Septate‐tubular textures in 2.0‐Ga pillow lavas from the Pechenga Greenstone Belt: a nano‐spectroscopic approach to investigate their biogenicity
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Bibliographic record
Abstract
Pillow lava rims and interpillow hyaloclastites from the upper part of the Pechenga Greenstone Belt, Kola Peninsula, N-Russia contain rare tubular textures 15-20 μm in diameter and up to several hundred μm long in prehnite-pumpellyite to lower greenschist facies meta-volcanic glass. The textures are septate with regular compartments 5-20 μm across and exhibit branching, stopping and no intersecting features. Synchrotron micro-energy dispersive X-ray was used to image elemental distributions; scanning transmission X-ray microscopy, Fe L-edge and C K-edge were used to identify iron and carbon speciation at interfaces between the tubular textures and the host rock. In situ U-Pb radiometric dating by LA-MC-ICP-MS (laser ablation multicollector inductively coupled plasma mass spectrometry) of titanite from pillow lavas yielded a metamorphic age of 1790 ± 89 Ma. Focused ion-beam milling combined with transmission electron microscopy was used to analyze the textures in three dimensions. Electron diffraction showed that the textures are mineralized by orientated pumpellyite. On the margins of the tubes, an interface between mica or chlorite and the pumpellyite shows evidence of dissolution reactions where the pumpellyite is replaced by mica/chlorite. A thin poorly crystalline Fe-phase, probably precipitated out of solution, occurs at the interface between pumpellyite and mica/chlorite. This sequence of phases leads to the hypothesis that the tubes were initially hollow, compartmentalized structures in volcanic glass that were mineralized by pumpellyite during low-grade metamorphism. Later, a Fe-bearing fluid mineralized the compartments between the pumpellyite and lastly the pumpellyite was partially dissolved and replaced by chlorite during greenschist metamorphism. The most plausible origin for a septate-tubular texture is a progressive etching of the host matrix by several generations of microbes and subsequently these tubes were filled by authigenic mineral precipitates. This preserves the textures in the rock record over geological time. The micro textures reported here thus represent a pumpellyite-mineralized trace fossil that records a Paleoproterozoic sub-seafloor biosphere.
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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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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 it