Palaeozoic stromatoporoid diagenesis: a synthesis
Bibliographic record
Abstract
Abstract Palaeozoic stromatoporoids, throughout their 100-million + year history (Middle Ordovician to Late Devonian and rare Carboniferous), are better preserved than originally aragonite molluscs, but less well-preserved than low magnesium-calcite brachiopods, bryozoans, trilobites and corals. However, the original mineralogy of stromatoporoids remains unresolved, and details of their diagenesis are patchy. This study of approximately 2000 stromatoporoids and the literature recognises three diagenetic stages, applicable throughout their geological history. Timing of processes may vary in and between stages; some components are not always present. Stage 1, on or just below sediment surface, comprises the following: micrite filling of upper gallery space after death, then filling of any remaining space by non-ferroan then ferroan calcite in decreasing oxygen of pore-waters; partial lithification of associated sediment from which stromatoporoids may be exhumed and redeposited, evidence of general early lithification of middle Palaeozoic shallow-marine carbonates; microdolomite formation, with the Mg interpreted to have been derived from original high-Mg calcite (HMC) mineralogy (likely overlaps Stage 2). Stage 2, short distance below sediment surface, comprising the following: fabric-retentive recrystallisation (FRR) of stromatoporoid skeletons forming fabric-retentive irregular calcite (FRIC), mostly orientated normal to growth layers, best seen in cross-polarised light. FRIC stops at stromatoporoid margins in contact with sediment and bioclasts. FRIC geometry varies, indicating some taxonomic control. Evidence that FRIC formed early in diagenetic history includes syntaxial continuation of FRIC into some sub-stromatoporoid cavities (Type 1 cement), although others were pre-occupied by early cement fills (Type 2 cement) formed before FRR, preventing syntaxial continuation of FRIC into cavities. Likely contemporaneous with FRIC formation, stromatoporoids in argillaceous micrites drew carbonate from adjacent sediment during reorganisation of argillaceous micrite into limestone–marl rhythms that are also early diagenetic. Stage 3, largely shallow burial, comprises the following: dissolution and silicification, but these may have occurred earlier in stromatoporoid diagenetic histories (more data required); burial pressure dissolution forming stylolites.
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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 | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.004 | 0.007 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.008 | 0.001 |
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".