Abstract Carbonates and cherts in the 3.35 billion-year-old Strelley Pool Formation (Fm.; Australia) host stromatolites that are among the oldest remnants of life on Earth. However, it is still not entirely clear whether these mineral phases are authigenic precipitates, and whether they represent reliable geochemical archives of early Earth environments. Here we present major/trace-element and Nd-isotope data of stromatolitic carbonates, associated crystal-fan carbonates, and cherts in the Strelley Pool Fm. (i) to assess the reliability of these chemical sediments as geochemical archives of the fluids from which they precipitated, (ii) to date the time of formation of carbonate and silica phases, and (iii) to trace the sources of elements prevailing in microbial habitats 3.35 Ga ago. Stromatolitic carbonates plot together with the stratigraphically underlying Marble Bar cherts on a Sm-Nd regression line yielding 3253 ±320 Ma. In contrast, associated crystal-fan carbonates together with altered Marble Bar cherts yield 2718 ±220 Ma, suggesting that their Sm-Nd isotope system was reset after deposition. Both types of carbonates, as well as white cherts, show shale-normalized rare earth element and yttrium patterns (REYSN; with the exception of redox-sensitive Ce and Eu and heavy REYSN to middle REYSN depletion) that are parallel to those of modern seawater, indicating a predominantly seawater-derived origin. Positive EuSN anomalies (2.1 - 2.4), combined with heterogeneous ɛNd3.35Ga values between -3.2 and +5.8 within individual alternating stromatolite laminae, further support that the dissolved fraction of seawater on the ancient carbonate platform was variably affected by both continental weathering and high-temperature hydrothermal fluids contributing elements of both young mafic or older felsic rocks. In conclusion, trace element and Nd isotope data presented here match well with the depositional environment, as characterized based on lithological, geochemical, and stratigraphic relationships, on an early continent, showing at least episodic emergence above the sea level, supporting microbial life on a shallow marine platform.

中文翻译：

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碳酸盐和燧石作为 3.35 Ga 前碳酸盐平台上海水化学和宜居性的档案：来自西澳大利亚 Strelley 池组的 Sm/Nd 测年和微量元素分析的见解

摘要 具有 33.5 亿年历史的 Strelley 池组（Fm.；澳大利亚）中的碳酸盐和燧石含有叠层石，这些叠层石是地球上最古老的生命遗迹之一。然而，尚不完全清楚这些矿物相是否是自生沉淀物，以及它们是否代表了早期地球环境的可靠地球化学档案。在这里，我们展示了 Strelley 池 Fm 中叠层石碳酸盐、伴生晶扇碳酸盐和燧石的主要/微量元素和 Nd 同位素数据。(i) 评估这些化学沉积物作为它们从中沉淀出来的流体的地球化学档案的可靠性，(ii) 迄今为止碳酸盐和二氧化硅相形成的时间，以及 (iii) 追踪微生物中普遍存在的元素的来源栖息地 3.35 Ga 前。叠层质碳酸盐与地层下伏的 Marble Bar 燧石一起绘制在 Sm-Nd 回归线上，产生 3253 ±320 Ma。相比之下，伴生的晶体扇形碳酸盐连同改变的 Marble Bar 燧石产生 2718 ±220 Ma，表明它们的 Sm-Nd 同位素系统在沉积后被重置。两种类型的碳酸盐以及白色燧石都显示出与现代海水平行的页岩归一化稀土元素和钇模式（REYSN；氧化还原敏感的 Ce 和 Eu 以及重 REYSN 至中 REYSN 耗竭除外） ，表明主要来源于海水。正 EuSN 异常 (2.1 - 2.4)，结合单个交替叠层石薄片内 -3.2 和 +5.8 之间的异质 ɛNd3.35Ga 值，进一步支持古代碳酸盐台地海水的溶解部分受到大陆风化和高温热液流体的不同影响，这些流体贡献了年轻的基性岩或较老的长英质岩的元素。总之，这里提供的微量元素和 Nd 同位素数据与沉积环境非常吻合，根据岩性、地球化学和地层关系表征，在早期大陆上，至少显示出海平面以上的偶然出现，支持微生物生活浅海平台。