Early Cretaceous continental-scale sediment dispersal: towards resolving the McMurray Conundrum
Bibliographic record
Abstract
ABSTRACT Alternative interpretations of Early Cretaceous McMurray Formation environments of deposition in the Western Canada Sedimentary Basin of Alberta have been referred to as the McMurray Conundrum because they have been debated for more than a decade. Recent empirically grounded research has continued to support long-held views that favor both fluvial and estuarine depositional models, but have provided no further resolution of the controversy. Here, we use multiple quantitative macro-, meso- and micro-scale approaches to further advance discussion of the McMurray Conundrum. First, we present published results of a recent paleogeographical reconstruction of the McMurray river system paleodrainage basin area, which places McMurray deposition within the context of a continental-scale system. We then use a high-density McMurray subsurface dataset, including published 3-D seismic observations, to test for downstream morphological and sedimentary transformations that indicate a paleogeographic position in the normal flow reach, perhaps extending into the backwater reach, which indicate that McMurray environments of deposition were terrestrial, and formed far upstream from marine influence. Last, we deploy oxygen and carbon isotope analyses of unaltered mollusk shells in the McMurray, which indicate freshwater conditions during and shortly after deposition, and provide no evidence of brackish-water marine conditions. Our results from three types of data therefore converge on the following characteristics for the McMurray system: a) the McMurray, in the Alberta foreland, represents the axial river of a south-to-north-flowing continental-scale fluvial system that drained much of North America, serving as the Amazon River or the Mississippi River of its time, b) data collected in the Alberta foreland basin over a downstream distance of > 400 km, from the Cold Lake to Athabasca Oil Sands areas, shows no evidence of downstream morphological and sedimentary transformations that are characteristic of rivers in their backwater reach, indicating that the axial McMurray river system was characterized by normal flow, and was likely > 1000 km upstream (to the south) from a coeval shoreline, and c) the recently published carbon and oxygen isotope analyses from unrecrystalized mollusk shells (Hasiuk et al. 2024) show that McMurray deposition took place in a fully freshwater continental environment, significantly upstream from the influences of saltwater penetration or tidal processes that would indicate marine proximity and influence.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.004 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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 teacher head, 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".