An Ordovician “Lost City” — venting serpentinite and life oases on Iapetus seafloor
Bibliographic record
Abstract
Highly brecciated carbonate-rich serpentinites (or ophicalcites) of Early Ordovician age in the Dunnage Zone of Quebec are host to fracture-fill, high-temperature (80–230 °C) carbonate cements. Away from, or crosscut by the fractures, centimetre- to decimetre-thick crusts made up of massive to laminated micrite, peloidal layers and threads are associated with low-temperature botryoidal calcite cements. The peloidal masses are characterized by a clotted texture that is reminiscent of interpreted fossilized Ordovician microbial communities. The ophicalcite contains carbonate botryoids, morphology commonly found at shallow reefal margins but also at modern cold CH4 seeps and recently documented at hot CH4 vents from serpentinite, such as the modern Lost City hydrothermal field in the Atlantic Ocean. The δ18OVPDB ratios of the calcite botryoids and peloidal layers indicate formation and (or) precipitation out of cold Ordovician deep-marine waters. To the contrary of botryoids at cold methane seeps, the botryoids associated with the modern and Ordovician hot vents do not show the negative δ13CVPDB ratios indicative of microbial isotopic fractionation. Therefore, any microbial-derived HCO3– has been overwhelmed by the isotopically heavier marine-derived carbon during the open-system diagenesis. Carbonate-rich serpentinites should be carefully revisited in the search for evidence of microbial life in the Precambrian, as the negative δ13CVPDB ratios used as fingerprints of biological activity are not always reliable.
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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 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.006 | 0.001 |
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".