“Short” or “Long” Hettangian? Astronomical chronometry on the duration of lower Jurassic Hettangian stage and the recovery dynamics following the end – Triassic mass extinction. 
Bibliographic record
Abstract
The end-Triassic mass extinction (ETME) and global climatic perturbation coincide with the onset of Central Atlantic Magmatic Province (CAMP) emplacement. The associated perturbation to the global carbon cycle is reflected by a ~ 3 – 6 ‰ negative carbon isotope excursion (CIE) coinciding with the ETME. The magnitude and duration of the negative CIE are however poorly constrained. Furthermore, the Early Jurassic Hettangian stage, marking the initial recovery phase following the end-Triassic mass extinction, has been the subject of significant debate over its precise timing and duration. Estimated Hettangian stage durations derived from cyclostratigraphic and U-Pb geochronological analyses vary between a ‘short Hettangian’ of 1.8 – 2.5 Myr, and a ‘long Hettangian’ of 3.9 – 4.4 Myr. Poor time constraints for the Triassic–Jurassic interval impact understanding of the timing and rate of biogeochemical cycling, environmental and biological recovery after the end-Triassic mass extinction, and global climatic perturbation.We here conducted carbon isotopic and cyclostratigraphic analysis of the well-preserved, biostratigraphically complete, and expanded Hettangian succession in the Carnduff-2 core of the Larne Basin (Northern Ireland), nearby the Waterloo Bay outcrop. The studied sedimentary succession (~120 m in core) stratigraphically spans the upper Rhaetian (upper Triassic), including the end-Triassic mass extinction, Hettangian, and lower Sinemurian (lower Jurassic), and consists of predominantly mudstone, with varying degrees of limestone and silt throughout the succession. Cyclostratigraphic analyses of elemental and carbonate concentration data show a hierarchy of dominant frequencies, interpreted to reflect long and short eccentricity, obliquity, and precession. These observations suggest a total duration of ~2.2 Myr for the Hettangian Stage with a sedimentation rate of ~ 4.1 cm/kyr, confirming the ‘short-Hettangian’ hypothesis. The negative carbon isotope excursion (CIE) duration, which coincides with the ETME, is estimated at ~290 kyr. The first occurrence of the Jurassic ammonite Psiloceras tillmanni, marking the onset of Hettangian biotic recovery after the ETME across the British Isles, ~320 kyr after the end-Triassic negative CIE, suggesting a prolonged period of biotic demise in response to CAMP induced climatic and environmental upheaval at this time.Key Words: end-Triassic mass extinction, Early Jurassic, Hettangian stage, Milankovitch cycles
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.063 | 0.021 |
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".