Altered oceanic crust as an inorganic record of paleoseawater Sr concentration
Bibliographic record
Abstract
The minimum Sr content of seawater at 90–95 Ma is determined from the Sr content and Sr isotopic composition of the sheeted dike complex of oceanic crust that was hydrothermally altered at this time on the basis of simple mass and heat balances. When this approach is applied to sheeted dike complexes that were hydrothermally altered by modern seawater a minimum fluid Sr content of <3 μ g g −1 is calculated. This is substantially less than the modern ocean Sr content of ∼7.8 μ g g −1 supporting the arguments that the approach provides a robust minimum Sr content of the ocean at the time of crust formation. Applying the same approach to the sheeted dike complexes in the Cretaceous Troodos and Oman ophiolites gives minimum Sr contents for the ocean at this time of 27 and 38 μ g g −1 , respectively. These values are consistent with previous studies of biomineralized carbonate that suggest higher Sr/Ca in seawater at this time and fluid inclusion analyses that suggest higher Ca contents in the ocean at this time. The Ca content of the ocean must have been at the upper end of the range suggested by fluid inclusion analyses (≥30 mmol kg −1 ). The high Ca and Sr content of seawater at 90–95 Ma was, at least partially, due to enhanced submarine hydrothermal circulation which leaches Sr from the basaltic crust because it coincides with a time of low seawater 87 Sr/ 86 Sr. Elevated Sr contents at this time may have impacted the evolution and/or biogeochemical role of the Acantharians which secrete a SrSO 4 skeleton.
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How this classification was reachedexpand
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) | 0.000 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".