John Brown

Diapiric structures exposed within the Carboniferous rocks of western Cape Breton Island and on the Antigonish coast of Nova Scotia are unique and among the best exposed salt structures in the world. Complete sections through diapir structural carapaces and their associated drag zones are exposed as coastal cliff sections. The close tie between onshore exposures and near-shore seismic data provides a unique data set with which to examine halokinesis and salt tectonics at a scale over several orders of magnitude. The size, maturity, geometry and growth mechanism of the diapiric structures is directly related to the tectonics and sedimentary evolution of the field area which shows a division into three tectono-stratigraphic domains. Drag zone and the larger zone of rotation profiles are intimately related to the geometry of the diapir and the lithology of the strata adjacent to the diapir. Deformation within the drag zones was an interplay of brittle and plastic deformation mechanisms. Brittle faults exist as distinct generations that evolved in a systematic manner as the drag zone formed. Strain within the drag zones was biaxial, with extension parallel to the diapir margin being of similar magnitude to extension orthogonal to the diapir margin. Faults that developed late in the deformation history represent a localisation of extensional flexural slip. The distribution of competent and incompetent strata within a drag zone played a large role in determining the distribution of strain and deformation mechanisms within a drag zone. Deformation within the structural carapace mirrors the deformation within the underlying halite core of the diapir and reflects the maturity and geometry of the diapiric structure as a whole. The structural carapaces include curtain folds, which are bounded by curtain faults. Internal deformation was accommodated by a combination of brittle and ductile mechanisms and deformation was inherently triaxial. Halokinesis locally affected sedimentation by creating local sediment barriers source areas and depocentres in the form of diapiric exposures and withdrawal basins. This is indicated by local unconformities seen in outcrop and seismic profiles; conglomerates adjacent to some diapirs; progradational seismic facies adjacent to diapirs; and unusually variable paleoflow patterns. However, tectonic and eustatic events must be taken into account before the effects of halokinesis can be determined.

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Supervisor:Martin Gibling