Abstract The widespread occurrence of lower Eocene chert and porcellanite has been viewed as a major paleoceanographic issue since the advent of ocean drilling, and both biotic and abiotic forcings have been proposed to explain it. We present a reconstruction of indurated siliceous sediment (ISS) and preserved biosiliceous sediment (PBS) occurrences in the Atlantic Ocean through the Paleocene and Eocene (~66 through 34 Ma). ISS and PBS distributions reveal dissimilar temporal trends, with the peak of ISS occurrences coinciding with the Early Eocene Climatic Optimum, in line with previous studies. PBS occurrences show a generally increasing trend culminating between 44 and 43 Ma. The common co-occurrence of ISS and PBS, and their coherent geographic distribution lends strong support to the biogenic origin of the precursor to the widespread Paleogene ISS, and argues against an inorganic mode of early Cenozoic chert and porcellanite precipitation. Weight per cent biogenic opal records and trends in linear sedimentation rates indicate two plausible modes of silicification: 1) silicification due to prolonged exposure of biogenic opal-rich sediments to corrosive bottom waters; and 2) silicification due to elevated pressures and temperatures caused by rapid burial of biogenic opal-rich deposits. The confinement of ISS and PBS to proximal sites along continental margins points to the reliance of siliceous sedimentation through the Paleocene and Eocene on terrestrial supply of dissolved silicon. Consistent with this, quantitative siliceous microfossil assemblage records from the Blake Nose in the NW Atlantic indicate that the nutrient-rich marginal rather than oligotrophic pelagic settings hosted the majority of siliceous plankton production through the early Paleogene. The inorganic SiO2 precipitation model is unlikely to have been the dominant mechanism responsible for ubiquitous occurrences of early Paleogene ISS. We favor the biogenic ISS precursor scenario and reconcile it with the low-productivity early Cenozoic oceans by showing that large volumes of biogenic silica were supplied to the western North Atlantic Ocean from the North American margin through the Paleocene and Eocene. Dissolution of this surplus silica was facilitated by an early southwestward flow of young, SiO2-depleted waters from the North Atlantic. All these factors contributed to ISS and PBS focusing in the western North Atlantic through the early Paleogene.

中文翻译：

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大西洋早期古近纪生物硅质沉积：检验古新世和始新世燧石和瓷质的无机成因假说

摘要 自大洋钻探出现以来，下始新世燧石和瓷质岩的广泛分布一直被视为一个主要的古海洋学问题，并提出了生物和非生物强迫来解释它。我们展示了通过古新世和始新世（~66 至 34 Ma）在大西洋中的硬质硅质沉积物 (ISS) 和保存的生物硅质沉积物 (PBS) 的重建。ISS 和 PBS 分布揭示了不同的时间趋势，ISS 出现的峰值与早始新世气候最适相吻合，这与之前的研究一致。PBS 的出现显示出普遍增加的趋势，在 44 到 43 Ma 之间达到顶峰。ISS和PBS的共同出现，及其连贯的地理分布为广泛的古近系国际空间站的前体的生物起源提供了强有力的支持，并反对早期新生代燧石和瓷质沉淀的无机模式。生物蛋白石的重量百分比记录和线性沉积率的趋势表明两种可能的硅化模式：1）由于富含生物蛋白石的沉积物长时间暴露于腐蚀性底水而导致的硅化；2) 由于富含生物蛋白石的沉积物的快速掩埋导致压力和温度升高导致硅化。ISS 和 PBS 被限制在大陆边缘的近端位置，表明穿越古新世和始新世的硅质沉积依赖于陆地溶解硅的供应。与此一致，来自西北大西洋 Blake Nose 的定量硅质微化石组合记录表明，在古近纪早期，营养丰富的边缘而不是贫营养的远洋环境承载了大部分硅质浮游生物的产生。无机 SiO2 沉淀模型不太可能是古近纪早期 ISS 普遍存在的主要机制。我们支持生物源 ISS 前兆情景，并通过表明从北美边缘到古新世和始新世向北大西洋西部供应大量生物二氧化硅，将其与新生代早期低生产力的海洋相协调。来自北大西洋的年轻的、贫 SiO2 水的早期西南流促进了这种多余二氧化硅的溶解。