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 8.0Ma,这比灵台剖面的底界年龄老 1.0Ma.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———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～ 4.8Ma间为黄土高原地区 7.0Ma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.
In this study, two thick loess-red clay sequences located at Lingtai and Jingchuan, the Chinese Loess Plateau, are studied with emphases on magnetostratigraphy and sedimentology. Paleomagnetic measurements show that the Jingchuan red clay has a basal age of 8.0 Ma, which is one million years older than the previously studied Lingtai section. Field observations and grain size analyses both suggest an eolian origin of the red clay sediments at Lingtai and Jingchuan, thus extending available records of the eolian deposits in the Loess Plateau from 2.6 Ma back to 7.0～8.0 Ma. Correlation of five red clay sections in the Loess Plateau suggests that the Lingtai red clay sequence has a relatively continuous nature of sedimentation and can be regarded as the type-section of the Tertiary red clay 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 minimum distance from the source region to depositional areas were developed. According to these models, the estimated southeastern margin of the desert in northern China during the Tertiary red clay development is similar to that of the present Badain Jaran desert. To reconstruct the long-term East-Asia monsoon history from the celebrating eolian red clay-loess deposits, the ratios of CBD-extractable Fe 2O 3 to total Fe 2O 3 concentrations in the Lintai red clay-loess sequence, the proxy indicator for the summer monsoon changes, were measured. The Lingtai Fe 2O 3 ratio record indicates that the East-Asia summer monsoon has experienced a non-linear evolution over the past seven million years. The strongest East Asia summer monsoon may occur between 4.1 and 4.8 Ma, which may be causally related to the relatively small ice volume and high global temperature during the early Pliocene.
出处
《中国科学院研究生院学报》
CAS
CSCD
2002年第2期202-208,共7页
Journal of the Graduate School of the Chinese Academy of Sciences
基金
supportedbytheNationalNaturalScienceFoundationofChina(40 0 2 42 0 2 ).
