Sequence Stratigraphy, Porosity, and Primary Producers of the Middle to Late Devonian Canol Formation, Northwest Territories, Canada
Creators: LaGrange Rao,Maya Tessalie
Publisher: name: University of Alberta Library
Year: 2022

<p>The Devonian Canol Formation of the Northwest Territories (NWT) is an organic-rich mudstone interval deposited in a tropical marine setting along the west coast of Ancestral North America. This unit preserves a record of local marine conditions in the Middle to Late Devonian, a time characterized by successive global marine biodiversity crises and widespread deposition of fine-grained, organic-rich sediment. The Canol Formation is also of economic significance because it sourced the oil conventionally produced from the carbonate units at Norman Wells (NWT) and has potential as an unconventional reservoir. This thesis dissertation contributes to our understanding of the local oceanographic conditions at the time the Canol Formation was deposited and of the unconventional resource potential of this interval. Data was collected from cores in the Central Mackenzie Valley (NWT) and outcrops in the Mackenzie Mountains (NWT) where the Canol Formation is included in the Horn River Group (HRG), which also comprises the underlying Hare Indian and Ramparts Formations. <br>
    Chapter 1 introduces the Canol Formation and the research objectives. Chapter 2 investigates the stable C and N isotopic profile of the Canol Formation and surrounding units. Through the interpretation of δ13Corg (δ13C of organic matter) and δ15Nbulk (whole rock δ15N) values, I show that primary producers were dominantly diazotrophic (N2 fixing) throughout deposition of the HRG and that biological productivity varied through time as the Canol Formation accumulated. Through a synthesis of existing paleoredox interpretations and comparison to the modern, I also propose that episodic weak oxygenation of euxinic bottom waters during deposition of the Horn River Group could be produced by climatic variations causing periodic downwards migration of the upper OMZ boundary. These results contribute to our understanding of marine conditions in the study area, which adds to the growing body of research focused on the Middle to Late Devonian oceans.<br>
    Chapter 3 is an evaluation of porosity in the HRG relating to resource evaluation. Pores are characterized through scanning-electron microscope (SEM) imaging and quantified by bulk porosity measurements and N2 adsorption and desorption experiments. Relative to many other North American unconventional reservoirs, the Canol Formation and Bluefish Member of the Hare Indian Formation have similar bulk porosity, lower mesopore volume, and are dominated by mineral matrix pores, rather than organic matter pores. A comparison of porosity with mineralogy, lithofacies, and total organic carbon (TOC) shows that high quartz and low clay content are the best predictors of high porosity. Ultimately, this chapter further characterizes the properties and distribution of potential reservoir units in the HRG of the Central Mackenzie Valley. <br>
    In Chapter 4, I review the application of chemostratigraphic datasets to sequence stratigraphic interpretations in organic-rich, marine mudstone units. A synthesis of previous studies shows that the maximum flooding surface (MFS) and maximum regressive surface (MRS) have distinct chemostratigraphic signatures, allowing for delineation of the transgressive systems tract (TST) and regressive systems tract (RST). This review concludes that chemostratigraphic datasets are useful for the identification of transgressive-regressive (T-R) cycles. However, chemostratigraphic criteria do not yet exist to identify the basal surface of forced regression or the correlative conformity, which precludes subdivision of normal and forced regressions. The implications are that the highstand systems tract, lowstand systems tract, and forced regressive systems tract cannot be distinguished from one another based on chemostratigraphy alone.<br>
    Chapter 5 presents a sequence stratigraphic framework for the Horn River Group, primarily based on high-resolution chemostratigraphic profiles of Al, Si, and Ti. This interpretation comprises six complete T-R cycles from the base of the Horn River Group to the lower section of the overlying Imperial Formation. Redox-sensitive trace metals Mo and V are most enriched at or near MFS, suggesting that the most reducing conditions in the sediment and bottom waters coincided with the highest rates of relative sea level rise. I further demonstrate that this pattern in Mo and V is associated with unrestricted marine settings, supporting the preexisting hypothesis that the Horn River Group depositional setting was oceanographically open. The framework presented in Chapter 5 allows for mapping of higher reservoir quality (more siliceous) MFS and illustrates fluctuations in sedimentation, accommodation, and redox as the HRG was deposited. Chapter 6 summarizes the key conclusions and future research directions.</p>