School of Earth and Environment, University of Leeds, Leeds, UK.
Department of Earth Science, University of Bergen, Bergen, Norway.
Geobiology. 2021 May;19(3):228-249. doi: 10.1111/gbi.12434. Epub 2021 Feb 16.
Modern marine hydrothermal vents occur in a wide variety of tectonic settings and are characterized by seafloor emission of fluids rich in dissolved chemicals and rapid mineral precipitation. Some hydrothermal systems vent only low-temperature Fe-rich fluids, which precipitate deposits dominated by iron oxyhydroxides, in places together with Mn-oxyhydroxides and amorphous silica. While a proportion of this mineralization is abiogenic, most is the result of the metabolic activities of benthic, Fe-oxidizing bacteria (FeOB), principally belonging to the Zetaproteobacteria. These micro-organisms secrete micrometer-scale stalks, sheaths, and tubes with a variety of morphologies, composed largely of ferrihydrite that act as sacrificial structures, preventing encrustation of the cells that produce them. Cultivated marine FeOB generally require neutral pH and microaerobic conditions to grow. Here, we describe the morphology and mineralogy of filamentous microstructures from a late Paleoproterozoic (1.74 Ga) jasper (Fe-oxide-silica) deposit from the Jerome area of the Verde mining district in central Arizona, USA, that resemble the branching tubes formed by some modern marine FeOB. On the basis of this comparison, we interpret the Jerome area filaments as having formed by FeOB on the deep seafloor, at the interface of weakly oxygenated seawater and low-temperature Fe-rich hydrothermal fluids. We compare the Jerome area filaments with other purported examples of Precambrian FeOB and discuss the implications of their presence for existing redox models of Paleoproterozoic oceans during the "Boring Billion."
现代海洋热液喷口出现在多种构造环境中，其特征是海底排放富含溶解化学物质的流体和快速的矿物沉淀。一些热液系统仅排放低温富铁流体，这些流体在某些地方与锰氧化物和无定形二氧化硅一起沉淀出以铁氧化物为主的沉积物。虽然一部分矿化作用是无机的，但大多数是海底、铁氧化细菌 (FeOB) 代谢活动的结果，主要属于 Zetaproteobacteria。这些微生物分泌出各种形态的微米级茎、鞘和管，主要由黄铁矿组成，充当牺牲结构，防止产生它们的细胞结壳。培养的海洋 FeOB 通常需要中性 pH 值和微氧条件才能生长。在这里，我们描述了来自美国亚利桑那州中部 Verde 矿区 Jerome 地区的晚古元古代（17.4 亿年）碧玉（铁氧化物-二氧化硅）矿床中丝状微观结构的形态和矿物学特征，这些特征类似于一些现代海洋 FeOB 形成的分支管。基于这种比较，我们将 Jerome 地区的丝状结构解释为在深海海底，在弱氧化海水和低温富铁热液之间的界面处由 FeOB 形成的。我们将 Jerome 地区的丝状结构与其他被认为是前寒武纪 FeOB 的例子进行了比较，并讨论了它们在“无聊十亿年”期间对古元古代海洋现有氧化还原模型的存在的影响。
