Drainage reorganization during breakup of Pangea revealed by in-situ Pb isotopic analysis of detrital K-feldspar
Bibliographic record
Abstract
The Pb isotopic composition of detrital K-feldspar grains can be rapidly measured using laser ablation MC-ICPMS. The feldspar Pb signal can survive weathering, transport and diagenesis, and careful targeting avoids problems with inclusions and alteration. As common Pb isotopic compositions show broad (100s km scale) variation across the continents, the method provides a powerful provenance tracer for feldspathic sandstones. Here we combine a new Pb domain map for the circum-North Atlantic with detrital feldspar Pb isotopic data for Triassic and Jurassic sandstones from basins on the Irish Atlantic margin. The Pb compositions reveal otherwise cryptic feldspar populations that constrain the evolving drainage pattern. Triassic sandstones were sourced from distant Archean and Paleoproterozoic rocks, probably in Greenland, Labrador and Rockall Bank to the NW, implying long (>500 km) transport across a nascent rift system. Later Jurassic sandstones had a composite Paleo- and Mesoproterozoic source in more proximal sources to the north (<150 km away). Little or no feldspar was recycled from Triassic into Jurassic sandstones, and the change in provenance is consistent with distributed, low relief Triassic extension in a wide rift, followed by narrower Jurassic rifting with more localised fault-controlled sediment sources and sinks.
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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 | 0.002 |
| 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) | 0.003 | 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".