Paleodepositional Environments and Stratigraphic Framework for the Lower Cretaceous Bluesky Formation and Related Strata in the Peace River Oil Sands Deposit of Alberta

• Author / Creator

  Campbell, Sean, G

• The Early Cretaceous Bluesky Formation in the Peace River oil sands area of west-central Alberta, Canada hosts significant bitumen resources. This work is part of an ongoing endeavour by researchers and practitioners in academia and industry to develop paleodepositional and sequence stratigraphic models for the Bluesky Formation and related deposits of the underlying Gething Formation and the overlying Wilrich Member. In this thesis, sedimentological, ichnological, and micropaleontological datasets are acquired from core, and paleodepositional interpretations for the formations of interest are made. Sediments in the upper Gething Formation preserve remnants of brackish bay and paralic swamp and marsh deposits. The Bluesky Formation is described by thirteen facies. Recurring succession of these facies are grouped into six facies associations representing both proximal and distal marginal marine environments and include: 1) fluvial- to wave-influenced distributary channel and terminal mouth bars, 2) mixed-influence proximal delta fronts, 3) wave- and storm-influenced, proximal to distal delta fronts, 4) wave-influenced delta fronts and shoreface environments, 5) lower bay shoreface to distal bay settings, and 6) tidal flats. Wilrich Member successions are represented by a Glossifungites-demarcated discontinuity and marine mudstones. These depositional environments are linked spatially and temporally by important sequence stratigraphic surfaces that formed during a series of regressive and transgressive events. Bluesky successions were deposited at fourth- or fifth-order scales and formed within the longer duration third-order phase of sea-level rise in the Early Cretaceous. Importantly, relative sea-level rise was episodic. During stillstand episodes of transgression, Bluesky progradation ensued. Regressive surfaces of marine and fluvial erosion mark these retrogradational episodes. Cross-section analysis reveals an apparent backstepping of the Bluesky Formation in the region as transgression proceeded. These progradational pulses were interrupted by high-order flooding events that are correlatable across the study area. Complete inundation of the study area by the Boreal Sea is marked by a third-order major flooding surface and is represented by transgressive Wilrich Member deposits. In addition to building a depositional model for the study area and understanding the paleoenvironmental evolution of the area in terms of sequence stratigraphic events, a number of complimentary studies are conducted. One particular study focuses on a facies that preserves world-class specimens of stacked Rosselia, which formed when burrowing tracemakers vertically re-adjusted their positions in the sediment following depositional events. Where present, these traces help to refine paleoenvironmental interpretations and can be used as proxies for assessing the magnitude and frequency of depositional events. The use of Rosselia illustrates a method of evaluating sedimentation events within a brief temporal window, one lying beyond the resolution of more traditional dating methods. The second study considers palynomorphs and microfossils preserved in cored intervals. The micropaleontological assemblages are calibrated with sedimentological and ichnological features to fine-tune depositional interpretations. Foraminifera and microfossils provide semi-quantitative paleosalinity ranges for the various depositional environments preserved in cored successions. Dinoflagellate cysts are used to identify important stratigraphic boundaries between Gething, Bluesky, and Wilrich sediments and to constrain the age of the Bluesky Formation to Early Aptian, an age older than previously recorded.

• Subjects / Keywords

  • Micropaleontology
  • Rosselia
  • Stratigraphy
  • Bluesky Formation
  • Gething Formation
  • Ichnology
  • Sedimentology
  • Wilrich Member

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3C824V0N

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.