Chemical isolation and isotopic analysis of terrigenous sediments with emphasis on effective removal of contaminating marine phases including barite
Chemical isolation and isotopic analysis of terrigenous sediments with emphasis on effective removal of contaminating marine phases including barite
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DOI：
10.1016/j.chemgeo.2021.120673
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发表时间：
2021-12
期刊：
影响因子：
3.9
通讯作者：
A. M. Jewell;M. Cooper;J. Milton;R. James;A. J. Crocker;P. Wilson
中科院分区：
文献类型：
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作者：
A. M. Jewell;M. Cooper;J. Milton;R. James;A. J. Crocker;P. Wilson
陆源组分的放射性成因同位素组成（如87sr /86Sr和εNd）通常用于确定沉积物的物源和搬运史。在海洋沉积物中，在分析之前必须将陆源组分分离出来，以避免被海洋相污染。虽然人们普遍建议去除碳酸钙、有机物、生物蛋白石、自生涂层和吸附阳离子，但去除所有这些相的步骤并不一致，并且没有有效去除海洋重晶石的标准程序。海洋重晶石在世界各地的海洋中都有发现，特别是在高出口产量的地区，锶（Sr）含量很高，因此有可能使陆源87sr /86Sr的测量偏向于海水。本文介绍了对大西洋和太平洋海洋沉积物的连续浸出实验结果，以定量确定重晶石存在对87sr /86Sr和ε nx的污染效应，并制定了一种成功分离陆源组分的方案。研究结果表明，海洋重晶石会使陆源87sr /86Sr的测量值与海水87sr /86Sr的测量值偏差达bb0.01，并强调了评估重晶石污染对陆源87sr /86Sr的位置特异性影响的重要性。我们的研究结果表明，海相重晶石可以严重污染陆相87sr /86Sr，即使在海相重晶石积累速率较低的地方（分别<~ 5 mg/m3/yr和<~20 g C/m2/yr）。重晶石含有非常低浓度的Nd，因此重晶石对陆源εNd的污染不是主要问题，但我们方案的一个重要方面是它对陆源εNd的影响很小，允许在相同清洗的等分液上分析87sr /86Sr和εNd。我们系统的分级方法将有助于标准化87sr /86Sr数据，允许在站点之间进行可靠的比较，并将有助于提高对风吹大陆尘埃和河流沉积物的来源，运输和风化历史的理解。
The radiogenic isotope composition (e.g.87Sr/86Sr and εNd) of the terrigenous fraction is commonly used to determine the provenance and transport history of sediments. In ocean sediments, the terrigenous fraction must be isolated prior to analysis to avoid contamination by marine phases. While the removal of calcium carbonate, organic matter, biogenic opal, authigenic coatings and adsorbed cations is widely advised, steps to remove all these phases are not consistently employed, and there is no standard procedure for the effective removal of marine barite. Marine barite is found throughout the world's oceans, particularly in regions of high export production, is highly enriched in strontium (Sr) and therefore has the potential to bias measurements of terrigenous87Sr/86Sr towards seawater. Here we present results from sequential leaching experiments on marine sediments from the Atlantic and the Pacific Oceans to quantitatively determine the contaminating effect on87Sr/86Sr and εNdexerted by the presence of barite and develop a protocol to successfully isolate the terrigenous fraction. Our results show that marine barite can skew measurements of terrigenous87Sr/86Sr by >0.01 towards the87Sr/86Sr value of seawater, and we highlight the importance of assessing the location-specific impact of barite contamination on terrigenous87Sr/86Sr. Our results show that marine barite can severely contaminate terrigenous87Sr/86Sr, even where marine barite accumulation rates are modest (< ~5 mg/m3/yr and <~20 g C/m2/yr, respectively). Barite contains Nd in very low concentrations so barite contamination of terrigenous εNdis not a major concern but an important aspect of our protocol is that it has minimal effect on terrigenous εNd,allowing87Sr/86Sr and εNdto be analysed on identically cleaned aliquots. Our systematic graduated approach will help standardise87Sr/86Sr data, allow for robust comparisons between sites, and will contribute to an improved understanding of the provenance, transport and weathering histories of windblown continental dust and riverine sediments.