Geobiology of the Paleoproterozoic Belcher Group, Nunavut, Canada
Bibliographic record
Abstract
The ~2.0-1.8 Ga (billion years old) Belcher Group on the Belcher Islands in Nunavut provide a unique opportunity for studying Paleoproterozoic geobiology. The Belcher Group includes a sequence of low metamorphic grade peritidal carbonate rocks that preserve putative microbiota, as first described by Hofmann and Jackson (1969). Microbial mats, including stromatolites, are abundant in the peritidal carbonate succession. Additionally, morphologies possibly related to blue-green algae were first described in granular iron formation rocks of the Belcher Group by Moore (1918). The Belcher Group microbiota are a group of simple organisms, believed to be prokaryotic in nature. Microbiota morphologies include ellipsoids, spheroids, and filamentous chains of cells interpreted by previous workers to represent blue-green algae and acritarchs. Some microstructures are questionably biogenic and might be abiotic. The most significant field studies on the Belcher Group occurred from the late 1950s to the early 1980s, which provides the geological context for this study. This project aims to build on the previous work of H. Hofmann and others in the ‘60s and bring these microbiota into a modern context, drawing on the analytical advancements of the last 50 years. The main goal of the project is to determine if there is evidence that the microbiota are perhaps eukaryotic organisms. The emergence of eukaryotes is arguably the most significant geobiological event in Earth history, with eukaryotic cells believed to have evolved around 1.6 Ga (Knoll et al. 2006; Javaux and Lepot 2018), but some contentious fossils interpreted to represent eukaryotes have been dated to as early as 2.2 Ga (Retallack et al. 2013). In North America, the oldest discovered eukaryotic remains are around 1.5 Ga (Adam et al. 2017). If eukaryotic fossils were to be discovered in the Belcher Group, this would make them the oldest occurrence in North America. To test the hypothesis, samples from the microbiota-containing units were collected on the Belcher Islands. Both light microscopy and a collection of modern analytical techniques will be used to obtain high resolution images and chemical signatures of the microbiota and their biosignatures. Preliminary data from petrography, Raman Spectroscopy, and X-ray Photoelectron Spectroscopy (XPS) will be presented. Both Raman spectroscopy and XPS have been used as characterization tools in other studies looking at microbiota and organic matter remains (Qu et al. 2018; Arnarson and Keil 2001). Raman collects molecular and structural data from the sample, while XPS collects elemental chemical data. Both techniques are therefore particularly useful for identifying and characterizing organic carbon, which is the base of organic matter. References: Adam, Zachary R., Mark L. Skidmore, David W. Mogk, and Nicholas J. Butterfield. 2017. “A Laurentian Record of the Earliest Fossil Eukaryotes.” Geology 45 (5): 387–90. https://doi.org/10.1130/G38749.1. Arnarson, Thorarinn S., and Richard G. Keil. 2001. “Organic–Mineral Interactions in Marine Sediments Studied Using Density Fractionation and X-Ray Photoelectron Spectroscopy.” Organic Geochemistry 32 (12): 1401–15. https://doi.org/10.1016/S0146-6380(01)00114-0. Hofmann, H. J., and G. D. Jackson. 1969. “Precambrian (Aphebian) Microfossils from Belcher Islands, Hudson Bay.” Canadian Journal of Earth Sciences 6 (5): 1137–44. https://doi.org/10.1139/e69-115. Javaux, Emmanuelle J., and Kevin Lepot. 2018. “The Paleoproterozoic Fossil Record: Implications for the Evolution of the Biosphere during Earth’s Middle-Age.” Earth-Science Reviews 176 (January): 68–86. https://doi.org/10.1016/j.earscirev.2017.10.001. Knoll, A.H, E.J Javaux, D Hewitt, and P Cohen. 2006. “Eukaryotic Organisms in Proterozoic Oceans.” Philosophical Transactions of the Royal Society B: Biological Sciences 361 (1470): 1023–38. https://doi.org/10.1098/rstb.2006.1843. Moore, E. S. 1918. “The Iron-Formation on Belcher Islands, Hudson Bay, with Special Reference to Its Origin and Its Associated Algal Limestones.” The Journal of Geology 26 (5): 412–38. Qu, Yuangao, Shixing Zhu, Martin Whitehouse, Anders Engdahl, and Nicola McLoughlin. 2018. “Carbonaceous Biosignatures of the Earliest Putative Macroscopic Multicellular Eukaryotes from 1630 Ma Tuanshanzi Formation, North China.” Precambrian Research 304 (January): 99–109. https://doi.org/10.1016/j.precamres.2017.11.004. Retallack, Gregory J., Evelyn S. Krull, Glenn D. Thackray, and Dula Parkinson. 2013. “Problematic Urn-Shaped Fossils from a Paleoproterozoic (2.2Ga) Paleosol in South Africa.” Precambrian Research 235 (September): 71–87. https://doi.org/10.1016/j.precamres.2013.05.015.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.003 |
| Science and technology studies | 0.006 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| 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 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".