临夏盆地新生代沉积物高分辨率岩石磁学记录与亚洲内陆干旱化过程及原因  

HIGH RESOLUTION ROCK MAGNETIC RECORDS OF CENOZOIC SEDIMENTS IN THE LINXIA BASIN AND THEIR IMPLICATIONS ON DRYING OF ASIAN INLAND

作　　者：方小敏[1] 徐先海[2] 宋春晖[2] 韩文霞[2] 孟庆泉[2] 鸟居雅之[3] 

机构地区：[1]中国科学院青藏高原研究所盆地与资源环境研究中心,北京100085 [2]兰州大学资源环境学院西部环境教育部重点实验室,兰州730000 [3]日本京都大学大学院理学研究科

出　　处：《第四纪研究》2007年第6期989-1000,共12页Quaternary Sciences

基　　金：国家重点基础研究发展规划项目(批准号:2005CB422001);中国科学院知识创新工程重要方向项目(批准号:KZCX2-YW-104);国家自然科学基金项目(批准号:90211013)资助

摘　　要：亚洲内陆干旱化是全球新生代大陆环境变化中最引人瞩目的重大事件，与新生代全球变冷和青藏高原隆升密切相关。文章通过对甘肃临夏盆地几乎连续的新生代沉积物系统岩石磁学性质研究，获取了高分辨率磁化率和非磁滞剩磁记录，揭示在29．0～8．6Ma的漫长的以湖相粉砂岩和泥岩为主的渐新世晚期和中新世早、中期没有明显的长期变化，从8．6Ma开始持续增加，尤其从6．4Ma和5．3Ma开始表现出两次快速持续增加。同时，以8．6Ma为界磁性矿物相对含量发生明显变化，此前以赤铁矿为主，磁铁矿和磁赤铁矿次之，此后以磁铁矿和磁赤铁矿为主，赤铁矿次之，磁性矿物类型和性质类似于风成红粘土和黄土。因此，我们将这种沉积物中磁性矿物组合、性质和含量的长期变化解释为流域外风成物质的加入，指示我国西北内陆现代干旱气候可能从8．6Ma开始，7．4～6．4Ma后急剧加速变干，5．3Ma后再次加速变干，并最终形成今天的干旱区的过程。9～8Ma开始的青藏高原阶段性快速隆升和随后的全球变冷可能是驱动亚洲内陆干旱化进程的动力。Some important environmental events occurred in the Cenozoic that are closely related to our present earth system are global cooling, Asian monsoon, and drying of Asian inland. Among them, the aridification of Asian inland and other parts of the world is one of the most important scientific questions for its severe influence on wide areas with large population. The present state of the aridity in NW China is not only a result of long-term natural environmental evolution but also affected by severe human activities. In order to predict and reduce the aridity progress in NW China, we must answer firstly questions including： when did this aridity begin？ how was it evolved？ how does it run？ what is its driving mechanism？ and what are its relationships with the uplift of the Tibetan Plateau and global cooling？ For answering these questions, the most urgent thing at present is to obtain a series of Cenozoic continuous arid climatic environment records in semiarid and arid areas. Fortunately, there are many basins in NW China filled with thick Cenozoic sediments which archive great information on drying of NW China. One of these basins is the Linxia Basin located at the joint part of the southwestern Chinese Loess Plateau and the northeastern margin of the Tibetan Plateau in Linxia City, Gansu Province, an ideal place to carry the study above due to its almost continuous persistence of mostly fine lacustrine sediments in arid environment. The Linxia Basin yields one of the most abundant fossil mammal sites in China. Detailed paleontological, stratigraphical and paleomagnetic studies have divided the stratigraphy in seven formations upperwards as the Tala Fm. （ ca. 29.0 - 21.4Ma） , Zhongzhuang Fm. （ 21.40 - 14.68Ma） , Shangzhuang Fm. （ 14.68 - 13.07Ma）, Dongxiang Fm. （ 13.07 -7.80Ma）, Liushu Fm. （7.80 -6.25Ma） , and Hewangjia Fm. （6.25 -4.34Ma）. These formations reflect five sedimentary cycles manifested as alluvial-flood plain-shallow lake（29.0 -21.4Ma） , braided river-shallow la

关 键 词：临夏盆地 岩石磁学 亚洲内陆 干旱化 

分 类 号：P534.6[天文地球—古生物学与地层学] P318.41[天文地球—地质学]