A paleomagnetic study of ca. 580 Ma volcanics near Grand Bank, Avalon zone of Newfoundland, and implications for true polar wander in the ediacaran
Bibliographic record
Abstract
Paleomagnetic studies suggest that Laurentia moved from the equator to the pole and then back \nagain within ~60 Ma during the Ediacaran. Hypotheses to explain the large 90⁰ apparent oscillations \ninclude unreliable paleomagnetic data and/or unreliable dating and complex magnetic \nfield behaviour. Inertial interchange true polar wander (IITPW) has also been suggested. Since \nIITPW would be a global event, it would require the large oscillations suggested by the paleomagnetic \nrecord of Laurentia to have affected all the continents in the Ediacaran. Such oscillations \nhave been found in selected paleomagnetic data from Baltica and West Africa but not Australia. \nAvalonia paleomagnetism also does not appear to show the oscillations expected from the IITPW \nhypothesis. The present study provides new paleomagnetic data for the Marystown Group volcanics, \ndated at 580±3 Ma, collected near Grand Bank in the Avalon Zone of Newfoundland. \nThe volcanics were studied with alternating field and thermal demagnetization which showed that \nremanence is carried mostly by magnetite rather than hematite. Seven sites provide stable remanence \ndirections with mean tilt-corrected declination and inclination of D=287⁰ and I=58⁰ (α95 = \n13.7⁰). A positive conglomerate test, using rhyolitic crystal lithic tuff clasts from an agglomerate \nwithin the section of flows, shows that the magnetite-bearing clasts carry primary remanence. \nMagnetic polarity reversals are also present within the section (six normal flows and one reversed \nflow). The corresponding paleolatitude is 39⁰+17/-13⁰ at 580±3 Ma. This agrees with the paleolatitude \nof 35⁰+11/-10⁰ at 580±10 Ma previously found for three basalt flows and five red bed sites \nin the Marystown Group (omitting the likely Devonian Famine Back Cove basalts). The Marystown \nGroup results, along with other stable paleomagnetic data from Avalonia, suggest that Avalonia \nremained at mid to low latitudes during the mid-Ediacaran. The declination of Avalonia suggests \nthat it remained at 225⁰ from 606 Ma to 592 Ma and then underwent a steady change towards \n330⁰ at 550 Ma. Although IITPW cannot be disproved for the mid-Ediacaran, it is more likely \nthat complex magnetic field behaviour is the reason multiple large oscillations can be seen in the Laurentia, Baltica, and West African Craton paleomagnetic data.
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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 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".