北京西山大石河山峡阶地发育特征

Terrace development characteristics of Dashi River valley in Western Hills of Beijing

大石河山峡总体上阶地较发育,阶地类型以基座阶地为主。下游陈家台—红煤场一带1~4级阶地发育较全,上游至庄户台一带,阶地数量减少,仅见一级阶地。上游沉积物多为砾石,砂、粘土等含量较少;而至下游,沉积物中砂、粘土组分的含量增加。红煤厂四级阶地棕红色泥质含砾粉砂中获得ESR年龄567±56ka,显示大石河河谷在第四纪中更新世早期初始发育,由于新构造运动产生间歇性隆升,在高位宽谷之下发育4级阶地,形成了如今的地貌特征,对比得出大石河流域辛开口至龙门台一段(山区)平均比降为7.71‰,600ka以来,大石河流域山区隆升速率为0.96mm/a。

Terrace is developed in Dashi River valley. It is mainly bed rock seated terrace. The first to fourth terraces are relatively well developed from Chenjiatai to Hongmeichang in lower reaches. Only one terrace is seen in upstream Zhuanghutai Village. The sediments are mainly gravels and sands in upstream reaches. They are sands and clays in lower reaches. The dating of fourth terrace in Hongmeichang Village yielded an age of 567±56ka, suggesting that the Dashi River was formed in Mid-Pleistocene. The four terraces were formed by uplift of New Tectonic Movement. The longitudinal river slope is 7.71‰ from the river mouth of Xinkaikou Village to Longmentai Village in upstream reaches. Since 600 ka, the Hill in Dashi River valley has been uplifted by 0.96mm/a.