黄山北麓青弋江发育研究

青弋江位于黄山北麓,为长江下游最长的支流。野外考察发现青弋江泾县盆地段存在溪口剖面和城北剖面等2个天然剖面,共发育了1级洪积扇台地（P）和3级河流阶地（T3、T2和T1）,并相应堆积了4级砾石层。通过对砾石层进行砾组分析,并借助电子自旋共振（ESR）测年和古地磁测年等方法,初步探讨了青弋江发育的年代、过程和成因。研究结论为：① 砾组分析表明青弋江T3阶地是青弋江的最老阶地,并且其砾石层是青弋江的最老砾石层;② 测年结果表明青弋江发育的年代区间为1300~900 ka,其中~1300 ka为青弋江发育的最早年代,而~900 ka则为青弋江发育的最晚年代;③ 青弋江发育于~1377 ka前的洪积扇辫状河,并先后经历了洪积扇及辫状河发育、辫状河下切、青弋江形成等阶段,即所谓的源于洪积扇辫状河的青弋江发育过程;④ 青弋江发育可能是降水增加和构造抬升共同作用的结果。该研究有助于为中国东部地区中小河流发育研究提供参考。

The river development of the Qingyijiang River in the northern piedmont of Mt. Huangshan

The Qingyijiang River, which is located in the northern piedmont of Mt. Huangshan, is the longest branch of the lower Yangtze River. Based on the field survey, a well-preserved sequence of one diluvial platform (P) and three river terraces (i.e., T3, T2 and T1) was found, and a corresponding sequence of four gravel beds was also presented, according to two natural sections of Xikou cross section and Chengbei cross section in the Jingxian Basin. In addition to the gravel fabric analysis method, the Electron Spin Resonance dating and palaeomagnetic dating were used to discuss the age, process and cause of river development of the Qingyijiang River. This study concludes that: (1) the results of the gravel fabric analysis show that the T3 terrace is the oldest terrace of the Qingyijiang River, and the T3 gravel bed is the oldest gravel bed of the same river; (2) the dating results show that the formation timing of the Qingyijiang River can be traced back to the period from ~1300 ka BP to ~900 ka BP, and the oldest timing of the river is ~1300 ka BP, whereas the most recent timing is ~900 ka BP; (3) the Qingyijiang River originated from one of the braided rivers on the diluvial fan before 1377 ka BP, and successively experienced three stages of the diluvial fan and braided rivers, the incision by the braided river and the Qingyijiang River formation, that is, the so-called development model of the Qingyijiang River from one braided river on the diluvial fan; and (4) the development of the Qingyijiang River may be a combined result of precipitation increase and tectonic uplift. This study provides a reference for the studies of the small and medium river development in eastern China.