兰州地区黄河第五级小沙沟阶地古地磁年代研究

 兰州黄河阶地最新研究结果表明,在兰州地区已经总共发现九级黄河阶地。其中第五级小沙沟阶地（T5）是在原来发现的黄河五一山阶地和黄河墩洼山阶地之间新发现的一级阶地,但是第五级小沙沟阶地的形成时代是根据上覆黄土的古土壤序列和阶地关系推断得来的,一直没有进行绝对年代测定。通过对阶地河漫滩及其之上覆盖的风成黄土的磁性地层研究,结合黄土古土壤序列轨道调谐年龄,确定兰州地区黄河第五级（T5）阶地的形成时代为0.96 Ma。T5阶地年龄的确定使兰州地区获得了一个有完整年代的黄河阶地序列,是对兰州黄河阶地发育模式证据的补充。

Paleomagnetic Dating of Fifth Yellow River Terrace at Xiaoshagou in Lanzhou Area

Results of the latest studies show that there are nine terraces at Lanzhou section of the Yellow River. Among them the fifth Yellow River terrace near Xiaoshagou( T5) is the newly discovered one. It lies between Dunwashan terrace and Wuyishan terrace, but its age is inferred only according to the overlay paleosol stratigraphic sequence on the terrace and their relations with terrace. This paper, based on the paleomagnetic datings of the aeolian loess-paleosol sequence on terrace and the orbit-tuning age mode, measured the age of the fifth Yellow River terrace in Lanzhou at 0.96 Ma. Till now a whole terrace sequence of the Yellow River at Lanzhou section has been presented. The study result is also a supplement to the proof on the developing model of the Yellow River terrace formation.