Late Cretaceous and Early Paleogene Fluid Circulation and Microbial Activity in Deep Fracture Networks of the Precambrian Basement of Western Greenland
Bibliographic record
Abstract
Abstract Deep fracture‐hosted fluids of Precambrian bedrock cratons are relatively stagnant over long time spans compared to near‐surface systems. However, episodic events, such as fracture reactivations, transgressions, and deglaciations, may introduce dilute water, replacing, and mixing with the deep continental brines, thereby sparking microbial activity. Secondary minerals that line bedrock fractures serve as important geochemical archives for such episodic events. Here we explore the fracture mineral record of Archean rocks of Western Greenland by analyzing samples from deep boreholes with the aim to trace and characterize episodic paleofluid flow and paleomicrobial activity. A sequence of hydrothermal to low temperature fluid flow events is demonstrated. For the youngest generation, microscale S‐isotope analysis of pyrite reveals substantial 34 S‐depletion (minimum δ 34 S:−58‰V‐CDT) compared to fracture‐hosted barite (δ 34 S:13‰ ± 2‰) and gypsum (δ 34 S:2.6‰–10.6‰). This suggests the formation of pyrite following S isotope fractionation during microbial sulfate reduction. This metabolism is further indicated by several methyl‐branched fatty acids preserved in calcite. A general discrepancy between calcite and groundwater δ 18 O‐values suggests that calcite formed from water different from the presently residing glacial meltwater‐influenced groundwater mix. High spatial resolution U‐Pb carbonate geochronology of the youngest generation of calcite yielded ages for two samples: 64 ± 3, 75 ± 7 Ma (2 σ ). These ages overlap with tectonic events related to early stages, or prestages, of the opening of the Atlantic and Labrador Seas. This suggests that deep fracture networks in Western Greenland were colonized by microorganisms, such as sulfate reducers, in the course of this extensional event.
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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) | 0.000 | 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".