Diagenesis and Reservoir-Quality Evolution of Fluvial Sandstones During Progressive Burial and Uplift: Evidence from the Upper Jurassic Boipeba Member, Reconcavo Basin, Northeastern Brazil
Bibliographic record
Abstract
Abstract The reservoir quality of fluvial sandstones of the Upper Jurassic Boipeba Member, Recôncavo basin, northeastern Brazil, is highly heterogeneous and controlled by eodiagenesis under semiarid climate, mesodiagenesis during burial to a depth of 3500 m, and telodiagenesis due to local uplift. Eodiagenesis resulted in mechanical compaction, calcite cementation, clay infiltration, and limited grain dissolution, whereas mesodiagenesis resulted in the precipitation of calcite cement and quartz over growths, intergranular quartz-grain dissolution, chloritization and illitization of smectite, and albitization of feldspars. Sandstones continuously buried at maximum burial depths of about 1600 m (T = 65°C) since 125 Ma display a relatively greater degree of mesogenetic modifications and, on average, poorer reservoir quality than sandstones that were buried deeper (2100 m, T = 75°C) prior to uplift, but only since 13 Ma. Uplift, which affected the sequence along the western border of the basin, has resulted in telogenetic dissolution of framework silicates and formation of kaolinite. Relatively good reservoir quality in the deeply buried sandstones occurs when (1) the grains are coated with a thin layer of chloritized infiltrated smectite, (2) there is little or no pseudomatrix, and (3) there are widely scattered patches of eogenetic calcite cement that supported the framework of sandstones against compaction.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 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".