Global Ca isotope variations in c. 0.7 Ga old post-glacial carbonate successions
Why this work is in the frame
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Bibliographic record
Abstract
Terra Nova, 22, 188–194, 2010 Abstract To discriminate and correlate Neoproterozoic post-glacial carbonate successions, isotopic stratigraphy has been attempted in recent years. We report here the development of a new, promising discriminant, the 44Ca/40Ca isotope ratio. Two well-preserved carbonate successions overlying c. 0.7 Ga old glaciogenic deposits in central Brazil and NW Canada display similar Ca isotope time series. The Ca isotope stratigraphic profiles of these are similar to that of a weakly metamorphosed c. 0.7 Ga old carbonate succession in NE Brazil, suggesting robust preservation of the original Ca isotopic compositions. The Ca isotopic record is a reliable archive of changes in the oceanic Ca isotopic composition. It suggests rapid glacier melting and large increase in the Ca input to the ocean immediately after deglaciation, followed by progressive increase in carbonate precipitation, balancing the large initial Ca input. The global δ44Ca pattern recorded by c. 0.7 Ga old cap carbonates monotonically increases from ∼0‰ to 1‰, very different from the oscillation between ∼0‰ and 2‰ of the c. 0.64 Ga old global glaciation. This implies a difference in Ca mass balance evolution amongst the two deglaciation events. A possible explanation is that the high pCO2 built up during the first glaciation was consumed quickly by silicate weathering, while after the subsequent glaciation, the recently formed cap carbonates were redissolved first, followed only later by silicate weathering. The different Ca isotopic evolutions support Ca isotope stratigraphy as a reliable tool to discriminate amongst Neoproterozoic post-glacial carbonate successions.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.006 | 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 it