Abstract Deep-water cherts are common in early Precambrian successions. Their mode of formation is unclear but proposed mechanisms include seawater silica precipitation, silica adsorption onto iron oxide particles and silica replacement of seafloor sediments. Here we document ≥80 laminated chert beds (0.02-7 m thick) in 2.56-2.49 Ga shelf sequences in drill-hole ABDP9 from the Hamersley Group, Australia. The laminated chert beds, including thin intervals of banded iron formation (BIF), are concentrated in six major intervals that first appear ca. 75 m.y. before deposition of the 2.49 Ga Brockman Iron Formation. The chert beds do not preserve textures indicative of seafloor replacement of precursor grains but of a chemical sediment comprising greenalite nanoparticles enclosed in silica cement with syneresis cracks that truncate sedimentary lamination. The greenalite is interpreted to have precipitated from dissolved Fe(II) and SiO2(aq) transported by hydrothermal plumes. Its ubiquity in laminated chert cement and the capacity of clay minerals to sorb silica, suggest the operation of a greenalite-silica shuttle by which excess dissolved silica in the seawater-plume mixture adsorbed onto settling Fe(II)-silicate nanoparticles. Upon deposition, pore-water silica concentrations surpassed the threshold for cementation due to the drawdown of silica into sediment pore waters and dewatering of underlying siliceous muds. In contrast, the lack of non-ferruginous chert beds in deep-water shelf sediments suggests that silica concentrations were lower in non-plume seawater. The appearance and disappearance of ferruginous cherts in shelf sequences is interpreted to record the waxing and waning of distal vent plumes. Deposition of chert beds starting at 2.56 Ga culminated with the development of thick, laterally extensive BIFs after 2.49 Ga, signalling enhanced ocean ridge volcanism and the transgression of vent plumes across a drowned shelf. The disappearance of basinal cherts and major BIFs after the Great Oxidation Event (2.45-2.3 Ga) may record the disruption or shutdown of the oceanic greenalite-silica shuttle.

中文翻译：

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在热液喷口羽流侵入澳大利亚哈默斯利地区的新太古代陆架期间，绿岩-二氧化硅穿梭的发展

摘要 深水硅质岩在早前寒武纪演替中很常见。它们的形成模式尚不清楚，但提出的机制包括海水二氧化硅沉淀、二氧化硅吸附到氧化铁颗粒上和海底沉积物的二氧化硅替代。在这里，我们记录了澳大利亚 Hamersley Group 钻孔 ABDP9 中 2.56-2.49 Ga 陆架序列中≥80 个层状燧石床（0.02-7 m 厚）。层状燧石床，包括带状铁层 (BIF) 的薄层，集中在 6 个首次出现的主要层段中。75 my 在 2.49 Ga Brockman Iron Formation 沉积之前。燧石床不保留指示海底替代前体颗粒的纹理，而是保留化学沉积物的纹理，该沉积物包含包裹在硅水泥中的绿泥石纳米颗粒，具有截断沉积层状的脱水收缩裂缝。绿岩被解释为由热液羽流输送的溶解的 Fe(II) 和 SiO2(aq) 沉淀。它在层状燧石水泥中的普遍存在和粘土矿物吸附二氧化硅的能力表明，绿岩-二氧化硅穿梭的运行，海水-羽状混合物中过量的溶解二氧化硅吸附在沉淀的 Fe(II)-硅酸盐纳米颗粒上。沉积后，由于二氧化硅下降到沉积物孔隙水中和下伏硅质泥浆脱水，孔隙水二氧化硅浓度超过了胶结阈值。相比之下，深水陆架沉积物中缺乏非铁质燧石床表明非羽状海水中的二氧化硅浓度较低。陆架序列中铁质燧石的出现和消失被解释为记录远端喷口羽流的增减。从 2.56 Ga 开始的燧石床沉积在 2.49 Ga 之后随着厚的、横向广泛的 BIF 的发展而达到顶峰，这表明洋脊火山活动增强和喷口羽流越过淹没的陆架。大氧化事件（2.45-2.3 Ga）后盆地硅质岩和主要BIFs的消失可能记录了海洋绿岩-二氧化硅穿梭的中断或关闭。陆架序列中铁质燧石的出现和消失被解释为记录远端喷口羽流的增减。从 2.56 Ga 开始的燧石床沉积在 2.49 Ga 之后随着厚的、横向广泛的 BIF 的发展而达到顶峰，这表明洋脊火山活动增强和喷口羽流越过淹没的陆架。大氧化事件（2.45-2.3 Ga）后盆地硅质岩和主要BIFs的消失可能记录了海洋绿岩-二氧化硅穿梭的中断或关闭。陆架序列中铁质燧石的出现和消失被解释为记录远端喷口羽流的增减。从 2.56 Ga 开始的燧石床沉积在 2.49 Ga 之后随着厚的、横向广泛的 BIF 的发展而达到顶峰，这表明洋脊火山活动增强和喷口羽流越过淹没的陆架。大氧化事件（2.45-2.3 Ga）后盆地硅质岩和主要BIFs的消失可能记录了海洋绿岩-二氧化硅穿梭的中断或关闭。表明洋脊火山活动增强以及喷口羽流越过淹没的陆架。大氧化事件（2.45-2.3 Ga）后盆地硅质岩和主要BIFs的消失可能记录了海洋绿岩-二氧化硅穿梭的中断或关闭。表明洋脊火山活动增强以及喷口羽流越过淹没的陆架。大氧化事件（2.45-2.3 Ga）后盆地硅质岩和主要BIFs的消失可能记录了海洋绿岩-二氧化硅穿梭的中断或关闭。