Zircon U–Pb ages of the Chiapas Amber-Lagerstätte in the uppermost Simojovel Formation, southwest Mexico
Bibliographic record
Abstract
The Chiapas Amber-Lagerstätte is a fossil preservation site in southern Mexico, consisting of three central localities: Simojovel, Totolapa, and Estrella de Belén. It is a repository that preserves a diverse range of estuarine-associated biota. These include but are not limited to arboreal, aerial, land-dwelling, soil-based, amphibiotic, aquatic, and microbial organisms. The age and stratigraphy of the amber-bearing beds near Simojovel have been interpreted differently. The amber outcrops were initially considered part of the late Oligocene to Early Miocene La Quinta Formation. Further studies identified several outcrops as part of the Early Miocene Mazantic Shale and the Middle Miocene Balumtum Sandstone. We present the zircon U–Pb dating results conducted on the amber-bearing beds in the uppermost section of the Simojovel Formation. The data indicate a maximum depositional age of 24 ± 1 Ma, corresponding to the uppermost late Oligocene. A limited section of the amber deposit in Totolapa is likely contemporary with the lowermost Early Miocene, ca. 20 Ma. Hence, the amber biota is constrained to the uppermost late Oligocene and the lowermost Early Miocene (ca. 24–20 Ma). Our data also suggest that the sedimentary environment of the upper strata oscillates from estuary to shallow shelf. It is characterized by low-energy zones with a constant influx of terrigenous sediments consisting of siltstone and fine-grained sandstone, with gastropods, bivalves, coral fragments, trace fossils, plant remains, lignite, and amber.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".