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中国沙漠 ›› 2004, Vol. 24 ›› Issue (1): 30-34.

• 研究论文 • 上一篇    下一篇

陕西洛川黄土中第5层古土壤与环境研究

赵景波1,2, 岳应利3, 杜娟1   

  1. 1. 陕西师范大学 地理系, 陕西 西安 710062;
    2. 中国科学院 地球环境研究所黄土与第四纪地质国家重点实验室, 陕西 西安 710075;
    3. 陕西师范大学 物理与信息技术学院, 陕西 西安 710062
  • 收稿日期:2002-07-02 修回日期:2002-09-11 出版日期:2004-02-20 发布日期:2004-02-20
  • 作者简介:赵景波(1953-),男(汉族),山东滕州人,博士,教授,博士生导师,主要从事自然地理研究。E-mail:jbzhao708@sohu.com
  • 基金资助:
    国家自然科学基金项目(40071006); 国际地质对比计划项目(IGCP448); 教育部重大项目(2000ZDXM770013)共同资助

The Fifth Paleosol in Loess and Its Environmental Significance at Luochuan of Shaanxi

ZHAO Jing-bo1,2, YUE Ying-li3, DU Juan1   

  1. 1. Department of Geography, Shaanxi Normal University, Xi'an 710062, China;
    2. State key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China;
    3. College of Physics and Information Technology, Shaanxi Normal University, Xi'an 710062, China
  • Received:2002-07-02 Revised:2002-09-11 Online:2004-02-20 Published:2004-02-20

摘要: 野外调查和室内分析资料表明, 黄土高原中部的洛川一带500ka前后发育的第5层古土壤上、下部分层的CaCO3淀积层和部分Fe2O3已迁出了古土壤层, 该层古土壤是不具CaCO3淀积层的淋溶性中酸性土壤, 剖面构型为Bts-Cs-Cl-Bk-C型。这一古土壤底部之下发育了风化淋滤黄土层, 指示当时风化淋滤深度和强度比现今大, 是250万年来最温湿气候事件的显示。该层古土壤发育时亚热带气候迁移到了黄土高原中部, 当时年均温度为15℃左右, 年均降水量为850mm左右。

关键词: 黄土古土壤, 深部风化, 深部淀积层, 气候带迁移, 陕西洛川

Abstract: Field observations in Luochuan of middle Loess Plateau discover that CaCO3 nodule illuvial layer and ferriferous clay film individually distribute at 0.4 m and 0.2 m deep under the 5th paleosol in loess and there is weathered and leached loess layer between the CaCO3 nodule illuvial layer and the clay layer, which show that the CaCO3 illuvial layer and a part of Fe2O2 has migrated out of the paleosol. Sample analyses show that the CaCO3 content in the paleosol and the weathered and leached loess layer is very low and generally less than 1%, which indicates that the paleosol has middle or acid character. Microstructure shows that red-brown optical clay film developed well in the paleosol and takes 5%~10% in content. The film exists in form of flowing colloid and lumps, which indicates that the paloeosol is leached forest soil type. The magnetic susceptibility is 160×10-6~250×10-6 SI in the 5th paleosol and 60×10-6~120×10-6 SI in unweathered loess layer. The magnetic susceptibility indicates that the weathered and leached loess layer is not the component part of the paleosol and also not the component of the loess but a transitional type between them. The formation of the weathered and leached loess layer under the 5th paleosol shows that effect of weathering and leaching at that time has exceeded the thick range of soil formation zone, which indicate a rich raining event. In the light of the characteristics of the weathered and leached profiles, it is determined that the subtropical climate with mean annual rainfall of about 850 mm prevailed at that time in Luochuan. Because the CaCO3 illuvial layer formed during the development of the 5th paleosol doesn't belong to the component part of the paleosol, and the parent material loess under the paleosol can be divided into dark brown-yellow weathered and leached loess layer(Cs) with red ferriferous clay film, light brown-yellow weathered and leached loess layer(Cl) without red ferriferous clay film, illuvial layer of CaCO3 nodules(Bk) and unweathered loess layer(C), so the profile component of the paleosol is Bts-Cs-Cl-Bk-C. The rich rainfall determined by the weathered and leached loess layer, CaCO3 illuvial layer and red ferriferous illuvial clay film is the important indication for the migration of climatic zone. In Loess Plateau beyond north Qinling Mountain, the mean annual rainfall is about 600 mm or less than 600 mm. During interglacial stage the climatic zone migrated from south to north in this area, and it couldn t make the rainfall in Luochuan increase. The obvious increase of rainfall in Luochuan before 0.5 Ma was caused by the migration to the middle Loess Plateau of the subtropical climate.

Key words: Loess, paleosol, deep weathering, deep illuvial layer, migration of climatic zone, Shaanxi Province

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