Marine ferromanganese deposits, often called the scavengers of the sea, adsorb and coprecipitate with a wide range of metals of great interest for paleo‐environmental reconstructions and economic geology. The long (up to ∼75 Ma), near‐continuous record of seawater chemistry afforded by ferromanganese deposits offers much historical information about the global ocean and surface earth including crustal processes, mantle processes, ocean circulation, and biogeochemical cycles. The extent to which the ferromanganese deposits hosting these geochemical proxies undergo diagenesis on the seafloor, however, remains an important and challenging factor in assessing the fidelity of such records. In this study, we employ multiple X‐ray techniques including micro–X‐ray fluorescence, bulk and micro–X‐ray absorption spectroscopy, and X‐ray powder diffraction to probe the structural, compositional, redox, and mineral changes within a single ferromanganese crust. These techniques illuminate a complex two‐dimensional structure characterized by crust growth controlled by the availability of manganese (Mn), a dynamic range in Mn oxidation state from +3.4 to +4.0, changes in Mn mineralogy over time, and recrystallization in the lower phosphatized portions of the crust. Iron (Fe) similarly demonstrates spatial complexity with respect to concentration and mineralogy, but lacks the dynamic range of oxidation state seen for Mn. Micrometer‐scale measurements of metal abundances reveal complex element associations between trace elements and the two major oxide phases, which are not typically resolvable via bulk analytical methods. These findings provide evidence of post‐depositional processes altering chemistry and mineralogy, and provide important geochemical context for the interpretation of element and isotopic records in ferromanganese crusts.

中文翻译：

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锰铁结壳形成和成岩的光谱学见解

海洋锰铁矿床通常被称为海洋的清除剂，它们吸附和共沉淀各种对古环境重建和经济地质具有重大意义的金属。锰铁矿床提供的长期（近75 Ma）近乎连续的海水化学记录提供了有关全球海洋和地表的许多历史信息，包括地壳过程，地幔过程，海洋环流和生物地球化学循环。但是，在这些海底沉积物上容纳这些地球化学代理的锰铁沉积物的程度成岩作用仍然是评估此类记录保真度的重要且具有挑战性的因素。在这项研究中，我们采用了多种X射线技术，包括微X射线荧光，体相和微X射线吸收光谱，X射线粉末衍射可探测单个锰铁结壳内的结构，成分，氧化还原和矿物变化。这些技术阐明了一个复杂的二维结构，其特征在于由锰（Mn）的可用性控制的结壳生长，Mn氧化态的动态范围（从+3.4到+4.0），Mn矿物学随时间的变化以及下部磷化中的重结晶。地壳部分。铁（Fe）同样显示出浓度和矿物学方面的空间复杂性，但缺乏Mn所见的氧化态的动态范围。微米级金属丰度的测量揭示了痕量元素与两个主要氧化物相之间的复杂元素关联，通常无法通过本体分析方法解决。