Sandstone provenance and insights into the paleogeography of the McMurray Formation from detrital zircon geochronology, Athabasca Oil Sands, Canada
Bibliographic record
Abstract
ABSTRACT The Lower Cretaceous McMurray Formation of northeastern Alberta hosts most of the bitumen resources of the Athabasca Oil Sands. Despite its importance, the sedimentary provenance and corresponding Early Cretaceous paleodrainage system associated with these fluvial deposits remain poorly understood. We collected 18 sandstone samples from five cored wells drilled in the McMurray Formation and analyzed these for detrital zircon uranium–lead (U–Pb) geochronology. Together, these samples yield detrital zircon U–Pb age populations of less than 250, 300–600, 1000–1200, 1800–1900, and 2600–2800 Ma. Almost all of the samples contain detrital zircons with ages of 300–600 and 1000–1200 Ma, which were originally derived from the Appalachian and Grenville provinces, respectively, of eastern North America. Lowermost strata of the McMurray Formation are characterized by relatively small fluvial channel deposits and detrital zircon ages of 1800–1900 and 2600–2800 Ma, which suggest a limited paleodrainage area that includes the adjacent Canadian shield. In contrast, channel deposits in the middle–upper part of the formation are relatively large and contain abundant Appalachian- and Grenville-derived detrital zircons. These data suggest that the paleodrainage system of the McMurray Formation evolved over time, increasing in size between deposition of the lowermost units and the middle–upper deposits. Detrital zircons from the Appalachian and Grenville regions may have been transported directly to western Canada during the Cretaceous or recycled multiple times prior to their deposition. Detrital zircons from the Cordillera (<250 Ma) are restricted to the northern part of the study area, which suggests that a tributary may have joined the main trunk fluvial system in this area.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.002 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".