【摘要】 黄土高原地区黄土之下的红粘土的年代和形成可为六盘山隆起、鄂尔多斯夷平面解体以及青藏高原隆升等构造事件提供重要证据。六盘山东麓厚达303m的朝那黄土-红粘土剖面的磁性年代地层学表明朝那红粘土开始堆积于8.1MaBP，是目前黄土高原上发现的最老的红粘土。8.1MaBP前后一次强烈构造运动使得鄂尔多斯夷平面解体，相对下沉地区接受红粘土沉积，六盘山地区开始隆起，这可能与青藏高原强烈的构造抬升事件有关。更多还原

【Abstract】 The red clay underlying the Chinese Loess Plateau was thought to be an eolian deposition continuous to loess and thus was linked to the history of monsoon and drying Asia in relation to tLhe Tibet uplift. The lower boundary of red bed has been regarded as a signal to indicate the Tibetan uplift or the initiation of the polar ice sheet. Thus, the age and origin of red clay hold the key to unravel uplift of Liupan Mountain and disintegration of Ordos plantation surface. Here we report a 303m complete loess-red clay sequence, which contains 175m of Quatemary loess-paleosols and 128m of red clay, from Chaona at the eastem foot of Liupan Mountain bordered by Liupan Mountain thrust connected physically to north boundary thrusts of the Tibet Plateau. Detailed paleomagnetism shows that the age of Chaona red clay reaches~8.1Ma B.P., at least 0.5 Ma older than previously reported oldest ages of the red clay sections in the Loess Plateau. It provides so far an oldest constraint to the Ordos planation surface below red clay.Morphostratigraphy shows that the tectonism was relatively stable between the late Cretaceous and the red clay, which led the relief in the region be greatly reduced to form a genily undulate but roughly horizontal planation surface. During the formation of the planahon surface, even if dusts could have, it would be hard for them to be preserved. Thus, the start of red clay at ~ 8.1Ma B.P. may imply that the planation surface was broken by the Haiyuan-Liupan Mountain faults at that time with one part to be uplifted to form Liupan Mountrin and the other to be down-faulted to begin to teceive dust deposition. We link this faulting to an initial uplift of the Tibet Plateau along its northern boundary faults synchroneous with the rise of the Himalaya-South TibeL which may result in the large environmental change and the inception of eolian red clay.更多还原