Early–Middle Permian strontium isotope stratigraphy of marine carbonates from the northern marginal areas of South China: Controlling factors and implications
Bibliographic record
Abstract
The radiogenic strontium isotope ( 87 Sr/ 86 Sr) system is a powerful tool for constraining sea‐level change and palaeoclimatic variations as well as tectonic activities. The Permian is a period that records the lowest seawater Sr‐isotopic ratios in the Earth's history. The near‐primary geochemical signatures retained in the micritic carbonates of the Luduba section (uppermost lower to Middle Permian) on the northern margin of the South China Block allowed the reconstruction of reliable carbon and Sr‐isotope profiles for global chemostratigraphic correlations. The investigated interval (~300 m) spans the Chihsia and overlying Maokou formations (Kungurian to Capitanian series). The 87 Sr/ 86 Sr values decrease consistently upward from 0.70833 to 0.70684, and their trend correlates well with a long‐term increase in the carbon isotope (δ 13 C) values. The negative correlation between the 87 Sr/ 86 Sr and δ 13 C values suggests that the sea‐level change, climatic conditions, opening of the Neo‐Tethys Ocean, and accretion of the Pangean Supercontinent are among the factors that might have contributed to the consistent depletion of the 87 Sr/ 86 Sr values. The rate of upward decrease in 87 Sr/ 86 Sr values throughout the Chihsia Formation is generally higher than that of the overlying Maokou Formation, which provides a possible marker for intra‐ and interbasinal basin stratigraphic correlations. The general increase in the δ 13 C values of the Luduba profile peaks at ~5‰, which correlates with the distinct lowest 87 Sr/ 86 Sr value (~0.70684) near the top of the Maokou Formation (Upper Capitanian). The δ 13 C values decrease to 3.6‰ at the top of the Maokou Formation, that correlates with the rapid sea‐level drop in the Late Guadaualupian worldwide. Meanwhile, the 87 Sr/ 86 Sr ratios remain low values, probably due to the development of cold climate, increasing input of hydrothermal flux and low terrestrial runoff.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".