Sebastian Reimann, Martin Homann, Deon J. Janse van Rensburg, Michael Wiedenbeck, Christian Hallmann, Runa Antony, Christoph Heubeck
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引用次数: 0
Abstract
Shallow-marine environments are thought to have been pivotal to the spreading, perhaps even the origin, of early life on Earth. The shallow-marine Archean sedimentary record of early life, however, is biased towards carbonates; nearshore siliciclastic environments have not received proportional attention. Here we describe densely laminated, silicified and dolomitized fossil calcareous mounds in tidal-facies sandstones of the Archean Moodies Group (ca. 3.22 Ga) in the Barberton Greenstone Belt, Eswatini. They vary between (1) cm- to dm-scale, isolated, club- to pedestal-shaped, nodular mounds on top of and within the conduits of fluid-escape structures, and (2) mm- to cm-scale, undulatory and wavily laminated structures, interbedded with well-bedded silt- and sandstones. Geochemical indicators of a possible biogenic origin were largely obliterated by local hydrothermal alteration and regional lower-greenschist-facies metamorphism: In situ SIMS δ13Ccarb isotope analyses from several traverses across the best-preserved laminae of a mound and δ34SVCDT values from diagenetic rims of nearby detrital pyrite grains yield ambiguous isotopic evidence about biologic processing; TOC of putative laminae is too low to measure δ13Corg, and Raman spectroscopy of finely dispersed carbonaceous particles and of kerogenous laminae indicate mean maximum metamorphic temperature of ca. 500°C. Textural and regional evidence, however, suggests that the carbonate laminae represent metabolic products of microbial communities that took advantage of sand volcanoes from which nutrient-rich fluids erupted episodically. We base this inference on the habitable depositional setting on a wave- or current-swept photic-zone tidal platform, the stromatolitic morphologies in two and three dimensions, the occurrence of in-situ kerogen, the carbonate mineralogy, and the presence of comparable mound structures elsewhere in the Moodies Group. Although the metabolic strategies utilized by the microorganisms remain unknown, this occurrence places a novel ecologic niche in the Paleoarchean microbial colonization of coastal regions.
期刊介绍:
The field of geobiology explores the relationship between life and the Earth''s physical and chemical environment. Geobiology, launched in 2003, aims to provide a natural home for geobiological research, allowing the cross-fertilization of critical ideas, and promoting cooperation and advancement in this emerging field. We also aim to provide you with a forum for the rapid publication of your results in an international journal of high standing. We are particularly interested in papers crossing disciplines and containing both geological and biological elements, emphasizing the co-evolutionary interactions between life and its physical environment over geological time.
Geobiology invites submission of high-quality articles in the following areas:
Origins and evolution of life
Co-evolution of the atmosphere, hydrosphere and biosphere
The sedimentary rock record and geobiology of critical intervals
Paleobiology and evolutionary ecology
Biogeochemistry and global elemental cycles
Microbe-mineral interactions
Biomarkers
Molecular ecology and phylogenetics.