Monazite as a provenance indicator for the Lower Cretaceous reservoir sandstones, Scotian Basin
Bibliographic record
Abstract
Geochronology of detrital monazite is a valuable tool for interpreting the detrital petrology of sedimentary basins. Because of its hardness, monazite can be transported long distances by rivers, but because it is susceptible to dissolution under acidic conditions, second cycle monazite is rarely abundant. Monazite geochronology has been applied to sandstones from the latest Jurassic and Lower Cretaceous Missisauga and Logan Canyon formations of the Scotian basin, in order to assess sediment sources and dispersal pathways for the deltaic sandstones. These sandstones are the principal reservoir rocks for oil and gas in the Scotian Basin. A total of 324 detrital monazite grains were identified from Lower Cretaceous sandstones from ten offshore fields or individual wells, providing an east to west transect of the Scotian Basin. Monazite grains were characterized by secondary electron or backscattered electron images, showing external morphology, zoning and inclusions, together with WDS X-ray maps and variations in major element chemistry (REE, Th, Y). From these grains, 688 age determinations with 1sin errors < ±20% were obtained by electron microprobe analysis. Based on all these criteria, about 30 distinct types of monazite grain are recognized, that show distinctive variations in their geographic and stratigraphic distribution and abundance. The one analysed sample from the Naskapi N-30 well appears to have had a discrete river source, draining only the Meguma Terrane. On the one hand, grains with a 440-550 Ma age mode in the central Scotian Basin closely resemble the dominant grain type in the Chaswood Formation in Nova Scotia, suggesting supply from the inboard Appalachian terranes of New Brunswick. On the other hand, the central Scotian Basin also includes common grains with Proterozoic ages that are absent from the Chaswood Formation, suggesting important supply from a river draining through Cabot Strait from western Newfoundland, or perhaps with minor supply from Labrador and the North Shore of Quebec. The Lower Missisauga Formation at Thebaud and Venture has significantly more Neoproterozoic monazites compared with the Upper Missisauga Formation and Cree Member throughout the central Scotian Basin. In the eastern Scotian Basin, Proterozoic grains predominate, but most monazite types are also recognised in the central Scotian Basin. This distribution suggests different dominant river supply to Peskowesk compared with the central Scotian Basin, probably draining the eastern side of the Long Range and the Appalachian rocks of western Newfoundland.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.014 | 0.001 |
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".