocks and depressions also show distinguishable facies associations which are thought to reflect the differential fill of the depressions by morphologically diverted turbidity currents. These facies associations are probably applicable to other destructional slopes. The area lay close to the late Wisconsinan ice margin; it is not clear whether this ice margin had any significant effect on the types of facies developed.

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Supervisor:聽 D. J. W. Piper