Geochemistry of the Tremadocian Tiñu Formation (Southern Mexico): Provenance in the Underlying ∼1 Ga Oaxacan Complex on the Southern Margin of the Rheic Ocean
Bibliographic record
Abstract
In southern Mexico, the Tremadocian Tiñu Formation with a Gondwanan fauna rests unconformably upon the ∼1 Ga Oaxacan Complex, and is unconformably overlain by Carboniferous sedimentary rocks containing a Laurentian fauna. The Tiñu Formation is inferred to represent deposition along the southern margin of the Rheic Ocean in its early stages of development. The geochemistry of sandstones and shales of the formation show: (1) high iron, magnesium, and titanium, indicating chemical immaturity in some samples; (2) a positive correlation between Zr and SiO2; (3) derivation from crust with mafic and felsic components; (4) LREE enrichment with a moderate Eu anomaly; (5) low εNd(t) values (-7.0 to 7.8, calculated for t = 485 Ma); and (vi) Mesoproterozoic TDM ages (1.5-1.83 Ga). Taken together, these data indicate a proximal source with two main components, an ancient, felsic-intermediate, moderately differentiated continental component, and a minor mafic component. These data are consistent with derivation from the underlying Oaxacan Complex, with little or no input from distal or juvenile sources. This is in accord with: (1) published Nd data from the Oaxacan Complex that yielded TDM ages of 1.5-1.8 Ga; (2) detrital zircon data from the Tiñu Formation, which gave 990-1200 Ma ages; and (3) the Gondwanan affinity of Silurian fauna from northeastern Mexico. The lack of a juvenile, Cambrian signature in these geochemical data is inconsistent with an origin in the Iapetus Ocean, and is compatible with a rift-to-drift model involving opening of the Rheic Ocean.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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 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".