Abstract

The Scotian Slope just west of Verrill Canyon was surveyed using the Sea MARC I deep-towed sidescan-sonar system, high-resolution seismic-reflection profiles, and 25 piston cores.

The generally smooth continental slope has a gradient of ∼2.5°. It is crossed by 2 small valleys that are 1 km wide and 100 m deep. Much of the sea bed shows evidence of surficial sliding that removed 10–20 m of sediment, and the slide scars give the sea bed a steplike morphology. From the 600-m isobath to ∼1,800 m, there extend 2 zones of disturbed sediment. These disturbed zones have the rough surface and transparent acoustic character previously regarded as characteristic of debris flows, but sidescan-sonar images and cores suggest that they are principally rotational slide deposits, with true debris flows at their distal limits. Streamlined erosional depressions near the downslope edge of the debris flows cut both the flow and sediment farther down-slope. These may have been produced by a turbidity current associated with the debris flows. Sorted coarse sand in piston cores provides further evidence of current activity. This widespread sediment failure on relatively low slopes was probably the result of a large earthquake that can be dated from cores as occurring between 5000 and 12000 yr B.P.

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