Fossil fuel related water-rock interaction in the Appalachian Basin, Pennsylvania and New York: A geochemical and strontium isotope investigation
Bibliographic record
Abstract
Fossil fuel resources (coal/oil/natural gas) have been extracted from the Appalachian Basin for over a century. Related fluids, including outflows from inactive coal mines and produced water from oil and gas wells, pose environmental concern. Three studies are presented which integrate strontium (Sr) isotopes with geologic and geochemical analyses to investigate the movement of fossil fuel-related fluids through the environment and their interactions with natural waters and geologic materials. In the first study, abandoned oil and gas wells tapping Upper Devonian units in northwestern Pennsylvania serve as conduits for the movement of waters with high amounts of total dissolved solids (TDS). This work demonstrates that the waters originate as acid mine drainage (AMD), which infiltrates shallow, siderite-cemented sandstone aquifers. Dissolution of the siderite cement produces waters rich in dissolved iron, which flow to the surface via wells with compromised casings. The second study focuses upon high-TDS water produced during natural gas extraction from the Middle Devonian Marcellus Shale. Strontium isotopic ratios of produced waters collected from across Pennsylvania define a relatively narrow set of values (87Sr/86Sr = 0.71008-0.71212) that falls above that of Devonian seawater, and is distinct from most western Pennsylvania AMD and Upper Devonian Venango Formation oil and gas brines. The uniformity of the isotope ratios suggests a basin-wide source of dissolved solids. Mixing models indicate that Sr isotopes can potentially detect even small amounts (<0.01%) of Marcellus produced water interacting with natural waters. In the third study, a sequential extraction procedure was carried out on drill cuttings from a well in south-central New York that penetrates the Marcellus Shale and adjacent units. Sr isotopic values of water and ammonium acetate leachates, representing soluble salt and clay-exchangeable fractions, fall within or just below the range measured for Marcellus produced waters, indicating that the waters’ dissolved solids originate from within the shale. Acetic acid leaches targeting carbonate minerals yield 87Sr/86Sr ratios below those of the water and ammonium acetate leaches, but higher than those expected for Devonian seawater. Rb-Sr isotope systematics suggest mixing between a seawater-derived source and more radiogenic material, and multiple generations of carbonate mineral precipitation.
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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 | 0.001 |
| 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 | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".