Vanadium is an important redox-sensitive trace metal for paleoenvironmental reconstructions. Modern organic-rich sediments persistently contain sediment V enrichments <500 μg/g, but many ancient marine organic-rich mudrocks record enrichments >500 μg/g. Previous studies propose that ancient V enrichments of these magnitudes (“V hyper-enrichments”) were deposited from hyper-sulfidic bottom-waters with higher H₂S levels (≥10 mM) than observed in modern euxinic basins. To test the importance of hyper-sulfidic conditions for generating V hyper-enrichments, we compare V concentrations with Mo isotope (δ⁹⁸Mo) compositions from mudrock samples ranging in age from Ediacaran to Pleistocene. In the modern ocean, sediments deposited from strongly euxinic bottom waters ([H₂S]_aq > 11 μM) closely record global seawater δ⁹⁸Mo because conversion of molybdate to tri- and tetra-thiomolybdate is quantitative. By contrast, large Mo isotope fractionations occur during Mo adsorption to Fe-Mn particulates or because of incomplete formation of the most sulfidic thiomolybdates in weakly euxinic settings ([H₂S]_aq < 11 μM), which both favor removal of lighter-mass Mo isotopes to sediments. We find multiple examples when mudrocks with V hyper-enrichments are associated with a wide range of δ⁹⁸Mo for a single time interval, including values at or below oceanic input δ⁹⁸Mo (0.3–0.7‰). This observation suggests significant isotopic offset from reasonable seawater values (typically ≥1.0‰). Thus, we conclude that hyper-sulfidic conditions were not responsible for many V hyper-enrichments in Ediacaran–Phanerozoic mudrocks. Instead, sediment V hyper-enrichments can be explained by high Fe-Mn particulate fluxes to weakly euxinic sediments or by moderately restricted euxinic settings with strongly euxinic ([H₂S]_aq > 11 μM but not necessarily > 10 mM) or weakly euxinic (with slow clastic sedimentation rates and high organic carbon fluxes) bottom waters where vigorous water exchange provides a continuous V supply from the open ocean.

中文翻译：

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钼同位素限制了埃迪卡拉-超生代海洋鱼群中钒超富化的起源

钒是用于古环境重建的重要的氧化还原敏感的痕量金属。现代富含有机物的沉积物持久地含有小于500μg/ g的沉积物V富集，但许多古代海洋富含有机物的泥岩记录的富集度均大于500μg/ g。先前的研究表明，这些数量级的古代V富集（“ V超富集”）是从H ₂ S水平（≥10 mM）的高硫硫化物底水中沉积的，比现代富余盆地中观察到的高。为了测试的用于产生V超富集超硫化条件的重要性，我们比较V浓度与沫同位素（δ ⁹⁸ Mo）的从泥岩样品年龄从埃迪卡拉到更新世组合物。在现代海洋中，沉积物是从强烈富余的底水（[H ₂S]_水溶液> 11μM）密切记录全球海水δ ⁹⁸沫由于转换到钼酸三和四硫代是定量的。相比之下，在Mo吸附到Fe-Mn颗粒过程中或由于在弱共溶环境（[H ₂ S] _aq < 11μM）中大多数硫化硫代钼酸盐的不完全形成，会发生较大的Mo同位素分馏，这两者都有利于去除质量轻的物质。钼同位素沉积物。我们发现多个例子时采用V超富集泥岩与宽范围δ的相关联的⁹⁸沫为一个单一的时间间隔，包括在等于或低于δ海洋输入值⁹⁸钼（0.3–0.7‰）。该观察结果表明，同位素值偏离了合理的海水值（通常≥1.0‰）。因此，我们得出的结论是，高硫化物条件对Ediacaran-Phanerozoic泥岩中的许多V超富化并不负责。取而代之的是，沉积物V的超富化可以通过高铁锰颗粒通量到弱共济的沉积物来解释，也可以通过强共济（[H ₂ S] _aq > 11μM但不一定> 10 mM）或中等低共济的中等限制的共济环境来解释。 （碎屑沉积速率慢，有机碳通量高）在剧烈的水交换作用下，从开阔的海洋连续提供V的底水。