Vanadium (V) is a redox-sensitive trace metal often used as a paleoredox proxy in ancient marine sediments. However, our understanding of the early diagenesis of V is limited to laboratory-based simulations and bulk geochemical measurements of natural sediments. Microscale measurements are essential to exploring V geochemistry in organic-rich coastal sediments, where redox zonation changes over small spatial scales. Here, we describe an innovative in situ two-dimensional (2D) imaging approach to study redox-driven changes of V-bearing iron oxyhydroxides (lepidocrocite and ferrihydrite) in intertidal mudflat sediments of an Australian lagoon lake (Coombabah Lake, Queensland). Vanadium-bearing iron oxyhydroxides were suspended in a polyurethane-based hydrogel matrix, loaded on laser-cut acrylic probes, and exposed to mudflat sediments for up to 6 weeks. Changes in V speciation and Fe mineralogy were examined using synchrotron-based X-ray fluorescence (XRF) microspectroscopy for high-resolution chemical imaging of elemental (V, S, Fe) distributions combined with micro-X-ray absorption near-edge structure (μXANES) spectroscopy at the V and Fe K-edges for speciation analysis. Linear combination fitting of μXANES data revealed that solid-phase V^V was reduced to V^IV in the ferruginous zone of sediments and to a mixture of mainly V^IV and some V^III (up to 10–20%) in the sulfidic zone, where the reduction correlated with the degree of sulfidation and conversion of the iron oxyhydroxides to FeS (up to 96%). The combination of gel-based mineral probes with synchrotron-based μXRF tools can unravel small-scale geochemical relationships and provide new insights into the early diagenesis of trace elements in marine sediments.

中文翻译：

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海洋沉积物中含钒羟基氧化铁的归宿：基于凝胶的原位矿物探针与同步加速器 X 射线荧光显微光谱学的集成

钒 (V) 是一种氧化还原敏感的微量金属，通常用作古代海洋沉积物中的古氧化还原替代物。然而，我们对 V 早期成岩作用的理解仅限于基于实验室的模拟和天然沉积物的大量地球化学测量。微尺度测量对于探索富含有机物的沿海沉积物中的 V 地球化学至关重要，其中氧化还原分区在小空间尺度上发生变化。在这里，我们描述了一种创新的原位二维（2D）成像方法，用于研究澳大利亚泻湖（昆士兰库姆巴巴湖）潮间带泥滩沉积物中含钒羟基氧化铁（纤铁矿和水铁矿）氧化还原驱动的变化。含钒羟基氧化铁悬浮在聚氨酯基水凝胶基质中，装载在激光切割的丙烯酸探针上，并暴露在泥滩沉积物中长达 6 周。使用基于同步加速器的 X 射线荧光 (XRF) 显微光谱技术对元素（V、S、Fe）分布进行高分辨率化学成像，并结合微 X 射线吸收近边缘结构，检查 V 形态和 Fe 矿物学的变化（ μXANES) V 和 Fe K边缘光谱用于形态分析。 μXANES 数据的线性组合拟合表明，在沉积物的铁质带中，固相 V ^V减少为 V ^{IV ，在硫化物带中，固相 V V 减少为主要为 V IV}和一些 V ^III的混合物（高达 10-20%），其中还原程度与硫化程度以及羟基氧化铁转化为 FeS 的程度相关（高达 96%）。基于凝胶的矿物探针与基于同步加速器的 μXRF 工具的结合可以揭示小规模的地球化学关系，并为海洋沉积物中微量元素的早期成岩作用提供新的见解。