Geochemistry of carbonate formations of the Chhattisgarh Supergroup, central India: implications for Mesoproterozoic global events
Bibliographic record
Abstract
The Chhattisgarh Supergroup is one of the major Proterozoic marine sedimentary sequences of India. It consists of largely undeformed and unmetamorphosed siliciclastic, volcaniclastic, and carbonate formations deposited in two sub-basins, Hirri and Bharadwar, separated by an Archean greenstone belt. In spite of its apparent importance for Mesoproterozoic oceanic records, very few geochemical studies have been carried in the basin. Here, we present results of our high resolution geochemical and C–O–Sr isotopic studies in two carbonate formations of the supergroup: the Charmuria and the Chandi. We observe elevated δ13C values increasing from 2.6‰ to 3.6‰ in these formations, which is consistent with the globally reported late Mesoproterozoic values. Such consistently positive δ13C values are attributed to increased organic carbon burial in the basin margins during the deposition of these carbonates. Based on the principles of δ13C isotope stratigraphy, we suggest a depositional age between 1.0 and 1.2 Ga for these carbonates which form the upper part of the supergroup. The lowest 87Sr/86Sr ratios obtained from the Charmuria and Chandi formations, 0.70723 and 0.70816, respectively, are more radiogenic than the contemporaneous seawater, suggesting that the Sr isotopic system of the formations are altered. Based on the similarity in the δ13C values, we stratigraphically correlate the carbonate formations of the Raipur Group in both the Hirri and Bharadwar sub-basins. We also present a compilation of available δ13C and 87Sr/86Sr records from all the Proterozoic sedimentary successions of India and compare it with the global datasets. We find that while the Indian basins possess records of the Bitter Springs and Shuram δ13C anomalies, they lack evidence for the other major global events of the Proterozoic.
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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 | 0.002 |
| 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) | 0.001 | 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
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