Contrasting Deep-water Records from the Upper Permian and Lower Triassic of South Tibet and British Columbia: Evidence for a Diachronous Mass Extinction
Bibliographic record
Abstract
Remarkably different Late Permian–Early Triassic marine records are seen in sections from the western deep-water mar-gin of Pangea (Ursula Creek, British Columbia) and the high paleolatitude, southern margin of the Neotethyan Ocean (Se-long, South Tibet). The Ursula Creek section reveals the pro-gressive decline of seafloor oxygen values in the Changxingian Stage (loss of bioturbation, authigenic U enrichment, appear-ance of pyrite framboid populations), followed by the persistent development of euxinic conditions in the latest Changxingian and throughout the Early Triassic; an event that coincides with the disappearance of a siliceous sponge fauna and the loss of diverse radiolarian populations. The Selong section, which was located on a distal passive margin, records regres-sion and erosion in the mid-Changxingian, followed by a phase of deepening that began in the late Changxingian. The boundary interval is associated with a marked diversity in-crease due to the appearance of equatorial taxa (foraminifera, brachiopods, and sponges), suggesting warming without ex-tinction in marine waters at high southern paleolatitudes. Only in the late Griesbachian Stage are the diverse Permian holdovers eliminated, again at a level showing evidence for dy-soxia (thinly-bedded, authigenic U-enriched, pyrite-rich lime-stone). Thus, the end-Permian mass extinction is seen to be diachronous by half a million years or more, with late Chang-xingian extinction in Panathalassa coinciding with diversity increase associated the migration of warm-water taxa into the high southerly paleolatitudes regions of Neotethys.
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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 | 0.004 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".