Constraining temperatures of formation and composition of dolomitizing fluids in the Upper Devonian Nisku Formation (Alberta, Canada) with clumped isotopes:
Bibliographic record
Abstract
Three dolomite phases in the burial dolomitization system of the Nisku Formation in central Alberta(Canada) were measured for carbonate clumped isotopes. Independent temperature constraints using fluid inclusions and traditional oxygen isotope geothermometry allow us to test the application of this method using a new calibration curve extrapolated to higher temperatures. These three phases of dolomite correspond to three diagenetic stages in the burial history. The oldest phase is replacive gray matrix dolomite formed during relatively shallow burial depths at average clumped-isotope temperatures (Δ47T) of +80 ¡76C. Previous temperature estimates from standard oxygen isotope geothermometry ranged from 50 to 806C. A calculated δ18O(H2O) of 3 ¡ 1.4‰ VSMOW points to precipitation from Devonian seawater modified by evaporation and/or water–rock interaction. The first phase of saddle dolomite cement formed by pressure-solution during intermediate burial depths yielded average Δ47T of 96 ¡46C (previously calculated at ~806C) and δ18O(H2O) of 4 ¡ 1‰ VSMOW. A second phase of saddle dolomite formed in association with thermochemical sulphate reduction during deep burial records average Δ47T of 151 ¡56C, comparable to fluid inclusion temperatures ranging from 125 to 1456C. The average δ18O(H2O) of the fluid that formed this saddle dolomite phase is calculated as 8 ¡ 1‰ VSMOW, suggesting much more advanced water–rock interaction. Δ47T are consistent with previous temperature estimates from a combination of geological data conventional O-isotope and fluid-inclusion thermometry. Another important finding is that the Δ47 signatures are preserved even after reaching deeper burial and/ or during uplift and cooling, which points to a closure temperature in dolomites in excess of 1806C. Thus, dolomite appears to be a better phase for clumped-isotope analysis than calcite for rocks that have been exposed to higher temperatures upon further burial. This study demonstrates the power of the clumped-isotope thermometer to reconstruct complex diagenetic histories in burial diagenetic environments where multiple generations of diagenetic cements can be analyzed individually.
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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 | 0.002 | 0.003 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.002 | 0.000 |
| Open science | 0.001 | 0.001 |
| 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".