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AAPG Bulletin

Abstract

AAPG Bulletin, V. 88, No. 7 (July 2004), P. 991-1006.

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

Early Cretaceous sediment failure in the southwestern Sable Subbasin, offshore Nova Scotia

David J. W. Piper, Georgia Pe-Piper, Stephen C. Ingram

1 Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia, Canada, B2Y 4A2; email: [email protected]
2Department of Geology, Saint Mary's University, Halifax, Nova Scotia, Canada, B3H 3C3; email: [email protected]
3Department of Geology, Saint Mary's University, Halifax, Nova Scotia, Canada, B3H 3C3; present address: ChevronTexaco Canada, 500 Fifth Ave SW, Calgary, Alberta, Canada, T2P O7L; email: [email protected]

AUTHORS

David J. W. Piper obtained his B.Sc. degree and his Ph.D. from the University of Cambridge, United Kingdom. After a decade of teaching at Dalhousie University, he joined the Geological Survey of Canada as a marine geologist, presently working on deep-water geohazards offshore southeast Canada. He has a long-standing interest in the application of insights from the marine realm to ancient sedimentary successions.

Georgia Pe-Piper graduated from the University of Athens, Greece, and gained her Ph.D. in volcanic geochemistry from the University of Cambridge, United Kingdom. She is best known for work on igneous rocks, but for many years, her teaching responsibilities included petroleum geology. Her current interests include the application of mineralogical studies to the provenance and diagenesis of sedimentary systems.

Steve Ingram graduated with an honors B.Sc. with the Co-operative Education option degree in geology in 2002 from Saint Mary's University, Nova Scotia. His thesis was on the Alma and Glenelg fields. Since then, he has been working as a geoscientist for ChevronTexaco in Canadian Frontier Exploration. Areas of interest include offshore Newfoundland, Nova Scotia, and the Beaufort Sea/Mackenzie delta region.

ACKNOWLEDGMENTS

The seismic profile in Figure 2 is used courtesy of the ex-Parex group. We thank Andrew MacRae for introducing us to the lithofacies of the Glenelg and Alma fields and sharing with us his detailed knowledge of the Glenelg field. We also thank the staff of the Canada-Nova Scotia Offshore Petroleum Board core repository for assistance. This work was supported principally by a Natural Sciences and Engineering Research Council (NSERC) Discovery Grant to G. Pe-Piper, but our work on Cretaceous sedimentary rocks is also supported by ExxonMobil and partners in the Sable project, Petroleum Research-Atlantic Canada, and an NSERC Collaborative RampD grant. D.J.W. Piper's work on modern slides is supported by the Canada Program of Energy RampD. Geological Survey of Canada contribution 2003175. Reviews by Andrew MacRae, John Shimeld, Ken Skene, Roger Slatt, Ernest Mancini, and John Lorenz led to substantial improvements in the manuscript.

ABSTRACT

Conventional cores from Lower Cretaceous outer-shelf and upper-slope prodelta facies in the Alma and Glenelg fields of the Scotian Basin show a wide range of synsedimentary deformation. Storm-dominated prodelta sandstone and mudstone beds have common load casts and structureless sandstone beds overlain by deformed sediment and sandstone dykes that are caused by storm- or earthquake-induced local liquefaction. Blocks of sediment 5–15 m (15–50 ft) thick, principally on the outer shelf, have foliated mudstone at their base, common internal shear zones in mudstone, shear deformation of sandstone, and are capped by intraclast conglomerates that are interpreted as debris-flow deposits. These are all features observed in shallow slides on the modern Mississippi prodelta. At the paleoshelf edge and upper slope, larger slide blocks are recognized with zones of intense internal deformation and high-angle thrusts near their base. The lack of a basal foliated mudstone may be the result of more rapid slide motion than on the shelf, resulting in hydroplaning. In addition, there is early postdepositional interstratal deformation as a result of loading by sandy delta distributaries and by slide blocks on the upper slope. The scale of many deformation structures is below the limits of three-dimensional seismic vertical resolution, yet they are likely to substantially influence reservoir properties.

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