黄河二级阶地兰州石峡口次生黄土剖面的环境磁学研究

Secondary loess is widely distributed on the bottom of different level of all the terraces of Yellow River and its tributaries. As contemporary sediments of the aeolian loess-paleosol sequence, secondary loess recorded important supplementary information about paleo-environmental changes. In the paper, we carried a detailed environmental magnetic study at Shixiakou section, which is a typical loess-secondary loess section on the 2nd-level terrace of the Yellow river in Lanzhou basin. According to the variation characteristics of susceptibility, magnetic fabric and grain-size of 6 meters primary loess on the top and 19 meters secondary loess on the bottom, we conclude that there were four sedimentary stages, and then suggest a wet and dry climate fluctuation trend and ultimate development towards drought since the late Pleistocene. The results in this paper have important indications for the study of paleoclimate and paleo-environment changes in northwestern China during the formation period of the second terrace in upper-stream of the Yellow River.