Has Earth ever been ice-free? Implications for glacio-eustasy in the Cretaceous greenhouse age using high-resolution sequence stratigraphy
Bibliographic record
Abstract
Abstract Controls on high-frequency sequences formed during super-greenhouse conditions in the Late Cretaceous Western Interior Seaway remain equivocal because of the active foreland basin tectonic setting and the lack of direct evidence of polar glaciations to support a glacio-eustatic origin. This paper quantifies eustatic sea-level changes based on high-resolution sequence stratigraphic analysis and improved chronometry of shallow marine deposits of the Late Cretaceous Gallup Sandstone in New Mexico, USA. Backstripping techniques remove tectonic and compactional subsidence and enable quantification of the magnitude of eustatic sea-level change, that allow evaluation of the dominant controls on the high-frequency sequences to resolve the role of orbitally controlled, climate-driven eustasy versus tectonics. Sixty-five parasequences, constituting 29 parasequence sets and 12 sequences are identified in the ∼1.2 m.y. duration of the Late Cretaceous Gallup system. New 40Ar/39Ar dating of bentonites constrains the durations of the individual parasequences, parasequence sets, and sequences, and that these match Milankovitch periodicity, indicating an orbital climate control. The magnitudes of sea-level changes between parasequences range between −28 m and +22 m, which are compatible with hypotheses of both aquifer and glacio-eustasy. Aquifer-eustasy predicts a reciprocal relationship between floodplain cycles and shallow marine sequences, such that aquifer drawdown and falling water tables should correlate to rising sea levels (highstands), whereas increased aquifer storage and rising water tables should correlate to falling sea levels (lowstands). Our preliminary observations show synchronous, versus reciprocal, relationships that may be more compatible with a glacio-eustatic origin. The results of this study support the hypothesis that the Cretaceous greenhouse was marked by high-frequency, low-amplitude glaciations driven by orbital climate cycles, but further work is required to evaluate the contribution of aquifer-eustasy.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.002 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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 teacher head, 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".