| 晚中新世以来中国北方风成沉积的磁性地层学和沉积学研究及其古气候意义 |
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| 引用本文： | 杨石岭,丁仲礼.晚中新世以来中国北方风成沉积的磁性地层学和沉积学研究及其古气候意义[J].中国科学院研究生院学报,2002,19(2):202-208. |
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| 作者姓名： | 杨石岭 丁仲礼 |
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| 作者单位： | 中国科学院地质与地球物理研究所,北京,100029 |
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| 摘 要： | 对黄土高原的灵台和泾川黄土-红粘土序列进行了磁性地层学和沉积学研究.古地磁研究表明,泾川剖面的底界年龄为8.0
Ma,这比灵台剖面的底界年龄老1.0 Ma.通过空间上红粘土剖面的地层对比,发现灵台红粘土序列相对较为完整和连续.该剖面可以作为中国北方晚第三纪红粘土的标准剖面.野外观察和粒度分析均表明灵台和泾川红粘土沉积为风成沉积.通过对南北向黄土大断面粒度参数的系统分析,初步建立了"粉尘沉积的粒度参数一沉积区距源区最小距离"的半定量模型.根据这些模型推测,红粘土的主要源区可能在现代的巴丹吉林沙漠及其以西地区.灵台剖面的游离铁/全铁值变化表明,晚中新世以来东亚夏季风经历了非线性的演化历史.约4.1～4.8
Ma间为黄土高原地区7.0 Ma以来东亚夏季风最为强盛的时期.该气候事件的出现可能同全球温度背景较高及全球冰量较小有着动力学上的联系.
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| 关 键 词： | 黄土 红粘土 风成沉积 粒度 古季风 |
Magnetostratigraphy and Sedimentology of the Eolian Deposits Since the Late Miocene in Northern China and the Paleoclimatic Implications |
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| Abstract.Magnetostratigraphy and Sedimentology of the Eolian Deposits Since the Late Miocene in Northern China and the Paleoclimatic Implications[J].Journal of the Graduate School of the Chinese Academy of Sciences,2002,19(2):202-208. |
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| Authors: | Abstract |
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| Abstract: | In this study, two thick loess-red clay sequences located at Lingtai and Jingchuan, theChinese Loess Plateau, are studied with emphases on magnetostratigraphy and sedimentology. Paleo-magnetic measurements show that the Jingchuan red clay has a basal age of 8.0 Ma, which is one mil-lion years older than the previously studied Lingtai section. Field observations and grain size analysesboth suggest an eolian origin of the red clay sediments at Lingtai and Jingchuan, thus extending avail-able records of the eolian deposits in the Loess Plateau from 2.6 Ma back to 7.0 ～ 8.0 Ma. Correla-tion of five red clay sections in the Loess Plateau suggests that the Lingtai red clay sequence has a rel-atively continuous nature of sedimentation and can be regarded as the type-section of the Tertiary redclay deposits in northern China. On the basis of spatial changes in the grain size of one northwest-southeast loess transect, several semiquantitative models of grain size parameters versus the minimumdistance from the source region to depositional areas were developed. According to these models, theestimated southeastern margin of the desert in northern China during the Tertiary red clay developmentis similar to that of the present Badain Jaran desert. To reconstruct the long-term East-Asia monsoonhistory from the celebrating eolian red clay-loess deposits, the ratios of CBD-extractable Fe2O3to totalFe2O3 concentrations in the Lintai red clay-loess sequence, the proxy indicator for the summer mon-soon changes, were measured. The Lingtai Fe2 O3 ratio record indicates that the East-Asia summermonsoon has experienced a non-linear evolution over the past seven million years. The strongest EastAsia summer monsoon may occur between 4.1 and 4.8 Ma, which may be causally related to the rela-tively small ice volume and high global temperature during the early Pliocene. |
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| Keywords: | loess red clay eolian deposits grain size paleomonsoon |
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