Sedimentary Facies, Lithostratigraphy, and Sequence Stratigraphy of the Lower Cretaceous Dina and Cummings, Alberta, Canada
Creators: Botterill, Scott Edward
Publisher: name: University of Alberta Library
Year: 2024

<p>The Lower Cretaceous Aptian to Albian Dina and Cummings lithostratigraphic units comprise a complex assemblage of siliciclastic strata deposited in the Western Canada Sedimentary Basin (WCSB) during transgression of the Lower Cretaceous Boreal Sea. The internal stratigraphic complexity of this interval results from several factors, including significant topographic variation along the underlying sub-Cretaceous unconformity (more than 50 metres), internal complexity of the constituent continental to shallow marine environments, and the occurrence of several high-frequency base-level fluctuations nested within the lower frequency transgressive system. This complexity has resulted in historical inconsistencies in top placement, geological definitions, and formal rank (Formation versus Member). Despite the production of hydrocarbons ranging from the 1940’s to present no regional, high-resolution sedimentary facies and sequence stratigraphic analysis of the Dina and Cummings has been published. Such studies are essential to inform several aspects including exploration and development of hydrocarbon resources, pore space distribution, and the presence of sub-surface intervals suitable for CO2 sequestration.<br>
    The overarching goal of this study is to develop a regional, geologically consistent, stratigraphic framework for the Dina and Cummings lithostratigraphic units in the east-central plains region of Alberta. To achieve this goal, the application of high-resolution sedimentary facies analysis and sequence stratigraphic principles were applied to a subsurface dataset consisting of seventy-two stratigraphic core, and ca. 7800 petrophysical wireline logs in an area between Townships 45-55, Ranges 1-8W4 Meridian (8800 km2). Focus was placed on the analysis of physical sedimentology (lithology, sedimentary structures, lithological accessories) and ichnology (ichnogeneric identification, bioturbation intensity, trace fossil distribution) to identify the range of depositional environments preserved within the Dina and Cummings interval. These sedimentological observations where then used to revise the formal lithostratigraphic stratigraphy and develop a high-resolution sequence stratigraphic framework.<br>
    The high-resolution facies and sequence stratigraphic analysis resulted in the identification of seven geologically distinct facies association complexes (FAC-A to FAC-G) bound by seven discontinuity surfaces (S1 to S7). These seven facies association complexes and discontinuity surfaces form the building blocks of depositional sequences at two scales. These sequences are referred to as medium-frequency Sequence 1, within which are nested two higher-frequency depositional sequences – high-frequency Sequence 1 and high-frequency Sequence 2. The goal of establishing a regionally consistent lithostratigraphic framework for the Dina and Cummings was also achieved, with the revision of stratigraphic tops, elevation in rank from Member to Formation, and the recognition of four new members resulting from these high-resolution facies analysis. In ascending stratigraphic order these are the McLaughlin and Rivercourse members of the Dina Formation, and the Lindbergh and Paradise Valley members of the Cummings Formation.</p>