Using structure-from-motion photogrammetry to recognize lateral versus forward accretion bedforms in the Lower Cretaceous McMurray Formation, NE Alberta, Canada
Bibliographic record
Abstract
Abstract The juxtaposition of trough cross-bedded sand underlying inclined heterolithic stratification (IHS) is commonly interpreted to represent the growth of a fluvial or estuarine point-bar through time in the lower Cretaceous McMurray Formation. This paradigm has led to the development of a bias regarding the depositional architecture of McMurray Formation sediment, such that the majority of geobodies in the McMurray Formation are interpreted to represent point-bar deposition. This study addresses this bias by using an Unmanned Aerial Vehicle and Structure-from-Motion photogrammetry to generate three-dimensional outcrop models from which bedding architecture can be analyzed. The purpose of this study is to recognize and discuss the stratigraphic significance of two types of facies architectures prevalent in outcrop exposures of the middle McMurray Formation: laterally-accreting point-bar deposits and forward-accreting compound-dune deposits. Bed orientation data, when compared to sediment transport directions, show that outcrops along the Steepbank River are composed of stacked lateral accretion bar elements. At the Amphitheatre outcrop exposure along the MacKay River, master bedding surfaces are parallel to sediment transport direction, which suggests that the cross-bedded sand geobody is forward-accreting. Based on these distinct relationships, two dominant facies associations are recognized. The Steepbank #3 outcrops preserve a laterally accreting estuarine point-bar complex sharply overlying a fluvial dune succession, while sediments at the Amphitheatre outcrop are ascribed to a forward-accreting middle estuary compound dune complex that is truncated by an overlying IHS channel fill. The recognition of compound dunes, in addition to well-recognized laterally accreted point-bars in the McMurray Formation, is important for the establishment of reservoir and stratigraphic models. In McMurray Formation subsurface studies, large-scale, middle estuary compound dune complexes are rarely recognized, despite their presence in outcrop exposures — this is an important theme that is explored in this paper. To this end, bed orientation data are combined with 3D photogrammetric outcrop models. Bed orientation data show two main facies associations: 1) laterally accreted bars which are bounded by bedding discontinuities and are characterized by IHS bedsets that thin, increase in mud content and increase in bioturbation intensity upwards; and 2) large-scale forward-accreting compound dunes which are characterized by low-angle planar tabular and trough cross-stratified medium-grained sand with current reversals and unevenly distributed bioturbation throughout.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".