祁连山东段剥蚀面与青藏高原隆升

祁连山北麓广泛分布着一级剥蚀面, 它是山地阶段性隆升的产物. 通过对剥蚀面之上砾石层中细砂物质的ESR测年以及黄土地层的古地磁测定, 认为祁连山东段的剥蚀面最终解体于1.4 Ma BP. 这与邻近区域陇西盆地的剥蚀面解体时代(1.8 Ma BP)有所差异, 这或许是第四纪期间青藏高原阶段性隆升在区域间存在着差异特征的重要表现.

Erosion Surfaces in the East Qilian Mountains and Uplift of the Tibetan Plateau

The planation surface is a remnant of landform of old age and the erosion surface is of a mature landform, according to the Davisian cycle. So the dismantling of erosion surface indicates drastic mountain uplift. It is found that in the east Qilian Mountains there are two planation surfaces and one erosion surface. These are viewed as direct indications of episodic, dramatic uplift of mountains, and therefore have important implications for inferring the ages of mountain uplifts. The outcropped strata are mainly composed of the Neogene reddish sandstone, except for locations truncated by the erosion surface which consist in Mesozoic or older strata. On the top of the strata there preserved a thin veneer of prismatic sandstone gravel bed and thicker loess. From the paleomagnetic measurements on the loess strata overlying the erosion surface, and the result from ESR chronology on gravel beds, it is demonstrated that the erosion surfaces dismantled around 1.4 Ma BP. Therefore, a dramatic uplift event at around 1.4 Ma BP is discover in the east Qilian Shan. However, the erosion surface in the Yellow River watershed, west to Liupan Shan, is found dismantling around 1.8 Ma BP. The discrepancy in timing the dismantling of the erosion surface may reflect, to some extent, the regional difference in the uplift of the Tibetan Plateau during the late Cenozoic. With the subsequent uplifting of the Tibetan Plateau, episodic river down-cutting, stream captures and headwater erosions can be seen widely throughout this region, accompanied by a formation of river terrace sequences.