TERTIARY-AGED MEGASLUMPS UNDER THE SCOTIAN SLOPE, SOUTH OF THE LAHAVE PLATFORM, OFFSHORE NOVA SCOTIA

A surge of hydrocarbon exploration activity over the past five years has led to the acquisiton of about 60000 km of high-quality multichannel seismic data with an average line spacing of 4 to 8 km over the continental slope offshore of Nova Scotia. The data allow, for the first time, systematic regional examination of anomalously large, sediment mass-failures along the ancient margin.

Of the mass-failures that have been identified, the most spectacular are three megaslumps of differing ages within the Tertiary section of the upper slope region, south of the LaHave Platform. All three are of roughly equivalent dimensions. The youngest, and best imaged, involves an average sediment thickness of about 600 m over a 26 by 12 km elliptical area of 230 square km, oriented parallel to the paleo-shelf edge. The megaslump volume is roughly 140 cubic km. An extensive debrite extends beyond the edge of the data, 120 km downslope of the compressional megaslump toe. Although its full extent is not yet ascertained, it covers an area of at least 9000 square km. Likely processes that may have contributed to the mass-failure of this portion of the Scotian slope include seismicity, excess pore pressure, salt tectonics, and a reduction of confining stress due to creep of downslope blocks.

Extensive, high quality, regional multichannel seismic surveys acquired over continental slopes are generally not yet available for academic research. Consequently, the occurence of ancient megaslumps along passive margins is undoubtedly under-reported in the literature. From the current study, it is evident that anomalously large mass wasting processes exerted significant control over the evolution of depositional systems along portions of the Scotian margin.