Magnetostratigraphic investigations of the lower paleozoic system boundaries, and associated paleogeographic implications
Bibliographic record
Abstract
Continued refinement of a global Geologic Timescale solely through increased precision of biostratigraphic correlations philosophically suffers from the inherent lack of a universal reference frame. Geomagnetic polarity reversals, which occur relatively rapidly and simultaneously on a global scale, can provide the necessary universal reference frame, provided the polarity reversals are correlated within a well-defined biostratigraphic framework and occur with a fairly distinctive pattern. Magnetostratigraphic correlations across the Cambrian-Ordovician boundary interval indicate that normal polarity zones correlative to Late Cambrian conodont zones occur within sections from Texas, northern China, western Newfoundland, central Australia, and possibly Kazakhstan. These correlations strongly suggest that temporal differences may exist between sections in the absolute time value of key biostratigraphic horizons. There may also be very brief normal polarity zones correlative with Early Ordovician conodont and graptolite zonations, but those relationships have not yet been well-established. Magnetostratigraphic correlations allow polarity to be unambiguously determined for the relevant continental unit, even in the absence of previous paleomagnetic investigation. Extension of this to Late Cambrian and Early Ordovician paleogeographic problems indicate that North China, and probably also South China, underwent approximately 90° counterclockwise rotation during the Cambrian, and were most likely attached to or very near the present northern margin of Australia during that time. Paleomagnetic results from Upper Silurian through Middle Devonian carbonates of the Barrandian area, Czechoslovakia have at least three components of magnetization preserved within them. Two of the components appear to pass the fold test, indicating that they pre-date the deformation creating the basin, constrained to be not later than Late Carboniferous. Differences between the two components probably correspond to different times of acquisition, and may record rapid plate motion of the Bohemian Massif during the Middle Paleozoic. Paleomagnetic results from Upper Ordovician to Lower Silurian carbonates from Anticosti Island, Quebec are not reliable because of the extremely weak magnetization of these rocks. Sharp increases in intensity during thermal demagnetization experiments may provide insight into the chemical changes which occur within carbonate rocks during thermal demagnetization, but at the present time those phenomenon are not well understood.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.004 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| 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 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".