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Sonar images of the path of recent failure events on the continental margin off Nice, France

By
Alberto Malinverno
Alberto Malinverno
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William B. F. Ryan
William B. F. Ryan
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Gerard Auffret
Gerard Auffret
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Guy Pautot
Guy Pautot
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Published:
January 01, 1988

When examined in plan view with side-looking sonar, the path of recent sub-sea failure events on the continental margin off Nice displays morphologic features indicative of the passage of sediment flows that interacted with the sea-bed substrate. The path begins as chutes incised on a steep prodelta slope. These chutes feed into the floor of a submarine canyon, which is covered with trains of bedforms oriented at right angles to the flow direction. The bedforms have wavelengths between 35 and 100 m and heights estimated at less than 5 m. The waves are made of coarse material ranging from sand to boulders. Giant bedforms of similar character and scale in the Channeled Scabland (eastern Washington) were produced by a sudden catastrophic flood. Near the base of the slope, where the canyon floor widens and the thalweg gradient decreases, the path becomes a scoured surface with depressions up to 70 m deep produced by the erosion of bedded sediments. As the bottom slope decreases, the width of the area scoured and the cross section of the flows increase. Along the 80 km of the path that was imaged, which was entirely upslope from the location where submarine cables were disrupted by a failure event in 1979, there is little sign of deposition, but extensive evidence of substrate reworking. Our plan-view study of a present-day surface and its bedforms offers an instantaneous picture of an unconformity in development that contrasts with the classical study of similar unconformities in cross section where the emphasis is placed on the time dimension.

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Contents

GSA Special Papers

Sedimentologic Consequences of Convulsive Geologic Events

H. Edward Clifton
H. Edward Clifton
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Geological Society of America
Volume
229
ISBN print:
9780813722290
Publication date:
January 01, 1988

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