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What do Ce anomalies in marine carbonates really mean? A perspective from leaching experiments
Chemical Geology ( IF 3.6 ) Pub Date : 2020-01-01 , DOI: 10.1016/j.chemgeo.2019.119413
Cheng Cao , Xiao-Ming Liu , Clement P. Bataille , Chao Liu

Abstract Yttrium and rare earth elements (REY) in aqueous environments have been intensively studied because they record important geochemical information. For example, the cerium anomaly, measured in marine sedimentary rocks, has been widely applied as a paleoredox indicator. Marine carbonates are the main substrate used to reconstruct REY signal in paleo-oceans with the underlying assumption that REY incorporated into carbonate minerals preserve the authigenic seawater signal. However, extracting authigenic REY signals from carbonate rocks are challenging. It requires dissolving carbonate phases using acid leaching procedures without contamination from other non‑carbonate phases such as Mn/Fe oxides (hydroxides), clay minerals, siliciclastic and organic phases. Multiple dissolution protocols, especially partial leaching, were proposed to eliminate potential contaminations. Yet, the efficiency of these procedures in reducing contamination remains ambiguous. Additionally, no systematic study on how each non‑carbonate phase can modify the authigenic REY signal from carbonates. First, we systematically investigated the efficiency of using ammonium acetate buffer pre-treatment to remove exchangeable ions prior to dissolution. We tested a range of concentration, pH, and reaction time of the buffer and we found that ammonium acetate of 1 M with a pH slightly 75% CaCO3) using two steps of ammonium acetate pre-leaching followed by three steps of 0.3 M acetic acid leaching.

中文翻译:

海洋碳酸盐中的 Ce 异常究竟意味着什么?浸出实验的观点

摘要 水环境中的钇和稀土元素(REY)由于记录了重要的地球化学信息而受到了广泛的研究。例如,在海洋沉积岩中测量的铈异常已被广泛用作古氧化还原指示剂。海洋碳酸盐是古海洋中用于重建 REY 信号的主要基质,其基本假设是 REY 并入碳酸盐矿物中保留了自生海水信号。然而,从碳酸盐岩中提取自生 REY 信号具有挑战性。它需要使用酸浸程序溶解碳酸盐相,而不会受到其他非碳酸盐相的污染,例如 Mn/Fe 氧化物(氢氧化物)、粘土矿物、硅质碎屑和有机相。多种溶解方案,尤其是部分浸出,建议消除潜在的污染。然而,这些程序在减少污染方面的效率仍然不明确。此外,没有关于每个非碳酸盐相如何修改来自碳酸盐的自生 REY 信号的系统研究。首先,我们系统地研究了使用醋酸铵缓冲液预处理在溶解前去除可交换离子的效率。我们测试了缓冲液的一系列浓度、pH 值和反应时间,我们发现 1 M 乙酸铵和 pH 值略为 75% CaCO3) 使用两步乙酸铵预浸,然后是三步 0.3 M 乙酸浸出。没有关于每个非碳酸盐相如何修改来自碳酸盐的自生 REY 信号的系统研究。首先,我们系统地研究了使用醋酸铵缓冲液预处理在溶解前去除可交换离子的效率。我们测试了缓冲液的一系列浓度、pH 值和反应时间,我们发现 1 M 乙酸铵和 pH 值略为 75% CaCO3) 使用两步乙酸铵预浸,然后是三步 0.3 M 乙酸浸出。没有关于每个非碳酸盐相如何修改来自碳酸盐的自生 REY 信号的系统研究。首先,我们系统地研究了使用醋酸铵缓冲液预处理在溶解前去除可交换离子的效率。我们测试了缓冲液的一系列浓度、pH 值和反应时间,我们发现 1 M 乙酸铵和 pH 值略为 75% CaCO3) 使用两步乙酸铵预浸,然后是三步 0.3 M 乙酸浸出。
更新日期:2020-01-01
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