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Lateral and Proximal to Distal Variations in Salt Tectonic Styles on the Central and Western Scotian Margin, Offshore Nova Scotia, Canada

Deptuck, Mark *1; Kendell, Kris 1
(1) Canada - Nova Scotia Offshore Petroleum Board, Halifax, NS, Canada.

A major Late Triassic to Early Jurassic(?) synrift salt basin underpins much of the Scotian Margin, and formed as Nova Scotia rifted and ultimately broke apart from its Moroccan conjugate. Like other salt basins, the distribution, style and timing of salt-related structures varies widely. Using available 2D/3D seismic data-sets, we contrast two considerably different salt tectonic styles that dominated the western versus the central parts of the margin, and provide a higher order structural subdivision of each. In the west, only a small portion of the primary salt basin is found under the present day continental shelf, where minor amounts of postrift subsidence took place. Most of the salt basin is now located in deepwater after subsiding up to 8 km after continental break-up. Increased subsidence seaward of the margin hinge zone tilted the landward parts of the salt basin, generating a major region of gravity gliding and raft tectonics above the autochthonous salt layer. Though it is possible that some seaward inflation of the primary salt basin took place immediately following break-up, vertical diapirism and sediment downbuilding dominated and our preferred interpretation is that increased rift subsidence allowed more salt to accumulate in the seaward parts of the salt basin prior to continental break-up. Proximal to distal variations in salt tectonic style in the west are believed to be controlled by variations in the amount, rate, and symmetry of postrift basement subsidence, but preconditioned by the synrift basement fabric (including transfer zones) and development of rift-related accommodation that controlled the original thickness and distribution of salt. In contrast, much of the primary salt basin on the central parts of the margin occupied a more landward position below the present day shelf. Increased Jurassic and Cretaceous sedimentation here more efficiently expelled salt up to 60 km seaward of its source layer, emplacing amalgamated salt tongues and canopies, or their equivalent welds, in deepwater settings. Two seaward salt expulsion styles dominate the canopy complex: expulsion rollovers and allochthonous salt based detachments (e.g. roho systems). The relative importance of each can be linked to the density of seaward leaning salt feeders extending from the autochthonous salt layer. In contrast to the west, gravity loading associated with increased sedimentation was a more important process in the central part of the margin.


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California