High-resolution organic carbon isotope record across the Cretaceous–Tertiary boundary in south-central Alberta: implications for the post-impact recovery rate of terrestrial ecosystems and use of δ<sup>13</sup>C as a boundary marker
Bibliographic record
Abstract
A high-resolution study identified a δ13C excursion of –1.8 to –2.3 in terrestrial organic matter across the Cretaceous–Tertiary (K–T) boundary at two localities in the Scollard Formation of south-central Alberta, one of the northernmost occurrences of the K–T boundary in terrestrial settings. δ13C values are at their lowest within 6 cm above the K–T boundary claystone and return to pre-boundary levels within 10 cm above the boundary claystone. Statistical analyses reveal that the K–T isotopic shift in Alberta is related to the nature of floral changes that occurred across the K–T boundary. A radiometrically dated bentonite resting on the boundary-hosting Nevis coal at one of the localities permits us to estimate that the terrestrial carbon cycle recovered ~100 000 years after the K–T boundary event, a value that supports an existing hypothesis that terrestrial ecosystems recovered more rapidly than marine ecosystems. The organic carbon isotope record of the entire Scollard Formation demonstrates that the δ13C excursion across the K–T boundary did not reach anomalously low values by late Maastrichtian standards in Alberta. Furthermore, the occurrence of the K–T carbon isotope shift within a restricted stratigraphic interval (<10 cm) greatly limits the probability of its preservation in the context of terrestrial sedimentary environments. These observations suggest that, on their own, δ13C profiles may be unreliable for locating the K–T boundary (and possibly other geologically instantaneous events) and that they should be used in combination with other approaches (e.g., palynology) to identify the K–T boundary in sections lacking the boundary claystone and iridium anomaly.
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 | 0.001 | 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) | 0.001 | 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".