Biological organic source and depositional environment of over-mature source rocks of Longtan Formation in Sichuan basin
Bibliographic record
Abstract
The source rocks of Longtan Formation in Sichuan basin have vitrinite reflectance values ranging mostly from 2.0% to 3.0% and kerogen H/C atomic ratios mainly in 0.3 to 0.5,suggesting a post-mature level with regard to hydrocarbon-generating.Distribution of their various biomarkers is found to change abnormally and could be limited to geochemical applications.However,their aromatic hydrocarbons,in conjunction with kerogen carbon isotope and element(sulfur and nitrogen) composition,can be used as indicators for organic source and sedimentary environment.Near-marine swamp-lacustrine facies coal-bearing source rocks in the southeastern Sichuan basin show 2,6-/2,10-DMP(dimethylphenanthrene) and 1,7-/1,9-DMP values higher than 0.65 and 3.0 respectively and 4-/1-MDBT(dibenzothiophene) ratios over 15.The kerogens exhibit isotopically heavy δ13C values mostly in excess of –25‰,along with low S/C and N/C atomic ratios(0.003 to 0.056 and 0.012 to 0.025,respectively).The combined data indicate a dominantly terrestrially derived source and oxidizing depositional environment with a type-Ⅲ organic matter.Whereas,the bay-lagoon facies intervals in the northeastern region of this basin display 2,6-/2,10-DMP ratios lower than 0.65,1,7-/1,9-DMP mainly below 3.0 and 4-/1-MDBT mostly under 5.Moreover,carbon isotopes of the kerogens are relatively depleted in 13C with the δ13C values around –27‰,with slightly higher S/C and N/C ratios(0.020 to 0.140 and 0.014 to 0.038,respectively),implying a type-Ⅱ kerogen derived from a predominantly aquatic organic source deposited in a reducing or less oxic condition.These geochemical parameters for source rocks from other parts in this basin are believed to vary between the two regions.
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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 | 0.001 |
| Science and technology studies | 0.001 | 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 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".