Detrital Zircon Evidence of a Recycled Orogenic Foreland Provenance for Alleghanian Clastic‐Wedge Sandstones
Bibliographic record
Abstract
Late Paleozoic synorogenic clastic wedges in the Appalachian foreland basin contain erosional detritus from the Alleghanian orogenic belt; however, the relative importance of detrital contributions from the frontal orogen, the orogenic hinterland, and the distal craton has not been resolved. To evaluate these components, we analyzed detrital zircons from two sandstones in the Pennington‐Lee clastic wedge in eastern Tennessee: the Lower Pennsylvanian Sewanee Conglomerate and the Middle Pennsylvanian Cross Mountain Formation. Ages of detrital zircons are similar in the two sandstones, ranging from 365 to 2860 Ma. The age range spans the Acadian and Taconic orogenies, the Grenville province, and pre‐Grenville rocks (Granite‐Rhyolite province, midcontinent orogens, and Superior province) of the Laurentian craton. The Acadian‐, Taconic‐, and Grenville‐age detrital zircons have sources in Alleghanian frontal crystalline thrust sheets. The pre‐Grenville zircons indicate an original source in the Laurentian craton (Canadian shield), and a longitudinal river system headed in the shield might have supplied detritus directly to the Appalachian foreland basin in Tennessee. Alternatively, all of the Proterozoic and Archean ages of zircons represented in the Sewanee and Cross Mountain sandstones have been identified in the detrital zircon populations of preorogenic Iapetan synrift and passive‐margin strata along the eastern Laurentian margin, suggesting a source of recycled zircons from preorogenic rocks exposed in Alleghanian thrust sheets. A lack of detrital zircons contemporaneous with the Alleghanian orogeny shows that Alleghanian igneous rocks had not been integrated into the drainage network and/or had not been exhumed. The age distribution of the detrital zircons suggests deformation and erosion of rocks of the Laurentian margin and emphasizes the importance of preorogenic architecture of the continental margin in the construction and erosion of the orogenic belt.
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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 | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 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".