Distribution of Diagenetic Alterations in Siliciclastic Shoreface Deposits within a Sequence Stratigraphic Framework: Evidence from the Upper Jurassic, Boulonnais, NW France
Bibliographic record
Abstract
Abstract The distribution of diagenetic alterations in Upper Jurassic, siliciclastic shoreface sediments from NW France has been linked to the sequence stratigraphic framework. Calcite cement in mudrocks and sandstones of the transgressive (TST) and lower part of the highstand (HST) systems tracts is microcrystalline and occurs as continuously cemented layers and stratabound concretions. The average δ18OV-PDB (−2.6‰) and 87Sr/86Sr (0.7078) compositions of microcrystalline calcite indicate precipitation from largely marine pore waters. Calcite cement in sandstones of the forced regressive wedge (FRWST) and lowstand (LST) systems tracts is poikilotopic and occurs mainly as stratabound concretions. Complete dissolution of the carbonate grains and concomitant precipitation of poikilotopic calcite cement with low average δ18O (−5.3‰) and radiogenic Sr-isotope (0.70882) signatures suggest incursion of meteoric waters into sandstones during relative sea-level lowstand. The poorly lithified sandstones interbedded with sandstones cemented by poikilotopic calcite concretions display evidence of diagenesis under episodes of arid to semiarid paleoclimate, including: (i) partial cementation by opal, chalcedony, gypsum, and minor vadose calcite cement, (ii) mechanically infiltrated clays and Fe-oxides, and (iii) secondary porosity owing to partial dissolution of carbonate grains. The integration of diagenesis into sequence stratigraphy allows better elucidation and prediction of the spatial and temporal distribution of diagenetic alterations and related reservoir-quality modifications in shoreface sediments.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".