贵州高原北部河流阶地发育与喀斯特地貌演化

贵州高原北部发育平缓丘丛和深切峰丛2种喀斯特地貌组合,保存于喀斯特山间盆地的河流阶地对区域地貌演化具有指示意义。本文根据阶地发育特征和光释光（OSL）测年,分析阶地形成的时代和动力,结合区域地质背景,探讨构造抬升和河流侵蚀对黔北喀斯特地貌演化的驱动作用。结果显示,绥阳盆地T1阶地时代18.8~8.2 ka,T2时代144.4~104.1 ka;旺草盆地T1年龄为5.5 ka,T2年龄为45.1 ka。绥阳盆地阶地以漫滩相沉积物为主,旺草盆地阶地则多切割了白云岩基岩。分析认为,气候条件影响了阶地的沉积过程,但差异性构造抬升应为区域河流阶地差异发育的主要因素。阶地测年显示,旺草盆地的河流平均下切速率明显高于绥阳盆地,表明芙蓉江流域构造抬升和河流下切强度明显高于洋川河。在差异性构造抬升和河流侵蚀综合作用下,北部大娄山区形成了深切的喀斯特峰丛-峡谷地貌,南部乌江中游流域则发育以平坦盆地和宽缓丘丛为主的地貌组合。

River terraces in the northern Guizhou Plateau and their implications for karst landform evolution

Geologists pay much attention to mountainous geomorphic evolution of Guizhou Plateau, because of its core region of karst area in Southwest China. There are two different geomorphic blocks in the northern Guizhou Plateau, which is representative for the karst landforms in Guizhou. River terraces in the karst intermontane basin, as an important step-like landform system in this area, are of great significance for the study of regional geomorphic evolution. In this work, we studied sediment characteristics and optical stimulated luminescence(OSL) dating of the terraces in the Suiyang Basin and the Wangcao Basin in the northern Guizhou Plateau. And then, the terrace ages and associated evolutionary dynamics of Guizhou Plateau have been discussed. Combining the terrace development and geological background, we explored karst landform evolution of northern Guizhou Plateau. It is found that in the Suiyang Basin, the ages of terrace are ranged between 18.8 ka-8.2 ka for T1 and 144.4 ka-104.1 ka for T2. In the Wangcao Basin, the ages of terrace are 5.5 ka for T1 and 45.1 ka for T2.In the Suiyang Basin, the terraces mainly deposited floodplain sandy sediments, while the terraces in the Wangcao Basin mostly cut the thick dolomite bedrock. The dating results show that in the formation stage of terrace T1, the average cutting rate of the Furong River in Wangcao Basin is 1.67 m/ka, significantly greater than that of the Yangchuan River in the Suiyang Basin, which is 0.35 m/ka. According to dating and regional geological correlation, we hold that climate change may affect the sedimentary characteristics of the terraces, but tectonic uplift is the dominant driving force for terrace formation. Different terrace ages are the results of differential uplifts in the Guizhou Plateau. Based on the terrace characteristics and dating,we found that tectonic uplift and river undercutting in the Wangcao Basin were more intensive than those in the Suiyang Basin. Actively driven by differential tectonic uplift and river erosion, the karst deep-cutting gorges and peak clusters landform is formed in the Furong River Basin, a part of Dalou Mountain, while the flat intermontane basins and hill clustered landform has been developed in the middle reaches of Wujiang River Basin.