DIAGENETIC‐GEOCHEMICAL PATTERNS AND FLUID EVOLUTION HISTORY OF A LOWER JURASSIC PETROLEUM SOURCE ROCK, MIDDLE ATLAS, MOROCCO
Why this work is in the frame
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Bibliographic record
Abstract
Pliensbachian to earliest Toarcian marls and argillaceous limestones exposed at the surface near Aït Moussa (Boulemane Province, Middle Atlas) include the only examples of effective petroleum source rocks so far known in the Moroccan Atlas rift basins. The outcrop interval includes hemipelagic, peri‐Tethyan low latitude source rocks with Type II kerogen (total thickness of 2.5 m with mean TOC of around 3.2%). Early diagenetic, anoxic remineralisation of sedimentary organic matter resulted in hydraulic fractures, calcite cementation, a negative shift of carbon and oxygen stable isotopes relative to marine values (Δδ 13 C = ‐1.1; Δδ 18 O = ‐2.0), framboidal pyrite, and relative enrichment of the middle weight rare earth elements (REE). In combination, these attributes of early diagenesis may assist in the identification of other source rock intervals of similar age and setting. Progressive burial produced three generations of Fe‐calcite cemented veins, followed by three generations of replacive dolomite and concluded by ankerite replacing dolomite. Compaction fluids initially caused a slight positive shift of δ 13 C values (Δδ 13 C =+0.4), a flattening of the REE distribution pattern and an increase in REE content, together related to the dewatering of clay. Dolomitizing fluids (dol‐2 and dol‐3) record a positive shift of δ 13 C values (Δδ 13 C =+0.9) suggesting the effects of methanogenesis or an uptake of heavy δ 13 C from underlying rock formations during fluid migration. Dol‐3 is an Fe‐bearing saddle dolomite that carries a positive Eu‐anomaly (Eu/Eu*= 8.1) best explained by ascending hydrothermal fluids which are presumably of Middle Eocene age. A first migration of bitumen is recorded as fluorescent inclusions in dol‐2 (Late Jurassic ‐ Cretaceous), but bituminous fluids remained normally pressured until the establishment of inclined stylolites during Late Eocene tectonic compression. Comparative organic‐geochemical analyses (GC, NMR of inclusions, non‐expelled and expelled bitumen) indicate that thermal maturation advanced significantly after the onset of migration. Differences in terms of Pr/n‐C 17 , Ph/n‐C 18 ratios and aromaticity corroborate the effects of differential expulsion. An exploration strategy should consider both secondary migration via opened tectonic stylolites in association with late‐diagenetic fractures and a persisting tightness that then could have created an unconventional oil reservoir.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 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 it