Early Cretaceous giant glendonites: A record of (sub-)millennial-scale cooling?
Bibliographic record
Abstract
The Lower Cretaceous succession in Svalbard contains numerous glendonites, pseudomorphs after the cold-water carbonate mineral ikaite, which have been used in conjunction with other evidence to argue for episodic global cooling punctuating the greenhouse climates of the Early Cretaceous. Recent fieldwork in central Spitsbergen has recovered giant bladed glendonites of up to half a metre long, the largest ever recorded in a Lower Cretaceous site, and comparable in size to outlier glendonites found in similar-aged strata of the Sverdrup Basin in Arctic Canada. Unlike the rosette to pineapple-like morphologies seen in some of the largest Canadian Arctic specimens, the new finds in Svalbard appear only as single or crossed blades. These large glendonites, found clo indicate that very local variations in pore water chemistry governed whether numerous small ikaite crystals or few large crystals grew. Taken with evidence from modern ikaite and other large ancient glendonites, we argue that large glendonites such as these (>30 cm long) are pseudomorphs after ikaites that took, at the shortest, decades, but potentially millennia to even tens of millennia to attain their massive size. As growth of the parent ikaite took place in the sediments just below the seafloor of the shallow, epicontinental seas of the High Arctic (then situated at c. 63–66°N), this is consistent with the hypothesis that geologically short-term cooling episodes interrupted the background warmth of the Early Cretaceous greenhouse, although the duration, extent, and cause of such cooling is still debated. • Largest glendonites ever discovered in a Cretaceous sections found in Svalbard. • Modern ikaite growth rates suggest they could have formed over decadal timescales. • Sedimentary relationships give an upper limit for their growth of millennial timescales. • These findings indicate short-term cooling often not resolvable in deep-time records.
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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 | 0.001 |
| 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 | 0.001 |
| 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".