A new vanadium species in black shales: Updated burial pathways and implications
A new vanadium species in black shales: Updated burial pathways and implications
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DOI：
10.1016/j.gca.2022.09.035
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发表时间：
2022-09
影响因子：
5
通讯作者：
L. Bian;A. Chappaz;N. Schovsbo;H. Sanei
中科院分区：
文献类型：
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作者：
L. Bian;A. Chappaz;N. Schovsbo;H. Sanei
研究富有机质岩石中的钒（V）地球化学可能为地球历史上古海洋和大气的氧化还原演化提供新的见解。以前的工作，主要是基于实验和热力学预测，建议V主要是绑定到氧（O）原子和/或O单键N（氮）基团的氧化态范围从+III到+V，当从水柱中删除。这个概念模型代表了我们对沉积档案中V埋藏过程的理解。然而，直到我们的研究，V的形态还没有在古代沉积物中进行过研究。微聚焦X射线吸收近边结构（µ-XANES）分析首次应用于斯堪的纳维亚地区晚寒武世-早奥陶世有机质丰富的明矾页岩中的V形态特征。结果表明，在富氧条件下沉积的样品中，V（+IV）-S结构占主要地位（>80%），V（+III）-O结构占次要地位（<20%）。V（+IV）-S/∑V比值似乎受缺氧条件强度的影响。我们认为新的V（+IV）-S结构可能是在强硫化物条件下形成的。有机物是最有可能是这个新发现的物种的主要宿主相。此外，我们提出了一个更新的模型，描述了在广泛的氧化还原条件下的V的埋葬过程中所涉及的过程。该模型表明，V的形态有可能提供一个更细致入微的图片的氧化还原条件下，在沉积的时间。
Examining vanadium (V) geochemistry in organic-rich rocks might provide new insights into the redox evolution of paleo ocean and atmosphere through Earth’s history. Previous work, mainly based on experiments and thermodynamic predictions, suggested that V is mainly bound to oxygen (O) atoms and/or Osingle bondN (nitrogen) groups with oxidation states ranging from +III to +V, when removed from the water column. This conceptual model represented our understanding of the burial processes of V in sedimentary archives. However, until our study, the speciation of V had not been investigated in ancient sediments. For the first time, micro-focused X-ray Absorption Near Edge Structure (µ-XANES) analysis is applied to characterize V speciation in the late Cambrian – Early Ordovician, organic-rich Alum Shale of the Scandinavian region. The result shows the presence of a new V(+IV)–S structure that largely dominates the V speciation (>80%), subordinated by a V(+III)–O structure (<20%) in our samples deposited under euxinic conditions. The V(+IV)–S/∑V ratio seems to be influenced by the intensity of euxinic conditions. We suggest that the new V(+IV)–S structure may have been formed under strongly sulfidic conditions. Organic matter is most likely to be the dominant host phase for this newly identified species. Additionally, we propose an updated model describing the processes involved during the burial of V under a wide range of redox conditions. This model shows that the V speciation has the potential to provide a more nuanced picture of the redox conditions that prevailed at the time of deposition.