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中文摘要：
甘肃临夏盆地中广泛分布新生代红色地层，其中尤其以青灰色-紫红色交替出现的地层最具特色，被学者们形象地称之为“斑马层”。该地层基本水平分布，因为夹带灰白色层，看起来显然与第四纪黄土一古土壤差别较大，于是过去人们通常认为这套新生代红色堆积是湖相沉积地层。但是野外观察发现，许多地方红色地层的土壤层次和钙积层依然普遍存在，就如同新近纪的红粘土；红白相间的互层在现代沟谷的边坡，能够随地形倾斜披覆并沿着边坡向下收敛变薄，这种地层能够随地形斜披现象很难用湖湘沉积物来解释。我们对这套红白交互层的边坡倾斜层位和水平层位分别采集定向样品，测量其磁化率的各向异性，同时采集附近现代边坡倾斜黄土层和水平黄土层样品进行对比研究。磁组构测量结果表明：水平地层和边坡倾斜地层均代表原生地层形态，并非后期构造运动使得水平地层变斜；同时这套随现代边坡地形倾斜收敛的红白色互层也并非原生水下环境中形成，而更可能是与第四纪黄土相似，是在原本倾斜的古地形上堆积形成，当时在水上地形接受风积物沉积，由于顺坡和沟中流水作用使得边坡地层逐渐变薄，而显得收敛。流水的作用还可能使得磁颗粒被扰动，破坏了上覆黄土磁组构收敛的特点。因此，灰白颜色很可能并非沉积当时本色，而是由于原生风成堆积后经滞水浸泡还原，导致潜育而被改变成为灰白色。斑马层在边坡随古地形倾斜，并且沉积物明显受到水的作用，证实大夏河水系内的椒子沟、毛沟和毛毛沟在斑马层沉积以前就被河流下切形成，而且当时河流排水不畅，造成低处有时短期被淹，留下水平层理等痕迹。现代的沟谷就沿着过去的地形进一步深切发展起来，反映了大夏河水系可能在13Ma以前就已经发育。大
英文摘要：
Linxia is a district in Gansu Province, locates in the north-east edge of the Tibetan Plateau. Huge thick of Cenozoic red stratum over last 4 -29Ma was reported there, providing valuable geological record to recognize the Plateau uplifting process and climatic evolution during Cenozoic. Of which deposits, red-gray interbeds with paleomagnetic age of 13.07 -7.78Ma are especially very eye-catching. These beds were vividly named as ＂Zebra Layer＂. These interbed layers are nearly horizontal. Because of the gray layers,which are absolutely different from aeolian loess,it is generally accepted as lacustrine sediment： during Late Tertiary,this region was a lake,gray and white layers were formed during deeper water, and the red beds were formed during shallow water, repeating several times formed the above-mentioned across-layers. Through large area inspection in the field, we found that there are still many paleosols with calcium nodules/or layers in the red stratum, which are similar to the later Tertiary Red Clay; These Zebra Layers tilt with the terrain in side-slope of the modern valley. This common geological phenomenon is difficult to be explained by lacustrine sediments. In order to explore the process of its＇ formation, one section from Maomao Ditch （35°40＇11＂N, 103°21 ＇56.8＂E） ,where Zebra Layers follow the terrain tilting in side-slope of the modern valley, was selected for paleotopographic study. Two groups of orientated samples were collected from the Zebra Layers： 1）horizontal layers,and 2）the side-slope layers （50 samples in total）to measure their anisotropy of magnetic susceptibility （AMS）. Meanwhile Quaternary aeolian loess samples from both positions： 1 ）horizontal layers （18 samples）and 2）the side-slope （15 samples）, were also collected for comparison. The overlaying Quaternary loess, no mater samples from horizontal or from side-slope, their minimum axis K3 always focus around 90°, indicating aeolian almost ＂ horizontal bedding＂. The horizontal Z
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