title: An integrative geological characterization of the Lower Triassic Montney and Sulphur Mountain formations: implications for sediment routing, depositional architecture, and reservoir heterogeneity in siltstone deposits
Creators: name: Fraino, Patricia Elena
Publisher: name: Science
Year: 2025
Subjects: subject: Sedimentoly
subject: Education--Sciences
subject: Geology
subject: FOS: Earth and related environmental sciences

description: This dissertation focuses on the Lower Triassic Sulphur Mountain and Montney formations in the Western Canada Sedimentary Basin, integrating sedimentological, compositional, and geomechanical analyses at multiple scales to: (i) challenge traditional views of mudstone as homogeneous deposits and (ii) elucidate their complexity. Outcrop investigation of shallow-water clinothems in the Sulphur Mountain Formation illustrate how changes in accommodation-to-sediment supply ratios (δA/δS) influence clinoform geometry, stacking patterns, and sedimentary processes. Analysis reveals two clinothem types, which are organized into three distinct clinothem sets with contrasting stacking patterns, illustrating that the evolution of fine-grained systems is sensitive to change in the δA/δS ratio and its collective effects on stratigraphic architecture. Furthermore, based on extensive compiled paleocurrent data, sediment dispersal mechanisms within these clinothems are demonstrated to result from the interplay of fair-weather waves, episodic storm-induced and gravity-driven processes, and parallel-to-shoreline semi-permanent oceanographic shelf currents. These sediment transport mechanisms, resulted in variable sediment dispersal trends, emphasizing the three-dimensional nature of sediment dispersal of fine-grained sediment in shallow-water marine settings. Building on this complex sediment transport, a diverse suite of small-scale, unidirectional bedforms, including starved, barchan, sinuous, and linguoid forms occur in beds with very similar grain size and mineralogy. Consequently, traditional flow velocity-grain size models are inadequate to explain the observed bedforms in non-cohesive siltstone deposits. Instead, the sediment flux-to-transport capacity ratio influences ripple morphologies, thus providing a framework for bedform development in silt-sized sediments. Lastly, using a systematic gridding methodology integrating petrography, CT scans, XRF, and microhardness tools in core samples from the subsurface Montney Formation, the relationships between sedimentary fabric and rock mechanics, were quantified in samples with subtle grain size and mineralogical characteristics across three rock fabric. Using a new statistical approach, a discriminant analysis, compositional and mechanical trends across microfacies were evaluated, distinguishing massive siltstone, stratified siltstone, and bioturbated siltstone fabrics. These findings illustrate how sedimentary fabric and mineralogical variations impact geomechanical proxies and natural fracture terminations in siltstone-dominated facies, with implications for predictive modeling in unconventional reservoirs. Collectively, this dissertation provides a comprehensive understanding of fine-grained sedimentary processes, from basin-scale dynamics to micro-scale heterogeneities, with implications for stratigraphic interpretation, sediment transport modeling, and reservoir characterization.