Cody MacDonald

B.Sc., Honours Earth Sciences, Dalhousie University (2008)

M. Sc. Thesis

Salt Tectonics of the Western Sable Sub-Basin: Insights from Regional Seismic Interpretation and 4D Scaled Physical Experiments

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Salt tectonics strongly influenced the post-rift evolution of the western Sable sub-basin at the north-central Scotian margin. Understanding the interplay between structures and reservoir distribution is crucial for success in further exploration programs. Primary factors controlling salt tectonics in this area include: the rift basin geometry, salt thickness and varying sediment input and delta progradation during the Mid Jurassic to Late Cretaceous. Understanding the role of these primary factors on salt tectonics and regional depocenters is critical for unraveling the complex tectono-stratigraphic framework of the Scotian basin.

This study integrates interpretation of basin-scale 2D seismic reflection profiles of the Ion GX Technologies NovaSPAN data set, public domain seismic and well data with innovative 4D scaled physical experiments, to gain insight into the mechanics of thin-skinned salt tectonics and basin evolution of the western Sable sub-basin. Interpretation of seismic reflection data reveals that the original salt basin at the western Sable sub-basin was characterized by the small proximal Abenaki graben that is separated from the wide Sable sub-basin by the North Sable High. The Sable sub-basin floor is characterized by several asymmetric rift grabens that are infilled by syn-rift sediments. The basin floor of the Sable sub-basin climbs toward the transition to salt basin terminus via two distal ramp segments. Salt structures in the Abenaki sub-basin are shutdown reactive diapirs and basinward dipping growth faults. The Sable sub-basin is characterized by major salt with drawal basins and passive diapirs that appear to be positioned at changes in basin floor morphology. Key features of the Sable sub-basin are two allochthonous salt canopy systems that are present in the Sable sub-basin and developed during transgression events: 1) the Balvenie Roho System that is positioned beneath the modern-day slope and developed in the Early Cretaceous, and 2) an extensive allochthonous salt tongue canopy system that spread during the Late Cretacous.

4D scaled physical experiments demonstrate that downdip variations in salt structures from shelf to deepwater can be grouped into three kinematic domains: (1) Salt Weld and Reactive Diapir, (2) Expulsion Rollover/Passive Diapir and Early Cretaceous Canopy, and (3) Passive Diapir and Late Cretaceous Canopy domains. Unlike the sequential seaward propagation of depocenters in the northern regions of the margin (e.g. the Laurentian sub-basin), all salt withdrawal basins developed at nearly the same time and the Early Cretaceous was the most active period for salt tectonics deformation in the western Sable sub-basin. Depocenter evolution was controlled by: 1) more regional deposition of deltaic and pro-deltaic sediments and 2) early post-rift, regional but low relief inflated salt complexes that did not hinder seaward transport of sediments. In a kinematic model of diaper and canopy evolution, early-inflated salt complexes in the downdip contractional domain focus at changes in the basin-floor and original salt thickness. These inflated salt complexes later evolved into passive diapirs and the extensive canopy systems during subsequent sediment progradation.

The derived kinematic concepts of salt tectonics and basin evolution for the first time explain the structural and related depocenter evolution in a regional framework, from the early post-rift stage to the modern margin. The evolution of early salt withdrawal basins and late canopy system evolution provide new ideas about reservoir distribution and trap formation in the slope and deepwater Sable basin.

Pages: 259
Supervisors: J. Adam, Mladen Nedimović