Distinguishing tectonic versus eustatic controls in Turonian strata of the Western Interior Seaway
Bibliographic record
Abstract
Abstract It is hypothesized that high-frequency, low-amplitude sea-level changes during the Turonian ultra-greenhouse period were caused by Milankovitch-driven freeze/thaw cycles in ephemeral ice sheets in Antarctica or aquifer eustasy. Here, we use two-dimensional airy back-stripping of five Turonian formations distributed along 1500 km of depositional strike from Alberta, Canada, to New Mexico, USA, within the Cretaceous Western Interior Seaway of North America, to isolate eustatic and tectonic effects from accommodation produced by sediment compaction and subsidence. The timing of eustatic cycles is constrained by newly acquired 40Ar/39Ar sanidine ages and regional biostratigraphy from the Ferron Notom deltaic complex and Gallup Sandstone, as well as previously reported radiometric ages based on regional biostratigraphic correlations from the Ferron Last Chance delta and Cardium Formation. Backstripped sea-level changes show frequencies that match Milankovitch cycles within error. We show primarily symmetrical sea-level changes, with falls and rises that average from +20 to 30 m in amplitude. The symmetry and magnitudes of sea-level changes are more consistent with glacio-eustatic than tectonic mechanisms. They are probably too large to be related to aquifer eustasy or steric effects. Several units show local tectonic rebound that likely enhanced the magnitude of sea-level drops. If Antarctic ice sheets had been present during the Turonian stage, they would have likely nucleated around the Gamburtsev Mountains, which would have been sufficiently high and had low erosion rates that are inconsistent with an ice-free environment.
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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 | 0.001 |
| Scholarly communication | 0.000 | 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 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".