Stromatolitic Mounds in Tidal-Facies Sandstones of the Paleoarchean Moodies Group (Barberton Greenstone Belt, Eswatini)

IF 2.7 2区 地球科学 Q2 BIOLOGY
Geobiology Pub Date : 2025-05-02 DOI:10.1111/gbi.70020
Sebastian Reimann, Martin Homann, Deon J. Janse van Rensburg, Michael Wiedenbeck, Christian Hallmann, Runa Antony, Christoph Heubeck
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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.

Abstract Image

Eswatini地区Barberton绿岩带modies群潮相砂岩中的叠层石丘
浅海环境被认为是地球早期生命传播的关键,甚至可能是起源的关键。然而,早期生命的浅海太古代沉积记录偏向于碳酸盐岩;近岸的硅质环境没有得到相应的重视。本文描述了Eswatini地区Barberton绿岩带中太古宙modies群(约3.22 Ga)潮相砂岩中致密层状、硅化和白云化的化石钙质丘。它们不同于(1)厘米到厘米尺度的,孤立的,棒状到基座状的,位于流体逸出构造管道顶部和管道内部的结节状土丘;(2)毫米到厘米尺度的,起伏的和波浪状的层状构造,与层状良好的粉砂和砂岩互层。可能的生物成因的地球化学指标在很大程度上被局部热液蚀变和区域低绿片岩相变质作用所湮没:对保存最完好的土丘纹层的几次穿越进行的原位SIMS δ13Ccarb同位素分析和附近碎屑黄铁矿颗粒成岩边缘的δ34SVCDT值提供了关于生物作用的模糊同位素证据;推测的层状岩TOC过低,无法测量δ13Corg,而细分散的碳质颗粒和干酪质层状岩的拉曼光谱显示,平均最高变质温度约为500℃。然而,结构和区域证据表明,碳酸盐纹层代表微生物群落的代谢产物,这些微生物群落利用了沙火山,从沙火山中间歇性地喷发出富含营养的流体。我们的这一推断是基于海浪或水流冲刷的光带潮汐台地的可居住沉积环境、二维和三维叠层石形态、原位干酪根的赋存情况、碳酸盐矿物学以及穆迪斯群其他地方类似土丘结构的存在。尽管微生物利用的代谢策略尚不清楚,但这一现象为沿海地区的古太古代微生物定植提供了一个新的生态位。
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来源期刊
Geobiology
Geobiology 生物-地球科学综合
CiteScore
6.80
自引率
5.40%
发文量
56
审稿时长
3 months
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.
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