ICHNOLOGY OF MUDDY SHALLOW-WATER CONTOURITES FROM THE UPPER JURASSIC–LOWER CRETACEOUS VACA MUERTA FORMATION, ARGENTINA: IMPLICATIONS FOR TRACE-FOSSIL MODELS
Bibliographic record
Abstract
ABSTRACT Contourites are increasingly being recognized in ancient fine-grained depositional environments. However, detailed ichnologic analyses focusing on shallow-water examples of these deposits are scarce. The Upper Jurassic–Lower Cretaceous Vaca Muerta Formation from Argentina constitutes an important unconventional reservoir that displays dm- to m-thick, laminated, rippled and bioturbated, crinoidal mudstone and fine to coarse mudstone deposited by wind- and thermohaline-driven contour currents. Four ichnofabrics were recognized in three facies associations. The Palaeophycus heberti ichnofabric is dominant in facies association 1, forming highly bioturbated intervals. The Palaeophycus heberti, Nereites isp., and Phycosiphon incertum ichnofabrics are present in facies association 2, displaying highly, moderately and sparsely bioturbated intervals, respectively. This association is locally characterized by m-thick successions comprising an upward decrease and then increase in bioturbation index, which may have a similar origin to bigradational sequences. The Equilibrichnia-Fugichnia ichnofabric mostly occurs in facies association 3 and less commonly in 2, forming distinctive bioturbated intervals within sparsely bioturbated successions. Benthic activity was controlled by food distribution, oxygenation, hydrodynamic energy, and water turbidity. Food was delivered to the surface or in suspension by currents, promoting deposit- or suspension-feeding strategies in the infauna, respectively. Oxygen levels increased during contour current activity yet remained relatively low (upper dysoxic). Hydrodynamic energy controlled bioturbation intensity, resulting in lower degrees of bioturbation during higher energy events. Suspension-feeding strategies suggest that water turbidity was relatively low during current transport. The herein example increases our understanding of environmental controls of shallow-water contour currents, supporting the fact that high bioturbation levels are typical of contourite deposits and providing an example of muddy contourites showing high preservation of sedimentary structures due to oxygen deficiency in bottom waters.
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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 | 0.002 | 0.002 |
| 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) | 0.003 | 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".