The paleoecology of paleoproterozoic microbial communities in the Ferriman Group, Labrador Trough, Canada
LE3 .A278 2010
Pufahl, Peir K.
Master of Science
Earth & Environmental Sciences
Chert and iron formation from the Ferriman Group (ca. 1.88 Ga) of the Labrador Trough, Canada, contain an exceptional assemblage of fossil bacteria and biofilms. Analysis of lithofacies in a well-defined stratigraphic framework suggests that these microbes were restricted to suboxic, shallow-water environments through three sea level cycles. Microfossils are preserved as chert and sedimentary apatite (francolite) in hematite-rich, peritidal facies. Morphologies include sphere- and filament-shaped bacteria, however, filamentous forms are the most common. Secondary electron imaging of freshly broken surfaces shows filaments are similar in size and shape to modern bacteria; filaments vary between 0.5 and 5 μm wide and reach tens of μm in length. They commonly envelop chert and iron oxide grains, which stabilized the seafloor and contributed to firm- and hardground development. The filamentous morphology, similar mat-forming behavior, and paleoenvironmental conditions where these fossils lived closely resemble traits of modern Fe-oxidizing bacteria such as Gallionella and Leptothrix. The close association between these fossil microbes and iron oxides within the Ferriman Group support the widely held view that Fe-oxidizing bacteria may have aided the precipitation of iron formation. These data, however, also suggest that such benthic bacterial precipitation was likely environment specific, occurring in shallow settings concomitant with abiotic precipitation processes. Approaches used in this study are timely and may prove useful in the search for evidence of extraterrestrial life on celestial bodies that once had environmental conditions similar to those of Earth, such as Mars, which has captured the public’s attention and led to a major global research effort.
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