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Three-dimensional Outcrop Modelling of Fluvial and Estuarine Outcrops in the Lower Cretaceous McMurray Formation, Northeast Alberta, Canada
- Author / Creator
- Hayes, Derek A
While it is widely accepted that both cross-bedded sand and Inclined Heterolithic Stratification (IHS) are the two main geobodies that compose Aptian-aged middle McMurray Formation strata, the stratigraphic relationship between the two units and their physiographic depositional positions in a fluvial-estuary system remain somewhat poorly constrained. It is well-known that there is a relatively widespread distribution of fluvial or estuarine lateral accretion point-bar deposits throughout the McMurray Formation, and this has led to a bias regarding the large-scale depositional architecture of the formation as a whole. In this paradigm, the cross-bedded sand overlain by IHS are interpreted to be contemporaneous channel and point-bar deposits, respectively. Because much of the recent research on the McMurray Formation has focused on subsurface datasets, deciphering the large-scale stratigraphic relationship and facies architecture between the two geobodies remains a challenge. This results in a propensity for interpreting these two geobodies as a single continuous point-bar interval.
The best way to characterize large-scale architectural elements within the McMurray Formation is to study outcropping strata. Although this approach has been used by a handful of workers for over 40 years, much of the work has focused solely on the sedimentology (and where applicable, the ichnology) of a small subset of outcropping McMurray strata. In the time since many of the previous outcrop studies were completed, the use of unmanned aerial vehicles (UAV’s, or drones) has permitted the development of high resolution georeferenced outcrop models using Structure-from-Motion photogrammetry. This thesis uses these photogrammetry techniques to acquire bed-by-bed orientation data from both cross-bedded sand and IHS geobodies to assess the large-scale depositional architecture of the outcropping strata.
This body of work shows that when architectural data are combined with sedimentological and ichnological observations at the Christina River, Steepbank #3, Amphitheatre, and Crooked Rapids outcrops, several facies architectures are recognized with at least three acting as reservoir-quality units in the McMurray Formation. Notably, in the former three outcrops, it is common to see forward- or oblique forward-accreting cross-bedded sand sharply overlain by laterally accreting IHS strata. When combined with sedimentological and ichnological data, it becomes clear that the contact between cross-bedded sand and IHS is often disconformable owing to significant changes in grain size, bioturbation index, and/or architectural variability across the contact separating the individual geobodies. In contrast, at the Crooked Rapids outcrop, an inter-fingering relationship between the cross-bedded sand and overlying IHS combined with consistent accretionary growth directions between the two units suggest both were deposited contemporaneously on the same point-bar. As such, a number of facies architectures including estuarine compound dunes, simple fluvial dunes, estuarine point-bar, fluvial point-bar, and fluvial counter point-bar deposits are interpreted among the studied outcrops. The physiographic location of these deposits in a fluvial-estuary environment are defined based on sedimentological and ichnological characteristics of the aforementioned facies architectures. In short, reservoir-quality units are not only constrained to fluvial or estuarine channel thalweg to lower point-bar sand: they occur in both fluvial and estuarine channels, in addition to a middle estuary compound dune environment near the estuary mouth.
- Graduation date
- Fall 2018
- Type of Item
- Master of Science
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