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Abstract

AAPG Bulletin, V. 88, No. 6 (June 2004), P. 703-723.

Copyright copy2004. The American Association of Petroleum Geologists. All rights reserved.

Near-surface geology and sediment-failure geohazards of the central Scotian Slope

David C. Mosher,1 David J. W. Piper,2 D. Calvin Campbell,2 Kimberley A. Jenner2

1Geological Survey of Canada-Atlantic, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada B2Y 4A2; [email protected]
2Geological Survey of Canada-Atlantic, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada B2Y 4A2

AUTHORS

David Mosher is a marine research geophysicist with the Geological Survey of Canada. He graduated with a Ph.D. from Dalhousie University in 1993. His research interests include marine geohazard investigations, with particular emphasis on neotectonics and slope stability. He has worked on Canada's east and west coasts, the Arctic, and the equatorial Atlantic and Pacific. He was recently co-chief scientist on Ocean Drilling Program (ODP) Leg 207.

David Piper is a marine research geologist with the Geological Survey of Canada. He completed his Ph.D. in sedimentary geology at Cambridge University in 1969. He has a long-standing interest in continental margin stratigraphy and sedimentation and is presently assigned to work on geohazards on the eastern Canadian margin. He has been senior scientist on more than 30 research cruises, including ODP Leg 155.

Calvin Campbell is a marine geoscientist with the Geological Survey of Canada, specializing in geohazard evaluation, digital geological interpretation, and geographic information systems, with a particular emphasis on deep-water environments. He graduated in 1999 with a B.Sc. degree in geology and environmental studies from St. Mary's University and conducted an honors thesis under the guidance of David Piper on Holocene storm signature in marine sediment cores.

Kimberley A. Jenner was employed as a sedimentologist with Gulf Canada Resources Incorporated from 1982 to 1986 before graduating with an M.Sc. degree from Dalhousie University in marine sedimentology in 1989. Kimberley has worked as a sedimentologist with Natural Resources Canada since 1990. Her research interests include arctic deltas, arctic gas hydrate host strata, and shallow mass-transport deposits in deep-water canyons.

ACKNOWLEDGMENTS

R. Pickrill was instrumental in facilitating the multibeam program, and CampC Technologies Ltd. acquired much of the multibeam data used in this investigation. The authors express their gratitude to the officers, crew, and scientific staff of the CCGS Hudson, Alert, and Anne S. Pierce for their efforts in the field, particularly during cruises 1999-036, 2000Alert, 2000Anne S. Pierce, 2000-036, 2000-042, and 2001-048A. The Geological Survey of Canada and the Canadian Program for Energy Research and Development funded this research. Partial funding and permission to illustrate the multibeam data were provided by CampC Technologies Ltd., Marathon Oil Co., EnCana Energy Corp., Norsk Hydro, Murphy Oil Co. Ltd., ChevronTexaco Canada Resources, and Clearwater Fine Foods Ltd. We thank the ex-Parex Group for providing the seismic data shown in Figure 14. The authors thank O. Langva, S. Migeon, B. Parsons, and W. Sager for their critical reviews and constructive comments. Geological Survey of Canada contribution no. 2003054.

ABSTRACT

The central Scotian Slope demonstrates a complex seafloor morphology superimposed on a regional gradient of 2ndash4deg across the margin. The west-central Scotian Slope is characterized by a relatively smooth seafloor, but with numerous 10ndash80-m (33ndash260-ft)-high escarpments representing slide failure scars. In the east, the seafloor is highly dissected by canyons. Throughout the region are scars and deposits of sediment mass failures, including retrogressive headwalls, rotational slumps, slides, creep, debris-flow deposits, and turbidites.

The complexity of failure styles and triggering mechanisms identified underscores the need for comprehensive site assessments for situating seabed facilities. Critical factors that need to be taken into account include local terrain analysis and shallow subbottom stratigraphy. Slope-stability analysis has shown the surface sediment to be statically stable, except on steep escarpments and canyon walls. There is evidence, however, of sediment failures that approximately correlate to glacial advances (25ndash12, sim75, and sim130 ka), providing some clue as to potential triggering mechanisms. Sparse, passive-margin, tectonic earthquakes, however, are the likely cause for large-scale, regionally correlated failures and failure escarpments.

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