Brachiopods in Epeiric Seas as Monitors of Secular Changes in Ocean Chemistry: A Miocene Example from the Murray Basin, South Australia
Bibliographic record
Abstract
Abstract Early and middle Miocene cool-water carbonates from the Murray Basin, South Australia, preserve an excellent stable-isotope record of ocean-climate change. These variably fossiliferous heterozoan deposits accumulated on a low-energy, mesotrophic, centripetal epeiric ramp during a gradual shift in climate from cool, wet conditions and abundant continent-derived nutrients to a seasonal, arid climate with reduced delivery of trophic resources to the marine realm. Temporal trends in δ13C and δ18O from unaltered brachiopods record an epeiric sea response to this warming. The globally recognized middle Miocene Monterey Event (~ 17 to 13.5 Ma) dominates the carbon isotope record, albeit with higher (~ 0.5‰) than open-ocean δ13C values. Such higher δ13C values are attributed to an increase in benthic carbonate production that accompanied climate change and the relatively short seawater mixing times characteristic of epeiric-sea systems. The Murray Basin oxygen isotope curve contains lower δ18O values (~ 2.0‰ lower) than those of the deep-sea record. This difference is ascribed to the warmer seawater temperatures (~ 17 to 22°C) that prevailed across the Miocene Murray Basin. These results show that the isotope chemistry of epeiric-sea brachiopods can be a reliable gauge of regional and global environmental evolution. Although diagenetic overprinting from meteoric cement-filled punctae and local forcing factors introduce "noise" that mutes isotopic signals, the open-ocean secular record is clearly discernible.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.004 | 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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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 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".