宛川河阶地的年代与下切机制

Terrace Formation Age and River Incision Mechanism of Wanchuan River

宛川河是黄河一条小规模支流,在榆中盆地中发育了至少四级堆积阶地。以"古土壤断代法"为基础,结合OSL测年和14C测年,较准确的确定了宛川河四级阶地形成的年代为330、130、50和10 ka。区域构造表明榆中盆地相对下陷,地面抬升不是引起河流下切的主要原因,同时阶地位相说明作为宛川河侵蚀基准面的黄河对宛川河下切影响只限于距河口不远的一小段距离。每级阶地面上都堆积一层古土壤指示宛川河下切于古土壤开始发育时期,对应于气候由冷干向暖湿转换的时期,河流下切的主要原因是气候变化。

The Wanchuan River, which is a small tributary of the Huanghe（Yellow） River, has developed four staircases ^14C dating of river terrace at least within Yuzhong Basin. Based on ＂Paleosol-dating＂, combining OSL dating and , we demonstrate that the beginning ages of incision of T4, T3, T2 and T1 were 330 ka, 130 ka, 50 ka and 10 ka, respectively. Analysis of regional geological structure and terrace feature indicates that tectonic uplift has not played significant role in river incision, and the Huanghe River, the base level of Wanchuan River, has influenced only a short segment of downstream of the river. The paleosal developed on the surface of each river terrace indicates that river incision began in the period during climate transformation from dry cold phase to humid warm phase, when the paleosal development began in the Loess Plateau, so the main cause of river incision is climate change.