Advances in carbon isotope analysis of trapped methane and volatile hydrocarbons in crystalline rock cores
Bibliographic record
Abstract
Rationale The isotopic composition of hydrocarbons trapped in rocks on the microscale (fluid inclusions, mineral grain boundaries, microfractures) can provide powerful information on geological and biological processes but are an analytical challenge due to low concentrations. We present a new approach for the extraction and carbon isotopic analysis of methane (CH 4 ) and hydrocarbons in trapped volatiles in crystalline rocks. Methods An off‐line crusher with cryogenic trapping and a custom‐made silica glass U‐trap were attached to an external injector port on a continuous flow gas chromatograph/combustion/isotope ratio mass spectrometer to demonstrate the accuracy, reproducibility, and sensitivity of δ 13 C measurements for CH 4 . Results The method can isotopically characterize CH 4 in crushed rock samples with concentrations as low as 3.5 × 10 −9 mol/g of rock, and both sample and isotopic standards are analyzed with an accuracy and reproducibility of ±0.5‰. High H 2 O/CH 4 ratios of 98 to 500 have no effect on measured δ 13 C CH4 values. The method is successfully applied to natural samples from the north range of Sudbury Basin, Ontario, Canada. The δ 13 C isotopic signatures of CH 4 trapped microscopically in rock from the north range overlap significantly with that of CH 4 contained in larger scale flowing fracture fluids from the same part of the Sudbury Basin, indicating a potential genetic link. Conclusions A novel method for δ 13 C CH4 analysis was developed for the extraction of nanomole quantities of CH 4 trapped microscopically in rocks. The technique has an accuracy and reproducibility comparable to that of on‐line crushing techniques but importantly provides the capability of crushing larger rock quantities (up to 100 g). The benefit is improved detection levels for trace hydrocarbon species. Such a capability will be important for future extension of such crushing techniques for measurement of 2 H/ 1 H for CH 4 , clumped isotopologues of CH 4 and other trapped volatiles species, such as C 2 H 6 , C 3 H 8 , C 4 H 10 , CO 2 and N 2 .
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".