玛纳斯河山麓冲积扇演变遥感研究

Evolution of Alluvial Fans at Range-Front of Tian Mountains in Manas River Valley Based on Remote Sensing Technology

基于地质过程,特别是沉积地质过程的理论和方法,通过对航空相片和遥感影像的解译,结合野外考察和地貌与沉积物分析,研究玛纳斯河山麓冲积扇的演变过程,并对其形成和演变原因进行探讨。晚第四纪以来,玛纳斯河山麓冲积扇从第二排山麓到下游冲积平原,可划分为四期规模较大和三期规模较小的冲积扇;玛纳斯河山麓冲积扇的形成演变受气候、构造或气候—构造耦合作用的共同影响,具有多成因性和多层次性。

Based on the geological processes,especially sedimentary geological processes and the theory of landscape evolution,the study of the evolution of alluvial fans at range-front of Tian Mountains in Manas River valley was carried out by remote sensing images interpreting,field investigating,physiognomy and sediments analyzing,and the cause of formation of alluvial fans was discussed. It indicated that there were four periods of larger alluvial fans and three periods of smaller alluvial fans from the foot of the second reverse fault and fold at the north margin of Tian Mountains since the later Quaternary Period. They were named F1, F2, F3, F4, FS, F6, and F7 by the sequence of their formation age. F1 which was shaped about 16-27 kaB. P.only remains its west part for being reconstructed and eroded by the natural factors. There are many channels and ridges radically distributing on its surface. It is composed mainly of gravels and a little grid in the interlayer;F2 of which the west part is not symmetrical with the east part has a trend to spread westward and completely covers the west part of F1. The distance from north margin to south margin is 17 krn and breadth is 28 kin. It could be concluded that its age is about 6-11 kaB. P from its sediments dating; F3 has the same spatial figure with F2. Differently, its size is larger than F2 and its material is smaller that F2＇s. Its sediments dating is about 3 680±70 aB. P. ;F4 whose length from south bounder to north hounder is 21 km, and its breadth from east to west is about 23 km is concluded to be figured 1 570±55-3 680±70 aB. P.. There were many billabengs in front of the F4 and most of them were rebuilt as the artificial reservoir;F5 and F6 were shaped by the branch of Manas River and they are smaller than former alluvial fans. F6 is younger than F5, but F7 is the youngest alluvial fan among them and it is still influenced by the Manas River. The formation and evolution of alluvial landform are related to the climate. In some period,dimate was the leading factor,but in another, it was the subordinate status. The alluvial fans are near the north foot of the Manas reverse fault-and-fold zone that formed on the early Pleistocene Qangze and had intermittent activity since later Pleistocene Qangze. Former study indicated that its ridge center had an obvious northward trend,so tectonic activity was another important factor that influences its formation and evolution.