Volcanic forcing of the Lomagundi–Jatuli carbon isotope excursion
Bibliographic record
Abstract
The Lomagundi–Jatuli Event (LJE), Earth’s most pronounced and prolonged positive carbon isotope excursion, followed the Great Oxidation Event and remains enigmatic in origin. We present a Pb–Pb isochron age of 2,194 ± 5 Ma for black shales from the Francevillian FB Formation, Gabon—an LJE type locality—coinciding with the emplacement of the Large Igneous Province that gave rise to the extensive Birimian–Eburnean orogenic segment. This orogeny produced very large volumes of juvenile crust in the form of oceanic plateau basalts that were eventually reworked through subduction and collisions. These processes released substantial volcanic CO 2 into the ocean–atmosphere system, disrupting the carbon and oxygen cycles for 100 to 200 My. Volcanic outgassing likely outpaced alkalinity production from weathering, leading to an increase in the δ 13 C of sedimentary carbonates. Reanalysis of global δ 13 C–δ 18 O datasets reveals a previously unrecognized dual bimodality, attributed here to episodic volcanic degassing and subsequent oceanic carbonate saturation. Weathering of emergent crust enhanced nutrient fluxes, driving primary productivity and organic carbon burial. We further propose that volcanic CO 2 emissions modulated the Dole Effect by shifting the balance between terrestrial and marine photosynthetic oxygen production, altering atmospheric oxygen isotope ratios independently of climate. These processes collectively drove the δ 13 C excursion of the LJE and may have fostered conditions conducive for early eukaryotic evolution.
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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 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 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".