珠江三角洲及其附近地区河流阶地的分布与特征——广东河流阶地研究之二

The Distribution and Characteristics of the River Terraces in the Pearl River Delta and Its Nearby Areas

依据珠江三角洲及其附近地区超过24条河流、80处河流阶地、97个沉积物年龄等情况,可知本区第一级半埋藏阶地具有天然堤地貌和加积型特征,与全新世河漫滩组成冲积平原。山前半埋藏洪冲积阶地与全新世洪冲积扇组成山前倾斜平原。这两种平原地貌衔接过渡,沉积物同期异相,全新统通常是上更新统阶地面被蚀低后的补偿性沉积。多项证据显示新构造运动趋势:在中更新世以间歇性构造抬升为主,自晚更新世以来却变成间歇性下沉或稳定。自晚更新世以来包括珠江三角洲及其汇入的各大河流中下游地区一起构造下沉,所以珠江三角洲不是断块型三角洲;横穿广从断裂和瘦狗岭断裂的众多小河河谷地貌在该断裂处无显著变化,显示自晚更新世这些小河河谷形成以来该两断裂无明显造貌运动。

According to 80 terraces along 24 rivers and 97 data of the deposition ages in the Pearl River Delta （PRD） and its nearby areas, the distribution and characteristics of the river terraces are studied. It is believed that there are at most 3-4 stages of river terraces in the PRD and its nearby regions. The first stage is semi-buried terrace with Holocene series, which have characteristics of natural levee and aggradations, and the terrace and recent flood plain constitute the alluvial plain. The semi-buried pluvial-alluvial terrace in front of the mountain and the Holocene pluvial-alluvial fan compose sloping plain in front of the mountain. The two plains join at landform, their depositions are at the same stage but different faces, and the Holocene series are usually complemental depositions after the upper Pleistocene series terraces were eroded. As considering the existence of the second stage terraces and higher stage terraces made up of middle Pleistocene series, and the Characteristics of the alluvial plain and Pearl River Delta Plain （the first stage terrace became further buried terrace）, the tendency of neotectonic movement in the region is evident： intermittence uplift was predominant during middle Pleistocene Epoch, but since late Pleistocene Epoch, intermittence subsidence or stabilization predominant. Since late Pleistocene Epoch, the PRD and the areas of the middle and lower reaches of the Pearl system has tectonically sunk together; therefore, the PRD is not a block type delta. A number of small streams cut across the Guangcong Fault and Shougouling Fault, and there is only the first stage terrace of several meters in height along the streams intermittently. No clear landform change occurred at the fault places, that means that there has been no evident morphogenesis in the two faults since the small valleys formed in late Pleistocene Epoch.