Anomalously high metal concentrations including iron enrichments are recorded in marine carbonates deposited during Ocean Anoxic Event 2 (OAE 2). These metal enrichments have been attributed to massive submarine eruptions during the formation of one or more large igneous provinces, the proposed trigger for OAE 2 (hydrothermal hypothesis), or to the release of metals from the reoxidation of formerly anoxic marine sediment during a period of temporary cooling during OAE 2 (sediment release hypothesis). Here we use iron stable isotopes to help distinguish between the two hypotheses for a trace metal enriched interval during OAE 2 in the Iona-1 core in the Western Interior Seaway, Texas. Our results show a two-step negative excursion during OAE 2 that is coincident with osmium isotope volcanic proxies measured in the same core, with peak negative values centered on a trace metal-enriched interval. After corrections for detrital and locally supplied iron to the study setting, the δ56Fe value of the remotely supplied iron is –0.28 ± 0.05 ‰, falling in the range of iron δ56Fe values observed in modern hydrothermal plumes (–0.1 to –0.5 ‰), thus supporting the hydrothermal hypothesis as the source of iron and other associated trace metals enriched in the study core during OAE 2. By contrast, the sediment release hypothesis predicts much lower δ56Fe values, between –1.0 ‰ to –3.3 ‰ predicted for benthic supplies of iron from anoxic marine sediment overlying re-oxygenated bottom waters. This study shows that combining iron with other proxies for environmental change, particularly submarine volcanism, can distinguish hydrothermally supplied iron from dust, rivers, and shelf sediment supplies of iron despite iron’s reputation for complicated cycling.

中文翻译：

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铁同位素揭示了海洋缺氧事件 2 期间的火山形成输入 （OAE 2 ∼ 94 马）


在海洋缺氧事件 2 （OAE 2） 期间沉积的海洋碳酸盐中记录了异常高的金属浓度，包括铁富集。这些金属富集归因于一个或多个大型火成岩省形成期间的大规模海底喷发，这是 OAE 2（热液假说）的拟议触发因素，或者归因于 OAE 2 期间临时冷却期间以前缺氧的海洋沉积物再氧化释放金属（沉积物释放假说）。在这里，我们使用铁稳定同位素来帮助区分德克萨斯州西部内陆航道 Iona-1 核心中 OAE 2 期间痕量金属富集区间的两种假设。我们的结果显示，在 OAE 2 期间有一个两步负偏移，这与在同一岩心中测量的锇同位素火山代理重合，峰值负值以富含痕量金属的区间为中心。在对研究环境中的碎屑和本地供应的铁进行校正后，远程供应的铁的 δ56Fe 值为 -0.28 ± 0.05 ‰，落在现代热液羽流中观察到的铁 δ56Fe 值范围内（-0.1 至 -0.5 ‰），从而支持热液假说，即在 OAE 2 期间，研究岩芯中富含铁和其他相关痕量金属的来源。相比之下，沉积物释放假说预测的 δ56Fe 值要低得多，预测的底栖铁供应来自再氧化底层水域的缺氧海洋沉积物的铁含量在 –1.0 ‰ 到 –3.3 ‰ 之间。这项研究表明，将铁与环境变化的其他替代指标（尤其是海底火山活动）相结合，可以将热液供应的铁与灰尘、河流和铁的大陆架沉积物供应区分开来，尽管铁以复杂的循环而闻名。