Age and provenance of the Middle Jurassic Norphlet Formation of south Texas: stratigraphic relationship to the Louann Salt and regional significance
Bibliographic record
Abstract
The age and provenance of the Norphlet Formation in south Texas and its stratigraphic relationship to the Louann Salt are documented for the first time using new detrital zircon U–Pb geochronological data. Nine samples from the Hockley salt diapir and four deep wells (three in south Texas, one offshore México) yielded 1001 zircon ages and eight age populations; the most important of these are Neoproterozoic (900–541 Ma), Cambrian–Middle Mississippian, and arc-related Middle to Late Mississippian–Permian–Triassic and Triassic–Jurassic, the latter two representing the first evidence of Nazas and Guerrero arc extrusive volcanism reaching south Texas. Statistical analyses of these data and published zircon ages support the interpretation that these age populations reflect the dominance of peri-Gondwanan sources, especially the Yucatán/Maya Block and Coahuila terrane, although Laurentian sources probably contribute to specific populations. The maximum depositional age of upper Norphlet Formation sandstones is 165.5 ± 1.5 Ma (Callovian). These upper sandstones are separated from lower Norphlet sandstones by an unconformity spanning 1.5–5 myr; the lower sandstones are interbedded with halite of the Louann Salt, and may be as old as Bathonian. These new data may be of regional significance when applied to future models of the Jurassic evolution of the Gulf of Mexico. Supplementary material : The detrital zircon dataset for this study, DZmix and DZmds model parameters, DZmix statistics and references for figures are available at https://doi.org/10.6084/m9.figshare.c.6002060
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| 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 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".