| 青海湖东岸全新世风成沉积地球化学特征及其古气候意义 |
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| 引用本文： | 薛红盼,曾方明.青海湖东岸全新世风成沉积地球化学特征及其古气候意义[J].沉积学报,2021,39(5):1198-1207. |
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| 作者姓名： | 薛红盼 曾方明 |
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| 作者单位： | 1.中国科学院青海盐湖研究所，中国科学院盐湖资源综合高效利用重点实验室，西宁 810008 |
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| 基金项目： | 国家自然科学基金U20A2078中国科学院青年创新促进会专项项目2017468第二次青藏高原综合科学考察研究2019QZKK0805 |
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| 摘 要： | 青海湖地区因独特的地理位置，其古气候演化一直为学者们所关注。由于各类环境替代指标的多解性，以往研究中对青海湖地区末次冰消期以来特别是早全新世的气候特征存在不一致的认识。对青海湖东岸种羊场风成沉积物的元素地球化学特征及其古气候意义进行分析，结合磁化率、粒度和色度指标重建了过去约11 ka青海湖地区古气候演变过程。结果表明:1）化学蚀变指数（CIA）值和Al2O3-（CaO*+Na2O）-K2O（A-CN-K）三元图指示种羊场风成沉积经历了弱风化、中等程度的风化强度。CIA值的波动变化反映青海湖地区全新世期间经历了较大的干湿变化。2）亮度（L*）与总有机碳（TOC）含量呈高度负相关（R2=0.71，P<0.01），可以间接地反映研究区古气候演变过程。3）种羊场（ZYC）剖面的多指标分析结果和剖面地层特征揭示青海湖地区在11.0~6.5 ka B.P.时期，风化作用较弱，气候可能相对温暖干旱；6.5~1.1 ka B.P.时期风化作用可能较强，为暖湿期，与古湖岸堤记录的湖面变化较为一致；1.1 ka B.P.至今，气候变得干旱。4）亚洲季风和太阳辐射的强弱变化可能造成有效湿度的高低变化，从而导致青海湖地区全新世气候干湿交替变化。
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| 关 键 词： | 青海湖 全新世 元素地球化学 风成沉积 古气候变化 |
| 收稿时间： | 2020-06-04 |
Geochemical Characteristics of Aeolian Deposits on the Eastern Shore of Qinghai Lake and Their Paleoclimatic Implications since the Holocene |
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| XUE HongPan,ZENG FangMing.Geochemical Characteristics of Aeolian Deposits on the Eastern Shore of Qinghai Lake and Their Paleoclimatic Implications since the Holocene[J].Acta Sedimentologica Sinica,2021,39(5):1198-1207. |
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| Authors: | XUE HongPan ZENG FangMing |
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| Institution: | 1.Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China2.Qinghai Provincial Key Laboratory of Geology and Environment of Salt Lakes, Xining 810008, China3.University of Chinese Academy of Sciences, Beijing 100049, China |
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| Abstract: | The paleoclimatic evolution of the Qinghai Lake area has long been studied due to the uniqueness of its geographical location. However， the nature of the climate in the area since the last deglaciation， especially in the early Holocene， has been controversial due to the large number of various proxies. In this study， aeolian deposits from the Zhongyangchang （ZYC） section on the eastern shore of Qinghai Lake were analyzed to determine their geochemical properties and associated paleoclimatic implications. The elemental characteristics were combined with magnetic susceptibility （MS）， median grain size （Md） and color parameters to reconstruct the evolution of the paleoclimate in the Qinghai Lake area over the past 11 000 years. The results indicate that aeolian deposits in the ZYC section experienced weak to moderate chemical weathering， and that they are still at the early stage of plagioclase weathering （mainly the removal of Ca and Na）， as indicated by the chemical index of alteration （CIA） and the Al2O3-（CaO*+Na2O）-K2O （A-CN-K） ternary diagram. The climate in the study area has alternated greatly between dry and wet， as reflected by the variation of CIA values since the early Holocene. The lightness （L*） is highly negatively correlated with total organic carbon （TOC） content （R2 = 0.71， P < 0.01）， indicating changes of regional vegetation coverage and indirectly revealing the evolution of the paleoclimate in the area. The results of multi-proxies together with the stratigraphic distribution characteristics in the ZYC section indicate weak weathering in the Qinghai Lake area from 11.0 to 6.5 ka B.P.， and that the climate may have been relatively warm and dry. The high CIA， MS and Rb/Sr ratio， and low （CaO+Na2O+MgO）/Ti2O ratio， Md and L* indicate a warm， humid climate from 6.5 to 1.1 ka B.P.， consistent with the high lake level indicated by shoreline evidence. Since 1.1 ka B.P.， the Qinghai Lake area has become dry. Variation of the intensity of the Asian monsoon and solar radiation may cause the effective humidity to vary， resulting in the alternating wet and dry climate in the Qinghai Lake area. |
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