Freshwater molluscan fauna from the Florissant Formation, Colorado: paleohydrologic reconstruction of a latest Eocene lake
Bibliographic record
Abstract
The freshwater molluscan assemblage from the uppermost Eocene Florissant Formation (34.07 ± 0.10 Ma), Colorado, USA, provides a reliable proxy in reconstructing past ecology and environmental characteristics of ancient Lake Florissant. In particular, stable-isotope analyses of aragonitic shell material contribute to our understanding of the paleohydrologic history of this ancient lake. Re-examination of molluscan taxonomy in the middle shale and caprock conglomerate (informal) units produces three sphaeriid bivalves (family Sphaeriidae, genus Sphaerium) and two pulmonate gastropod genera (family Planorbidae, genus Gyraulus; and family Lymnaeidae, genus Lymnaea). The middle-shale assemblage, representing quiet-lake deposition, is dominated by pulmonate gastropods; the shell material in all specimens in this unit has been replaced by silica. The caprock conglomerate assemblage, representing redeposition by a debris flow, is dominated by bivalves; specimens within the caprock conglomerate unit are aragonite, interpreted to be biogenic (original). Carbon and oxygen isotope analyses of the aragonite show a strong covariance (all molluscan data: r = 0.83; sphaeriids: r = 0.76) with consistent grouping (δ13C: 0‰ to −5.5‰, δ18O: +2‰ to −5‰) from all families. This result indicates that ancient Lake Florissant was “closed” and that evaporation had a stronger effect on isotopic values than precipitation, for the duration of the sampled interval. This finding is in agreement with our current understanding of how the sediments of the Florissant Formation were deposited within a lake that formed because of a paleoriver being dammed by debris flows.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".