Hirnantian (Late Ordovician) chemostratigraphy of Anticosti Island, eastern Canada: Comparison of stable carbon and oxygen isotope compositions from brachiopod shells and bulk carbonate
Bibliographic record
Abstract
Brachiopod shells and bulk micritic carbonate have been widely used for Paleozoic stable carbon (C) and oxygen (O) isotope studies of paleoclimate and the carbon cycle. This study presents a systematic sampling and examination to determine the C and O isotope variations in well-preserved Hirnantian brachiopod shells from the Ellis Bay Formation of Anticosti Island. Analyses include intra-shell, inter-shell and inter-species comparisons, as well as comparisons among punctate, epipunctate and impunctate shells, and between shell substance and micritic matrix inside the shell. Intra-shell isotopic variations show a common trend of increasing δ 13 C (usually ~0.5 ‰, up to ~1 ‰) from early to late growth stages in all ten brachiopod species examined, indicating a pristine isotopic signature and the absence of diagenetic overprinting. In some taxa (e.g., Eospirigerina , Hindella , Parastrophinella ), intra-shell and inter-shell δ 13 C variations reach 1.5–2.0 ‰, sufficient to encompass moderate-amplitude excursions in most Late Ordovician chemostratigraphic records. Inter-species differences in average δ 13 C and δ 18 O for shells are generally small at a given stratigraphic level, supporting the comparability of isotopic signatures among brachiopod shells from a single locality, regardless of family or order. Despite species-specific variations, δ 13 C and δ 18 O are broadly consistent between brachiopod shells and bulk micrite samples in most cases. During the peak Hirnantian Isotopic Carbon Excursion (HICE), however, the δ 13 C of brachiopod shells are significantly higher than those of bulk micrite from the Laframboise Member (middle to upper Hirnantian). This supports the view that brachiopod shells can provide a more sensitive and faithful archive of ancient seawater composition, serving as a reliable proxy for paleoenvironment reconstruction, as demonstrated here for the Hirnantian glaciation event.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.002 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".