title: Natural Fracture Systems in Outcrop of the Lower Triassic Sulphur Mountain Formation: Investigation of Fracture Timing Using Structural, Petrographic, and Geochemical Datasets
Creators: name: Kenzie, Thomas Andrew
Publisher: name: Graduate Studies
Year: 2024
Subjects: subject: Natural Fractures
subject: Triassic
subject: Sulphur Mountain Formation
subject: Montney Formation
subject: Stable Isotopes
subject: Fracture Cement
subject: Geology
subject: FOS: Earth and related environmental sciences
subject: Geochemistry

description: Natural fractures are common structures observed affecting rocks within the earth’s shallow crust and are often interpreted to be the result of deformational conditions related to fold-and-thrust tectonics. However, multiple studies have identified the development of natural fracture systems prior to and following tectonic uplift. In the Western Canada Sedimentary Basin (WCSB), a complex structural history has developed an intricate suite of fluid and fracture systems that remain poorly understood, even in highly economic reservoirs such as the Lower Triassic Montney Formation where resource extraction relies on natural and hydraulically induced fracture systems. This means there is a significant knowledge gap in our understanding of the structural and diagenetic evolution of Triassic sedimentary strata through orogenesis, subsidence, and their related fracture systems. This thesis aims to bridge this gap by investigating a robust dataset of field data, petrographic data, and geochemical data, including fracture orientations and cross-cutting relationships, fracture-filling cement textures, mineralogies, and stable isotope geochemistry collected from an exposure of the Sulphur Mountain Formation. This multi-faceted approach allows us to constrain the relative timing of fracture generation by characterizing distinct cement phases within fracture apertures, define the mechanisms driving fracture generation, and determine genetically related fracture generations through isotopic signatures. Three distinct fracture sets were identified from field observations in Lower Triassic strata in the study area. Detailed petrographic and geochemical investigation indicates a complex evolutionary story of natural fracture systems that involves multiple generation, reactivation, and recementation events. These events occurred at different phases in the tectonic history of the Sulphur Mountain Formation and involved significantly different fluid regimes. Ultimately, this research reveals that Lower Triassic strata in the WCSB underwent initial fracture generation occurring as early as the Late Triassic, prior to significant uplift, and continued into the Quaternary, long after development of the Rocky Mountain fold-and-thrust belt. Findings from this research directly contributes to our understanding of fracture timing, diagenetic processes, and fluid evolution in Lower Triassic strata in the Western Canadian Sedimentary basin. Furthermore, this research provides the foundation for future studies focusing on fluid inclusion thermometry which will allow for further constraint of fracture timing and correlation of natural fracture networks in outcrop to those observed in the subsurface.