Differential loading induced deformation of a mobile substrate (e.g., salt tectonics) is an important process for the development of accommodation space and stratigraphic architectures in intra-slope minibasins. Numerous studies of minibasin systems have focused on either the tectonic processes involved in salt body deformation or the stratigraphic interpretation of the overburden sediment deposits. This study, however, focuses on coevolution of depositional and tectonic processes and provides a new insight of the linked evolution into the stratigraphic patterns. Using a silicone polymer to simulate a viscous mobile substrate, a series of 2D experiments were conducted to explore the effects of variation in 1) sedimentation rate, 2) depositional style (intermittent sediment supply), and 3) the thickness of the deformable salt substrate on subsidence patterns and minibasin evolution. Experiments results have shown that larger initial thickness of salt substrate as well as lower sedimentation rate caused greater amounts of subsidence for a given amount of deposit. Furthermore, increase in subsidence rate was observed as sedimentation continued, while decrease in subsidence rate occurred once sedimentation ceased. Due to the linked depositional and tectonic processes, higher sediment supply resulted in relatively slower subsidence and more actively widening minibasins. Lower sediment supply was observed to have the reverse effect, resulting in higher relative subsidence and a narrow basin width. A numerical model that captures viscous flow under the deposit is also presented here. The model for minibasin formation showed the effects of interaction of the two processes (deposition and tectonics) on the development of minibasin strata in the experiments. Experimental and modeled findings have resulted in a new model of minibasin development that incorporates the effects of sedimentation rates on subsidence patterns into basin evolution. / text

The Kennetcook-Windsor basin is a part of the large composite Maritimes Basin in Atlantic Canada. Subsurface seismic data indicate a very complex basinal history in terms of syn-depositional deformation and superimposition of numerous episodes of fault reactivation in the basin. Faults mapped and correlated at the tops of basement, the Horton Bluff, and the Cheverie formations can be subdivided into six categories. On the basis of interpretation of seismic reflection geometries and fault modeling, at least six episodes of deformation are suggested in the Kennetcook-Windsor basin. Flower structures mapped in the subsurface clearly indicate a strike-slip setting that remained active during the entire history of the basin. Structural collapse features represented by high angle chaotic seismic reflections within the Windsor Group indicate evaporite withdrawal that played a key role in the creation of accommodation space for the Pennsylvanian sediments in the basin. A Two-way-time (TWT) structure map at the top of basement shows tilted fault-blocks stepping down to north and northeast. The TWT maps at the tops of the Horton Bluff and the Cheverie formations show a structural low in the central area and rising in the northeast, west, and south. However, the structural low on the top of the Cheverie Formation is narrower and indicates that the faults in the northeast were inverted more than those mapped on the top of the Horton Bluff Formation. Comparison of the thickness maps of the Horton Bluff and the Cheverie formations indicate an overall thickening in the north and northeast. Episodic dextral strike-slip movement on the basin-bounding fault (Minas Fault) controlled the basement architecture and the development of the basin. Probably oblique movement (SW-NE) on the local subsurface faults caused compartmentalization of the tilted fault-blocks within the Horton and Windsor groups.

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This dissertation advances our understanding of how turbidity currents interact with three-dimensional (3-D) minibasin topography and the resulting deposits that form. Conceptual Gulf of Mexico-centric models of minibasin fill development have become the foundation for exploring and identifying strategic deep-water hydrocarbon reserves on continental slopes around the world. Despite the abundance of subsurface data, significant questions remain about the 3-D physical processes through which minibasins fill and the relationship between these processes and the topography of the basin. To overcome this problem, I utilize techniques in physical laboratory modeling to query established models of the role that turbidity currents play in minibasin fill development, and observe the relationships between fill from the Lobster minibasin located in a proximal continental slope position in the Gulf of Mexico and from the Safi Haute Mer (SHM) minibasin located in the distal continental slope of offshore western Morocco. First, existing published literature are reviewed and assessed for the known state of minibasin development and fill processes, and the strengths and weaknesses of our current knowledge base. Second, results are presented from two series of experiments that document the interaction between steady, depletive turbidity currents and 3-D minibasin topography. Experimental results suggest that turbidity currents produce deposits that are more likely to drape pre-flow topography than pond within it. Turbidity current velocity data show a strong 3-D physical component in minibasin fill sedimentation that also influences extra-basinal sedimentation patterns. Details of these results provide insight into processes that have not been previously considered in published conceptual models of minibasin fill. Third, a comparison of the two subsurface datasets show that the types and abundance of architectural elements vary depending on the location of the minibasin on the continental slope (i.e. proximal vs. distal), and suggests key differences in the processes responsible for their infilling. Finally, a comparison of experimental results to preserved deposit architectures in the Lobster and SHM datasets suggest a more complex relationship of process-driven sedimentation than that derived primarily from suspension fallout. This improved understanding of minibasin fill is applicable to industry for increasing confidence in subsurface interpretations and reducing risk while exploring for quality reservoirs in deepwater regions. / text

archives@tulane.edu / Minibasins, i.e., small basins that can be up to 8 km in depth and a few tens of km in diameter, often form in regional salt basins and on salt-rich passive margins. As salt walls grow through time, brittle strain localizes in zones directly above the salt walls leading to complex fault arrays surrounding the minibasins. These fault arrays provide insight into the relative movement of minibasins and the local deformation field, which influences the hydrocarbon exploration around them. Using high-resolution bathymetry and 2D reflection seismic data, we have examined fault systems and their interaction with salt walls around the Lyons minibasin in the Gulf of Mexico, offshore USA. This analysis shows that the geometry of salt walls varies and controls the development of faults form in the overlying sedimentary layer. The wide plateau-like salt wall creates a mechanical constraint that restricts the development of faults vertically and laterally. The narrow ridge of the salt wall has less mechanical restriction and allows faults to grow in displacement. Deformation is more localized above the narrow ridge of salt wall. This study suggests that the intricate fault patterns around minibasins result from multi-phase deformation caused by the variation of salt flow within the salt walls. Initially, minibasin subsidence expels salt upward and outward. After the minibasins is welded, the regional slope enhances the lateral flow and allows salt to flow around welded minibasins. During this stage, the lateral flow of salt is constrained by the salt wall orientation. Moreover, this study demonstrates a new approach that provides an additional perspective to understand the evolution of minibasins and their interaction, which is a limitation of 2D modeling studies. / 1 / Thi Quan H. Pham