Pennsylvanian emergence of anabranching fluvial deposits: the parallel rise of arborescent vegetation and fixed-channel floodplains
Bibliographic record
Abstract
Anabranching (anastomosing) rivers are low-energy fluvial systems consisting of multiple channels separated by stable islands which evolve over time through avulsion. Such river systems host a variety of terrestrial sub-environments and habitats that have been relatively common during the Mesozoic and Cenozoic and into the present day. Anabranching requires bank stability, usually provided by vegetation or cohesive floodplain muds, both of which were prominent in the fluvial realm by the Siluro-Devonian. However, based on a literature review of 144 Cambrian–Devonian and 188 Carboniferous fluvial successions, facies interpreted as anabranching river deposits do not appear in abundance until the Pennsylvanian (Bashkirian). Original field data from Carboniferous fluvial strata in Atlantic Canada and the SW USA support the assertion that a distinct suite of fluvial facies and sandbody geometries, still apparent in recent anabranching fluvial deposits, makes its first appearance at about this time. The channel deposits are narrow (width: thickness typically <15) with steep margins and aggradational fills, with little evidence for lateral accretion, and encased in floodplain muds with paleosols. Although it is rarely possible to demonstrate that the parent channels formed 3D networks, it is probable that some suites were anabranching. Although a few small, narrow channel bodies are known from Devonian and Mississippian formations, this “fixed-channel” style is conspicuously absent from older fluvial formations but is widespread from the Pennsylvanian onwards. It is argued that the seemingly delayed appearance of this fluvial style in part reflects the infrequency of repeated shortterm triggers for avulsion prior to a threshold-crossing increase in arborescent floodplain vegetation. The increase in arborescent vegetation through the Carboniferous would have resulted in an increase in the size, abundance, and distribution of large woody debris in fluvial channels. Such debris would have provided, for the first time, one of the most common triggers for river avulsion; as demonstrated by the fact that large log-jam deposits also first appear in the rock record during the Bashkirian.
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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 | 0.001 | 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".