Constraining the conditions of phosphogenesis: stable isotope and trace element systematics of Recent Namibian phosphatic sediments (dataset)
Bibliographic record
Abstract
Modern phosphogenesis occurs on continental margins influenced by upwelling and high primary productivity. The formation of phosphatic sediments is coupled to global climate fluctuations, biological cycling of phosphorus and local redox conditions. Although the processes involved in phosphogenesis are well described, high-resolution data on the redox and stable isotope systematics in Recent in-situ phosphorites are scarce. In this contribution, we investigate the trace element and sulfur, nitrogen and organic carbon stable isotope composition of Recent in-situ phosphatic sediments off the coast of Namibia. Also, we examine the reliability of different widely used geochemical proxies in phosphatic sediments. Our results suggest a shift from sulfidic to suboxic conditions, coinciding with the maximum in solid calcium phosphate mineral concentration. This shift is accompanied by unidirectional changes in Mo and Re enrichments and TOC abundance. Relatively low pyrite δ34S values (ca -20‰) of phosphatic sediments indicate open system fractionation during phosphogenesis. The initiation of phosphogenesis is also accompanied by negative shifts in sedimentary δ13Corg and δ15N values. Phosphate associated sulfate (PAS) δ34S values are lower than modern seawater sulfate values, suggesting the involvement of chemolithotrophic sulfur oxidation. Our results show a shift in redox conditions from sulfidic to (sub)oxic, coupled with active sulfur cycling are prerequisites for phosphogenesis. Phosphatic sediments show substantial enrichments in U and V highlighting the complexity of using these elements, as well as V/(V+Ni) and V/Cr, as redox proxies particularly in phosphorites and phosphatic sediments.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.003 |
| Science and technology studies | 0.001 | 0.000 |
| 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
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".