Abstract Although redox conditions are the dominant control on authigenic enrichment of trace metals in marine sediments, other factors may be important within environments having relatively uniform redox characteristics, such as some anoxic silled basins. Notably, watermass chemistry (specifically, aqueous trace-metal concentrations) and sedimentation rate can also influence the authigenic accumulation of redox-sensitive trace metals such as molybdenum (Mo) and uranium (U) in the sediment, although these effects have received less attention than redox controls to date. Here, we (1) utilize a diffusion-reaction model to evaluate the effects of variations in watermass chemistry and sedimentation rate on authigenic trace-metal enrichment, and (2) present case studies of Mo and U enrichment in modern Black Sea sediments and North American Devonian-Carboniferous boundary (DCB) black shales that illustrate these influences. In both case studies, redox conditions were assessed using non-trace-metal-based proxies (i.e., C-S-Fe, FeT/Al, and Corg:P). Stations 6 and 7 of the modern Black Sea, at water depths of 380 and 1176 m, respectively, exhibit marked differences in authigenic Mo and U enrichment: median Mo/TOC is 13.2 at Station 6 (range 11.5–14.8) versus 5.7 at Station 7 (range 3.7–7.6), and median U/TOC is 2.6 at Station 6 (range 1.5–3.0) versus 1.3 at Station 7 (range 0.7–1.9) (note: units are ppm/% or 10−4, and ranges are 16th-84th percentiles). Given the nearly identical redox conditions and sedimentation rates at these two sites, the most likely cause of the >2× enrichment of Mo and U at Station 6 relative to Station 7 is differences in aqueous Mo and U concentrations, which decline steeply through the upper part of the Black Sea water column, demonstrating the influence of watermass chemistry on patterns of authigenic trace-metal enrichment in the sediment. For the DCB black shales, the median Mo/TOC is 22.2 in the Lower and Upper Bakken (range 15.8–27.0), 28.8 in the Sunbury (range 19.2–37.2), and 14.3 in the Cleveland (range 9.3–22.5), and the median U/TOC is 6.2 in the Lower and Upper Bakken (range 3.5–9.6), 2.6 in the Sunbury (range 1.7–3.4), and 1.2 in the Cleveland (range 0.7–1.7). Differences in Mo and U concentrations between these formations show no relationship to inferred aqueous trace-metal concentrations, Mn–Fe particulate shuttles, or paleoenvironmental redox conditions, but they broadly correlate with variation in sedimentation rates, providing evidence that sedimentation rates can measurably influence the degree of authigenic trace-metal enrichment of marine sediments.

中文翻译：

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超越氧化还原：通过水团化学和沉积速率控制缺氧海相中痕量金属的富集

摘要 虽然氧化还原条件是海洋沉积物中痕量金属自生富集的主要控制因素，但在具有相对均匀氧化还原特性的环境中，例如一些缺氧的硅藻土盆地，其他因素可能也很重要。值得注意的是，水团化学（特别是水中痕量金属浓度）和沉降速率也会影响沉积物中钼 (Mo) 和铀 (U) 等氧化还原敏感的痕量金属的自生积累，尽管这些影响很少受到关注比迄今为止的氧化还原控制。在这里，我们 (1) 利用扩散反应模型来评估水团化学和沉降速率的变化对自生痕量金属富集的影响，(2) 目前在现代黑海沉积物和北美泥盆纪-石炭纪边界 (DCB) 黑色页岩中 Mo 和 U 富集的案例研究，说明了这些影响。在这两个案例研究中，氧化还原条件都使用非痕量金属基替代物（即 CS-Fe、FeT/Al 和 Corg:P）进行评估。现代黑海的第 6 和第 7 站，水深分别为 380 和 1176 m，在自生 Mo 和 U 富集方面表现出显着差异：第 6 站的中值 Mo/TOC 为 13.2（范围 11.5-14.8），而在站为 5.7 7（范围 3.7–7.6），站点 6（范围 1.5–3.0）的 U/TOC 中值为 2.6，而站点 7（范围 0.7–1.9）的 U/TOC 中值为 1.3（注意：单位为 ppm/% 或 10−4，范围为是第 16-84 个百分位数）。鉴于这两个地点几乎相同的氧化还原条件和沉积速率，最可能的原因是 > 站点 6 相对于站点 7 的 Mo 和 U 的 2 倍富集是水性 Mo 和 U 浓度的差异，通过黑海水柱的上部急剧下降，证明了水团化学对自生痕量金属模式的影响沉积物中的富集。对于 DCB 黑色页岩，下巴肯和上巴肯的中值 Mo/TOC 为 22.2（范围 15.8-27.0），桑伯里为 28.8（范围 19.2-37.2），克利夫兰为 14.3（范围 9.3-22.5），和下巴肯和上巴肯的 U/TOC 中位数为 6.2（范围 3.5-9.6），森伯里为 2.6（范围 1.7-3.4），克利夫兰为 1.2（范围 0.7-1.7）。这些地层之间 Mo 和 U 浓度的差异表明与推断的含水痕量金属浓度、Mn-Fe 颗粒穿梭或古环境氧化还原条件无关，