Rifting, salt tectonics, and oblique shortening: insights from seismic-reflection data and scaled experimental models
Creators: name: Hanafi, Bari Rozak
Publisher: name: No Publisher Supplied
Year: 2022

description: This study investigates structures associated with extensional deformation, gravitational loading of interbedded salt, and oblique shortening along a preexisting fault zone. Using well data and high-quality seismic-reflection profiles, I have examined the diverse structures and established the tectonostratigraphy of the salt-rich eastern Orpheus rift basin of offshore southeastern Canada. This basin is part of the eastern North American (ENAM) rift system that formed during the Late Triassic to Early Jurassic. In my study area, igneous sheets associated with the latest Triassic-earliest Jurassic Central Atlantic Magmatic Province (CAMP) intruded the synrift salt of the Argo Formation, indicating that the synrift salt in the eastern Orpheus rift basin accumulated mostly in the Late Triassic. My work also reveals a complex interplay between rifting, synrift salt and clastic deposition, and salt flow during and after rifting. In this basin, the border-fault system affected synrift deposition by providing pathways for clastic sediment input into the salt-rich rift basin. As a result, two distinct salt facies developed: the shale-rich and shale-poor salt facies that accumulated near the northern border-fault system and within the basin center, respectively. Subsequent minibasin formation near the northern border-fault system caused the underlying salt to move distally (i.e., toward the south). In response, detachment folds and thrust faults developed in regions with interbedded salt, whereas salt walls and columns developed in regions with more massive salt.Also, I have used scaled experimental (analog) models to investigate how interbedded salt deforms during gravitational loading. My models suggest that the presence of brittle/ductile layers within viscous materials facilitates the development of boudins and detachment folds during differential loading. The number and geometries of the structures depend on the following factors: 1) the thickness and distribution of the interbedded brittle/ductile layers relative to the viscous layers, 2) the rate of deposition of the overburden, and 3) the behavior of the internal layers. The development of tight and overturned folds increases with decreasing thickness of the internal layers, increasing distance of the internal layers from the surface and base of the models, increasing rate of deposition, and decreasing ductility of the internal layers. Unlike typical detachment folds, however, many folds in my models are highly asymmetric and show dramatic thickness changes of the fold limbs. Although this study requires future work to determine the kinematic development of these folds, key processes during detachment folding in my models likely include variation in viscous flow throughout the model, layer-parallel shearing, gravity-induced subsidence, and contact behavior between modeling materials.My other experimental modeling study shows how a preexisting fault zone influences the development of a shear zone during oblique shortening. Structures formed within the shear zone include a broad anticline and numerous oblique-slip faults with large right-lateral strike-slip components. The fault geometries vary considerably with depth and along strike, ranging from gentle listric to steep planar oblique-slip faults. Fault orientations also change systematically with depth. The strike of the shallow faults is parallel to subparallel to the displacement direction of the moving plate, whereas the strike of the deep faults is parallel to subparallel to the basal discontinuity.