An anomalous shallow-marine ichnofacies gradient from the Lower Devonian Talacasto Formation of the Argentine Precordillera
Bibliographic record
Abstract
The Lower Devonian Talacasto Formation in western Argentina records deposition in wave-dominated shallow-marine environments. This unit comprises a large-scale progradational succession, transitioning from black, parallel-laminated mudstone in the lower interval to siltstone and very fine- to medium-grained sandstone in the upper interval. The succession spans environments ranging from the shelf to the upper shoreface. Three trace-fossil assemblages have been identified: (1) Palaeophycus assemblage, including Palaeophycus heberti, P. tubularis, and Helminthopsis isp., corresponding to the shelf; (2) Phycosiphon-Zoophycos assemblage with Zoophycos isp., Phycosiphon incertum, Nereites missouriensis, and Chondrites isp., ranging from the lower offshore to the lower/middle shoreface; and (3) Rosselia assemblage containing Rosselia socialis, Skolithos isp., Arenicolites isp., Palaeophycus tubularis, and escape trace fossils, corresponding to the offshore transition and the lower/middle shoreface. Two ichnofacies have been identified: distal Cruziana and Skolithos Ichnofacies. Unlike the traditional ichnofacies model, the Talacasto Formation shows an onshore expansion of the distal Cruziana Ichnofacies, which is present not only in the lower offshore, but in the upper offshore, offshore transition, and lower shoreface as well. In contrast, the archetypal Cruziana Ichnofacies is not present. This anomalous distribution is attributed to an interplay of ecologic and taphonomic factors combined with the restricted topography of the southern portion of the Precordillera Basin. Low-energy conditions and high food supply for prolonged times allowed for the obliteration of shallow-tier trace fossils by deeper and widely distributed burrows, favoring the onshore expansion of the distal Cruziana Ichnofacies and preventing the preservation of the typical elements of the archetypal Cruziana Ichnofacies. Areas subjected to greater storm influence provided favorable conditions for the development of the Skolithos Ichnofacies.
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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 | 0.000 | 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) | 0.002 | 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".