Abstract The upper Ediacaran-lower Cambrian (551–526 Ma) sedimentary succession of the Yangtze Block, South China, hosts abundant chert that formed contemporaneously with the Neoproterozoic Oxidation Event and the Cambrian Explosion. The effect of biological evolution, especially the rise of silica-secreting organisms, on marine Si cycling during the Ediacaran-Cambrian (E-C) transition remains controversial. This paper describes results of a petrological and geochemical investigation aimed at elucidating the origin of the chert and silica biogeochemical cycling during the E-C transition. Our results reveal that the studied chert is dominated by quartz and carbonate. The widespread presence of relict carbonate in inferred peritidal chert deposits suggests that carbonate replacement was an especially common silicification pattern of this facies, whereas the lack of carbonate precursors in subtidal strata argues in favor of primary and biogenic silica precipitation in deposits of this facies. Silicon isotope compositions, relative abundances of Al, Fe, and Mn and rare earth element (REE) + Y concentrations suggest that seawater rather than high-temperature hydrothermal fluid was the primary silica source of the studied cherts. Secular variation of chert Si isotopes reveals that marine silica cycling was closely linked with biological activity. Although silicification was abiological during the Precambrian, it may have been facilitated by microbial activities, especially the widespread formation of cyanobacterial mats. The flourishing of siliceous sponges and radiolarians in the early Cambrian ocean may have served as a global silica sink thus enhancing biological control of the silica cycle after Cambrian time. The studied chert deposits not only demonstrate the silica-rich nature of the global ocean during the E-C transition, but also record the transition of silica cycling from abiological to biological processes and the effect of the evolutionary radiation of silica-secreting organisms during the Cambrian Explosion on silica cycling.

中文翻译：

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埃迪卡拉纪-寒武纪过渡期间富含二氧化硅的海洋中的硅化和硅循环

摘要 华南扬子地块上埃迪卡拉纪-下寒武统（551-526 Ma）沉积层序含有丰富的燧石，与新元古代氧化事件和寒武纪大爆发同时期形成。在埃迪卡拉纪-寒武纪 (EC) 过渡期间，生物进化，尤其是分泌二氧化硅的生物的兴起，对海洋硅循环的影响仍然存在争议。本文描述了旨在阐明 EC 转变过程中燧石和二氧化硅生物地球化学循环起源的岩石学和地球化学调查的结果。我们的结果表明，所研究的燧石以石英和碳酸盐为主。在推断的潮汐燧石沉积物中广泛存在残余碳酸盐表明碳酸盐替代是该相的一种特别常见的硅化模式，而潮下地层中碳酸盐前体的缺乏有利于该相沉积物中的原生和生物二氧化硅沉淀。硅同位素组成、Al、Fe 和 Mn 的相对丰度以及稀土元素 (REE) + Y 浓度表明，海水而不是高温热液是研究燧石的主要二氧化硅来源。燧石Si同位素的长期变化表明海洋二氧化硅循环与生物活动密切相关。虽然硅化在前寒武纪是非生物的，但它可能是由微生物活动促进的，尤其是蓝藻垫的广泛形成。早期寒武纪海洋中硅质海绵和放射虫的繁盛可能起到了全球二氧化硅汇的作用，从而加强了寒武纪后二氧化硅循环的生物控制。研究的燧石沉积物不仅证明了在 EC 过渡期间全球海洋富含二氧化硅的性质，而且还记录了二氧化硅循环从非生物到生物过程的转变以及寒武纪大爆发期间分泌二氧化硅的生物进化辐射的影响关于二氧化硅循环。