Karst topography paces the deposition of lower Permian, organic-rich, marine–continental transitional shales in the southeastern Ordos Basin, northwestern China
Bibliographic record
Abstract
ABSTRACT Organic-rich continental and marine–continental (i.e., transitional) shales are characterized by numerous hydrocarbon production layers having an uneven horizontal distribution, which are challenging to locate and exploit. We examined the effects of karst topography on organic carbon accumulation during the early Permian in the southeastern Ordos Basin, northwestern China, using outcrop and well data. Our study involved geomorphological, sedimentological, petrological, and geochemical methods. We identified a regional unconformity on the Dongdayao Limestone (DDYL) that formed in the early Permian (Asselian; i.e., in the Shanxi Formation) in the study area based on (1) cave, pore, and breccia development in outcrops and drill cores; (2) high Mn–Fe and low Sr contents associated with negative δ18O and normal δ13C values, which are indicative of strong leaching by meteoric waters; and (3) the irregular thickness of the DDYL that is indicative of differential karstification, resulting in the formation of horizontal gullies. The karst topography of the DDYL was identified based on the moldic and residual thickness methods, including karst highland, gentle slope, and microbasin geomorphic units. We propose that the karst topography controlled the redox environment and led to enrichment of the organic-rich transitional shales in the selected submember of the Shanxi Formation. The U/Th, V/Cr, and V/(V+Ni) ratios exhibit a linear relationship with geomorphic unit types. The karst microbasins had a weakly oxic environment, which widely preserved thick, organic-rich, transitional shales having high total organic carbon content and gas-bearing potential.
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How this classification was reachedexpand
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) | 0.000 | 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) | 0.002 | 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 teacher head, 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".