New paleotemperature and paleobiological results consistent with a far-traveled alternative for the Baja-BC hypothesis
Bibliographic record
Abstract
ABSTRACT This study tested the Baja–British Columbia (Baja-BC) hypothesis using paleobiological and geochemical data in three separate ways. First, the pattern and values of paleotemperatures obtained from mollusks sampled from the Nanaimo Group, British Columbia (part of the Insular superterrane), were compared to those from basins in western North America (Sacramento and San Joaquin Valleys, California, and Rosario Basin, Baja California, Mexico) during the Coniacian–Maastrichtian time interval. Sequentially younger fossils in the Nanaimo Group show cooling that is consistent with a northernly moving microcontinent into higher latitudes with cooler climate and seawater temperature. The fossils in the basins in western North America do not show this pattern. Second, there is a reduction in the number of ammonite species shared by the Nanaimo Group and western North American sedimentary basins during the Santonian–Maastrichtian time interval. These data are consistent with increasing distance between the two regions over Late Cretaceous time. Third, nautiloid cephalopod assemblages from the Nanaimo Group and North America basins differ sufficiently to allow estimates of the possible deep, open-water distance between the Insular superterrane and North America during the Coniacian–Maastrichtian interval. These results are all consistent with the “far-traveled” Insular microcontinent hypothesis. However, the data also suggest that the Insular superterrane could have been farther offshore than previous models invoking the Baja–British Columbia hypothesis.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".