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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