Chemostratigraphy of the Paleoproterozoic Duitschland Formation, South Africa: implications for coupled climate change and carbon cycling
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Bibliographic record
Abstract
The Paleoproterozoic Duitschland Formation lies stratigraphically beneath the Timeball Hill Formation, which contains the only unequivocal glacial unit of this era in the Transvaal Basin, South Africa. Lithologic evidence in Paleoproterozoic successions of North America, however, indicates the existence of three discrete and potentially global ice ages within this 300 my interval. Carbonates of the Duitschland Formation are significantly enriched in ^13^C up to +10.1 permil in the upper part of the succession above a notable sequence boundary. In contrast, the lower part of this unit contains carbonates with consistently negative δ^13^C values. Trace and major element compositions of these carbonates as well as carbon-isotopic compositions of coexisting organic matter support a primary origin for the markedly positive carbon isotope anomaly. The stratigraphic constraints indicate that ^13^C-enriched carbonates were deposited prior to Paleoproterozoic glaciation in southern Africa, similar to carbonates stratigraphically beneath Neoproterozoic glacial diamictites worldwide. Also mirroring the Neoproterozoic record are strongly negative δ^13^C values in cap carbonates atop glacial diamictites in Paleoproterozoic strata of Wyoming and Ontario. The litho- and chemostratigraphic constraints indicate that the interval of negative carbon isotope values in well-preserved carbonates of the lower Duitschland Formation may reflect a second Paleoproterozoic ice age in the Transvaal succession. This interpretation is further supported by recently discovered bullet-shaped clasts with striations in diamictite from the basal part of the succession. Thus, the emerging temporal pattern of carbon isotope variations and glaciation in the Paleoproterozoic has a close analogue to Neoproterozoic events, suggesting a coupling of climatic and biogeochemical changes at both ends of the eon.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.002 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 it