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Evidence for cavity-dwelling microbial life in 3.22 Ga tidal deposits

Homann, M; Heubeck, C; Bontognali, TRR; Bouvier, A-S; Baumgartner, LP; Airo, A; (2016) Evidence for cavity-dwelling microbial life in 3.22 Ga tidal deposits. Geology , 44 (1) pp. 51-54. 10.1130/G37272.1. Green open access

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Abstract

Cavities are considered plausible and favorable habitats for life on early Earth. In such microenvironments, organisms may have found an adequate protection against the intense ultraviolet radiation that characterized the Archean ozone-free atmosphere. However, while there is clear evidence that benthic life existed in the Paleoarchean, the oldest traces of cavity-dwelling microbes (coelobionts) have been found in Neoarchean rocks. Here we present the results of a detailed investigation of early silicified cavities occurring in the oldest well-preserved siliciclastic tidal deposits, the 3.22 Ga Moodies Group of the Barberton Greenstone Belt (South Africa). Downward-growing microstromatolitic columns composed of kerogenous laminae are commonly present in planar, bedding-parallel, now silica-filled cavities that formed in sediments of the peritidal zone. In-situ δ13CPDB (PDB—Peedee belemnite) measurements of the kerogen range from –32.3‰ to –21.3‰ and are consistent with a biogenic origin. Scanning electron microscopy analysis of the silicified cavities shows well-preserved chains of cell-sized molds that are interpreted as fossil filamentous microorganisms. The geological context, the morphology of the microstromatolites, the δ13C composition of the kerogen, and the presence of microfossils all suggest that a microbial community inhabited the cavities. These results extend the geological record of coelobionts by ∼500 m.y., supporting the view that cavities were among the first ecological niches to have been occupied by early microorganisms.

Type: Article
Title: Evidence for cavity-dwelling microbial life in 3.22 Ga tidal deposits
Open access status: An open access version is available from UCL Discovery
DOI: 10.1130/G37272.1
Publisher version: https://doi.org/10.1130/G37272.1
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Barberton greenstone belt, C-13/C-12, carbon, Africa, isotopes, Mesoarchean, Archean, isotope ratios, microfossils, Precambrian, South Africa, siliciclastics, Southern Africa, problematic fossils, problematic microfossils, stable isotopes
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10087313
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