Dolomitization process of oolites in the Lower Triassic Feixianguan Formation, northeastern Sichuan Basin, China: evidence from magnesium isotopes
Bibliographic record
Abstract
Oolitic dolostones are widely distributed in the Triassic Feixianguan Formation (FXG Fm) in the northeastern Sichuan Basin, South China. Although multiple dolomitization processes have been proposed, including a meteoric-mixing zone, seepage-reflux and burial dolomitization, their origin remains controversial. While traditional petrological and geochemical analyses provide valuable insights into the formation mechanism of the oolitic dolostones, the source of Mg 2+ and formation processes cannot be exclusively constrained. In this study, we investigated three representative sedimentary intervals within the FXG Fm: a non-oolitic shoal interval in the platform interior (S1), an oolitic shoal interval at the platform margin (S2) and an oolitic shoal interval in the platform interior (S3). These intervals, characterized by multiple shallowing-upward cycles, collectively record the deposition–diagenesis process of oolitic facies in the FXG Fm. By integrating sedimentary, petrographic and geochemical data, including major and trace elements, carbon and oxygen isotopes, and Mg isotopes, the dolomitization process of the oolitic dolomite in the FXG Fm can be constrained. The stratigraphic covariation of δ 26 Mg dol values with sedimentary cycles suggests periodic dolomitization controlled by sea-level fluctuations. During the relatively high sea-level stage, oolitic limestone precipitates in the grain shoals. When sea-level falls, the carbonate platform is prone to experience penecontemporaneous sabkha dolomitization characterized by a downward decreasing δ 26 Mg dol trend in intertidal flat facies, and seepage-reflux dolomitization marked by a downward increasing or unchanging δ 26 Mg dol trend in shoal facies. Thus, this study provides a testable approach to investigate the origin of oolitic dolostone formed in grain shoals.
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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 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".