川西硕曲河流阶地及其对山地抬升和气候变化的响应

River Terraces in the Shuoqu River and Their Response to Mountain Uplift and Climate Changes in Western Sichuan Province

山地抬升和气候变化是影响内陆地区河流地貌发育的两个关键因素,不同地区的河流对它们的响应方式多种多样.位于川西高原西部活动构造区的硕曲河谷下游亚金段保留有6级河流阶地,运用ESR和TL技术对其中T2到T6级阶地的砾石层及邻近的冰碛物进行了测年,并结合阶地沉积物特征分析了阶地对山地抬升和气候变化的响应.结果表明:亚金T2～T6级阶地砾石层均堆积于冰期;阶地基座均形成于间冰期-冰期过渡时段;形成这些阶地的下切过程均开始于冰期晚期,可分别与深海同位素阶段的MIS 2、6、8、14和16阶段晚期相对应.自MIS16阶段晚期以来,硕曲河谷亚金段平均下切速率约为1.22 mm.a-1,小于该地区山地同期平均抬升速率2 mm.a-1,这与"河谷下切速率不大于山地抬升速率"一致.

Tectonic uplift and climate change are two key factors controlling the river terrace formation in hinterlands. Rivers in different areas, however, respond to the two drivers in different ways. There are six river terraces on both sides of the Yajin Section of Shuo Qu, which are located in the tectonically active area in western Sichuan Province and are climatically controlled by the south Asian monsoon. Electron spin resonance （ESR） and thermoluminescence （TL） techniques were used to date the sediments from the five higher terraces （T2～T6） and the glacial sediments adjacent to the terraces. The evolution processes of the five terraces are analyzed on the basis of the dating results and the geomorphological and sedimentological characteristics of the terraces. It is revealed that the straths of the terraces （T2～T6） formed during the glacial-interglacial transitions. The sediments on the straths deposited during glacial periods. The incisions for forming these terraces began at the late glacial period, corresponding to the late periods of marine isotope stages 2, 6, 8, 14, and 16, respectively. The incision ratio of the Yajin Section of the Shuo Qu was ～1.22 mm · a^-1 since the late marine isotope stage 16, less than the uplifting ratio of 2 mm · a^- 1 in this region, which is consistent with the previous conclusions that incision ratio was no more than uplifting ratio.