Terminal Proterozoic-Early Cambrian ecosystems: ichnology of the Puncoviscana Formation, northwest Argentina
Bibliographic record
Abstract
The Puncoviscana Formation consists of a thick, folded and slightly metamorphosed succession of sandstones, mudstones and conglomerates of terminal Proterozoic to earliest Cambrian age, representing the metasedimentary basement of northwest Argentina. The Puncoviscana ichnofauna is recorded in lowermost Cambrian strata and includes a wide variety of ichnotaxa, such as Archaeonassa fossulata, Circulichnis montanus, Cochlichnus anguineus, Didymaulichnus lyelli, Diplichnites isp., Helminthopsis abeli, Helminthopsis tenuis, Helminthoidichnites tenuis, Multina isp., Nereites saltensis, Oldhamia antiqua, Oldhamia curvata, Oldhamia flabellata, Oldhamia radiata, Oldhamia isp., Palaeophycus tubularis, Saerichnites isp., Treptichnus pollardi and Volkichnium volki. Structures considered in previous studies as graphoglyptids (agrichnia), such as Protopaleodictyon and Squamodictyon, are reinterpretcd as wrinkle marks and elephant skin textures. Vertical dwelling structurcs (domichnia) are absent. Nearly all the ichnofossils in the association are oriented parallel to the bedding plane, displaying restriction to two-dimensional biotopes, and therefore they do not disturb the primary sedimentary fabric. The recognition of trace fossil associations in both shallow- and deep-marine deposits of the Puncoviscana Formation provides valuable information on evolutionary and ecological controls on Early Cambrian marine infaunal communities. Shallow-marine ichnofaunas are dominated by moderate- to large-sized, shallow grazing and feeding traces of deposit feeders. Deep-marine ichnofaunas are dominated by Oldhamia and non-specialised grazing trails and reflect lifeslyles relatcd to microbial matgrounds. Early Cambrian deep-marine ichnofaunas are of "Ediacaran aspect", recording persistence of relict communities after the onset of the "Agronomic Revolution" that pervaded shallow-marine ecosystems during those times. Early Cambrian tiering was moderately developed in both shallow- and deep-marine communities. Biogenie structures were emplaced within the uppermost millimetres of the sediment (i.e. micro-tiering), with the exception of burrowers that record post-event colonisation of tempestites and turbidites.
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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 | 0.001 | 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".