Migrations of Devonian brine up-section and the origin of calcite-cemented sand in the Lower Cretaceous McMurray Formation, Athabasca Oil Sands
Bibliographic record
Abstract
Calcite-cemented sand intervals are widely distributed in the lower interval of the McMurray Formation of the Lower Cretaceous Athabasca Oil Sands deposit, northeastern Alberta. Flows of Devonian brine were driven up-section upon mixture with meteoric-charged groundwater that came in contact with the Prairie Evaporite Formation only 200 m below. Voluminous migrations of carbonate-saturated Devonian formation water during lower McMurray Formation deposition account for the distribution of decimetre to multimetre thick calcite-cemented sand intervals and giant concretions within the syndepositional fill of the Bitumount Trough, a 100 km long salt dissolution–collapse structure that floored the northern Athabasca Oil Sands deposit. Precipitations of calcite cement concurrent with deposition of the lower McMurray Formation provide insight into the eventual disposition of the voluminous brine that would have resulted from the dissolution of as much as 130 m of Middle Devonian salt section below the Bitumount Trough in contrast to deep basin storage elsewhere. Breccia pipes developed in Middle–Upper Devonian carbonate beds flooring the Bitumount Trough provided migration pathways up-section for the carbonate-saturated Devonian brines. Giant concretions of calcite-cemented sand, 1–2 m across, developed in homogeneous sands proximal to collapse-breccia pipes that vent along the Trough floor, whereas brine flows directed along heterogeneous sands resulted in tabular calcite-cemented beds. Similar but volumetrically less significant Quaternary brine migrations diluted with glacial meltwater were discharged at the surface as saline springs along the modern river valleys, resulting in geochemical trends characterized by concentration of total dissolved solids but without associated precipitations of calcite cement.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".