Changes in grain-size and sedimentation rate of the Neogene Red Clay deposits along the Chinese Loes

来源 :Science in China(Series D:Earth Sciences) | 被引量 : 0次 | 上传用户:oqo235
下载到本地 , 更方便阅读
声明 : 本文档内容版权归属内容提供方 , 如果您对本文有版权争议 , 可与客服联系进行内容授权或下架
论文部分内容阅读
The wind system responsible for transporting dust onto the Chinese Loess Plateau during the late Miocene and Pliocene is still unknown and recent investigations highlight many controversies. This report aims to investigate spatiotemporal changes in grain-size and sedi- mentation rate of the Neogene Red Clay deposits in north China and to explore palaeoclimatic changes during the late Miocene and Pliocene, in particular the palaeowind system that trans- ported dust. Samples were collected from eight Red Clay sections on the Loess Plateau. Meas- urement and analysis show that there is a clear southward decrease in the mean grain-size index and in the coarse particle fraction (>20 μm). At Jiaxian site on the northern Loess Plateau, the average mean grain-size is around 20 μm, while at Lantian site in the south, the mean is around 9 μm. The coarse particle fraction >20 μm makes up 24.4% and 5.6%, at the two sites respec- tively. This distinct diversity of grain-size in the aeolian Red Clay deposit between the north and south indicate that the palaeodust was transported mainly by northerly low-level winds. The grain-size variations in the Red Clay deposits can also be divided into three stages (the lower, the middle and the upper interval): grain-size of the lower stage is significantly coarser than that of the middle stage, but finer than that of the upper stage. As a consequence, the intensity of pa- laeowind and desiccation of the dust source region during the late Miocene and Pliocene can be divided into three stages: 6.2―5.4 Ma, 5.4―3.5 Ma and 3.5―2.6 Ma. Strength of the palaeowind during the middle stage (5.4―3.5 Ma) is weaker than that of the previous and subsequent stages and the intensity of palaeowind during the latest stage (3.5―2.6 Ma) is stronger than that of the early time (6.2―5.4 Ma). Variations in the sedimentation rate of the Red Clay deposit can also be divided into three stages: the earlier, the middle and the later interval. The sedimentation rate of the earlier stage is higher than during the middle stage, but lower than during the later one. This is a clear indicator of changes in the palaeowind intensity and aridity in the dust source region and may be linked with global ice volume changes during the late Miocene and the Pliocene. The wind system responsible for transporting dust onto the Chinese Loess Plateau during the late Miocene and Pliocene is still unknown and recent investigations highlight many controversies. This report aims to investigate spatiotemporal changes in grain-size and sediment mentation rate of the Neogene Red Clay deposits in north China and to explore palaeoclimatic changes during the late Miocene and Pliocene, in particular the palaeowind system that trans- ported dust. Measured urease and analysis show that there is a clear southward decrease in the mean grain-size index and in the coarse particle fraction (> 20 μm). At Jiaxian site on the northern Loess Plateau, the average mean grain-size is around 20 μm, while at Lantian site in the south, the The coarse particle fraction> 20 μm makes up 24.4% and 5.6% at the two sites respecively. This distinct diversity of grain-size in the aeolian Red Clay deposit between the north and south indicate that the palaeodust was transported mainly by northerly low-level winds. The grain-size variations in the Red Clay deposits can also be divided into three stages (the lower, the middle and the upper interval): grain-size of the lower stage is significantly coarser than that of the middle stage, but finer than that of the upper stage. As a consequence, the intensity of pa- laeowind and desiccation of the dust source region during the late Miocene and Pliocene can be divided into three stages: 6.2-5.4 Ma, 5.4-3.5 Ma and 3.5-2.6 Ma. Strength of the palaeowind during the middle stage (5.4-3.5 Ma) is weaker than that of the previous and subsequent stages and the intensity of palaeowind during the latest stage (3.5-2.6 Ma) is stronger than that of the early time (6.2-5.4 Ma). Variations in the sedimentation rate of the Red Clay deposit can also be divided into three stages: the earlier, the middle and the later interval. The sedim entation rate ofthe earlier stage is higher than during the middle stage, but lower than during the later one. This is a clear indicator of changes in the palaeowind intensity and aridity in the dust source region and may be linked with global ice volume changes during the late Miocene and the Pliocene.
其他文献
在机床夹具设计中的“双向夹紧机构”有关书籍互相引用,一直被当作一种具有双向夹紧力的典型央紧机构来介绍。本文作者根据自己多年的探讨,认为该机构的双向夹紧作用有误解,
一、前言 CrWMn钢是应用较广泛的低合金工具钢,常用以制造冷冲、切边等冷作模具。根据对这些模具失效形式的分析,有相当多的CrWMn钢模具不是正常的磨损失效,而是因强、韧性
缩口成形能制成美观高强度与刚度的零件。相同零件如以拼焊或旋压法制造,则在产量及质量上都相差甚远。有关缩口理论分析及设计方法的文献甚少。对变形过程的研究也不够充分
开国总理周恩来,人们见到的他总是衣冠楚楚,风度翩翩。《周恩来着装逸事》透露了他着装的“秘密”。 The founding Prime Minister Zhou Enlai, people always see him dres
一、前言轧板厂常化炉炉底辊长期在工业煤气为燃料的高温(850℃~1000℃)环境下使用。炉底辊起着转动输送钢板的作用,底辊辊环不仅承受着钢板的压力,同时还受着运动中的钢板给
迄今规模最大的世界华商大聚会——第六届世界华商大会将于2001年9月 17日至9月 19 日在南京召开,届时3000多名来自世界各地的华裔商贾将同中国内地的1000多位企业家一道,出席这次具有历史意义的
对国内外机床主轴回转精度的理论及测试技术的发展状况作了全面系统地介绍;指出了目前在这方面研究中存在的问题以及这一研究工作的发展前景。 This paper introduces the t
国资在创业中实现增值钻石虽小,价值连城,座落于上海市闸北区的市北工业新区现仅为1.26平方公里面积,是一个很小的工业区,称得上是“袖珍”开发区,然而,就是这样一个小工业
加强对加工贸易进口料件消耗定额的管理是为了确保进口原材料用于生产出口,保证投入产出的准确性、合理性,防止利用加工贸易名义走私或偷逃税款的一项重要措施。准确的消耗定
中国“国力”世界排名怎样?2月27日,中科院发布了总计300多页的《2003中国可持续发展战略报告》,首次对中国可持续发展综合国力进行评价。在与美国、英国、俄罗斯、日本、意