AMS radiocarbon dating of pollen concentrates in a karstic lake system
AMS radiocarbon dating of pollen concentrates in a karstic lake system
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DOI：
10.1016/j.quageo.2017.02.006
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发表时间：
2017-04-01
影响因子：
2.7
通讯作者：
Fink, David
中科院分区：
文献类型：
--
作者：
Fletcher, William J.;Zielhofer, Christoph;Fink, David
在湖泊沉积物中，陆地宏体化石是罕见的或不存在的，AMS放射性碳测年的花粉浓缩物可能是一个重要的替代解决方案，开发一个强大的和高分辨率的年代学适合贝叶斯建模的年龄-深度关系。在这里，我们报告的应用程序的重液体密度分离方法（Vandergoes和之前，放射性碳45：479-492，2003年）全新世湖泊沉积物的喀斯特湖西迪阿里，摩洛哥。与许多喀斯特湖泊一样，450-900年的显着C-14湖水库效应是明显的，陆地宏化石和水生（介形虫）或散装沉积物样本的配对日期证明了这一点。对23种花粉浓缩物进行了AMS测年，并与实验室标准（烟煤、无烟煤、IAEA C5木材）进行了对比。使用一系列密度逐渐降低（1.9-1.15 g/cm（3））的聚钨酸钠（SPT）溶液制备浓缩物，并对所得残留物进行显微镜分析，以量化陆生花粉含量。最好的级分（通常在1.4 - 1.2 g/cm（3）下沉淀）产生0.5-5 mg的可测日期的样品（来自类似于15 g的沉积物样品），其中C含量通常类似于50重量%。陆地花粉纯度范围为29%至88（mu = 67%），反映了从常见的水生藻类（如盘星藻和葡萄球菌）中分离花粉粒的挑战。泊松过程贝叶斯沉积模型结合放射性碳（花粉和宏体化石）和Pb-210/Cs-137数据。由于所有的花粉样本都含有一些非陆地有机物，我们假设一个指数离群值分布，将每个花粉浓度数据视为一个旧的离群值和终点。这种方法产生强大的数据模型的协议，和先验和后验年龄分布之间的差异是一致的，而且与理论偏移预期已知的水库年龄和样本特定的陆地内容。花粉浓缩物定年法的应用加强了在分离和筛分阶段对残留物进行显微镜检查的重要性。样本特定差异意味着花粉浓缩物的制备不能简化为简单的“黑匣子”协议，测年和随后的年龄模型开发必须得到沉积物微体化石含量的详细分析的支持。(C)2017爱思唯尔B. V.保留所有权利。
In lake sediments where terrestrial macrofossils are rare or absent, AMS radiocarbon dating of pollen concentrates may represent an important alternative solution for developing a robust and high resolution chronology suitable for Bayesian modelling of age-depth relationships. Here we report an application of the heavy liquid density separation approach (Vandergoes and Prior, Radiocarbon 45:479-492, 2003) to Holocene lake sediments from karstic Lake Sidi Ali, Morocco. In common with many karstic lakes, a significant lake C-14 reservoir effect of 450-900 yr is apparent, evidenced by paired dates on terrestrial macrofossils and either aquatic (ostracod) or bulk sediment samples. AMS dating of 23 pollen concentrates alongside laboratory standards (bituminous coal, anthracite, IAEA C5 wood) was undertaken. Concentrates were prepared using a series of sodium polytungstate (SPT) solutions of progressively decreasing density (1.9-1.15 g/cm(3)) accompanied by microscopic analysis of the resulting residues to allow quantification of the terrestrial pollen content. The best fractions (typically precipitating at 1.4 -1.2 g/cm(3)) yielded dateable samples of 0.5-5 mg (from sediment samples of similar to 15 g), with C content typically similar to 50% by weight. Terrestrial pollen purity ranges from 29% to 88(mu = 67%), reflecting the challenge of isolating pollen grains from common aquatic algae, e.g. Pediastrum and Botryococcus. A Poisson-process Bayesian depositional model incorporating radiocarbon (pollen and macrofossil) and Pb-210/Cs-137 data is employed. As all pollen samples incorporate some non-terrestrial organic matter, we assume an exponential outlier distribution treating each pollen concentrate datum as an old outlier and terminus post quem. This approach yields strong data-model agreement, and differences between the prior and posterior age distributions are furthermore consistent with theoretical offsets anticipated for the known reservoir ages and sample-specific terrestrial content. This application of the pollen concentrate dating approach reinforces the importance of microscopic inspection of the residues during the separation and sieving stages. Sample specific differences mean that the pollen concentrate preparation cannot be reduced to a simplistic "black box" protocol, and dating and subsequent age-model development must be supported by detailed analysis of the microfossil content of the sediments. (C) 2017 Elsevier B.V. All rights reserved.