青弋江是长江下游最大的一条支流,发源于安徽省黄山北麓。野外考察发现青弋江在泾县段共发育了三级河流阶地,其中最高阶地(T3)存在两个天然剖面,即CB-T3剖面和SJ-T3剖面。运用电子自旋共振(ESR)测年法,并结合相关文献资料,确定青弋江泾县段最高阶地的形成年代并探讨其构造气候意义。研究结果表明:青弋江泾县段最高阶地的年代约900 ka B. P.,是早中更新世过渡时期河流作用的产物;青弋江泾县段900 ka B. P.阶地是可能是构造抬升和东亚夏季风变化共同作用下的产物,其中构造抬升为阶地的形成提供了河流下切的动力条件,而东亚夏季风的强度变化为阶地的形成提供了气候条件。研究结果有助于为长江中下游地区的河流地貌研究提供基础数据和参考资料。
英文摘要:
On the northern fringe of Mt. Huangshan,many river terraces are developed at the junction between mountains and plains. The river terraces are most typical in the Jinxian Basin,Anhui Province,where the Qingyijiang River,one of the longest tributraies of the lower Yangtze River,developed three staircase terraces. The topmost terrace (i. e.,the T3 terrace) tread is 38 ~ 39 m above river level,and the top of the gravels is generally covered by 3 ~ 10.9 m of red clay deposits. There are two natural section of the topmost terrace (T3),namely CBT3 section and SJ-T3 section. To determine the formation time of the topmost terrace,the ESR dating was applied. Furthermore the tectonic-climate significance of the topmost terrace were discussed combining with extensive related literature. The main results showed that the topmost terrace developed no later than 900 kyr ago,and this terrace was the product of the fluvial process during the transition period from Early Pleistocene to Middle Pleistocene. According to the relevant literatures,the widespread existence of 900 ka B. P. terraces in Jingxian county and the middle-lower reaches of the Yangtze river indicated that an universal incision event had occurred in the middlelower reaches Yangtze river around 900 ka B. P. This incision event might be a fluvial geomorphic response to the environmental change in the transition period of Early-Middle Pleistocene. The 900 ka B. P. terrace of the Qingyijiang River in Jingxian county was developed under the combination of regional tectonic uplift and climate change. Furthermore,the tectonic movement provided the driving force for the fluvial incision,and the intensity variation of East Asian summer monsoon provided climate conditions for the formation of terrace. The study is helpful for offering basic data and reference materials for the fluvial landform research in the middle and lower reaches of the Yangtze River.