MAGNETOSTRATIGRAPHY OF THE MIZIWAN MIOCENE EOLIAN DEPOSITS IN QIN′AN COUNTY (GANSU PROVINCE)
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摘要: 文章对西部黄土高原糜子湾黄土-古土壤剖面进行了磁性地层学研究。该剖面厚度为164.4m,记录了15个正磁极性段和15个负磁极性段,可与标准极性表中从C5r.3r到C5En之间的极性带对比。根据极性界限用平均沉积速率外推,得到该剖面顶界年龄为约11.6MaB.P.,底界年龄为约18.5MaB.P.。糜子湾剖面位于已发表的QAⅠ中新世黄土剖面以东约30km,两剖面相同时代的地层在岩性地层结构和磁化率曲线波动上具有高度的一致性,表明中新世黄土-古土壤序列与第四纪黄土-古土壤序列一样,地层在空间上有很好的可对比性。文章的结果为从空间角度研究中新世环境变化行为提供了新剖面的年代地层框架。Abstract: Earlier studies on two sections (QA-Ⅰ and QA-Ⅱ) in the Qin′an County from the western Loess Plateau demonstrated that loess deposits started by 22MaB.P., indicating the onset of Asian desertification and winter monsoon circulation by the Early Miocene time. Another Miocene loess section, Miziwan section with a thickness of 164.4m, 30km in east to the QA-Ⅰ section, is geomagnetically dated in this study.
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Key words:
- loess-paleosolsequence /
- magnetostratigraphy /
- eolian deposits /
- paleoclimate /
- Miocene
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