黄土高原0.8Ma以来地面抬升的时空特征研究

The Spatial and Temporal Features of Surface Uplift in Loess Plateau Since 0.8 Ma

根据黄土高原地区黄河阶地的形态特征和成因分析,认为其形成主要是地面抬升所致并且在黄河达到均衡状态下形成,可以推断黄土高原的地面抬升。根据对黄土高原地区黄河0.8 Ma阶地的研究并结合相关文献资料,选取兰州段、黑山峡段、晋陕峡谷段和三门峡段作为典型研究区域,得出黄土高原0.8 Ma以来的地面抬升存在显著的时空特征,即空间特征表现为地面抬升量有西大东小的规律,时间特征表现为地面抬升速率有后期加速趋势、特别是晚更新世以来。并认为黄土高原0.8 Ma以来的地面抬升与青藏高原的构造抬升有成因上的联系。

The river terrace is one of the direct geomorphic evidences of the surface uplift. By analyzing the characteristics of the Yellow River terraces in Loess Plateau, it is presented that the terraces are mainly tectonic genesis, and formed after the Yellow River reached a quasi-equilibrium state. It is reasonable to use the Yellow River terraces for representing the surface uplift of the Loess Plateau. In the Lanzhou Basin, two fourth terrac- es of the Yellow River are selected as the study sections, namely the Zaoshugou terrace and the Wuyishan ter- race. At the Zaoshugou terrace, the altitude of gravel stratum is 80 m higher than the river level. The top of the gravel stratum is overlain by at least 64 m eolian loess, and the paleosol S8 is at the bottom of the eolian loess. At the Wuyishan terrace, the altitude of gravel stratum is 140 m higher than the river level. The top of the grav- el stratum is overlain by at least 100 m eolian loess, and the paleosol S8 is at the bottom of the eolian loess. The optically stimulated luminescence （OSL） dating result indicates that the age of the upper part of paleosol S, at the Zaoshugou terrace is 70.44-7.6 ka. The results of paleomagnetic dating, optically stimulated luminescence dating and loess-paleosol sequence matching indicate that the two terraces have the same age, and both were formed at about 0.865Ma. Therefore this paper advances that there is the Yellow River terraces at 0.8Ma in the Lanzhou Basin, and the fourth terrace of the Yellow River may be a geomorphic response to the event of the surface uplift at 0.8Ma around the Qinghai-Tibetan Plateau. According to the research on the Yellow River ter- races at 0.8Ma in the Loess Plateau and the correlative literature, this paper verifies that there was a large-scale surface uplift at about 0.8Ma in the Loess Plateau, and the surface uplift resulted in river incision and terrace formation. Lanzhou, Heishan Canyon, Shanxi-Shaanxi Canyon and Sanmenxia were also selected as the typi- cal research areas in the Loess Plateau, and obvious spatial and temporal features of the surface uplift of the Loess Plateau since 0.8Ma was discovered, basing on the characteristic analysis of the sequences of the Yellow River terraces at this four sites. The rates of surface uplift are calculated by the rates of river incision and the amounts of surface uplift are calculated by the depth of river incision （height above river）. The spatial feature is that the surface uplift of the western Loess Plateau is more intense than that of the eastern Loess Plateau, and the temporal feature is that the uplift speeds up gradually, especially since the late Pleistocene. This paper also proposes that the surface uplift of the Loess Plateau since 0.8 Ma is related to the surface uplift of the Qing- hai-Xizang plateau.