Tide-influenced sedimentation in a rift basin—Cretaceous Qishn Formation, Masila Block, Yemen: A billion barrel oil field
Bibliographic record
Abstract
Abstract The Lower Cretaceous Qishn Clastics Member in Masila Block 14, Hadhramaut region, Republic of Yemen, has estimated reserves of 1.1 billion bbl recoverable oil and has produced 600 million bbl of oil. Sedimentation took place in an elongate paleogulf of the Say'un-al Masila basin, with open-marine carbonates to the east. The Qishn Clastics Member unconformably overlies mixed carbonates and clastics of the Sa'af Member. Lower Qishn onlap resulted in deposition of brackish and tidal (likely macrotidal) estuarine to open-bay or gulf deposits. The middle portion of the lower Qishn Clastics Member shows evidence of arid nonmarine sedimentation, including debris-flow deposits, red beds, and shale-clast conglomerates, in turn, overlain by interfingering coastal and nonmarine deposits. The lower Qishn Clastics Member is truncated by a sequence boundary overlain by an extensive sandstone deposited in a low-accommodation braid plain close to the shoreline. A flooding surface is present at the top of the sandstone, over which progradational, tide-influenced deltaic strata were deposited. Delta progradation culminated in shallow-water clastic dolomitic deposits on the coastal plain. With subsequent transgression, a rising water table caused a nonmarine flooding surface with lakes and lacustrine deltas, overlain by tidal-flat deposits. Ongoing transgression resulted in wave ravinement overlain by shallow-shelf clastics and then deposition of slightly deeper shelf carbonates. The uppermost unit comprises bioturbated, clastic-shelf deposits related to a drop in relative sea level. Throughout much of the Qishn Clastics interval, accommodation was moderate, except for low accommodation associated with regional sheet sandstone at the base of the upper Qishn Clastics Member. Virtually all marine and brackish deposits show evidence of tidal sedimentation. Climate was arid and seasonally wet.
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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 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".