| 粒度端元模型在新疆黄土粉尘来源与古气候研究中的初步应用 |
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| 引用本文： | 程良清,宋友桂,李越,张治平.粒度端元模型在新疆黄土粉尘来源与古气候研究中的初步应用[J].沉积学报,2018,36(6):1148-1156. |
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| 作者姓名： | 程良清 宋友桂 李越 张治平 |
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| 作者单位： | 1.中国科学院地球环境研究所 黄土与第四纪地质国家重点实验室, 西安 710061; |
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| 基金项目： | 国家重点研发计划全球变化专项（2016YFA0601902）；国家自然科学基金项目（41572162）；中国科学院国际合作重点项目（132B61KYS20160002） |
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| 摘 要： | 基于新疆伊犁盆地肖尔布拉克黄土剖面粒度数据，以贝叶斯粒度端元模型法为主，粒级标准偏差法为辅探寻对气候变化响应敏感的粒级组分及其对粉尘来源示踪和古气候重建的意义。研究结果表明粒度端元组分EM1（众数粒径:21.22 μm）代表大气粉尘中较为稳定的背景值，其含量的变化与高空西风环流强度有关。EM2（75.29 μm）主要代表了近源河流沉积物的悬移搬运组分，可视为较敏感的古气候指标。EM3（47.5 μm）也代表了近距离的悬移搬运组分，可能主要由较粗颗粒对地表的碰撞磨蚀作用而产生。EM2记录了深海氧同位素2阶段（MIS2）以来的北大西洋气候波动事件，如Heinrich事件、YD事件等。贝叶斯粒度端元模型能够区分不同的沉积动力过程，在新疆黄土古气候研究中具有广泛的应用前景。
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| 关 键 词： | 粒度端元模型 粒级标准偏差 新疆黄土 粉尘来源 气候事件 |
| 收稿时间： | 2017-09-18 |
Preliminary Application of Grain Size End Member Model for Dust Source Tracing of Xinjiang Loess and Paleoclimate Reconstruction |
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| Institution: | 1.State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China;2.University of Chinese Academy of Sciences, Beijing 100049, China;3.Research Center for Ecology and Environment Central Asia, Chinese Academy of Sciences, Urumqi 830011, China;4.Environmental Monitoring Station of Ili Kazakh Autonomous Prefecture, Yining, Xinjiang 835000, China |
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| Abstract: | Grain size as an important proxy that reflects sedimentary provenance, transport, and deposition processeshas been widely used to reconstruct paleoclimatein loess, lacustrine, and marine sediments. There are two methods to present the result of grain size analysis:the parametric method, which analyzes grain size parameters, and the graphical method, which analyzes the frequency curve. Conceptually, the observed grain size distribution can be regarded as a mixing process of a finite number of end members, which in turn leads to a complex spectrum, commonly with a multimodal and asymmetrical form. Therefore, a method to decompose the different fractions becomes necessary. Although different methods of decomposing grain-size fractions have been successfully applied in the Chinese loess plateau, central Asia loess, which is under the control of westerlies, Siberian high pressure, and the Polar Front, may record complex dynamic processes. This study has analyzed the grain size of the XEBLK section in the Ili Basin, Xinjiang. Using the Bayesian end-member modeling analysis (BEMMA) and graded standard deviation (GSD) methods, the sensitive fractions of grain size and their significance for dust source have been examined. The results of the GSD method distinguish three fractions:0.4-31.7 μm (fine), 31.7-282.5 μm (middle), and 282.5-709.6 μm (coarse). Linearregressions indicate that the content of the middle fraction has a higher coefficient with mean grain size. This fraction implies that dust disperses into different high-altitude atmospheric layers downwind. The middle fraction reflects the component that becomes suspended a few hundred meters above the surface during dust storms and is carried over a distance of roughly 1 000 km. Therefore, the middle fraction is a particularly sensitive paleoclimate proxy. The coarse fraction may indicate the frequency of strong dust storms. The results from BEMMA distinguish three fractions:End Member(EM)1, EM2, and EM3. EM1(modal grain size:21.22 μm)may represent fine dust in the air background that reflects information on high-level atmospheric circulation. EM2 (modal grain size:75.29 μm) representsthe proximal fraction from river sedimentation. EM3 (modal grain size:47.5 μm) also represents a suspended fraction from nearby proximal sources, but this fraction was probably produced during an aeolian abrasion process. By analyzing the relationship between the fractions and the median grain size of bulk samples, EM2 was found to have the highest correlation coefficient. Therefore, EM2 is probably a more sensitive paleoclimate proxy than the other two fractions. EM2 not only records climatic rapid fluctuation since Marine Isotope Stage (MIS)2, but also provides evidence that Xinjiang loess has recorded the Heinrich, Younger Dryas, 8.2 ka, and 4.2 ka events. In summary, the BEMMA and GSD grain-size analysis methods can be used to trace the dust source of loess and to perform paleoclimate reconstruction in the Ili Basin. This paper provides new insights into dust sources and paleoclimate in Central Asia. |
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