Controls on organic-rich mudstone deposition: The Devonian Duvernay Formation, Alberta, Canada

  • Author / Creator
    Knapp, Levi J
  • The Upper Devonian Duvernay Formation of Western Canada is a prolific source rock that in recent years has become an exploration target for shale gas and liquids. Development of the Duvernay Formation has demonstrated the importance of robust models for rock properties such as porosity, permeability, organic richness, and fracturability. Depositional processes and conditions govern the character and distribution of mudstone lithofacies, which are directly linked to variations in rock properties. The depositional and sequence stratigraphic models presented here are based on a detailed sedimentology and stratigraphy study. Twelve lithofacies were characterized based on lithology, sedimentary and biogenic structures, fossil type and abundance, and type and abundance of cement. Significant variation exists between organic-rich lithofacies, indicating that organic-rich mudstones were deposited in variably energetic and oxygenated environments, rather than within persistently anoxic, stagnant bottom waters. Correlation of core descriptions to a network of 759 wells with wireline logs led to the creation of a basin-scale sequence stratigraphic framework with 3 third order sequences. The sequence stratigraphic model shows a strong sea level and basin morphology control on basinal lithofacies. Transgression, and subsequent highstand normal regression in sequence 1 (oldest) resulted in significant platform construction in the northeast side of the basin. Sediments become consistently finer-grained and organic-rich away from the platform. Major transgression at the start of sequence 2 resulted in flooding of the platform and significant upslope trapping of sediments, locally so significant that no sediment reached the platform edge and large zones of non-deposition developed. Lithofacies basinward of these zones are especially clay mineral-poor and organic-rich. A sea level stillstand or lowstand at the base of sequence 3 resulted in progradation of basin-margin facies, reduction in the extent of organic-rich mudstone deposition, and an influx of clay minerals into the basin. The geographic extent of organic-rich, siliceous mudstone deposition was greatest during transgressive and highstand systems tracts. Sustained highstands resulted in increased carbonate sedimentation, which diluted organic matter. Sea level stillstands resulted in progradation of argillaceous sediment, and reduction of TOC values due to dilution and oxygenation.

  • Subjects / Keywords
  • Graduation date
    Spring 2016
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • 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.